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The Component Parts of a
Savage Beating
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Contents
Articles
Antenna (biology)
1
Arm
4
Basting (cooking)
6
Digit (anatomy)
8
Duct (HVAC)
10
Ear
15
Eye
23
Fork
35
Gill
39
Grater
43
Handle (grip)
45
Head
47
Hoof
49
Horn (anatomy)
50
Human leg
54
Knee
68
Ladle (spoon)
80
Meat slicer
81
Nail (anatomy)
82
Peel (tool)
88
Scraper (kitchen)
89
Skin
92
Spatula
97
Tongs
98
Wedge (mechanical device)
99
Zester
101
References
Article Sources and Contributors
102
Image Sources, Licenses and Contributors
107
Article Licenses
License
110
Antenna (biology)
1
Antenna (biology)
Antennae (singular: antenna) in biology have historically been paired
appendages used for sensing in arthropods. More recently, the term has
also been applied to cilium structures present in most cell types of
eukaryotes.
In arthropods, antennae are connected to the front-most segments. In
crustaceans, they are biramous and present on the first two segments of
the head, with the smaller pair known as antennules. All other
arthropod groups, except chelicerates, proturans and arachnids which
have none, have a single, uniramous pair of antennae. These antennae
Electron micrograph of antenna surface detail of a
are jointed, at least at the base, and generally extend forward from the
wasp (Vespula vulgaris)
head. They are sensory organs, although the exact nature of what they
sense and how they sense it is not the same in all groups, nor always
clear. Functions may variously include sensing touch, air motion, heat, vibration (sound), and especially olfaction
(smell) or gustation (taste).
Insects
Antennae are the primary olfactory sensors of insects[1] and are
accordingly well-equipped with a wide variety of sensilla (singular:
sensillum). Paired, mobile, and segmented, they are located between
the eyes on the forehead. Embryologically, they represent the
appendages of the second head segment.[2]
All insects have antenna though these may be greatly reduced in the
larval forms. Amongst the non-insect classes of Hexapoda, Collembola
and Diplura have antenna, but Protura do not.[3]
Terms used to describe antennae shapes
Structure
The three basic segments of the typical insect antenna are the scape
(base), the pedicel (stem), and finally the flagellum, which often
comprises many units known as flagellomeres.[4]
The number of flagellomeres can vary greatly, and is often of
diagnostic importance. True flagellomeres have a membranous
articulation between them, but in many insects, especially the more
primitive groups, the flagellum is entirely or partially composed of a
flexible series of small annuli, which are not true flagellomeres.[4]
Antennal shape in the Lepidoptera from C. T.
Bingham (1905)
In many beetles and in the chalcidoid wasps, the apical flagellomeres form a club, and the collective term for the
segments between the club and the antennal base is the funicle; for traditional reasons, in beetles it is the segments
between the club and the scape, but in wasps, it is the segments between the club and the pedicel.[4]
In the groups with more uniform antennae (for example: Diplopoda), all segments are called antennomeres. Some
groups have a simple or variously modified apical or subapical bristle called an arista (this may be especially
well-developed in various Diptera).[5]
Antenna (biology)
2
Functions
Olfactory receptors on the antennae bind to free-floating molecules, such as water vapour, and odours including
pheromones. The neurons that possess these receptors signal this binding by sending action potentials down their
axons to the antennal lobe in the brain. From there, neurons in the antennal lobes connect to mushroom bodies that
identify the odour. The sum of the electrical potentials of the antenna to a given odour can be measured using an
electroantennogram.[6]
In the case of the Monarch butterfly, it has been shown that antennae are necessary for proper time-compensated
solar compass orientation during migration, that antennal clocks exist in monarchs, and that they are likely to provide
the primary timing mechanism for Sun compass orientation.[7]
Crustaceans
Crustaceans bear two pairs of antennae. The first pair are uniramous and are often referred to as antennules, while
the second pair are biramous, meaning that each antenna is composed of two parts, joined at their base .[8] In most
adults, the antenna are sensory organs, but they are used by the nauplius larva for swimming. In some groups of
crustaceans, such as the spiny lobsters and slipper lobsters, the second antennae are enlarged, while in others, such as
crabs, the antennae are reduced in size.
A spiny lobster, showing the enlarged second antennae
The large flattened plates in front of the eyes of a slipper lobster are the modified second antennae.
The crab Cancer pagurus, showing its reduced antennae
Antenna (biology)
3
Antennules of the Caribbean hermit crab
Cellular antennae
Within the biological and medical disciplines, recent discoveries have
noted that primary cilia in many types of cells within eukaryotes serve
as cellular antennae. These cilia play important roles in
chemosensation, mechanosensation, and thermosensation. The current
scientific understanding of primary cilia organelles views them as
"sensory cellular antennae that coordinate a large number of cellular
signaling pathways, sometimes coupling the signaling to ciliary
motility or alternatively to cell division and differentiation."[9]
"Almost every vertebrate cell has a specialized cell surface projection
called a primary cilium. …primary cilia are key participants in
Structural diagram of a single cilium extending
intercellular signaling. This new appreciation of primary cilia as
into extra-cellular space
cellular antennae that sense a wide variety of signals could help explain
why ciliary defects underlie such a wide range of human disorders, including retinal degeneration, polycystic kidney
disease, Bardet-Biedl syndrome, and neural tube defects."[10]
References
[1] Darby, Gene (1958). What is a butterfly?. Chicago: Benefic Press. p. 8. OCLC 1391997.
[2] Gullan, Penny J.; Cranston, Peter S. (2005). The Insects: an Outline of Entomology (3rd ed.). Oxford, UK: Blackwell Publishing. p. 38.
ISBN 1-4051-1113-5.
[3] Chapman, Reginald Frederick (1998). The Insects: Structure and Function (4th ed.). New York: Cambridge University Press. p. 8.
ISBN 0-521-57890-6.
[4] Thomas A. Keil (1999). "Morphology and development of the peripheral olfactory organs". In Hansson, Bill S.. Insect Olfaction (1st ed.).
Springer. pp. 5–48. ISBN 978-3540650348.
[5] Lawrence, Eleanor, ed (2005). Henderson's Dictionary of Biological Terms (13th ed.). Pearson Education. p. 51. ISBN 978-0-13-127384-9.
[6] "Electroantennography (EAG)" (http:/ / www. uni-goettingen. de/ en/ 71544. html). Georg-August-Universität Göttingen. . Retrieved March
27, 2010.
[7] Merlin, Christine; Gegear, Robert J.; Reppert, Steven M. (September 2009). "Antennal circadian clocks coordinate sun compass orientation in
migratory monarch butterflies". Science 325 (5948): 1700–1704. doi:10.1126/science.1176221. PMC 2754321. PMID 19779201.
[8] "Superphylum Arthropoda" (http:/ / www. geo. arizona. edu/ geo3xx/ geo308_fall2002/ 6arthropods. htm). University of Arizona. .
[9] Satir, Peter; Christensen, Søren T. (June 2008). "Structure and function of mammalian cilia". Histochemistry and Cell Biology 129 (6):
687–693. doi:10.1007/s00418-008-0416-9. PMC 2386530. PMID 18365235.
[10] Singla, Veena; Reiter, Jeremy F. (August 2006). "The primary cilium as the cell's antenna: signaling at a sensory organelle". Science 313
(5787): 629–633. doi:10.1126/science.1124534. PMID 16888132.
Arm
4
Arm
Arm
The human arm
Cross-section through the middle of upper arm.
Latin
brachium
In human anatomy, the arm is the part of the upper limb between the shoulder and the elbow joints. In other animals,
the term arm can also be used for analogous structures, such as one of the paired forelimbs of a four-legged animal
or the arms of cephalopods. In anatomical usage, the term arm refers specifically to the segment between the
shoulder and the elbow,[1] [2] while the segment between the elbow and wrist is the forearm. However, in common,
literary, and historical usage, arm refers to the entire upper limb from shoulder to wrist. This article uses the former
definition; see upper limb for the wider definition.
In primates the arm is adapted for precise positioning of the hand and thus assist in the hand's manipulative tasks.
The ball and socket shoulder joint allows for movement of the arms in a wide circular plane, while the structure of
the two forearm bones which can rotate around each other allows for additional range of motion at that level.
Skeleton
The humerus is the bone of the arm. It joins with the scapula above in
the shoulder at the glenohumeral joint and with the ulna and radius
below at the elbow. The elbow joint is the hinge joint between the
distal end of the humerus and the proximal ends of the radius and ulna.
The humerus cannot be broken easily. Its strength allows it to handle
loading up to 300 pounds (140 kg).
Muscles
The arm is divided by a fascial layer (known as lateral and medial
intermuscular septa) separating the muscles into two osteofascial
Bone structure of a human arm.
compartments: the anterior and the posterior compartments of the arm.
The fascia merges with the periosteum (outer bone layer) of the humerus. The compartments contain muscles which
are innervated by the same nerve and perform the same action.
Two other muscles are considered to be partially in the arm:
Arm
5
• The large deltoid muscle is considered to have part of its body in the anterior compartment. This muscle is the
main abductor muscle of the upper limb and extends over the shoulder.
• The brachioradialis muscle originates in the arm but inserts into the forearm. This muscle is responsible for
rotating the hand so its palm faces forward (supination).
Nerve and blood supply
The cubital fossa (colloquially known as the elbow pit) is clinically important for venepuncture and for blood
pressure measurement.
Innervation
The musculocutaneous nerve, from C5, C6, C7, is the main supplier of
muscles of the anterior compartment. It originates from the lateral cord
of the brachial plexus of nerves. It pierces the coracobrachialis muscle
and gives off branches to the muscle, as well as to brachialis and
biceps brachii. It terminates as the anterior cutaneous nerve of the
forearm.
The radial nerve, which is from the fifth cervical spinal nerve to the
first thoracic spinal nerve, originates as the continuation of the
posterior cord of the brachial plexus. This nerve enters the lower
triangular space (an imaginary space bounded by, amongst others, the
shaft of the humerus and the triceps brachii) of the arm and lies deep to
the triceps brachii. Here it travels with a deep artery of the arm (the
profunda brachii), which sits in the radial groove of the humerus. This
fact is very important clinically as a fracture of the bone at the shaft of
the bone here can cause lesions or even transections in the nerve.
Cutaneous innervation of the right upper
extremity.
Other nerves passing through give no supply to the arm. These include:
• The median nerve, nerve origin C5-T1, which is a branch of the lateral and medial cords of the brachial plexus.
This nerve continues in the arm, travelling in a plane between the biceps and triceps muscles. At the cubital fossa,
this nerve is deep to the pronator teres muscle and is the most medial structure in the fossa. The nerve passes into
the forearm.
• The ulnar nerve, origin C8-T1, is a continuation of the medial cord of the brachial plexus. This nerve passes in the
same plane as the median nerve, between the biceps and triceps muscles. At the elbow, this nerve travels posterior
to the medial epicondyle of the humerus. This means that condylar fractures can cause lesion to this nerve.
Arteries
The main artery in the arm is the brachial artery. This artery is a
continuation of the axillary artery. The point at which the axillary
becomes the brachial is distal to the lower border of teres major. The
brachial artery gives off an important branch, the profunda brachii
(deep artery of the arm). This branching occurs just below the lower
border of teres major.
Main arteries of the arm.
Arm
6
The brachial artery continues to the cubital fossa in the anterior compartment of the arm. It travels in a plane between
the biceps and triceps muscles, the same as the median nerve and basilic vein. It is accompanied by venae comitantes
(accompanying veins). It gives branches to the muscles of the anterior compartment. The artery is in between the
median nerve and the tendon of the biceps muscle in the cubital fossa. It then continues into the forearm.
The profunda brachii travels through the lower triangular space with the radial nerve. From here onwards it has an
intimate relationship with the radial nerve. They are both found deep to the triceps muscle and are located on the
spiral groove of the humerus. Therefore fracture of the bone may not only lead to lesion of the radial nerve, but also
haematoma of the internal structures of the arm. The artery then continues on to anastamose with the recurrent radial
branch of the brachial artery, providing a diffuse blood supply for the elbow joint.
Veins
The veins of the arm carry blood from the extremities of the limb, as well as drain the arm itself. The two main veins
are the basilic and the cephalic veins. There is a connecting vein between the two, the median cubital vein, which
passes through the cubital fossa and is clinically important for venepuncture (withdrawing blood).
The basilic vein travels on the medial side of the arm and terminates at the level of the seventh rib.
The cephalic vein travels on the lateral side of the arm and terminates as the axillary vein. It passes through the
deltopectoral triangle, a space between the deltoid and the pectoralis major muscles.
References
[1] " arm (http:/ / www. mercksource. com/ pp/ us/ cns/ cns_hl_dorlands_split. jsp?pg=/ ppdocs/ us/ common/ dorlands/ dorland/ one/
000007845. htm)" at Dorland's Medical Dictionary
[2] MeSH Arm (http:/ / www. nlm. nih. gov/ cgi/ mesh/ 2011/ MB_cgi?mode=& term=Arm)
Basting (cooking)
Basting is a cooking technique that involves cooking meat with either
its own juices or some type of preparation such as a sauce or marinade.
The meat is left to cook, then periodically coated with the juice.
Prominently used in grilling, rotisserie, roasting, and other meat
preparations where the meat is over heat for extended periods of time,
basting is used to keep meat moist during the cooking process and also
to apply or enhance flavor. Improperly administered basting, however,
may actually lead to the very problem it is designed to prevent: the
undesired loss of moisture (drying out) of the meat.
If not compensated by countermeasures, the opening of the oven door
and the resulting loss of temperature and moisture content of the air
circulating inside can lead to increased evaporation from the meat
surfaces. In the case of tough meats such as beef, bison, and deer, the
result can be a hardened, shell-like, overcooked or burned outer crust,
while inner layers of the meat may still be undercooked or raw; with
soft meats such as poultry, the result can be a thorough drying from the
surface to the bone, as in the case of the traditional American turkey.
Basting a turkey with a turkey baster
Basting (cooking)
To prevent this, the easiest solution is to place the meat in a closed oven bag, which traps evaporating moisture and
does not let it disseminate into the oven space and then out to the kitchen. The meat is "auto basted" when the air
trapped inside the bag reaches the point of its maximum possible moisture content, and the resulting precipitate
forms into drops on the surfaces of the meat or the wall of the bag. The drops roll down to the lowest point of the
closed space, where the meat sits and cooks in the resulting juices. This technique often requires very minimal or no
added liquids other than what the meat already contains, for loss of moisture is virtually negligible from inside the
bag.
However, oven bags lose their advantage if they are opened even one time during the cooking process, and seasoned
cooks, who prefer adding flavoring, natural oils (herbs), or aromatics in different times and portions during the
process, generally use alternate practices to avoid drying out the meat. For instance, they allow extended cooking
time, administer increased amounts of juices, coat the meat with moisture rich fruits or fat-rich cuts, such as bacon,
or actual fat, place moisture rich fruits and vegetables around the cooking meats, and if possible, use a convection
oven.
This is a type of cooking usually recommended for dishes that generally taste mild, but are served with sauces that
provide complimenting or overpowering flavor to them, for example Chicken chasseur.
Basting is a technique generally known to be used for turkey, pork, chicken, duck, and beef (including steak), but
may be applied to virtually any type of meat.
External links
How Stuff Works - Basting [1]
References
[1] http:/ / recipes. howstuffworks. com/ basting-questions. htm
7
Digit (anatomy)
8
Digit (anatomy)
A digit is one of several most distal parts of a limb, such as fingers or toes, present in many vertebrates.
Names
Some languages have different names for hand and foot digits (English: respectively "finger" and "toe", French:
"doigts" and "orteils").
In other languages, e.g. Russian, Polish, Portuguese, Italian, Czech, Tagalog, Turkish & Persian there are no specific
one-word names for fingers and toes; these are called "digit of the hand" or "digit of the foot" instead.
Human digits
Humans normally have five digits on each extremity. Each digit is formed by several bones called phalanx,
surrounded by soft tissues. Every human finger normally has a nail on its distal phalanx. There can be polydactyly
number variation and extra fingers can be useful. In one individual with seven fingers, exploited his extra digits and
claimed, they “gave him some advantages in playing the piano.”[1]
Brain representation
Each finger has an orderly somatotopic representation on the cerebral cortex in the somatosensory cortex area 3b, [2]
part of area 1[3] and a distributed, overlapping representations in the supplementary motor area and primary motor
area.[4]
The somatosensory cortex representation of the hand is a dynamic reflection of the fingers on the external hand: in
syndactyly people have a clubhand of webbed, shortened fingers. However, not only are the fingers of their hands
fused, but the cortical maps of their individual fingers also form a club hand. The fingers can be surgically divided to
make a more useful hand. Surgeons did this at the Institute of Reconstructive Plastic Surgery in New York to a
32-year-old man with the initials O. G.. They touching O. G.’s fingers before and after surgery while using MRI
brain scans. Before the surgery, the fingers mapped onto his brain were fused close together; afterward, the maps of
his individual fingers did indeed separate and take the layout corresponding to a normal hand.[5]
Evolution
Two ideas about the homology of arms, hands and digits have existed
in the past 130 years. First that digits are unique to tetrapods[6] [7] and
second that antecedents were present in the fins of early sarcopterygian
fish.[8] Until recently it was concluded that "Both genetic and fossil
data support the hypothesis that digits are evolutionary novelties".[9] p.
640.
A reconstruction of a Panderichthys
However new research that has created a three-dimensional reconstruction of a Panderichthys, a coastal fish from the
Devonian period 385 million years ago, shows that these animals already had many of the homologous bones present
in the forelimbs of limbed vertebrates.[10] For example, they had "radial" bones similar to rudimentary fingers but
positioned in the arm-like base of their fins.[10] Thus there was in the evolution of tetrapods a shift such that the
outermost part of the fins were lost and came to be replaced by early digits. This change is consistent with additional
evidence from the study of actinopterygians, sharks and lungfish that the digits of tetrapods arose from pre-existing
distal radials present in more primitive fish.[10] [11]
Digit (anatomy)
Controversy still exists since Tiktaalik, a vertebrate often considered to be the missing link between fishes and
land-living animals, had stubby leg-like limbs that lacked the finger-like radial bones found in the Panderichthys.
The researchers of the paper commented that "It is difficult to say whether this character distribution implies that
Tiktaalik is autapomorphic, that Panderichthys and tetrapods are convergent, or that Panderichthys is closer to
tetrapods than Tiktaalik. At any rate, it demonstrates that the fish–tetrapod transition was accompanied by significant
character incongruence in functionally important structures.".[10] p. 638.
Bird and theropod dinosaur digits
Birds and theropod dinosaurs (from which birds evolved) have three digits on their hands. Paradoxically the two
digits that are missing are different: the bird hand (embedded in the wing) is thought to derive from the second, third
and fourth digits of the ancestral five-digit hand. In contrast, the theropod dinosaur seem to be the first, second and
third digits. Recently a Jurassic theropod intermediate fossil Limusaurus has been found in the Junggar Basin in
western China that has a complex mix: it has a first digit stub and full second, third and fourth digits but its wrist
bones are like those that are associated with the second, third and fourth digits while its finger bones are those of the
first, second and third digits.[12] This suggests the evolution of digits in birds resulted from a "shift in digit identity
characterized early stages of theropod evolution"[12]
Notes
[1] Dwight T. (1892). Fusion of hands. Memoirs of the Boston Society of Natural History, 4, 473-486.
[2] van Westen D, Fransson P, Olsrud J, Rosén B, Lundborg G, Larsson EM. (2004). Fingersomatotopy in area 3b: an fMRI-study (http:/ / www.
pubmedcentral. nih. gov/ picrender. fcgi?artid=517711& blobtype=pdf). BMC Neurosci. 5:28. PMID 15320953
[3] Nelson AJ, Chen R. (2008). Digit somatotopy within cortical areas of the postcentral gyrus in humans. Cereb Cortex. 18(10):2341-51. PMID
18245039
[4] Kleinschmidt A, Nitschke MF, Frahm J. (1997). Somatotopy in the human motor cortex hand area. A high-resolution functional MRI study.
Eur J Neurosci. 9(10):2178-86. PMID 9421177
[5] Mogilner A, Grossman JA, Ribary U, Joliot M, Volkmann J, Rapaport D, Beasley RW, Llinás RR. (1993). Somatosensory cortical plasticity
in adult humans revealed by magnetoencephalography (http:/ / www. pubmedcentral. nih. gov/ picrender. fcgi?artid=46347& blobtype=pdf).
Proc Natl Acad Sci U S A. 90(8):3593-7. PMID 8386377
[6] Holmgren N. (1933). On the origin of the tetrapod limb. Acta Zoologica 14, 185–295.
[7] Vorobyeva EI.(1992). The role of development and function in formation of tetrapod like pectoral fins. Zh. Obshch. Biol. 53, 149–158.
[8] Watson DMS. (1913). On the primitive tetrapod limb. Anat. Anzeiger 44, 24–27.
[9] Shubin N, Tabin C, Carroll S. (1997). Fossils, genes and the evolution of animal limbs. Nature. 388(6643):639-48. doi:10.1038/41710 PMID
9262397
[10] Boisvert CA, Mark-Kurik E, Ahlberg PE. (2008). The pectoral fin of Panderichthys and the origin of digits. Nature. 456(7222):636-8. PMID
18806778
[11] Than, Ker (September 24, 2008). "Ancient Fish Had Primitive Fingers, Toes" (http:/ / news. nationalgeographic. com/ news/ 2008/ 09/
080924-fish-fingers. html?source=rss). National Geographic News. .
[12] Xing Xu et al.(2009). A Jurassic ceratosaur from China helps clarify avian digital homologies. Nature 459: 940-944
doi:10.1038/nature08124
9
Duct (HVAC)
10
Duct (HVAC)
Ducts are used in heating, ventilation, and air
conditioning (HVAC) to deliver and remove air. These
needed airflows include, for example, supply air, return
air, and exhaust air.[1] Ducts also deliver, most
commonly as part of the supply air, ventilation air. As
such, air ducts are one method of ensuring acceptable
indoor air quality as well as thermal comfort.
A duct system is often called ductwork. Planning
('laying out'), sizing, optimizing, detailing, and finding
the pressure losses through a duct system is called duct
design.[2]
A round galvanized steel duct connecting to a typical diffuser
Materials
Ducts can be made out of the following materials:
Galvanized mild steel is the standard and most common
material used in fabricating ductwork.
Polyurethane and Phenolic insulation
panels (pre-insulated air ducts)
Traditionally, air ductwork is made of sheet metal
which is installed first and then lagged with insulation
as a secondary operation. Ductwork manufactured from
rigid insulation panels does not need any further
insulation and is installed in a single fix. Light weight
and installation speed are among the features of
preinsulated aluminium ductwork, also custom or
special shapes of ducts can be easily fabricated in the shop or on site.
Fire-resistance rated mechanical shaft with
HVAC sheet metal ducting and copper piping, as
well as "HOW" (Head-Of-Wall) joint between
top of concrete block wall and underside of
concrete slab, firestopped with ceramic
fibre-based firestop caulking on top of rockwool.
The ductwork construction starts with the tracing of the duct outline onto the aluminium preinsulated panel, then the
parts are typically cut at 45 degree, bent if required to obtain the different fittings (i.e. elbows, tapers) and finally
assembled with glue. Aluminium tape is applied to all seams where the external surface of the aluminium foil has
been cut. A variety of flanges are available to suit various installation requirements. All internal joints are sealed
with sealant.
Among the various types of rigid polyurethane foam panels available, a new water formulated panel stands out. In
this particular panel, the foaming process is obtained through the use of water instead of the CFC, HCFC, HFC and
HC gasses. And most manufacturers of rigid polyurethane foam panels use normal pentane as foaming agent instead
of the CFC, HCFC, HFC and HC gasses, so do manufacturers of rigid phenolic foam panels.
A rigid phenolic insulation ductwork system is available and complies with the UL 181 standard for class 1 air
ductwork.
Both polyurethane foam panels and phenolic foam panels are then coated with aluminum sheets on both sides, with
outside aluminum thicknesses that can vary from 80 micrometres for indoor use to 200 micrometres for external use
or high air pressure in order to guarantee the high mechanical characteristics of the duct, or then coated with
aluminum sheets on inside, and coated with 200 micrometres sheet metal or pre-painted sheet metal on outside.
Duct (HVAC)
Fiberglass duct board (preinsulated non metallic ductwork)
Fiberglass duct board panels provide built-in thermal insulation and the interior surface absorbs sound, helping to
provide quiet operation of the HVAC system. The duct board is formed by sliding a specially-designed knife along
the board using a straightedge as a guide; the knife automatically trims out a "valley" with 45° sides; the valley does
not quite penetrate the entire depth of the duct board, providing a thin section that acts as a hinge. The duct board can
then be folded along the valleys to produce 90° folds, making the rectangular duct shape in the fabricator's desired
size. The duct is then closed with staples and special aluminum or similar 'metal-backed' tape. Commonly available
duct tape should not be used on air ducts, metal, fiberglass, or otherwise, that are intended for long-term use; the
adhesive on so called 'duct tape' dries and releases with time.
Flexible Ducting
Flexible ducts, known as flex, have a variety of configurations, but for
HVAC applications, they are typically flexible plastic over a metal
wire coil to make round, flexible duct. In the United States, the
insulation is usually glass wool, but other markets such as Australia,
use both polyester fibre and glass wool for thermal insulation. A
protective layer surrounds the insulation, and is usually composed of
polyethylene or metalised PET. Flexible duct is very convenient for
attaching supply air outlets to the rigid ductwork. However, the
pressure loss through flex is higher than for most other types of ducts.
As such, designers and installers attempt to keep their installed lengths
Example of flexible ducting.
(runs) short, e.g., less than 15 feet or so, and to minimize turns. Kinks
in flex must be avoided. Some flexible duct markets prefer to avoid
using flexible duct on the return air portions of HVAC systems, however flexible duct can tolerate moderate negative
pressures - the UL181 test requires a negative pressure of 200 Pa.[3]
Fabric
Fabric ducting, also known as air socks, duct socks or textile ducts, are designed for even air distribution throughout
the entire length. Usually made of special polyester material, fabric ducts can provide air to a space more effectively
than a conventional exposed duct system.
Fabric duct is a misnomer as "fabric duct" is actually an "air distribution device" and is not intended as a conduit
(duct) for conditioned air. However, as it often replaces hard or metal ductwork it is easy to perceive it simply as
duct. Fabric air dispersion systems, is the more definitive name. As they may be manufactured with venting or
orifices for even air distribution along any length of the system, they commonly will provide a more even
distribution and blending of the conditioned air in a given space. As "fabric duct" is used for air distribution, textile
ducts are not rated for nor should they be used in ceilings or concealed attic spaces. Applications for fabric duct in
raise floor applications; however, are available. Depending on the manufacturer, "fabric duct" is available in standard
and custom colours with options for silk screening or other forms of appliques.
"Fabric duct", depending on the manufacturer, may be available in air permeable(porous) or non-porous fabric. As a
benchmark, a designer may make the determination of which fabric is more applicable by asking the question if the
application would require insulated metal duct? If metal duct would be insulated in a given application or
installation, air permeable fabric would be recommended as it will not commonly create condensation on its surface
and can therefore be used where air is to be supplied below the dew point. Again; depending on the material and
manufacturer, material that eliminates moisture may also be healthier and may also be provided with an active
anti-microbial agent to inhibit bacteria growth. Porous material also tends to require less maintenance as it repels
11
Duct (HVAC)
dust and other airborne contaminants.
Duct system components
Besides the ducts themselves, complete ducting systems contain many other components.
Vibration isolators
A duct system often begins at an air handler. The blowers in the air handlers can create substantial vibration and the
large area of the duct system would transmit this noise and vibration to the inhabitants of the building. To avoid this,
vibration isolators (flexible sections) are normally inserted into the duct immediately before and after the air handler.
The rubberized canvas-like material of these sections allow the air handler to vibrate without transmitting much
vibration to the attached ducts.
Take-offs
Downstream of the air handler, the supply air trunk duct will commonly fork, providing air to many individual air
outlets such as diffusers, grilles, and registers. When the system is designed with a main duct branching into many
subsidiary branch ducts, fittings called take-offs allow a small portion of the flow in the main duct to be diverted
into each branch duct. Take-offs may be fitted into round or rectangular openings cut into the wall of the main duct.
The take-off commonly has many small metal tabs that are then bent to retain the take-off on the main duct; round
versions are called spin-in fittings. Other take-off designs use a snap-in attachment method, sometimes coupled with
an adhesive foam gasket to provide improved sealing. The outlet of the take-off then connects to the rectangular,
oval, or round branch duct.
Stacks, boots, and heads
Ducts, especially in homes, must often allow air to travel vertically within relatively thin walls. These vertical ducts
are called stacks and are formed with either very wide and relatively thin rectangular sections or oval sections. At the
bottom of the stack, a stack boot provides a transition from an ordinary large round or rectangular duct to the thin
wall-mounted duct. At the top, a stack head can provide a transition back to ordinary ducting while a register head
allows the transition to a wall-mounted air register.
Volume Control Dampers
Ducting systems must often provide a method of adjusting the volume of air flow to various parts of the system.
VCDs (Volume Control Dampers - Not To Be confused with Smoke/Fire Dampers) provide this function. Besides
the regulation provided at the registers or diffusers that spread air into individual rooms, dampers can be fitted within
the ducts themselves. These dampers may be manual or automatic. Zone dampers provide automatic control in
simple systems while VAVs allow control in sophisticated systems.
Smoke/Fire Dampers
Smoke and Fire dampers are found in ductwork, where the duct passes through a firewall or firecurtain. Smoke
dampers are automated with the use of a mechanical motor often referred to as an Actuator. A probe connected to the
motor is installed in the run of duct, and detects smoke within the duct system which has been extracted from a
room, or which is being supplied from the AHU (Air Handling Unit) or elsewhere within the run. Once smoke is
detected within the duct, the Actuator triggers the motor release and the smoke damper will automatically close until
manually re-opened.
You will also find Fire dampers in the same places as smoke dampers, depending on the application of the area after
the firewall. Unlike smoke dampers, they are not triggered by any electrical system, which is perfect in the event of
12
Duct (HVAC)
an electrical failure where the Smoke dampers would fail to close. A fire damper is held open by a bar crossing the
corrigated screen, which will break and allow the damper to close when air in the duct is above a certain temperature.
This again will then have to be manually re-opened.
Plenums
Plenums are the central distribution and collection units for an HVAC system. The return plenum carries the air from
several large return grills (vents) to a central air handler. The supply plenum directs air from the central unit to the
rooms which the system is designed to heat or cool.
Terminal units
While single-zone constant air volume systems typically don't have them, other types of air distribution systems
often have terminal units in the branch ducts. Usually there is one terminal unit per thermal zone. Some types of
terminal units are VAV 'boxes' of either single or dual duct, fan-powered mixing boxes of either parallel or series
arrangement, and induction terminal units. Terminal units may also include either, or both, a heating or cooling coil.
Air terminals
'Air terminals' are the supply air outlets and 'return' or 'exhaust air inlets'. For supply, diffusers are most common, but
grilles, and for very small HVAC systems such as in residences, 'registers' are also used widely. Return or 'exhaust
grilles' are used primarily for appearance reasons, but some also incorporate an air filter and are known as 'filter
returns'.[4]
Duct cleaning
The position of the U.S. Environmental Protection Agency (EPA) is that "If no one in your household suffers from
allergies or unexplained symptoms or illnesses and if, after a visual inspection of the inside of the ducts, you see no
indication that your air ducts are contaminated with large deposits of dust or mold (no musty odor or visible mold
growth), having your air ducts cleaned is probably unnecessary."[5]
Studies by the EPA and the Canadian Mortgage and Housing Corporation (CMHC) in the 1990s has lead CMHC to
conclude that "duct cleaning will not usually change the quality of the air you breathe, nor will it significantly affect
airflows or heating costs".[6]
Signs and indicators
•
•
•
•
•
•
•
When cleaning, you need to sweep and dust your furniture more than usual.
After cleaning, there's still left over dust floating around the house that you can see.
After or during sleep you experience headaches, nasal congestion, or other sinus problems.
Rooms in your house have little or no air flow coming from the vents.
You're constantly getting sick or are experience more allergies than usual
When you turn on the furnace or air conditioner there's musty or stale odor
You're experiencing signs of sickness: fatigue, headache, sneezing, stuffy or running nose, irritability, nausea, dry
or burning sensation in eyes, nose and throat.[7]
13
Duct (HVAC)
Duct sealing
Duct Sealing is the sealing of leaks in air ducts in order to reduce air leakage, optimize efficiency, and control entry
of pollutants into the home or building. Air pressure combined with air duct leakage can lead to a loss of energy in a
HVAC system and duct sealing solves issues of energy loss in the system.
Duct tape is not used for sealing ducts. Building codes call for special fire-resistant tapes, often with foil backings
and long lasting adhesives.
Signs of leaky or poorly performing air ducts include:
• Utility bills in winter and summer months above average relative to rate fluctuation
• Spaces or rooms that are difficult to heat or cool
• Duct location in an attic, attached garage, leaky floor cavity, crawl space or unheated basement.[8]
References
[1] The Fundamentals volume of the ASHRAE Handbook, ASHRAE, Inc., Atlanta, GA, USA, 2005
[2] HVAC Systems -- Duct Design, 3rd Ed., SMACNA, 1990
[3] "Factory-Made Air Ducts and Air Connectors UL 181" (http:/ / ulstandardsinfonet. ul. com/ scopes/ scopes. asp?fn=0181. html), UL
Standards, retrieved September 2, 2009
[4] Designer's Guide to Ceiling-Based Room Air Diffusion, Rock and Zhu, ASHRAE, Inc., Atlanta, GA, USA, 2002
[5] "Should You Have the Air Ducts in Your Home Cleaned?" (http:/ / www. epa. gov/ iaq/ pubs/ airduct. html), U.S. Environmental Protection
Agency, retrieved April 17, 2008
[6] "Should You Get Your Heating Ducts Cleaned?" (http:/ / www. cmhc-schl. gc. ca/ en/ co/ maho/ gemare/ gemare_011. cfm), Canadian
Mortgage and Housing Corporation, retrieved April 17, 2008
[7] Air Conditioning Explained (http:/ / airconditioningexplained. com/ ?p=15), retrieved 27 July 2009
[8] (http:/ / www. energystar. gov/ index. cfm?c=home_improvement. hm_improvement_ducts)
Further reading
• Air Diffusion Council Flexible Duct Performance and Installation Standard, 4th Ed., 2003
14
Ear
15
Ear
Ear
Human (external) ear
The ear is the anatomical organ that detects sound. It not only acts as a receiver for sound, but also plays a major
role in the sense of balance and body position. The ear is part of the auditory system.
The word "ear" may be used correctly to describe the entire organ or just the visible portion. In most mammals, the
visible ear is a flap of tissue that is also called the pinna and is the first of many steps in hearing. In people, the pinna
is often called the auricle. Vertebrates have a pair of ears, placed symmetrically on opposite sides of the head. This
arrangement aids in the ability to localize sound sources.
Introduction to ears and hearing
Audition is the scientific name for the sense of sound. Sound is a form of energy that moves through air, water, and
other matter, in waves of pressure. Sound is the means of auditory communication, including frog calls, bird songs
and spoken language. Although the ear is the vertebrate sense organ that recognizes sound, it is the brain and central
nervous system that "hears". Sound waves are perceived by the brain through the firing of nerve cells in the auditory
portion of the central nervous system. The ear changes sound pressure waves from the outside world into a signal of
nerve impulses sent to the brain.
The outer part of the ear collects sound.
That sound pressure is amplified through the
middle portion of the ear and, in land
animals, passed from the medium of air into
a liquid medium. The change from air to
liquid occurs because air surrounds the head
and is contained in the ear canal and middle
ear, but not in the inner ear. The inner ear is
hollow, embedded in the temporal bone, the
densest bone of the body. The hollow
channels of the inner ear are filled with
liquid, and contain a sensory epithelium that
is studded with hair cells. The microscopic
"hairs" of these cells are structural protein
filaments that project out into the fluid. The
hair cells are mechanoreceptors that release
a
chemical
neurotransmitter
when
Anatomy of the human ear. The length of the auditory canal is exaggerated for
viewing purposes.
stimulated. Sound waves moving through fluid push the filaments; if the filaments bend over enough it causes the
hair cells to fire. In this way sound waves are transformed into nerve impulses. In vision, the rods and cones of the
Ear
16
retina play a similar role with light as the hair cells do with sound. The nerve impulses travel from the left and right
ears through the eighth cranial nerve to both sides of the brain stem and up to the portion of the cerebral cortex
dedicated to sound. This auditory part of the cerebral cortex is in the temporal lobe.
The part of the ear that is dedicated to sensing balance and position also sends impulses through the eighth cranial
nerve, the VIIIth nerve's Vestibular Portion. Those impulses are sent to the vestibular portion of the central nervous
system. The human ear can generally hear sounds with frequencies between 20 Hz and 20 kHz (the audio range).
Although the sensation of hearing requires an intact and functioning auditory portion of the central nervous system
as well as a working ear, human deafness (extreme insensitivity to sound) most commonly occurs because of
abnormalities of the inner ear, rather than the nerves or tracts of the central auditory system.[1]
Mammalian ear
The shape of outer ear of mammals varies widely
across species. However the inner workings of
mammalian ears (including humans') are very similar.
Outer ear (pinna, ear canal, surface of ear
drum)
The outer ear is the most external portion of the ear.
The outer ear includes the pinna (also called auricle),
the ear canal, and the very most superficial layer of the
ear drum (also called the tympanic membrane). In
humans, and almost all vertebrates, the only visible
portion of the ear is the outer ear. The word "ear" may
properly refer to the pinna (the flesh covered cartilage
appendage on either side of the head). This portion of
the ear is very vital for hearing. The outer ear does help
get sound (and imposes filtering), but the ear canal is
very important. Unless the canal is open, hearing will
be dampened. Ear wax (cerumen) is produced by
glands in the skin of the outer portion of the ear canal.
This outer ear canal skin is applied to cartilage; the
thinner skin of the deep canal lies on the bone of the
Bat pinnae come in different sizes and shapes
skull. Only the thicker cerumen-producing ear canal
skin has hairs. The outer ear ends at the most
superficial layer of the tympanic membrane. The tympanic membrane is commonly called the ear drum. The pinna
helps direct sound through the ear canal to the tympanic membrane (eardrum).
The framework of the auricle consists of a single piece of yellow fibrocartilage with a complicated relief on the
anterior, concave side and a fairly smooth configuration on the posterior, convex side. The Darwinian tubercle,
which is present in some people, lies in the descending part of the helix and corresponds to the true ear tip of the
long-eared mammals. The lobule merely contains subcutaneous tissue.[2] In some animals with mobile pinnae (like
the horse), each pinna can be aimed independently to better receive the sound. For these animals, the pinnae help
localize the direction of the sound source. Human beings localize sound within the central nervous system, by
comparing arrival-time differences and loudness from each ear, in brain circuits that are connected to both ears. This
process is commonly referred to as EPS, or Echo Positioning System.
Ear
17
Human outer ear and culture
The auricles also have an effect on facial appearance. In Western
societies, protruding ears (present in about 5% of ethnic Europeans)
have been considered unattractive, particularly if asymmetric. The first
surgery to reduce the projection of prominent ears was published in the
medical literature in 1881.
The ears have also been ornamented with jewelry for thousands of
years, traditionally by piercing of the earlobe. In some cultures,
ornaments are placed to stretch and enlarge the earlobes. Tearing of the
earlobe from the weight of heavy earrings, or from traumatic pull of an
earring (for example by snagging on a sweater being removed), is
fairly common.[3] The repair of such a tear is usually not difficult.
Stretching of the earlobe and various cartilage
piercings
A cosmetic surgical procedure to reduce the size or change the shape of the ear is called an otoplasty. In the rare
cases when no pinna is formed (atresia), or is extremely small (microtia) reconstruction of the auricle is possible.
Most often, a cartilage graft from another part of the body (generally, rib cartilage) is used to form the matrix of the
ear, and skin grafts or rotation flaps are used to provide the covering skin. Recently ears have been grown on a rat's
back and attached to human heads after. However, when babies are born without an auricle on one or both sides, or
when the auricle is very tiny, the ear canal is ordinarily either small or absent, and the middle ear often has
deformities. The initial medical intervention is aimed at assessing the baby's hearing and the condition of the ear
canal, as well as the middle and inner ear. Depending on the results of tests, reconstruction of the outer ear is done in
stages, with planning for any possible repairs of the rest of the ear.[4] [5] [6]
Middle ear
The middle ear, an air-filled cavity behind the ear drum (tympanic membrane), includes the three ear bones or
ossicles: the malleus (or hammer), incus (or anvil), and stapes (or stirrup). The opening of the Eustachian tube is also
within the middle ear. The malleus has a long process (the manubrium, or handle) that is attached to the mobile
portion of the eardrum. The incus is the bridge between the malleus and stapes. The stapes is the smallest named
bone in the human body. The three bones are arranged so that movement of the tympanic membrane causes
movement of the malleus, which causes movement of the incus, which causes movement of the stapes. When the
stapes footplate pushes on the oval window, it causes movement of fluid within the cochlea (a portion of the inner
ear).
In humans and other land animals the middle ear (like the ear canal) is normally filled with air. Unlike the open ear
canal, however, the air of the middle ear is not in direct contact with the atmosphere outside the body. The
Eustachian tube connects from the chamber of the middle ear to the back of the nasopharynx. The middle ear is very
much like a specialized paranasal sinus, called the tympanic cavity; it, like the paranasal sinuses, is a hollow
mucosa-lined cavity in the skull that is ventilated through the nose. The mastoid portion of the human temporal bone,
which can be felt as a bump in the skull behind the pinna, also contains air, which is ventilated through the middle
ear.
Ear
18
Middle Ear
Malleus
Tensor Tympani
Incus
Stapedius
Labyrinth
Stapes
Auditory Canal
Tympanic Membrane
(Ear Drum)
Eustachian Tube
Tympanic cavity
Components of the middle ear
Normally, the Eustachian tube is collapsed, but it gapes open both with swallowing and with positive pressure. When
taking off in an airplane, the surrounding air pressure goes from higher (on the ground) to lower (in the sky). The air
in the middle ear expands as the plane gains altitude, and pushes its way into the back of the nose and mouth. On the
way down, the volume of air in the middle ear shrinks, and a slight vacuum is produced. Active opening of the
Eustachian tube is required to equalize the pressure between the middle ear and the surrounding atmosphere as the
plane descends. The diver also experiences this change in pressure, but with greater rates of pressure change; active
opening of the Eustachian tube is required more frequently as the diver goes deeper into higher pressure.
The arrangement of the tympanic membrane and ossicles works to efficiently couple the sound from the opening of
the ear canal to the cochlea. There are several simple mechanisms that combine to increase the sound pressure. The
first is the "hydraulic principle". The surface area of the tympanic membrane is many times that of the stapes
footplate. Sound energy strikes the tympanic membrane and is concentrated to the smaller footplate. A second
mechanism is the "lever principle". The dimensions of the articulating ear ossicles lead to an increase in the force
applied to the stapes footplate compared with that applied to the malleus. A third mechanism channels the sound
pressure to one end of the cochlea, and protects the other end from being struck by sound waves. In humans, this is
called "round window protection", and will be more fully discussed in the next section.
Abnormalities such as impacted ear wax (occlusion of the external ear canal), fixed or missing ossicles, or holes in
the tympanic membrane generally produce conductive hearing loss. Conductive hearing loss may also result from
middle ear inflammation causing fluid build-up in the normally air-filled space. Tympanoplasty is the general name
of the operation to repair the middle ear's tympanic membrane and ossicles. Grafts from muscle fascia are ordinarily
used to rebuild an intact ear drum. Sometimes artificial ear bones are placed to substitute for damaged ones, or a
disrupted ossicular chain is rebuilt in order to conduct sound effectively.
Ear
19
Inner ear: cochlea, vestibule, and semicircular canals
Inner Ear
Posterior Canal
Superior Canal
Utricle
Horizontal
Canal
Vestibule
Cochlea
Saccule
Components of the inner ear
The inner ear includes both the organ of hearing (the cochlea) and a sense organ that is attuned to the effects of both
gravity and motion (labyrinth or vestibular apparatus). The balance portion of the inner ear consists of three
semicircular canals and the vestibule. The inner ear is encased in the hardest bone of the body. Within this ivory hard
bone, there are fluid-filled hollows. Within the cochlea are three fluid filled spaces: the scala tympani, the scala
vestibuli and the scala media. The eighth cranial nerve comes from the brain stem to enter the inner ear. When sound
strikes the ear drum, the movement is transferred to the footplate of the stapes, which presses it into one of its
fluid-filled ducts through the oval window of cochlea . The fluid inside this duct is moved, flowing against the
receptor cells of the Organ of Corti, which fire. These stimulate the spiral ganglion, which sends information through
the auditory portion of the eighth cranial nerve to the brain.
Hair cells are also the receptor cells involved in balance, although the hair cells of the auditory and vestibular
systems of the ear are not identical. Vestibular hair cells are stimulated by movement of fluid in the semicircular
canals and the utricle and saccule. Firing of vestibular hair cells stimulates the Vestibular portion of the eighth
cranial nerve.[7]
Damage to the human ear
Outer ear trauma
Auricle
The auricle can be easily damaged. Because it is skin-covered cartilage, with only a thin padding of connective
tissue, rough handling of the ear can cause enough swelling to jeopardize the blood-supply to its framework, the
auricular cartilage. That entire cartilage framework is fed by a thin covering membrane called the perichondrium
(meaning literally: around the cartilage). Any fluid from swelling or blood from injury that collects between the
perichondrium and the underlying cartilage puts the cartilage in danger of being separated from its supply of
nutrients. If portions of the cartilage starve and die, the ear never heals back into its normal shape. Instead, the
cartilage becomes lumpy and distorted. Wrestler's Ear is one term used to describe the result, because wrestling is
one of the most common ways such an injury occurs. Cauliflower ear is another name for the same condition,
Ear
20
because the thickened auricle can resemble that vegetable.
The lobule of the ear (ear lobe) is the one part of the human auricle that normally contains no cartilage. Instead, it is
a wedge of adipose tissue (fat) covered by skin. There are many normal variations to the shape of the ear lobe, which
may be small or large. Tears of the earlobe can be generally repaired with good results. Since there is no cartilage,
there is not the risk of deformity from a blood clot or pressure injury to the ear lobe.
Other injuries to the external ear occur fairly frequently, and can leave a major deformity. Some of the more
common ones include, laceration from glass, knives, and bite injuries, avulsion injuries, cancer, frostbite, and burns.
Ear canal
Ear canal injuries can come from firecrackers and other explosives, and mechanical trauma from placement of
foreign bodies into the ear. The ear canal is most often self-traumatized from efforts at ear cleaning. The outer part of
the ear canal rests on the flesh of the head; the inner part rests in the opening of the bony skull (called the external
auditory meatus). The skin is very different on each part. The outer skin is thick, and contains glands as well as hair
follicles. The glands make cerumen (also called ear wax). The skin of the outer part moves a bit if the pinna is
pulled; it is only loosely applied to the underlying tissues. The skin of the bony canal, on the other hand, is not only
among the most delicate skin in the human body, it is tightly applied to the underlying bone. A slender object used to
blindly clean cerumen out of the ear often results instead with the wax being pushed in, and contact with the thin
skin of the bony canal is likely to lead to laceration and bleeding.
Middle ear trauma
Like outer ear trauma, middle ear trauma most often comes from blast injuries and insertion of foreign objects into
the ear. Skull fractures that go through the part of the skull containing the ear structures (the temporal bone) can also
cause damage to the middle ear. Small perforations of the tympanic membrane usually heal on their own, but large
perforations may require grafting. Displacement of the ossicles will cause a conductive hearing loss that can only be
corrected with surgery. Forcible displacement of the stapes into the inner ear can cause a sensory neural hearing loss
that cannot be corrected even if the ossicles are put back into proper position. Because human skin has a top
waterproof layer of dead skin cells that are constantly shedding, displacement of portions of the tympanic membrane
or ear canal into the middle ear or deeper areas by trauma can be particularly traumatic. If the displaced skin lives
within a closed area, the shed surface builds up over months and years and forms a cholesteatoma. The -oma ending
of that word indicates a tumour in medical terminology, and although cholesteatoma is not a neoplasm (but a skin
cyst), it can expand and erode the ear structures. The treatment for cholesteatoma is surgical.
Inner ear trauma
There are two principal damage mechanisms to the inner ear in industrialized society, and both injure hair cells. The
first is exposure to elevated sound levels (noise trauma), and the second is exposure to drugs and other substances
(ototoxicity).
In 1972 the U.S. EPA told Congress that at least 34 million people were exposed to sound levels on a daily basis that
are likely to lead to significant hearing loss.[8] The worldwide implication for industrialized countries would place
this exposed population in the hundreds of millions. The National Institute for Occupational Safety and Health has
recently published research on the estimated numbers of persons with hearing difficulty (11%) and the percentage
that can be attributed to occupational noise exposure (24%).[9] Furthermore, according to the National Health and
Nutrition Examination Survey (NHANES), approximately twenty-two million (17%) US workers reported exposure
to hazardous workplace noise.[10] Workers exposed to hazardous noise further exacerbate the potential for
developing noise induced hearing loss when they do not wear (hearing protection).
Ear
21
Vestigial structures
It has long been known that humans, and indeed primates such as the
orangutan and chimpanzee have ear muscles that are minimally
developed and non-functional, yet still large enough to be easily
identifiable.[11] These undeveloped muscles are vestigial structures. A
muscle that cannot move the ear, for whatever reason, can no longer be
said to have any biological function. This serves as evidence of
homology between related species. In humans there is variability in
these muscles, such that some people are able to move their ears in
various directions, and it has been said that it may be possible for
others to gain such movement by repeated trials.[11] In such primates
the inability to move the ear is compensated mainly by the ability to
turn the head on a horizontal plane, an ability which is not common to
most monkeys—a function once provided by one structure is now
replaced by another.[12]
Comparative anatomy of primate ears: Human
(left) and Barbary Macaque (right).
The outer structure of the ear also shows some vestigial features, such
as the node or point on the helix of the ear known as Darwin's tubercle
which is found in around 10% of the population, this feature is labelled
(a) in the accompanying figure.
Invertebrate hearing organs
Only vertebrate animals have ears, although many invertebrates are
able to detect sound using other kinds of sense organs. In insects,
tympanal organs are used to hear distant sounds. They are not confined
to the head, but can occur in different locations depending on the group
of insects.[13]
Human ear (from Descent of Man)
The tympanal organs of some insects are extremely sensitive, offering
acute hearing beyond that of most other animals. The female cricket fly
Ormia ochracea has a tympanal organs on each side of her abdomen. They are connected by a thin bridge of
exoskeleton and they function like a tiny pair of ear drums, but because they are linked, they provide acute
directional information. The fly uses her "ears" to detect the call of her host, a male cricket. Depending on where the
song of the cricket is coming from the fly's hearing organs will reverberate at slightly different frequencies. This
difference may be as little as 50 billionths of a second, but it is enough to allow the fly to home in directly on a
singing male cricket and parasitize it.[14]
Simpler structures allow arthropods to detect near field sounds. Spiders and cockroaches, for example, have hairs on
their legs which are used for detecting sound. Caterpillars may also have hairs on their body that perceive
vibrations[15] and allow them to respond to the sound.
Ear
22
References
[1] Greinwald, John H. Jr MD; Hartnick, Christopher J. MD The Evaluation of Children With Hearing Loss. Archives of Otolaryngology —
Head & Neck Surgery. 128(1):84-87, January 2002
[2] Stenström, J. Sten: Deformities of the ear; In: Grabb, W., C., Smith, J.S. (Edited): “Plastic Surgery”, Little, Brown and Company, Boston,
1979, ISBN 0-316-32269-5 (C), ISBN 0-316-32268-7 (P)
[3] Deborah S. Sarnoff, Robert H. Gotkin, and Joan Swirsky (2002). Instant Beauty: Getting Gorgeous on Your Lunch Break (http:/ / books.
google. com/ books?id=ljeY_Tvyl_MC& pg=PA60& ots=pt_I8xjg9k& dq=earlobe+ tear+ earring& sig=YBnRJSoIUiA1Kjhrzpq_Odd_0yk).
St. Martin's Press. ISBN 031228697X. .
[4] Lam SM. Edward Talbot Ely: father of aesthetic otoplasty. [Biography. Historical Article. Journal Article] Archives of Facial Plastic Surgery.
6(1):64, 2004 Jan-Feb.
[5] Siegert R. Combined reconstruction of congenital auricular atresia and severe microtia. [Evaluation Studies. Journal Article] Laryngoscope.
113(11):2021-7; discussion 2028-9, 2003 Nov.
[6] Trigg DJ. Applebaum EL. Indications for the surgical repair of unilateral aural atresia in children. [Review] [33 refs] [Journal Article.
Review], American Journal of Otology. 19(5):679-84; discussion 684-6, 1998 September
[7] Anson and Donaldson, Surgical Anatomy of the Temporal Bone, 4th Edition, Raven Press, 1992
[8] Senate Public Works Committee, Noise Pollution and Abatement Act of 1972, S. Rep. No. 1160, 92nd Cong. 2nd session.
[9] Tak SW, Calvert GM, "Hearing Difficulty Attributable to Employment by Industry and Occupation: An Analysis of the National Health
Interview Survey - United States, 1997 to 2003," J. Occup. Env. Med. 2008, 50:46-56
[10] Tak SW, Davis RR, Calvert GM "Exposure to Hazardous Workplace Noise and Use of Hearing Protection Devices Among US WOrkers,
1999-2004," Am. J. Ind. Med. 2009, 52:358-371
[11] Darwin, Charles (1871). The Descent of Man, and Selection in Relation to Sex. John Murray: London.
[12] Mr. St. George Mivart, Elementary Anatomy, 1873, p. 396.
[13] Yack, JE, and JH Fullard, 1993. What is an insect ear? Ann. Entomol. Soc. Am. 86(6): 677-682.
[14] Piper, Ross (2007), Extraordinary Animals: An Encyclopedia of Curious and Unusual Animals, Greenwood Press.
[15] Scoble, MJ. 1992. The Lepidoptera: Form, function, and diversity. Oxford University Press.
External links
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•
•
•
•
Protein behind hearing (http://news.bbc.co.uk/2/hi/health/3740680.stm)
3D Ear page (http://audilab.bmed.mcgill.ca/~daren/3Dear/3d_ear_homepage.html)
Details of various ear problems (http://www.entusa.com/external_ear_canal.htm)
Ear wiggling mechanism unmasked (http://www.abc.net.au/science/articles/2006/05/25/1647353.htm)
Cotton swabs can pose serious health risk: coroner from ctv.ca (http://www.ctv.ca/servlet/ArticleNews/story/
CTVNews/20080205/cotton_swab_080205/20080205?hub=Health)
• Radiology of the Ear Canal (http://rad.usuhs.edu/medpix/master.php3?mode=case_viewer&pt_id=13048&
imid=49500&quiz=no#top) from MedPix
Eye
23
Eye
Eye
Schematic diagram of the vertebrate eye.
Compound eye of Antarctic krill
Eyes are organs that detect light, and convert it to electro-chemical impulses in neurons. The simplest photoreceptors
in conscious vision connect light to movement. In higher organisms the eye is a complex optical system which
collects light from the surrounding environment; regulates its intensity through a diaphragm; focuses it through an
adjustable assembly of lenses to form an image; converts this image into a set of electrical signals; and transmits
these signals to the brain, through complex neural pathways that connect the eye, via the optic nerve, to the visual
cortex and other areas of the brain. Eyes with resolving power have come in ten fundamentally different forms, and
96% of animal species possess a complex optical system.[1] Image-resolving eyes are present in molluscs, chordates
and arthropods.[2]
The simplest "eyes", such as those in microorganisms, do nothing but detect whether the surroundings are light or
dark, which is sufficient for the entrainment of circadian rhythms. From more complex eyes, retinal photosensitive
ganglion cells send signals along the retinohypothalamic tract to the suprachiasmatic nuclei to effect circadian
Eye
24
adjustment.
Overview
Complex eyes can distinguish shapes and colours. The visual
fields of many organisms, especially predators, involve large
areas of binocular vision to improve depth perception; in
other organisms, eyes are located so as to maximize the field
of view, such as in rabbits and horses, which have monocular
vision.
According to the theory of biological evolution, the first
proto-eyes evolved among animals 600 million years ago,
about the time of the Cambrian explosion.[3] The last
common ancestor of animals possessed the biochemical
toolkit necessary for vision, and more advanced eyes have
evolved in 96% of animal species in six of the thirty-plus[4]
main phyla.[1] In most vertebrates and some molluscs, the
Eye of the wisent,
the European bison
eye works by allowing light to enter and project onto a
light-sensitive panel of cells, known as the retina, at the rear
of the eye. The cone cells (for colour) and the rod cells (for low-light contrasts) in the retina detect and convert light
into neural signals for vision. The visual signals are then transmitted to the brain via the optic nerve. Such eyes are
typically roughly spherical, filled with a transparent gel-like substance called the vitreous humour, with a focusing
lens and often an iris; the relaxing or tightening of the muscles around the iris change the size of the pupil, thereby
regulating the amount of light that enters the eye,[5] and reducing aberrations when there is enough light.[6]
The eyes of most cephalopods, fish, amphibians and snakes have fixed lens shapes, and focusing vision is achieved
[7]
by telescoping the lens—similar to how a camera focuses.
Compound eyes are found among the arthropods and are composed of many simple facets which, depending on the
details of anatomy, may give either a single pixelated image or multiple images, per eye. Each sensor has its own
lens and photosensitive cell(s). Some eyes have up to 28,000 such sensors, which are arranged hexagonally, and
which can give a full 360-degree field of vision. Compound eyes are very sensitive to motion. Some arthropods,
including many Strepsiptera, have compound eyes of only a few facets, each with a retina capable of creating an
image, creating vision. With each eye viewing a different thing, a fused image from all the eyes is produced in the
brain, providing very different, high-resolution images.
Possessing detailed hyperspectral colour vision, the Mantis shrimp has been reported to have the world's most
complex colour vision system.[8] Trilobites, which are now extinct, had unique compound eyes. They used clear
calcite crystals to form the lenses of their eyes. In this, they differ from most other arthropods, which have soft eyes.
The number of lenses in such an eye varied, however: some trilobites had only one, and some had thousands of
lenses in one eye.
In contrast to compound eyes, simple eyes are those that have a single lens. For example, jumping spiders have a
large pair of simple eyes with a narrow field of view, supported by an array of other, smaller eyes for peripheral
vision. Some insect larvae, like caterpillars, have a different type of simple eye (stemmata) which gives a rough
image. Some of the simplest eyes, called ocelli, can be found in animals like some of the snails, which cannot
actually "see" in the normal sense. They do have photosensitive cells, but no lens and no other means of projecting
an image onto these cells. They can distinguish between light and dark, but no more. This enables snails to keep out
of direct sunlight. In organisms dwelling near deep-sea vents, compound eyes have been secondarily simplified and
adapted to spot the infra-red light produced by the hot vents–in this way the bearers can spot hot springs and avoid
Eye
25
being boiled alive.[9]
Evolution
Photoreception is phylogenetically very old, with
various theories of phylogenesis.[10] The common
origin (monophyly) of all animal eyes is now widely
accepted as fact. This is based upon the shared
anatomical and genetic features of all eyes; that is,
all modern eyes, varied as they are, have their
origins in a proto-eye believed to have evolved some
540 million years ago.[11] [12] [13] The majority of
the advancements in early eyes are believed to have
taken only a few million years to develop, since the
first predator to gain true imaging would have
touched off an "arms race".[14] Prey animals and
competing predators alike would be at a distinct
disadvantage without such capabilities and would be
less likely to survive and reproduce. Hence multiple
eye types and subtypes developed in parallel.
Eyes in various animals show adaption to their
requirements. For example, birds of prey have much
greater visual acuity than humans, and some can see
ultraviolet light. The different forms of eye in, for
example, vertebrates and mollusks are often cited as
examples of parallel evolution, despite their distant
common ancestry.
Evolution of the eye
The very earliest "eyes", called eyespots, were
simple patches of photoreceptor protein in unicellular animals. In multicellular beings, multicellular eyespots
evolved, physically similar to the receptor patches for taste and smell. These eyespots could only sense ambient
brightness: they could distinguish light and dark, but not the direction of the lightsource.[15]
Through gradual change, as the eyespot depressed into a shallow "cup" shape, the ability to slightly discriminate
directional brightness was achieved by using the angle at which the light hit certain cells to identify the source. The
pit deepened over time, the opening diminished in size, and the number of photoreceptor cells increased, forming an
effective pinhole camera that was capable of dimly distinguishing shapes.[16]
The thin overgrowth of transparent cells over the eye's aperture, originally formed to prevent damage to the eyespot,
allowed the segregated contents of the eye chamber to specialize into a transparent humour that optimized color
filtering, blocked harmful radiation, improved the eye's refractive index, and allowed functionality outside of water.
The transparent protective cells eventually split into two layers, with circulatory fluid in between that allowed wider
viewing angles and greater imaging resolution, and the thickness of the transparent layer gradually increased, in most
species with the transparent crystallin protein.[17]
The gap between tissue layers naturally formed a bioconvex shape, an optimally ideal structure for a normal
refractive index. Independently, a transparent layer and a nontransparent layer split forward from the lens: the cornea
and iris. Separation of the forward layer again formed a humour, the aqueous humour. This increased refractive
power and again eased circulatory problems. Formation of a nontransparent ring allowed more blood vessels, more
circulation, and larger eye sizes.[17]
Eye
26
Types of eye
There are ten different eye layouts—indeed every way of capturing an optical image commonly used by man, with
the exceptions of zoom and Fresnel lenses. Eye types can be categorized into "simple eyes", with one concave
photoreceptive surface, and "compound eyes", which comprise a number of individual lenses laid out on a convex
surface.[1] Note that "simple" does not imply a reduced level of complexity or acuity. Indeed, any eye type can be
adapted for almost any behaviour or environment. The only limitations specific to eye types are that of
resolution—the physics of compound eyes prevents them from achieving a resolution better than 1°. Also,
superposition eyes can achieve greater sensitivity than apposition eyes, so are better suited to dark-dwelling
creatures.[1] Eyes also fall into two groups on the basis of their photoreceptor's cellular construction, with the
photoreceptor cells either being cilliated (as in the vertebrates) or rhabdomeric. These two groups are not
monophyletic; the cnidaria also possess cilliated cells, [18] and some annelids possess both.[19]
Non-compound eyes
Simple eyes are rather ubiquitous, and lens-bearing eyes have evolved at least seven times in vertebrates,
cephalopods, annelids, crustacea and cubozoa.[20]
Pit eyes
Pit eyes, also known as stemma, are eye-spots which may be set into a pit to reduce the angles of light that enters and
affects the eyespot, to allow the organism to deduce the angle of incoming light.[1] Found in about 85% of phyla,
these basic forms were probably the precursors to more advanced types of "simple eye". They are small, comprising
up to about 100 cells covering about 100 µm.[1] The directionality can be improved by reducing the size of the
aperture, by incorporating a reflective layer behind the receptor cells, or by filling the pit with a refractile material.[1]
Pit vipers have developed pits that function as eyes by sensing thermal infra-red radiation, in addition to their optical
wavelength eyes like those of other vertebrates.
Spherical lensed eye
The resolution of pit eyes can be greatly improved by incorporating a material with a higher refractive index to form
a lens, which may greatly reduce the blur radius encountered—hence increasing the resolution obtainable.[1] The
most basic form, seen in some gastropods and annelids, consists of a lens of one refractive index. A far sharper
image can be obtained using materials with a high refractive index, decreasing to the edges; this decreases the focal
length and thus allows a sharp image to form on the retina.[1] This also allows a larger aperture for a given sharpness
of image, allowing more light to enter the lens; and a flatter lens, reducing spherical aberration.[1] Such an
inhomogeneous lens is necessary in order for the focal length to drop from about 4 times the lens radius, to 2.5
radii.[1]
Heterogeneous eyes have evolved at least eight times: four or more times in gastropods, once in the copepods, once
in the annelids and once in the cephalopods.[1] No aquatic organisms possess homogeneous lenses; presumably the
evolutionary pressure for a heterogeneous lens is great enough for this stage to be quickly "outgrown".[1]
This eye creates an image that is sharp enough that motion of the eye can cause significant blurring. To minimize the
effect of eye motion while the animal moves, most such eyes have stabilizing eye muscles.[1]
The ocelli of insects bear a simple lens, but their focal point always lies behind the retina; consequently they can
never form a sharp image. This capitulates the function of the eye. Ocelli (pit-type eyes of arthropods) blur the image
across the whole retina, and are consequently excellent at responding to rapid changes in light intensity across the
whole visual field; this fast response is further accelerated by the large nerve bundles which rush the information to
the brain.[21] Focusing the image would also cause the sun's image to be focused on a few receptors, with the
possibility of damage under the intense light; shielding the receptors would block out some light and thus reduce
their sensitivity.[21] This fast response has led to suggestions that the ocelli of insects are used mainly in flight,
Eye
27
because they can be used to detect sudden changes in which way is up (because light, especially UV light which is
absorbed by vegetation, usually comes from above).[21]
Multiple lenses
Some marine organisms bear more than one lens; for instance the copepod Pontella has three. The outer has a
parabolic surface, countering the effects of spherical aberration while allowing a sharp image to be formed. Another
copepod, Copilia's eyes have two lenses, arranged like those in a telescope.[1] Such arrangements are rare and poorly
understood, but represent an interesting alternative construction. An interesting use of multiple lenses is seen in some
hunters such as eagles and jumping spiders, which have a refractive cornea (discussed next): these have a negative
lens, enlarging the observed image by up to 50% over the receptor cells, thus increasing their optical resolution.[1]
Refractive cornea
In the eyes of most mammals, birds, reptiles, and most other terrestrial vertebrates (along with spiders and some
insect larvae) the vitreous fluid has a higher refractive index than the air.[1] In general, the lens is not spherical.
Spherical lenses produce spherical aberration. In refractive corneas, the lens tissue is corrected with inhomogeneous
lens material (See Luneburg lens.), or with an aspheric shape.[1] Flattening the lens has a disadvantage; the quality of
vision is diminished away from the main line of focus. Thus, animals that have evolved with a wide field-of-view
often have eyes that make use of an inhomogeneous lens.[1]
As mentioned above, a refractive cornea is only useful out of water; in water, there is little difference in refractive
index between the vitreous fluid and the surrounding water. Hence creatures that have returned to the
water—--penguins and seals, for example---lose their highly curved cornea and return to lens-based vision. An
alternative solution, borne by some divers, is to have a very strongly focusing cornea.[1]
Reflector eyes
An alternative to a lens is to line the inside of the eye with " mirrors", and reflect the image to focus at a central
point.[1] The nature of these eyes means that if one were to peer into the pupil of an eye, one would see the same
image that the organism would see, reflected back out.[1]
Many small organisms such as rotifers, copeopods and platyhelminths use such organs, but these are too small to
produce usable images.[1] Some larger organisms, such as scallops, also use reflector eyes. The scallop Pecten has up
to 100 millimeter-scale reflector eyes fringing the edge of its shell. It detects moving objects as they pass successive
lenses.[1]
There is at least one vertebrate, the spookfish, whose eyes include reflective optics for focusing of light. Each of the
two eyes of a spookfish collects light from both above and below; the light coming from above is focused by a lens,
while that coming from below, by a curved mirror composed of many layers of small reflective plates made of
guanine crystals.[22]
Eye
28
Compound eyes
A compound eye may consist of thousands of individual
photoreceptor units or ommatidia (ommatidium, singular). The
image perceived is a combination of inputs from the numerous
ommatidia (individual "eye units"), which are located on a convex
surface, thus pointing in slightly different directions. Compared
with simple eyes, compound eyes possess a very large view angle,
and can detect fast movement and, in some cases, the polarization
of light.[23] Because the individual lenses are so small, the effects
of diffraction impose a limit on the possible resolution that can be
obtained (assuming that they do not function as phased arrays).
This can only be countered by increasing lens size and number. To
see with a resolution comparable to our simple eyes, humans
would require compound eyes which would each reach the size of
their head.
An image of a house fly compound eye surface by
using Scanning Electron Microscope
Compound eyes fall into two groups: apposition eyes, which form
multiple inverted images, and superposition eyes, which form a
single erect image.[24] Compound eyes are common in arthropods,
and are also present in annelids and some bivalved molluscs.[25]
Compound eyes, in arthropods at least, grow at their margins by
[26]
the addition of new ommatidia.
Anatomy of the compound eye of an insect
Arthropods such as this Calliphora vomitoria fly
have compound eyes
Eye
29
Apposition eyes
Apposition eyes are the most common form of eye, and are presumably the
ancestral form of compound eye. They are found in all arthropod groups,
although they may have evolved more than once within this phylum.[1] Some
annelids and bivalves also have apposition eyes. They are also possessed by
Limulus, the horseshoe crab, and there are suggestions that other chelicerates
developed their simple eyes by reduction from a compound starting point.[1]
(Some caterpillars appear to have evolved compound eyes from simple eyes
in the opposite fashion.)
Apposition eyes work by gathering a number of images, one from each eye,
and combining them in the brain, with each eye typically contributing a single
point of information.
Structure of the ommatidia of apposition
compound eyes
The typical apposition eye has a lens focusing light from one direction on the
rhabdom, while light from other directions is absorbed by the dark wall of the
ommatidium. In the other kind of apposition eye, found in the Strepsiptera,
lenses are not fused to one another, and each forms an entire image; these
images are combined in the brain. This is called the schizochroal compound
eye or the neural superposition eye. Because images are combined additively,
this arrangement allows vision under lower light levels.[1]
Superposition eyes
The second type is named the superposition eye. The superposition eye is divided into three types; the refracting, the
reflecting and the parabolic superposition eye. The refracting superposition eye has a gap between the lens and the
rhabdom, and no side wall. Each lens takes light at an angle to its axis and reflects it to the same angle on the other
side. The result is an image at half the radius of the eye, which is where the tips of the rhabdoms are. This kind is
used mostly by nocturnal insects. In the parabolic superposition compound eye type, seen in arthropods such as
mayflies, the parabolic surfaces of the inside of each facet focus light from a reflector to a sensor array. Long-bodied
decapod crustaceans such as shrimp, prawns, crayfish and lobsters are alone in having reflecting superposition eyes,
which also have a transparent gap but use corner mirrors instead of lenses.
Parabolic superposition
This eye type functions by refracting light, then using a parabolic mirror to focus the image; it combines features of
[9]
superposition and apposition eyes.
Other
Good fliers like flies or honey bees, or prey-catching insects like praying mantis or dragonflies, have specialized
zones of ommatidia organized into a fovea area which gives acute vision. In the acute zone the eyes are flattened and
the facets larger. The flattening allows more ommatidia to receive light from a spot and therefore higher resolution.
There are some exceptions from the types mentioned above. Some insects have a so-called single lens compound
eye, a transitional type which is something between a superposition type of the multi-lens compound eye and the
single lens eye found in animals with simple eyes. Then there is the mysid shrimp Dioptromysis paucispinosa. The
shrimp has an eye of the refracting superposition type, in the rear behind this in each eye there is a single large facet
that is three times in diameter the others in the eye and behind this is an enlarged crystalline cone. This projects an
Eye
30
upright image on a specialized retina. The resulting eye is a mixture of a simple eye within a compound eye.
Another version is the pseudofaceted eye, as seen in Scutigera. This type of eye consists of a cluster of numerous
ocelli on each side of the head, organized in a way that resembles a true compound eye.
The body of Ophiocoma wendtii, a type of brittle star, is covered with ommatidia, turning its whole skin into a
compound eye. The same is true of many chitons. The tube feet of sea urchins contain photoreceptor proteins, which
together act as a compound eye; they lack screening pigments, but can detect the directionality of light by the
shadow cast by its opaque body.[27]
Nutrients of the eye
The ciliary body is triangular in horizontal section and is coated by a double layer, the ciliary epithelium. The inner
layer is transparent and covers the vitreous body, and is continuous from the neural tissue of the retina. The outer
layer is highly pigmented, continuous with the retinal pigment epithelium, and constitutes the cells of the dilator
muscle.
The vitreous is the transparent, colorless, gelatinous mass that fills the space between the lens of the eye and the
retina lining the back of the eye.[28] It is produced by certain retinal cells. It is of rather similar composition to the
cornea, but contains very few cells (mostly phagocytes which remove unwanted cellular debris in the visual field, as
well as the hyalocytes of Balazs of the surface of the vitreous, which reprocess the hyaluronic acid), no blood
vessels, and 98-99% of its volume is water (as opposed to 75% in the cornea) with salts, sugars, vitrosin (a type of
collagen), a network of collagen type II fibers with the mucopolysaccharide hyaluronic acid, and also a wide array of
proteins in micro amounts. Amazingly, with so little solid matter, it tautly holds the eye.
Relationship to life requirements
Eyes are generally adapted to the environment and life requirements of the organism which bears them. For instance,
the distribution of photoreceptors tends to match the area in which the highest acuity is required, with
horizon-scanning organisms, such as those that live on the African plains, having a horizontal line of high-density
ganglia, while tree-dwelling creatures which require good all-round vision tend to have a symmetrical distribution of
ganglia, with acuity decreasing outwards from the centre.
Of course, for most eye types, it is impossible to diverge from a spherical form, so only the density of optical
receptors can be altered. In organisms with compound eyes, it is the number of ommatidia rather than ganglia that
reflects the region of highest data acquisition.[1] :23-4 Optical superposition eyes are constrained to a spherical shape,
but other forms of compound eyes may deform to a shape where more ommatidia are aligned to, say, the horizon,
without altering the size or density of individual ommatidia.[29] Eyes of horizon-scanning organisms have stalks so
they can be easily aligned to the horizon when this is inclined, for example if the animal is on a slope.[30] An
extension of this concept is that the eyes of predators typically have a zone of very acute vision at their centre, to
assist in the identification of prey.[29] In deep water organisms, it may not be the centre of the eye that is enlarged.
The hyperiid amphipods are deep water animals that feed on organisms above them. Their eyes are almost divided
into two, with the upper region thought to be involved in detecting the silhouettes of potential prey—or
predators—against the faint light of the sky above. Accordingly, deeper water hyperiids, where the light against
which the silhouettes must be compared is dimmer, have larger "upper-eyes", and may lose the lower portion of their
eyes altogether.[29] Depth perception can be enhanced by having eyes which are enlarged in one direction; distorting
the eye slightly allows the distance to the object to be estimated with a high degree of accuracy.[9]
Acuity is higher among male organisms that mate in mid-air, as they need to be able to spot and assess potential
mates against a very large backdrop.[29] On the other hand, the eyes of organisms which operate in low light levels,
such as around dawn and dusk or in deep water, tend to be larger to increase the amount of light that can be
captured.[29]
Eye
31
It is not only the shape of the eye that may be affected by lifestyle. Eyes can be the most visible parts of organisms,
and this can act as a pressure on organisms to have more transparent eyes at the cost of function.[29]
Eyes may be mounted on stalks to provide better all-round vision, by lifting them above an organism's carapace; this
also allows them to track predators or prey without moving the head.[9]
Visual acuity
Visual acuity, or resolving power, is "the ability to distinguish fine
detail" and is the property of cones.[28] It is often measured in cycles
per degree (CPD), which measures an angular resolution, or how much
an eye can differentiate one object from another in terms of visual
angles. Resolution in CPD can be measured by bar charts of different
numbers of white/black stripe cycles. For example, if each pattern is
1.75 cm wide and is placed at 1 m distance from the eye, it will
subtend an angle of 1 degree, so the number of white/black bar pairs on
the pattern will be a measure of the cycles per degree of that pattern.
The highest such number that the eye can resolve as stripes, or
distinguish from a gray block, is then the measurement of visual acuity
of the eye.
A hawk's eye
For a human eye with excellent acuity, the maximum theoretical
resolution is 50 CPD[31] (1.2 arcminute per line pair, or a 0.35 mm line pair, at 1 m). A rat can resolve only about 1
to 2 CPD.[32] A horse has higher acuity through most of the visual field of its eyes than a human has, but does not
match the high acuity of the human eye's central fovea region.
Spherical aberration limits the resolution of a 7 mm pupil to about 3 arcminutes per line pair. At a pupil diameter of
3 mm, the spherical aberration is greatly reduced, resulting in an improved resolution of approximately 1.7
arcminutes per line pair.[33] A resolution of 2 arcminutes per line pair, equivalent to a 1 arcminute gap in an
optotype, corresponds to 20/20 (normal vision) in humans.
Perception of colours
"Colour vision is the faculty of the organism to distinguish lights of different spectral qualities."[28] All organisms
are restricted to a small range of electromagnetic spectrum; this varies from creature to creature, but is mainly
between wavelengths of 400 and 700 nm.[34] This is a rather small section of the electromagnetic spectrum, probably
reflecting the submarine evolution of the organ: water blocks out all but two small windows of the EM spectrum, and
there has been no evolutionary pressure among land animals to broaden this range.[35]
The most sensitive pigment, rhodopsin, has a peak response at 500 nm.[36] Small changes to the genes coding for this
protein can tweak the peak response by a few nm;[2] pigments in the lens can also filter incoming light, changing the
peak response.[2] Many organisms are unable to discriminate between colours, seeing instead in shades of grey;
colour vision necessitates a range of pigment cells which are primarily sensitive to smaller ranges of the spectrum. In
primates, geckos, and other organisms, these take the form of cone cells, from which the more sensitive rod cells
evolved.[36] Even if organisms are physically capable of discriminating different colours, this does not necessarily
mean that they can perceive the different colours; only with behavioural tests can this be deduced.[2]
Most organisms with colour vision are able to detect ultraviolet light. This high energy light can be damaging to
receptor cells. With a few exceptions (snakes, placental mammals), most organisms avoid these effects by having
absorbent oil droplets around their cone cells. The alternative, developed by organisms that had lost these oil droplets
in the course of evolution, is to make the lens impervious to UV light — this precludes the possibility of any UV
light being detected, as it does not even reach the retina.[36]
Eye
32
Rods and cones
The retina contains two major types of light-sensitive photoreceptor cells used for vision: the rods and the cones.
Rods cannot distinguish colours, but are responsible for low-light (scotopic) monochrome (black-and-white) vision;
they work well in dim light as they contain a pigment, rhodopsin (visual purple), which is sensitive at low light
intensity, but saturates at higher (photopic) intensities. Rods are distributed throughout the retina but there are none
at the fovea and none at the blind spot. Rod density is greater in the peripheral retina than in the central retina.
Cones are responsible for colour vision. They require brighter light to function than rods require. In humans, there
are three types of cones, maximally sensitive to long-wavelength, medium-wavelength, and short-wavelength light
(often referred to as red, green, and blue, respectively, though the sensitivity peaks are not actually at these colours).
The colour seen is the combined effect of stimuli to, and responses from, these three types of cone cells. Cones are
mostly concentrated in and near the fovea. Only a few are present at the sides of the retina. Objects are seen most
sharply in focus when their images fall on the fovea, as when one looks at an object directly. Cone cells and rods are
connected through intermediate cells in the retina to nerve fibres of the optic nerve. When rods and cones are
stimulated by light, the nerves send off impulses through these fibres to the brain.[36]
Pigmentation
The pigment molecules used in the eye are various, but can be used to define the evolutionary distance between
different groups, and can also be an aid in determining which are closely related – although problems of
convergence do exist.[36]
Opsins are the pigments involved in photoreception. Other pigments, such as melanin, are used to shield the
photoreceptor cells from light leaking in from the sides. The opsin protein group evolved long before the last
common ancestor of animals, and has continued to diversify since.[2]
There are two types of opsin involved in vision; c-opsins, which are associated with ciliary-type photoreceptor cells,
and r-opsins, associated with rhabdomeric photoreceptor cells.[37] The eyes of vertebrates usually contain cilliary
cells with c-opsins, and (bilaterian) invertebrates have rhabdomeric cells in the eye with r-opsins. However, some
ganglion cells of vertebrates express r-opsins, suggesting that their ancestors used this pigment in vision, and that
remnants survive in the eyes.[37] Likewise, c-opsins have been found to be expressed in the brain of some
invertebrates. They may have been expressed in ciliary cells of larval eyes, which were subsequently resorbed into
the brain on metamorphosis to the adult form.[37] C-opsins are also found in some derived bilaterian-invertebrate
eyes, such as the pallial eyes of the bivalve molluscs; however, the lateral eyes (which were presumably the ancestral
type for this group, if eyes evolved once there) always use r-opsins.[37] Cnidaria, which are an outgroup to the taxa
mentioned above, express c-opsins - but r-opsins are yet to be found in this group.[37] Incidentally, the melanin
produced in the raticate is produced in the same fashion as that in vertebrates, suggesting the common descent of this
pigment.[37]
Eye
33
References
Notes
[1] Land, M F; Fernald, R D (1992). "The Evolution of Eyes". Annual Review of Neuroscience 15: 1–29.
doi:10.1146/annurev.ne.15.030192.000245. PMID 1575438.
[2] Frentiu, Francesca D.; Adriana D. Briscoe (2008). "A butterfly eye's view of birds". BioEssays 30 (11-12): 1151–62. doi:10.1002/bies.20828.
PMID 18937365.
[3] Breitmeyer, Bruno (2010). Blindspots: The Many Ways We Cannot See. New York: Oxford University Press. p. 4. ISBN 9780195394269.
[4] The precise number depends on the author
[5] Nairne, James (2005). Psychology (http:/ / books. google. com/ ?id=6MqkLT-Q0oUC& pg=PA146& dq=iris+ intitle:psychology+
inauthor:Nairne). Belmont: Wadsworth Publishing. ISBN 049503150x. OCLC 61361417. .
[6] Vicki Bruce, Patrick R. Green, and Mark A. Georgeson (1996). Visual Perception: Physiology, Psychology and Ecology (http:/ / books.
google. com/ ?id=ukvei0wge_8C& pg=PA20& dq=iris+ aberrations+ intitle:psychology). Psychology Press. pp. 20. ISBN 0863774504. .
[7] BioMedia Associates Educational Biology Site: What animal has a more sophisticated eye, Octopus or Insect? (http:/ / ebiomedia. com/ gall/
eyes/ octopus-insect. html)
[8] Who You Callin' "Shrimp"? – National Wildlife Magazine (http:/ / www. nwf. org/ nationalwildlife/ article. cfm?issueID=77&
articleID=1114)
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[10] Autrum, H. "Introduction". In H. Autrum (editor). Comparative Physiology and Evolution of Vision in Invertebrates- A: Invertebrate
Photoreceptors. Handbook of Sensory Physiology. VII/6A. New York: Springer-Verlag. pp. 4, 8–9. ISBN 3540088377
[11] Halder, G.; Callaerts, P.; Gehring, W.J. (1995). "New perspectives on eye evolution". Curr. Opin. Genet. Dev. 5 (5): 602–609.
doi:10.1016/0959-437X(95)80029-8. PMID 8664548.
[12] Halder, G.; Callaerts, P.; Gehring, W.J. (1995). "Induction of ectopic eyes by targeted expression of the eyeless gene in Drosophila".".
Science 267 (5205): 1788–1792. doi:10.1126/science.7892602. PMID 7892602.
[13] Tomarev, S.I.; Callaerts, P.; Kos, L.; Zinovieva, R.; Halder, G.; Gehring, W.; Piatigorsky, J. (1997). "Squid Pax-6 and eye development".
Proc. Natl. Acad. Sci. USA 94 (6): 2421–2426. doi:10.1073/pnas.94.6.2421. PMC 20103. PMID 9122210.
[14] Conway-Morris, S. (1998). The Crucible of Creation. Oxford: Oxford University Press.
[15] Land, M.F.; Fernald, Russell D. (1992). "The evolution of eyes". Annu Rev Neurosci 15: 1–29. doi:10.1146/annurev.ne.15.030192.000245.
PMID 1575438.
[16] Eye-Evolution? (http:/ / library. thinkquest. org/ 28030/ eyeevo. htm)
[17] Fernald, Russell D. (2001). The Evolution of Eyes: Where Do Lenses Come From? (http:/ / www. karger. com/ gazette/ 64/ fernald/ art_1_4.
htm) Karger Gazette 64: "The Eye in Focus".
[18] Kozmik, Zbynek; Ruzickova, Jana; Jonasova, Kristyna; Matsumoto, Yoshifumi; Vopalensky, Pavel; Kozmikova, Iryna; Strnad, Hynek;
Kawamura, Shoji et al. (2008). "Assembly of the cnidarian camera-type eye from vertebrate-like components" (http:/ / www. pnas. org/ cgi/
reprint/ 0800388105v1. pdf) (PDF). Proceedings of the National Academy of Sciences 105 (26): 8989–8993. doi:10.1073/pnas.0800388105.
PMC 2449352. PMID 18577593. .
[19] Fernald, Russell D. (September 2006). "Casting a Genetic Light on the Evolution of Eyes". Science 313 (5795): 1914–1918.
doi:10.1126/science.1127889. PMID 17008522.
[20] "Vision Optics and Evolution" (http:/ / jstor. org/ stable/ 1311112). BioScience 39 (5): 298–307. 1 May 1989. doi:10.2307/1311112.
ISSN 00063568. .
[21] Wilson, M. (1978). "The functional organisation of locust ocelli". Journal of Comparative Physiology 124 (4): 297–316.
doi:10.1007/BF00661380.
[22] Wagner, H.J., Douglas, R.H., Frank, T.M., Roberts, N.W., and Partridge, J.C. (Jan. 27, 2009). "A Novel Vertebrate Eye Using Both
Refractive and Reflective Optics". Current Biology 19 (2): 108–114. doi:10.1016/j.cub.2008.11.061. PMID 19110427.
[23] Völkel, R; Eisner, M; Weible, K. J (June 2003). "Miniaturized imaging systems" (http:/ / www. suss-microoptics. com/ downloads/
Publications/ Miniaturized_Imaging_Systems. pdf) (PDF). Microelectronic Engineering 67-68 (1): 461–472.
doi:10.1016/S0167-9317(03)00102-3. .
[24] Gaten, Edward (1998). "Optics and phylogeny: is there an insight? The evolution of superposition eyes in the Decapoda (Crustacea)" (http:/
/ dpc. uba. uva. nl/ ctz/ vol67/ nr04/ art01#FIGURE1). Contributions to Zoology 67 (4): 223–236. .
[25] Ritchie, Alexander (1985). "Ainiktozoon loganense Scourfield, a protochordate? from the Silurian of Scotland". Alcheringa 9: 137.
doi:10.1080/03115518508618961.
[26] Mayer, G. (2006). "Structure and development of onychophoran eyes: What is the ancestral visual organ in arthropods?". Arthropod
Structure and Development 35 (4): 231–245. doi:10.1016/j.asd.2006.06.003. PMID 18089073.
[27] Ullrich-Luter, E. M.; Dupont, S.; Arboleda, E.; Hausen, H.; Arnone, M. I. (2011). "Unique system of photoreceptors in sea urchin tube feet".
Proceedings of the National Academy of Sciences 108 (20): 8367–8372. doi:10.1073/pnas.1018495108.
Eye
34
[28] Ali, Mohamed Ather; Klyne, M.A. (1985). Vision in Vertebrates. New York: Plenum Press. p. 8. ISBN 0-306-42065-1.
[29] Land, M. F. (1989). "The eyes of hyperiid amphipods: relations of optical structure to depth" (http:/ / www. springerlink. com/ index/
P0P467K474307K3N. pdf) (PDF). Journal of Comparative Physiology A: Sensory, Neural, and Behavioral Physiology 164 (6): 751–762.
doi:10.1007/BF00616747. .
[30] Zeil, J. (1996). "The variation of resolution and of ommatidial dimensions in the compound eyes of the fiddler crab Uca lactea annulipes
(Ocypodidae, Brachyura, Decapoda)" (http:/ / jeb. biologists. org/ cgi/ reprint/ 199/ 7/ 1569. pdf) (PDF). Journal of Experimental Biology 199
(7): 1569–1577. .
[31] John C. Russ (2006). The Image Processing Handbook (http:/ / books. google. com/ ?id=Vs2AM2cWl1AC& pg=PT110& dq="50+ cycles+
per+ degree"+ acuity). CRC Press. ISBN 0849372542. OCLC 156223054. . "The upper limit (finest detail) visible with the human eye is about
50 cycles per degree,… (Fifth Edition, 2007, Page 94)"
[32] Curtis D. Klaassen (2001). Casarett and Doull's Toxicology: The Basic Science of Poisons (http:/ / books. google. com/
?id=G16riRjvmykC& pg=PA574& dq=cycles-per-degree+ acuity+ rat). McGraw-Hill Professional. ISBN 0071347216. OCLC 47965382. .
[33] Robert E. Fischer; Biljana Tadic-Galeb. With contributions by Rick Plympton… (2000). Optical System Design (http:/ / books. google. com/
?id=byx2Ne9cD1IC& pg=PA164& dq=eye+ resolution+ line-pairs+ 1. 7). McGraw-Hill Professional. ISBN 0071349162. OCLC 247851267.
.
[34] Barlow, Horace Basil; Mollon, J. D (1982). The Senses (http:/ / books. google. com/ ?id=kno6AAAAIAAJ& pg=PA98& vq=human+
spectral+ sensitivity& dq=eye+ visible+ spectrum). Cambridge: Univ. Pr.. pp. 98. ISBN 0521244749. .
[35] Fernald, Russell D. (1997). "The Evolution of Eyes" (http:/ / www. stanford. edu/ group/ fernaldlab/ pubs/ 1997 Fernald. pdf) (PDF). Brain,
Behaviour and Evolution 50 (4): 253–259. doi:10.1159/000113339. PMID 9310200. .
[36] Goldsmith, T. H. (1990). "Optimization, Constraint, and History in the Evolution of Eyes" (http:/ / www. jstor. org/ stable/ pdfplus/
2832368. pdf) (PDF). The Quarterly Review of Biology 65 (10000): 281–322. doi:10.1086/416840. PMID 2146698. .
[37] Nilsson, E.; Arendt, D. (Dec 2008). "Eye Evolution: the Blurry Beginning". Current Biology 18 (23): R1096.
doi:10.1016/j.cub.2008.10.025. ISSN 0960-9822. PMID 19081043.
External links
• Evolution of the eye (http://www.pbs.org/wgbh/evolution/library/01/1/l_011_01.html)
• Diagram of the eye (http://webvision.med.utah.edu/anatomy.html)
• Webvision. The organisation of the retina and visual system. (http://webvision.med.utah.edu/) An in-depth
treatment of retinal function, open to all but geared most toward graduate students.
• Eye strips images of all but bare essentials before sending visual information to brain, UC Berkeley research
shows (http://www.berkeley.edu/news/media/releases/2001/03/28_wers1.html)
• A collection of resources for eye anatomy. (http://www.cotc.edu/studentlife/TutoringCenter/resourcessite/
heye.htm)
• Anatomy of the eye - flash animated interactive. (http://www.lensshopper.com/eye-anatomy.asp)
• Eyes (http://www.pharmacyproductinfo.com/eye.html)- Eyes are organs that detect light, and send signals
along the optic nerve to the visual and other areas of the brain.
• Detection of weak optical signals by the human visual system : Perspectives in Neuroscience and in Quantum
Physics (http://home.etu.unige.ch/~alvarra0/Roberto_ALVAREZs_Personal_Page/About_Me_files/
Eye_project.pdf)
• Macro photo of Eye (http://www.post35mm.com/photo.php?photo_id=32966)
• Are Your Eyes Right (http://www.popsci.com/archive-viewer?id=oiUDAAAAMBAJ&pg=120&query=Vol.
+144) February 1944 Popular Science
Fork
35
Fork
As a piece of cutlery or kitchenware, a fork is a tool consisting of a
handle with several narrow tines on one end. The fork, as an eating
utensil, has been a feature primarily of the West, whereas in East Asia
chopsticks have been more prevalent. Today, forks are increasingly
available throughout East Asia. The utensil (usually metal) is used to
lift food to the mouth or to hold food in place while cooking or cutting
it. Food can be lifted either by spearing it on the tines, or by holding it
on top of the tines, which are often curved slightly. For this latter
function, in the American style of fork etiquette, the fork is held with
tines curving up; however, in continental style, the fork is held with the
tines curving down. A fork is also shaped in the form of a trident but
curved at the joint of the handle to the points.
Assorted forks. From left to right: dessert fork,
relish fork, salad fork, dinner fork, cold cuts fork,
serving fork, carving fork.
Blue Fork Sillhouette
Fork
36
History
Bronze forks made in Iran during the 8th or 9th century.
The word 'fork' comes from the Latin furca, meaning
"pitchfork." The ancient Greeks used[1] the fork as a
serving utensil, and it is also mentioned in the Hebrew
Bible, in the Book of I Samuel 2:13 ("The custom of
the priests with the people was that when any man
offered sacrifice, the priest’s servant came, while the
fresh flesh was boiling, with a fork of three teeth in his
hand..."). Bone forks had been found in the burial site
of Qijia culture as well as later Chinese dynasties'
tombs.[2]
In the Roman Empire, bronze and silver forks were used, indeed many examples are displayed in museums around
Europe.[3] [4] . But the use varied according to local customs, social class and the nature of food. After, in the western
area, the fork is only occasionally mentioned in high medieval sources however linked to Byzantium. However, it
was not commonly used in Western Europe until the 16th century when it became part of the etiquette.
Before the fork was introduced, Westerners were reliant on the spoon and knife as the only eating utensils. Thus,
people would largely eat food with their hands, calling for a common spoon when required. Members of the
aristocracy would sometimes be accustomed to manners considered more proper and hold two knives at meals and
use them both to cut and transfer food to the mouth, using the spoon for soups and broth.
The earliest forks usually had only two tines, but those with numerous tines caught on quickly. The tines on these
implements were straight, meaning the fork could only be used for spearing food and not for scooping it. The fork
allowed meat to be easily held in place while being cut. The fork also allowed one to spike a piece of meat and shake
off any undesired excess of sauce or liquid before consuming it. Wider use of the table fork in Western Europe was
facilitated by two Byzantine imperial princesses who married into the Western aristocracy: the Empress Theophanu,
wife of Emperor Otto II, in 972, and the Dogaressa Teodora Anna Dukaina Selvo, wife of the Doge of Venice
Domenico Selvo, in 1075.
By the 11th century, the table fork had made its way to Italy. In Italy, it became quite popular by the 14th century,
being commonly used for eating by merchant and upper classes by 1600. It was proper for a guest to arrive with his
own fork and spoon enclosed in a box called a cadena; this usage was introduced to the French court with Catherine
de' Medici's entourage. Long after the personal table fork had become commonplace in France, at the supper
celebrating the marriage of the duc de Chartres to Louis XIV's natural daughter in 1692, the seating was described in
the court memoirs of Saint-Simon: "King James having his Queen on his right hand and the King on his left, and
each with their cadenas." In Perrault's contemporaneous fairy tale of La Belle au bois dormant (1697), each of the
fairies invited for the christening is presented with a splendid "Fork Holder."
The fork's adoption in northern Europe was slower. Its use was first described in English by Thomas Coryat in a
volume of writings on his Italian travels (1611), but for many years it was viewed as an unmanly Italian affectation.
Some writers of the Roman Catholic Church expressly disapproved of its use, seeing it as "excessive delicacy": "God
in his wisdom has provided man with natural forks — his fingers. Therefore it is an insult to Him to substitute
artificial metallic forks for them when eating."[5] [6] It was not until the 18th century that the fork became commonly
used in Great Britain, although some sources say forks were common in France, England and Sweden already by the
early 17th century.[7] [8] The curved fork that is used in most parts of the world today, was developed in Germany in
the mid 18th century. The standard four-tine design became current in the early 19th century.
Fork
37
The 20th century also saw the emergence of the "spork", a utensil that is
half-fork and half-spoon. With this new "fork-spoon", only one piece of
cutlery is needed when eating (so long as no knife is required). The back of
the spork is shaped like a spoon and can scoop food while the front has
shortened tines like a fork, allowing spearing of food, making it convenient
and easy to use. It has found popularity in fast food and military settings.
Types of forks
• Asparagus fork
• Beef fork
A fork used for picking up very thin slices of meat. This fork is
shaped like a regular fork, but it is slightly bigger and the tines are
curved outward. The curves are used for piercing the thin sliced beef.
• Berry fork
• Carving fork
A 1908 design patent drawing for a spork,
[9]
from U.S. Patent D388,664
A two-pronged fork used to hold meat steady while it is being carved. They are often sold with carving knives
or slicers as part of a carving set.
• Cheese fork
• Chip fork
A two-pronged disposable fork, usually made out of sterile wood (though increasingly of plastic), specifically
designed for the eating of chips (known as french fries in North America).
• Cocktail fork
A small fork resembling a trident, used for spearing cocktail garnishes such as olives.
• Cold meat fork
• Crab fork
A short, sharp and narrow three-pronged or two-pronged fork designed to easily extract meat when consuming
cooked crab.
• Dessert fork (alternatively, pudding fork/cake fork in Great Britain)
Any of several different special types of forks designed to eat desserts, such as a pastry fork. They usually
have only three tines and are smaller than standard dinner forks. The leftmost tine may be widened so as to
provide an edge with which to cut (though it is never sharpened).
• Dinner fork
• Fish fork
• Fondue fork
A narrow fork, usually having two tines, long shaft and an insulating handle, typically of wood, for dipping
bread into a pot containing sauce
• Fruit salad fork
A fork used which is used to pick up pieces of fruit such as grapes, strawberries, melon and other varies types
of fruit.
• Ice cream fork
• Knork
A utensil combining characteristics of a knife and a fork
• Lunch fork
Fork
38
•
•
•
•
•
Meat fork
Olive fork
Oyster fork
Pastry fork
Pickle fork
A long handled fork used for extracting pickles from a jar, or an alternative name for a ball joint separator tool
used to unseat a ball joint.[10]
•
•
•
•
Pie fork
Pitchfork
Relish fork
Salad fork
Similar to a regular fork, but may be shorter, or have one of the outer tines shaped differently. Often, a "salad
fork" in the silverware service of some restaurants (especially chains) may be simply a second fork;
conversely, some restaurants may omit it, offering only one fork in their service.
• Sporf
A utensil combining characteristics of a spoon, a fork and a knife
• Spork
A utensil combining characteristics of a spoon and a fork
• Tea fork
• Toasting fork
A fork, usually having two tines, very long metal shaft and sometimes an insulating handle, for toasting food
over coals or an open flame
Novelty forks
• Extension Fork
A long-tined fork with a telescopic handle, allowing for its
extension or contraction.
• Spaghetti fork
A fork with a metal shaft loosely fitted inside a hollow plastic
handle. The shaft protrudes through the top of the handle, ending
in a bend that allows the metal part of the fork to be easily
rotated with one hand while the other hand is holding the plastic
handle. This supposedly allows spaghetti to be easily wound
onto the tines. Electric variations of this fork have become more
prevalent in modern times.
Spaghetti fork
Fork
39
References
[1] "Forks" (http:/ / research. calacademy. org/ research/ anthropology/ utensil/ forks. htm). .
[2] Needham (1986), volume 6 part 5 105–108
[3] "Fitzwilliam Museum - A combination Roman eating implement" (http:/ / www. fitzmuseum. cam. ac. uk/ opac/ search/ cataloguedetail.
html?& priref=70534& _function_=xslt& _limit_=10). .
[4] Sherlock, D. (1988) A combination Roman eating implement (1988). Antiquaries Journal [comments: 310-311, pl. xlix]
[5] "A History of the Table Fork" (http:/ / www. maybe. org/ ~rodmur/ sca/ fork. html). .
[6] "The Irrational Exhuberance of American Dining Etiquette" (http:/ / web. archive. org/ web/ 20091027152440/ http:/ / www. geocities. com/
rationalargumentator/ Dining_Etiquette. html). Archived from the original (http:/ / www. geocities. com/ rationalargumentator/
Dining_Etiquette. html) on 2009-10-27. .
[7] http:/ / www. bookrags. com/ research/ knife-fork-and-spoon-woi/
[8] http:/ / www. popularhistoria. se/ o. o. i. s?id=170& vid=707
[9] http:/ / www. google. com/ patents?vid=D388,664
[10] http:/ / news. carjunky. com/ how_stuff_works/ how_to_change_ball_joints_ab1444. shtml
Further reading
• A history of the evolution of fork design can be found in: Henry Petroski, The Evolution of Useful things (1992);
ISBN 0-679-74039-2
External links
• Cutlery of the Middle Ages and Renaissance (http://www.larsdatter.com/cutlery.htm) Forks from the
Greco-Roman era to the 17th century
• http://www.urbandictionary.com/define.php?term=viljuska
Gill
A gill is a respiratory organ found in many
aquatic organisms that extracts dissolved
oxygen from water, afterward excreting
carbon dioxide. The gills of some species
such as hermit crabs have adapted to allow
respiration on land provided they are kept
moist. The microscopic structure of a gill
presents a large surface area to the external
environment.
Many microscopic aquatic animals, and
some that are larger but inactive, can absorb
adequate oxygen through the entire surface
of their bodies, and so can respire
adequately without a gill. However, more
complex or more active aquatic organisms
usually require a gill or gills.
Caribbean hermit crabs have modified gills that allow them to live in humid
conditions
Gills usually consist of thin filaments of tissue, branches, or slender tufted processes that have a highly folded
surface to increase surface area. A high surface area is crucial to the gas exchange of aquatic organisms as water
contains only 1/20 the dissolved oxygen that air does.
Gill
40
With the exception of some aquatic insects, the filaments and lamellae (folds) contain blood or coelomic fluid, from
which gases are exchanged through the thin walls. The blood carries oxygen to other parts of the body. Carbon
dioxide passes from the blood through the thin gill tissue into the water. Gills or gill-like organs, located in different
parts of the body, are found in various groups of aquatic animals, including mollusks, crustaceans, insects, fish, and
amphibians.
Note that, contrary to some misconceptions, gills do not break up water molecules into hydrogen and oxygen, but
instead absorb the oxygen that is dissolved in the water.
Invertebrate gills
Respiration in the Echinodermata (includes starfish and sea urchins) is
carried out using a very primitive version of gills called papulae. These
thin protuberances on the surface of the body contain diverticula of the
water vascular system. Crustaceans, molluscs, and some insects have
gills that are tufted or plate-like structures at the surface of the body.
The gills of other insects are tracheal, and also include both thin plates
and tufted structures, and, in the larval dragon fly, the wall of the
A live individual of the sea slug Pleurobranchaea
caudal end of the alimentary tract (rectum) is richly supplied with
meckelii. The gill (or ctenidium) is visible in this
tracheae as a rectal gill. Water pumped into and out of the rectum
view of the right-hand side of the animal
provides oxygen to the closed tracheae. Aquatic insects use a tracheal
gill, which contains air tubes. The oxygen in these tubes is renewed through the gills.
Physical gills
Physical gills are a type of structural adaptation common among some types of aquatic insects, which holds
atmospheric oxygen in an area with small openings called spiracles. The structure (often called a plastron) typically
consists of dense patches of hydrophobic setae on the body, which prevent water entry into the spiracles. The
physical properties of the interface between the trapped air bubble and surrounding water accomplish gas exchange
through the spiracles, almost as if the insect were in atmospheric air. Carbon dioxide diffuses into the surrounding
water due to its high solubility, while oxygen diffuses into bubbles as the concentration within the bubble has been
reduced by respiration, and nitrogen also diffuses out as its tension has been increased. Oxygen diffuses into the
bubble at a higher rate than Nitrogen diffuses out. However, water surrounding the insect can become
oxygen-depleted if there is no water movement, so many aquatic insects in still water actively direct a flow of water
over their bodies.
The physical gill mechanism allows aquatic insects with plastrons to remain constantly submerged. Examples
include many beetles in the family Elmidae, aquatic weevils, and true bugs in the family Aphelocheiridae.
Gill
41
Vertebrate gills
The gills of vertebrates typically develop in the walls of the pharynx,
along a series of gill slits opening to the exterior. Most species employ
a countercurrent exchange system to enhance the diffusion of
substances in and out of the gill, with blood and water flowing in
opposite directions to each other. The gills are composed of comb-like
filaments, the gill lamellae, which help increase their surface area for
oxygen exchange.[1]
When a fish breathes, it draws in a mouthful of water at regular
intervals. Then it draws the sides of its throat together, forcing the
water through the gill openings, so that it passes over the gills to the
outside. Fish gill slits may be the evolutionary ancestors of the tonsils,
thymus gland, and Eustachian tubes, as well as many other structures
derived from the embryonic branchial pouches.
The red gills of this common carp are visible as a
result of a gill flap birth defect.
Cartilaginous fish
Sharks and rays typically have five pairs of gill slits that open directly
to the outside of the body, though some more primitive sharks have six
or seven pairs. Adjacent slits are separated by a cartilaginous gill arch
from which projects a long sheet-like septum, partly supported by a
further piece of cartilage called the gill ray. The individual lamellae of
the gills lie on either side of the septum. The base of the arch may also
support gill rakers, small projecting elements that help to filter food
from the water.[2]
Freshwater Fish Gills magnified 400 times
A smaller opening, the spiracle, lies in front of the first gill slit. This bears a small pseudobranch that resembles a
gill in structure, but only receives blood already oxygenated by the true gills.[2] The spiracle is thought to be
homologous to the ear opening in higher vertebrates.[3]
Most sharks rely on ram ventilation, forcing water into the mouth and over the gills by rapidly swimming forward. In
slow-moving or bottom dwelling species, especially among skates and rays, the spiracle may be enlarged, and the
[2]
fish breathes by sucking water through this opening, instead of through the mouth.
Chimaeras differ from other cartilagenous fish, having lost both the spiracle and the fifth gill slit. The remaining slits
are covered by an operculum, developed from the septum of the gill arch in front of the first gill.[2]
Gill
42
Bony fish
In bony fish, the gills lie in a branchial chamber covered by a bony
operculum. The great majority of bony fish species have five pairs of
gills, although a few have lost some over the course of evolution. The
operculum can be important in adjusting the pressure of water inside of
the pharynx to allow proper ventilation of the gills, so that bony fish do
not have to rely on ram ventilation (and hence near constant motion) to
breathe. Valves inside the mouth keep the water from escaping.[2]
The gill arches of bony fish typically have no septum, so that the gills
alone project from the arch, supported by individual gill rays. Some
species retain gill rakers. Though all but the most primitive bony fish
The red gills inside a detached tuna head
lack a spiracle, the pseudobranch associated with it often remains, being
(viewed from behind)
located at the base of the operculum. This is, however, often greatly
reduced, consisting of a small mass of cells without any remaining gill-like structure.[2]
Marine teleosts also use gills to excrete electrolytes. The gills' large surface area tends to create a problem for fish
that seek to regulate the osmolarity of their internal fluids. Saltwater is less dilute than these internal fluids, so
saltwater fish lose large quantities of water osmotically through their gills. To regain the water, they drink large
amounts of seawater and excrete the salt. Freshwater is more dilute than the internal fluids of fish, however, so
freshwater fish gain water osmotically through their gills.[2]
Other vertebrates
Lampreys and hagfish do not have gill slits as such. Instead, the gills
are contained in spherical pouches, with a circular opening to the
outside. Like the gill slits of higher fish, each pouch contains two gills.
In some cases, the openings may be fused together, effectively forming
an operculum. Lampreys have seven pairs of pouches, while hagfishes
An Alpine newt larva showing the external gills,
may have six to fourteen, depending on the species. In the hagfish, the
which flare just behind the head
pouches connect with the pharynx internally. In adult lampreys, a
separate respiratory tube develops beneath the pharynx proper,
separating food and water from respiration by closing a valve at its anterior end.[2]
Tadpoles of amphibians have from three to five gill slits that don't contain actual gills. There is usually no spiracle or
true operculum, though many species have an operculum-like structure. Instead of internal gills, they develop three
feathery external gills that grow from the outer surface of the gill arches. Sometimes adults retain these, but they
usually disappear at metamorphosis. Lungfish larvae also have external gills, as does the primitive ray-finned fish
Polypterus, though the latter has a structure different than amphibians.[2]
Gill
43
Branchia
Branchia (pl. branchiæ) is the Ancient Greek naturalists' name for gills. Galen observed that fish had multitudes of
openings (foramina), big enough to admit gases, but too fine to give passage to water. Pliny the Elder held that fish
respired by their gills, but observed that Aristotle was of another opinion.[4] The word branchia comes from the
Greek βράγχια, "gills", plural of βράγχιον (in singular, meaning a fin).[5]
References
[1] Andrews, Chris; Adrian Exell, Neville Carrington (2003). Manual Of Fish Health. Firefly Books.
[2] Romer, Alfred Sherwood; Parsons, Thomas S. (1977). The Vertebrate Body. Philadelphia, PA: Holt-Saunders International. pp. 316–327.
ISBN 0-03-910284-X.
[3] Laurin M. (1998): The importance of global parsimony and historical bias in understanding tetrapod evolution. Part I-systematics, middle ear
evolution, and jaw suspension. Annales des Sciences Naturelles, Zoologie, Paris, 13e Série 19: pp 1-42.
[4] This article incorporates content from the 1728 Cyclopaedia, a publication in the public domain.
[5] "Branchia". Oxford English Dictionary. Oxford University Press. 2nd Ed. 1989.
Grater
Grater
A box grater with multiple grating
surfaces.
Box grater with vegetable slicing surface displayed.
A grater (also known as a shredder in parts of the eastern United States) is a kitchen utensil used to grate foods into
fine pieces. It was invented by François Boullier in the 1540s.
Grater
44
Uses
Several types of graters feature different sizes of grating slots, and can therefore aid in the preparation of a variety of
foods. They are commonly used to grate cheese and lemon or orange peel (to create zest), and can also be used to
grate other soft foods. They are commonly used in the preparation of toasted cheese, Welsh rarebit, and macaroni
and cheese.
In Slavic cuisine, graters are commonly used to grate potatoes, for preparation of, e.g., draniki, bramborak or potato
babka.
In tropical nations, graters are also used to grate coconut meat. In Jamaica, a coconut grater is used as a traditional
musical instrument[1] (along with drums, fife, and other instruments) in the performance of kumina, jonkanoo, and
sometimes mento.
History
The cheese grater was invented by Issac Hunt in the 1540s so hard cheeses could still be used.
Variants
There are also complex food-processing machines with grater-like mechanisms. These mechanisms rotate by the turn
of a cluster or electric motor.
Media
A microplane
A zest
grater
Porcelain ginger
grater
Sharkskin grater
A nutmeg grater
Multiple graters
Grater
45
In popular culture
• In The Sopranos episode, "Mergers and Acqusitions", Valentina La Paz reports, in disgust, to Tony Soprano that
in lieu of having conventional sexual relations, Soprano family mob captain, Ralph Cifaretto, asks her to scrape a
cheese grater across his back and pour hot candle wax on his testicles.
• In recent times, the term 'cheese grating' has evolved, as slang, to mean 'screen cheating' in video games.
Therefore a 'cheese grater' can also reference a person who actively 'screen cheats'. For example: Mark grates
tonnes of cheese in Halo: Reach.
• Comedian Mitch Hedberg performed a joke in which he stated that the negative name of cheese grater would be
"a sponge ruiner."[2]
References
[1] Brad Fredericks. "American Rhythm and Blues Influence on Early Jamaican Musical Style" (http:/ / debate. uvm. edu/ dreadlibrary/
fredericks. html). . Retrieved 2007-07-14.
[2] Mitch Hedberg. "Mitch Hedberg - Cheese Shredder" (http:/ / www. funnyordie. com/ videos/ 01ebe428cd/
mitch-hedberg-cheese-shredder-from-standupfan). . Retrieved 2011-06-25.
Handle (grip)
A handle is a part of, or attachment to, an object that can be moved or used by hand. The design of each type of
handle involves substantial ergonomic issues, even where these are dealt with intuitively or by following tradition.
Alternatively, the term "handle" can be used to refer to the fleshy portion of the lower human buttock.
General design criteria
The three nearly universal requirements of are:
1. Sufficient strength to support the object, or to otherwise transmit the force involved in the task the handle serves.
2. Sufficient length to permit the hand or hands gripping it to reliably exert that force.
3. Sufficiently small circumference to permit the hand or hands to surround it far enough to grip it as solidly as
needed to exert that force.
Other requirements may apply to specific handles:
• A sheath or coating on the handle that provides friction against the hand, reducing the gripping force needed to
achieve a reliable grip.
• Designs such as recessed car-door handles, reducing the chance of accidental operation, or simply the
inconvenience of "snagging" the handle.
• Sufficient circumference to distribute the force comfortably and safely over the hand. An example where this
requirement is almost the sole purpose for a handle's existence is the handle that consists of two pieces: a hollow
wooden cylinder about the diameter of a finger and a bit longer than one hand-width, and a stiff wire that passes
through the center of the cylinder, has two right angles, and is shaped into a hook at each end. This handle permits
comfortable carrying, with otherwise bare hands, of a heavy package, suspended on a tight string that passes
around the top and bottom of it: the string is strong enough to support it, but the pressure the string would exert on
fingers that grasped it directly would often be unacceptable.
• Design to thwart unwanted access, for example, by children or thieves. In these cases many of the other
requirements may have reduced importance. For example, a child-proof doorknob can be difficult for even an
adult to use.
Handle (grip)
46
Pull handles
One major category of handles are pull handles, where one or more
hands grip the handle or handles, and exert force to shorten the
distance between the hands and their corresponding shoulders. The
three criteria stated above are universal for pull handles.
Many pull handles are for lifting, mostly on objects to be carried.
Horizontal pull handles are widespread, including drawer pulls,
handles on latchless doors and the outside of car doors. The inside
controls for opening car doors from inside are usually pull handles,
although their function of permitting the door to be pushed open is
Many drawers use pull handles.
accomplished by an internal unlatching linkage.
Two kinds of pull handles may involve motion in addition to the hand-focused motions described:
• Pulling the starting cord on a small internal-combustion engine may, besides moving the hand toward the
shoulder, also exploit simultaneously pushing a wheeled vehicle away with the other hand, stepping away from
the engine, and/or standing from a squat.
• Some throwing motions, as in a track-and-field hammer throw, involve pulling on a handle against centrifugal
force (without bringing it closer), in the course of accelerating the thrown object by forcing it into circular motion.
Twist handles
Another category of hand-operated device requires grasping (but not
pulling) and rotating the hand and either the lower arm or the whole
arm, about their axis. When the grip required is a fist grip, as with a
door handle that has an arm rather than a knob to twist, the term
"handle" unambiguously applies. Another clear case is a rarer device
seen on mechanically complicated doors like those of airliners, where
(instead of the whole hand moving down as it also rotates, on the door
handles just described) the axis of rotation is between the thumb and
the outermost fingers, so the thumb moves up if the outer fingers move
down.
Many doors use twist handles.
In first-world countries, handles often twist in a clockwise fashion, while in second-world countries, the twist of
handles is often counterclockwise. However, most double doors and double windows are used with one handle
clockwise and the other handle counterclockwise. This double twisting is often effective on windows, doors,
cabinets, and faucets.
Handles for wide-range motion
The handles of bicycle grips, club-style weapons, shovels and spades, axes, hammers, mallets and hatchets, baseball
bats, rackets, golf clubs, and croquet mallets involve a much greater range of ergonomic issues.
References
Head
47
Head
In anatomy, the head of an animal is the rostral part
(from anatomical position) that usually comprises the
brain, eyes, ears, nose and mouth (all of which aid in
various sensory functions, such as sight, hearing, smell,
and taste). Some very simple animals may not have a
head, but many bilaterally symmetric forms do.
Cultural importance
For humans, the head and particularly the face are the
main distinguishing feature between different people,
due to their easily discernible features such as hair and
eye color, nose, eye and mouth shapes, wrinkles, etc.
Human faces are easily differentiable to us due to our
brains' predispositions toward discriminating human
facial forms. When observing a relatively unfamiliar
species, all faces seem nearly identical, and human
infants are biologically programmed to recognize subtle
differences in anthropic facial features.
The human head drawn by Leonardo da Vinci
People who are more intelligent than normal are
sometimes depicted in cartoons as having bigger heads,
as a way of indicating that they have a larger brain; in
science fiction, an extraterrestrial having a big head is
often symbolic of high intelligence. Outside of this
symbolic depiction, however, advances in neurobiology
have shown that the functional diversity of the brain
means that a difference in overall brain size is not a
reliable indicator of how much, if any, difference in
overall intelligence exists between two humans.[1]
A cheetah's head
The head is a source for many metaphors and metonymies in human language, including referring to things typically
near the human head ( "the head of the bed"), things physically similar to the way a head is arranged spatially to a
body ("the head of the table"), metaphorically ("the head of the class/FBI"), and things that represent some
characteristic we associate with the head, such as intelligence ("there are a lot of good heads in this company").
These examples are all from English, but only some are possible expressions in other languages (depending on the
language). (See Lakoff and Johnson 1980, 1999)
Ancient Greeks had a method for evaluating sexual attractiveness based on the Golden Ratio, part of which included
measurements of the head.
Head
48
Clothing
In many cultures, covering the head is seen as a sign of respect. Often,
some or all of the head must be covered and veiled when entering holy
places, or places of prayer. For many centuries, women in Europe, the
Middle East, and South Asia have covered their hair as a sign of
modesty. This trend has changed drastically in Europe in the 20th
century, although is still observed in other parts of the world. In
addition, a number of religious paths require men to wear specific head
clothing—such as the Islamic Taqiyah, Jewish yarmulke, or the Sikh
turban; or Muslim women, who cover their hair, ears, and neck with a
scarf.
Original caption: on sale in the bazar in Isfahan
People may cover the head for other reasons. A hat, is a piece of clothing covering just the top of the head. This may
be part of a uniform, such as a Police uniform, a protective device such as a hard hat, a covering for warmth, or a
fashion accessory.
Different headpieces can also signify status, origin, religious/spiritual beliefs, social grouping, occupation, and
fashion choices.
Anthropometry
Static adult human Anthropometryphysical characteristics of the head.
Notes
[1] Brain Size and Intelligence (http:/ / www. ncbi. nlm. nih. gov/ books/ bv. fcgi?rid=neurosci. box. 1833)
References
• Campbell, Bernard Grant. Human Evolution: An Introduction to Man's Adaptations (4th edition), ISBN
0-202-02042-8
Hoof
49
Hoof
A hoof (
/ˈhuːf/ or /ˈhʊf/), plural hooves (
/ˈhuːvz/ or /ˈhʊvz/) or hoofs ( /ˈhʊfs/),
is the tip of a toe of an ungulate mammal,
strengthened by a thick horny (keratin)
covering. The hoof consists of a hard or
rubbery sole, and a hard wall formed by a
thick nail rolled around the tip of the toe.
The weight of the animal is normally borne
by both the sole and the edge of the hoof
wall. Hooves grow continuously, and are
constantly worn down by use.
Most even-toed ungulates (such as sheep,
goats, deer, cattle, bison and pigs) have two
main hooves on each foot, together called a
cloven hoof. Most of these cloven-hoofed
Cloven hooves of Roe Deer (Capreolus capreolus), with dew claws
animals also have two smaller hoofs called
dew-claws a little further up the leg – these are not normally used for walking, but in some species with larger
dew-claws (such as deer and pigs) they may touch the ground when running or jumping, or if the ground is soft.
Other cloven-hoofed animals (such as giraffes and pronghorns) have no dew claws. In some so-called
"cloven-hoofed" animals such as camels, there are no hooves proper – the toe is softer, and the hoof itself is reduced
to little more than a nail.
Some odd-toed ungulates (equids) have one hoof on each foot; others (including rhinoceroses, tapirs and many
extinct species) have (or had) three hoofed or heavily nailed toes, or one hoof and two dew-claws. The tapir is a
special case, with three toes on each hind foot and four toes on each front foot.
Sagittal section of a wild
horsehoof. Pink: soft tissues;
light gray: bone; blue:
tendons; red: corium;
yellow: digital cushion; dark
gray: frog; orange: sole;
brown: walls
camel hoof
Sheet plastinate of a horse hoof.
Rear foot of
a giraffe (no
dew claws)
Rear hooves of a horse
Hoof
50
Uses
Hooves have historical significance in ceremonies and games. They have been used in burial ceremonies[1] , in the
Dart Golf game Dolf.[2] and in the song Hooves of the Ibex by Wormhole.[3]
References
[1] M. E. Robertson-Mackay (1980). A head and hooves burial beneath a round barrow, with other Neolithic and Bronze Age sites on Hemp
Knoll, near Avebury, Wiltshire (http:/ / www. zotero. org/ samwalsh/ items/ 7EBE4GDE). Proceedings of the Prehistoric Society. .
[2] "WDFF Playing & Tournament Rules" (http:/ / www. dolfdarts. com/ the-rules-of-dolf). 1999. .
[3] "Wormhole" (http:/ / www. myspace. com/ wormholemusic). 2007. .
Horn (anatomy)
A horn is a pointed projection of the skin on the head of
various animals, consisting of a covering of horn
(keratin and other proteins) surrounding a core of living
bone. True horns are found mainly among the ruminant
artiodactyls, in the families Antilocapridae (pronghorn)
and Bovidae (cattle, goats, antelope etc.). One pair of
horns is usual, but two pairs occur in a few wild species
and in a few domesticated breeds of sheep. Partial or
deformed horns in livestock are called scurs.
Horns usually have a curved or spiral shape, often with
ridges or fluting. In many species only males have
horns. Horns start to grow soon after birth, and continue
to grow throughout the life of the animal (except in
pronghorns, which shed the outer layer annually, but
retain the bony core). Similar growths on other parts of
the body are not usually called horns, but spurs, claws or
hoofs, depending on the part of the body on which they
occur.
Other hornlike growths
The term "horn" is also popularly applied to other hard
and pointed features attached to the head of animals in
various other families:
A goat with spiral horns
• Giraffidae: Giraffes have one or more pairs of bony bumps on their heads, called ossicones. These are covered
with furred skin.
• Cervidae: Most deer have antlers, which are not true horns. When fully developed, antlers are dead bone without
a horn or skin covering; they are borne only by adults (usually males) and are shed and regrown each year.
• Rhinocerotidae: The "horns" of rhinoceroses are made of keratin and grow continuously, but do not have a bone
core.
• Chamaeleonidae: Many chameleons, most notably the Jackson's Chameleon, possess horns on their skulls, and
have a keratin covering.
Horn (anatomy)
51
• Ceratopsidae: The "horns" of the Triceratops were extensions of its skull bones although debate exists over
whether they had a keratin covering.
• Horned lizards (Phrynosoma): These lizards have horns on their heads which have a hard keratin covering over a
bony core, like mammalian horns.
• Insects: Some insects (such as rhinoceros beetles) have horn-like structures on the head or thorax (or both). These
are pointed outgrowths of the hard chitinous exoskeleton. Some (such as stag beetles) have greatly enlarged jaws,
also made of chitin.
• Canidae: Golden jackals are known to occasionally develop a horny growth on the skull, which is associated with
magical powers in south-eastern Asia.[1] [2]
Many mammal species in various families have tusks, which often serve the same functions as horns, but are in fact
oversize teeth. These include the Moschidae (Musk deer, which are ruminants), Suidae (Wild Boars), Proboscidea
(Elephants), Monodontidae (Narwhals) and Odobenidae (Walruses).
Polled animals or pollards are those of
normally-horned (mainly domesticated) species whose
horns have been removed, or which have not grown. In
some cases such animals have small horny growths in
the skin where their horns would be – these are known
as scurs.
On humans
Cutaneous horns are the only examples of horns
growing on people. They are believed to be caused by
exposure to radiation. They are most often benign
growths and can be removed by a razor.
Cases of people growing horns have been historically
described, sometimes with mythical status. Researchers
have not however discovered photographic evidence of
the phenomenon.[3] There are human cadaveric
A Hebridean sheep with one horn on one side and two on the other.
specimens that show outgrowings, but these are instead
classified as osteomas or other excrescences.[3] Theoretically, there may be children born with horns which are
corrected with early surgical intervention. The phenomenon of humans with horns has been observed in countries
lacking advanced medicine. There are living people, several in China, with cases of cutaneous horns, most common
in the elderly[4] .
Some people, notably The Enigma, have horn implants; that is, they have implanted silicone beneath the skin as a
[5]
form of body modification.
Horn (anatomy)
52
Animal uses of horns
Animals have a variety of uses for horns and antlers, including
defending themselves from predators and fighting members of their
own species for territory, dominance or mating priority. Horns are
usually present only in males but in some species, females too may
possess horns. It has been theorized by researchers that taller species
living in the open are more visible from longer distances and more
likely to benefit from horns to defend themselves against predators.
Female bovids that are not hidden from predators due to their large size
or open Savannah like habitat are more likely to bear horns than small
or camouflaged species.[6]
Both male and female African buffaloes bear
horns
In addition, horns may be used to root in the soil or strip bark from trees. In animal courtship many use horns in
displays. For example, the male blue wildebeest reams the bark and branches of trees to impress the female and lure
her into his territory. Some animals with true horns use them for cooling. The blood vessels in the bony core allow
the horns to function as a radiator.
Human uses of horns
• Horned animals are sometimes hunted so their
mounted head or horns can be displayed as a hunting
trophy or as decorative objects. This practice can be
considered controversial, especially as some animals
are threatened or endangered due to reduced
populations partially from pressures of such hunting.
• Some cultures use bovid horns as musical
instruments, for example the shofar. These have
evolved into brass instruments in which, unlike the
trumpet, the bore gradually increases in width
through most of its length—that is to say, it is
conical rather than cylindrical. These are called
horns, though now made of metal.
Water buffalo horn used as a hammer with cleaver to cut fish in
southeast China.
• Drinking horns are bovid horns removed from the bone core, cleaned and polished and used as drinking vessels.
(See also the legend of the Horn of plenty, or Cornucopia). It has been suggested that the shape of a natural horn
was also the model for the rhyton, a horn-shaped drinking vessel.[7]
• Powder horns were originally bovid horns fitted with lids and carrying straps, used to carry gunpowder. Powder
flasks of any material may be referred to as powder horns.
• Antelope horns are used in traditional Chinese medicine.
• Horns consist of keratin, and the term "horn" is used to refer to this material, sometimes including similarly solid
keratin from other parts of animals, such as hoofs. Horn may be used as a material in tools, furniture and
decoration, among other uses. In these applications, horn is valued for its hardness, and it has given rise to the
expression hard as horn. Horn is somewhat thermoplastic and (like tortoiseshell) was formerly used for many
purposes where plastic would now be used. Horn may be used to make glue.
• Horn bows are bows made from a combination of horn, sinew and usually wood. These materials allow more
energy to be stored in a short bow than wood alone.
• Ivory comes from the teeth of animals, not horns.
Horn (anatomy)
• "Horn" buttons are usually made from deer antlers, not true horn.
References
[1] Sketches of the natural history of Ceylon by Sir James Emerson Tennent, published by Longman, Green, Longman, and Roberts, 1861
[2] Mammals of Nepal: (with reference to those of India, Bangladesh, Bhutan and Pakistan) by Tej Kumar Shrestha, published by Steven
Simpson Books, 1997, ISBN 0952439069
[3] Tubbs, John C. III; Smyth, Matthew D.; Wellons; Blount, Jeffrey P.; Oakes, W. Jerry (June 2003). "Human horns: a historical review and
clinical correlation". Neurosurgery 52 (6): 1443–1448. doi:10.1227/01.NEU.0000064810.08577.49. PMID 12762889. (Literature Reviews)
[4] . http:/ / www. stern. de/ wissen/ mensch/ ungewoehnliche-operation-aerzte-befreien-frau-von-horn-1682189. html.
[5] Johann, Hari (2002-03-11). "Johann Hari on the bizarre world of radical plastic surgery" (http:/ / www. guardian. co. uk/ society/ 2002/ mar/
11/ health. lifeandhealth). London: Guardian News and Media. . Retrieved 2010-05-04.
[6] http:/ / www. physorg. com/ news172428997. html
[7] Chusid, Hearing Shofar: The Still Small Voice of the Ram's Horn, 2009, Chapter 3-6 - Ram's Horn of Passover
<http://www.hearingshofar.com>. The book also posits that the ancient Hebrews and neighboring tribes used horns as weapons and as
utensils.
External links
• A site with information about the history of the cow horn as a musical instrument. (http://www.ancientmusic.
co.uk/ancientinstruments/Blowing_Horns.html)
53
Human leg
54
Human leg
Human leg
Lateral aspect of right leg
Latin
membrum inferios
MeSH
Leg
[1]
Dorlands/Elsevier Leg [2]
The human leg is the entire lower extremity or limb[3] [4] of the human body, including the foot, thigh and even the
[5] [6] [7]
to the section of the lower limb
hip or gluteal region, the precise definition in human anatomy refers
extending between the knee and the ankle.
Legs are used for standing, walking, jumping, running, kicking, and similar activities, and constitute a significant
portion of a person's mass.
Anatomy
In human anatomical terms, the leg is the part of the lower limb that lies between the knee and the ankle,[8] the thigh
is between the hip and knee and the term "lower limb" is used to describe the colloquial leg. This article generally
follows the common usage.
The leg from the knee to the ankle is called the cnemis (née'mis) or crus. The calf is the back portion and the shin is
the front.
Evolution has provided the human body with two distinct features: the
specialization of the upper limb for visually guided manipulation and the lower
limb's development into a mechanism specifically adapted for efficient bipedal
gait. While the capacity to walk upright is not unique to humans, other primates
can only achieve this for short periods and at a great expenditure of energy. The
human adaption to bipedalism is not limited to the leg, however, but has also
affected the location of the body's center of gravity, the reorganisation of internal
organs, and the form and biomechanism of the trunk. In humans, the double
S-shaped vertebral column acts as a shock-absorber which shifts the weight from
the trunk over the load-bearing surface of the feet. The human legs are
Comparison between human and
exceptionally long and powerful as a result of their exclusive specialization to
gorilla skeletons. (Gorilla in
support and locomotion — in orangutans the leg length is 111% of the trunk; in
non-natural stretched posture.)
chimpanzees 128%, and in humans 171%. Many of the leg's muscles are also
adapted to bipedalism, most substantially the gluteal muscles, the extensors of the knee joint, and the calf muscles.[9]
Human leg
55
See also: Human skeletal changes due to bipedalism
Skeleton
The major (long) bones of the human leg are the femur (thighbone), tibia
(shinbone), and fibula (the smaller, rear calf bone). The patella (kneecap) is the
bone in front of the knee. Most of the leg skeleton has bony prominences and
margins that can be palpated, notable exceptions being the hip joint, and the neck
and shaft of femur. Many of these anatomical landmarks are used to define the
extent of the leg: most notably the anterior superior iliac spine, the greater
trochanter, the superior margin of the medial condyle of tibia, and the medial
malleolus.[10]
In the normal case, the large joints of the lower limb are aligned on a straight line
which represents the mechanical longitudinal axis of the leg, the Mikulicz line.
This line stretches from the hip joint (or more precisely the head of the femur),
Bones of the leg
through the knee joint (the intercondylar eminence of the tibia), and down to the
center of the ankle (the ankle mortise, the fork-like grip between the medial and lateral malleoli). In the tibial shaft,
the mechanical and anatomical axes coincide, but in the femoral shaft they diverge 6°, resulting in the femorotibial
angle of 174° in a leg with normal axial alignment. A leg is considered straight when, with the feet brought together,
both the medial malleoli of the ankle and the medial condyles of the knee are touching. Divergence from the normal
femorotibial angle is called genu varum if the center of the knee joint is lateral to the mechanical axis
(intermalleolar distance exceeds 3 cm), and genu valgum if it is medial to the mechanical axis (intercondylar
distance exceeds 5 cm). These conditions impose unbalanced loads on the joints and stretching of either the thigh's
adductors and abductors.[11] The angle of inclination formed between the neck and shaft of the femur, the
collodiaphysial angle, varies with age—about 150° in the newborn, it gradually decreases to 126-128° in adults, to
reach 120° in old age. Pathological changes in this angle results in abnormal posture of the leg: A small angle
produces coxa vara and a large angle in coxa valga; the latter is usually combined with genu varum and coxa vara
leads genu valgum. Additionally, a line drawn through the femoral neck superimposed on a line drawn through the
femoral condyles forms an angle, the torsion angle, which makes it possible for flexion movements of the hip joint to
be transposed into rotary movements of the femoral head. Abnormally increased torsion angles results in a limb
turned inward and a decreased angle in a limb turned outward; both cases resulting in a reduced range of
mobility.[12]
Muscles
Hip
Human leg
56
Function of hip muscles[13]
Movement
Muscles
(In order of
importance)
Lateral
rotation
• Sartorius • Gluteus maximus
• Quadratus femoris
• Obturator internus
• Gluteus medius and minimus
• Iliopsoas
(with psoas major♣)
• Obturator externus
• All functional adductors
except gracilis* and pectineus
• Piriformis
Medial
rotation
• Gluteus medius and
minimus (anterior fibers)
• Tensor fascia latae*
• Adductor magnus
(long medial fibers)
• Pectineus (with leg abducted)
Extension
• Gluteus maximus
• Gluteus medius and
minimus (dorsal fibers)
• Adductor magnus
• Piriformis
• Semimembranosus*
• Semitendinousus*
• Biceps femoris*
(long head)
Flexion
• Iliopsoas
(with psoas major♣)
• Tensor fascia latae*
• Pectineus
• Adductor longus
• Adductor brevis
• Gracilis*
• Rectus femoris*
• Sartorius*
Abduction
• Gluteus medius
• Tensor fascia latae*
• Gluteus maximus
(fibers to fascia lata)
• Gluteus minimus
• Piriformis
• Obturator internus
Human leg
57
Adduction
• Adductor magnus
(with adductor minimus)
• Adductor longus
• Adductor brevis
• Gluteus maximus (fibers
to gluteal tuberosity)
• Gracilis
• Pectineus
• Quadratus femoris
• Obturator externus
• Semitendinosus*
Notes
♣ Also act on vertebral
joints.
* Also act on knee joint.
There are several ways of classifying the muscles of the hip: (1) By location or innervation (ventral an dorsal
divisions of the plexus layer); (2) by development on the basis of their points of insertion (a posterior group in two
[14]
layers and an anterior group); and (3) by function (i.e. extensors, flexors, adductors, and abductors).
Some hip muscles also act on either the knee joint or on vertebral joints. Additionally, because the area of origin and
insertion of many of these muscles are very extensive, these muscles are often involved in several very different
movements. In the hip joint, lateral and medial rotation occur along the axis of the limb; extension (also called
dorsiflexion or retroversion) and flexion (anteflexion or anteversion) occur along a transverse axis; and abduction
and adduction occur about a sagittal axis.[13]
The anterior dorsal hip muscles are the iliopsoas, a group of two or three muscles with a shared insertion on the
lesser trochanter of the femur. The psoas major originates from the last vertebra and along the lumbar spine to
stretch down into the pelvis. The iliacus originates on the iliac fossa on the interior side of the pelvis. The two
muscles unite to form the iliopsoas muscle which is inserted on the lesser trochanter of the femur. The psoas minor,
only present in about 50 per cent of subjects, originates above psoas major to stretch obliquely down to its insertion
on the interior side of the major muscle.[15]
The posterior dorsal hip muscles are inserted on or directly below the greater trochanter of the femur. The tensor
fascia latae, stretching from the anterior superior iliac spine down into the iliotibial tract, presses the head of the
femur into the acetabulum but also flexes, rotates medially, and abducts to hip joint. The piriformis originates on the
anterior pelvic surface of the sacrum, passes through the greater sciatic foramen, and inserts on the posterior aspect
of the tip of the greater trochanter. In a standing posture it is a lateral rotator, but it also assists extending the thigh.
The gluteus maximus has its origin between (and around) the iliac crest and the coccyx from where one part radiates
into the iliotibial tract and the other stretches down to the gluteal tuberosity under the greater trochanter. The gluteus
maximus is primarily an extensor and lateral rotator of the hip joint, and it comes into action when climbing stairs or
rising from a sitting to standing posture. Furthermore, the part inserted into the fascia latae abducts and the part
inserted into the gluteal tuberosity adducts the hip. The two deep glutei muscles, the gluteus medius and minimus,
originate on the lateral side of the pelvis. The medius muscle is shaped like a cap. Its anterior fibers act as a medial
rotator and flexor; the posterior fibers as a lateral rotator and extensor; and the entire muscle abducts the hip. The
minimus has similar functions and both muscles are inserted onto the greater trochanter.[16]
Human leg
The ventral hip muscles function as lateral rotators and play an important role in the
control of the body's balance. Because they are stronger than the medial rotators, in the
normal position of the leg, the apex of the foot is pointing outward to achieve better
support. The obturator internus originates on the pelvis on the obturator foramen and
its membrane, passes through the lesser sciatic foramen, and is inserted on the
trochanteric fossa of the femur. "Bent" over the lesser sciatic notch, which acts as a
Muscles of hip
fulcrum, the muscle forms the strongest lateral rotators of the hip together with the
gluteus maximus and quadratus femoris. When sitting with the knees flexed it acts as an
abductor. The obturator externus has a parallel course with its origin located on the posterior border of the
obturator foramen. It is covered by several muscles and acts as a lateral rotator and a weak adductor. The inferior
and superior gemelli represent marginal heads of the obturator internus and assist this muscle. The three muscles
have been referred to as the triceps coxae. The quadratus femoris originates at the ischial tuberosity and is inserted
onto the intertrochanteric crest between the trochanters. This flattened muscle act as a strong lateral rotator and
adductor of the thigh.[17]
The adductor muscles of the thigh are innervated by the obturator nerve, with the exception of
pectineus which receives fibers from the femoral nerve, and the adductor magnus which receives
fibers from the tibial nerve. The gracilis arises from near the pubic symphysis and is unique
among the adductors in that it reaches past the knee to attach on the medial side of the shaft of the
tibia, thus acting on two joints. It share its distal insertion with the sartorius and semitendinosus,
all three muscles forming the pes anserinus. It is the most medial muscle of the adductors, and
with the thigh abducted its origin can be clearly seen arching under the skin. With the knee
extended, it adducts the thigh and flexes the hip. The pectineus has its origin on the iliopubic
eminence laterally to the gracilis and, rectangular in shape, extends obliquely to attach
immediately behind the lesser trochanter and down the pectineal line and the proximal part of the
linea aspera on the femur. It is a flexor of the hip joint, and an adductor and a weak medial rotator
of the thigh. The adductor brevis originates on the inferior ramus of the pubis below the gracilis
and stretches obliquely below the pectineus down to the upper third of the linea aspera. Except for
Hip adductors
being an adductor, it is a lateral rotator and weak flexor of the hip joint.[18] The adductor longus
has its origin at superior ramus of the pubis and inserts medially on the middle third of the linea aspera. Primarily an
adductor, it is also responsible for some flexion. The adductor magnus has its origin just behind the longus and lies
deep to it. Its wide belly divides into two parts: One is inserted into the linea aspera and the tendon of the other
reaches down to adductor tubercle on the medial side of the femur's distal end where it forms an intermuscular
septum that separates the flexors from the extensors. Magnus is a powerful adductor, especially active when crossing
legs. Its superior part is a lateral rotator but the inferior part acts as a medial rotator on the flexed leg when rotated
outward and also extends the hip joint. The adductor minimus is an incompletely separated subdivision of the
adductor magnus. Its origin forms an anterior part of the magnus and distally it is inserted on the linea aspera above
the magnus. It acts to adduct and lateral rotate the femur.[19]
Thigh
58
Human leg
59
Function of knee muscles[20]
Movement
Muscles
(In order of
importance)
Extension
• Quadriceps femoris
• Tensor fascia latae*
Flexion
• Semimembranosus
• Semitendinosus
• Biceps femoris
• Gracilis
• Sartorius
• Popliteus
• Gastrocnemius
Medial
rotation
• Semimembranosus
• Semitendinosus
• Gracilis
• Sartorius
• Popliteus
Lateral
rotation
• Biceps femoris
• Tensor fascia latae*
*Insignificant assistance.
The muscles of the thigh can be classified into three groups according to their location: anterior and posterior
muscles and the adductors (on the medial side). All adductors (see above) except gracilis insert on the femur and
therefore act only on the hip joint. The majority of the thigh muscles, the "true" thigh muscles, are insert on the leg
(either the tibia or the fibula) and thus act primarily on the knee joint. Functionally, the extensors lie anteriorly on the
thigh and are distinguished from flexors on the posterior side. Even though the sartorius flexes the knee, it is
ontogenetically considered an extensor since its displacement is secondarily.[14] Most of the adductors act
exclusively on the hip joint, so functionally they qualify as hip muscles.
Anterior and posterior thigh muscles.
Of the anterior thigh muscles the largest are the four muscles of the quadriceps femoris. The central rectus
femoris which is surrounded by the three vasti: The vastus intermedius, medialis, and lateralis. Rectus femoris is
attached to the pelvis with two tendons, while the vasti are inserted to the femur. All four muscles unite in a common
tendon inserted into the patella from where the patellar ligament extends it down to the tibial tuberosity. Fibers from
the medial and lateral vasti form two retinacula that stretch past the patella on either sides down to the condyles of
the tibia. The quadriceps is the knee extensor, but the rectus femoris additionally flexes the hip joint, and articular
muscle of the knee protects the articular capsule of the knee joint from being nipped during extension. The sartorius
runs superficially and obliquely down on the anterior side of the thigh, from the anterior superior iliac spine to the
pes anserinus on the medial side of the knee, from where it is further extended into the crural fascia. The sartorius
acts as a flexor on both the hip and knee, but, due to its oblique course, also contributes to medial rotation of the leg
Human leg
60
as one of the pes anserinus muscles (with the knee flexed), and to lateral rotation of the hip joint.[21]
There are four posterior thigh muscles. The biceps femoris has two heads: The long head has its origin on the
ischial tuberosity together with the semitendinosus and acts on two joints. The short head originates from the middle
third of the linea aspera on the shaft of the femur and the lateral intermuscular septum of thigh, and acts on only one
joint. These two heads unite to form the biceps which inserts on the head of the fibula. The biceps flexes the knee
joint and rotates the flexed leg laterally — it is the only lateral rotator of the knee and thus has to oppose all medial
rotator. Additionally, the long head extends the hip joint. The semitendiosus and the semimembranosus share their
origin with the long head of the biceps, and both attaches on the medial side of the proximal head of the tibia
together with the gracilis and sartorius to form the pes anserinus. The semitendinosus acts on two joints; extension of
the hip, flexion of the knee, and medial rotation of the leg. Distally, the semimembranosus' tendon is divided into
three parts referred to as the pes anserinus profondus. Functionally, the semimembranosus is similar to the
semitendinosus, and thus produces extension at the hip joint and flexion and medial rotation at the knee.[22]
Posteriorly below the knee joint, the popliteus stretches obliquely from the lateral femoral epicondyle down to the
posterior surface of the tibia. The subpopliteal bursa is located deep to the muscle. Popliteus flexes the knee joint and
medially rotates the leg.[23]
Foot
Function of foot muscles[24]
Movement
Muscles
(In order of
importance)
Dorsiflexion
• Tibialis anterior
• Extensor
digitorum
longus
• Extensor hallucis
longus
Plantar
flexion
• Triceps surae
• Peroneus longus
• Peroneus brevis
• Flexor digitorum
longus
• Tibialis posterior
Eversion
• Peroneus longus
• Peroneus brevis
• Extensor
digitorum
longus
• Peroneus tertius
Inversion
• Triceps surae
• Tibialis posterior
• Flexor hallucis
longus
• Flexor digitorum
longus
• Tibialis anterior
With the popliteus (see above) as the single exception, all muscles in the leg are attached to the foot and, based on
location, can be classified into an anterior and a posterior group separated from each others by the tibia, the fibula,
and the interosseous membrane. In turn, these two groups can be subdivided into subgroups or layers — the anterior
Human leg
61
group consists of the extensors and the peroneals, and the posterior group of a superficial and a deep layer.
Functionally, the muscles of the leg are either extensors, responsible for the dorsiflexion of the foot, or flexors,
responsible for the plantar flexion. These muscles can also classified by innervation, muscles supplied by the anterior
subdivision of the plexus and those supplied by the posterior subdivision.[25] The leg muscles acting on the foot are
called the extrinsic foot muscles whilst the foot muscles located in the foot are called intrinsic.
Dorsiflexion (extension) and plantar flexion occur around the transverse axis running through the ankle joint from
the tip of the medial malleolus to the tip of the lateral malleolus. Pronation (eversion) and supination (inversion)
occur along the oblique axis of the ankle joint.[24]
Extrinsic
Three of the anterior muscles are extensors. From its origin on the lateral surface of the tibia and
the interosseus mebrane, the three-sided belly of the tibialis anterior extends down below the
superior and inferior extensor retinacula to its insertion on the plantar side of the medial cuneiform
bone and the fifth metatarsal bone. In the non-weight-bearing leg, the anterior tibialis dorsal flexes
the foot and lifts the medial edge of the foot. In the weight-bearing leg, it pulls the leg towards the
foot. The extensor digitorum longus has a wide origin stretching from the lateral condyle of the
tibia down along the anterior side of the fibula, and the interosseus membrane. At the ankle, the
tendon divides into four that stretch across the foot to the dorsal aponeuroses of the last phalanges of
the four lateral toes. In the non-weight-bearing leg, the muscle dorsiflexes the digits and the foot,
and in the weight-bearing leg acts similar to the tibialis anterior. The extensor hallucis longus has
its origin on the fibula and the interosseus membrane between the two other extensors and is,
similarly to the extensor digitorum, is inserted on the last phalanx of big toe ("hallux"). The muscle
dorsiflexes the hallux, and acts similar to the tibialis anterior in the weight-bearing leg.[26] Two
Anterior
muscles.
muscles on the lateral side of the leg form the peroneal group. The peroneus longus and brevis
both have their origins on the fibula and they both pass behind the lateral malleolus where their
tendons pass under the peroneal retinacula. Under the foot, the longus stretches from the lateral to the medial side in
a groove, thus bracing the transverse arch of the foot. The brevis is attached on the lateral side to the tuberosity of the
fifth metatarsal. Together the two peroneals form the strongest pronators of the foot.[27] The peroneus muscles are
highly variable and several variants can occasionally be present.[28]
Superficial and deep posterior muscles.
Of the posterior muscles three are in the superficial layer. The major plantar flexors, commonly referred to as the
triceps surae, are the soleus, which arises on the proximal side of both leg bones, and the gastrocnemius, the two
heads of which arises on the distal end of the femur. These muscles unite in a large terminal tendon, the Achilles
tendon, which is attached to the posterior tubercle of the calcaneus. The plantaris closely follows the lateral head of
the gastrocnemius. Its tendon runs between those of the soleus and gastrocnemius and is embedded in the medial end
of the calcaneus tendon.[29]
Human leg
62
In the deep layer, the tibialis posterior has its origin on the interosseus membrane and the neighbouring bone areas
and runs down behind the medial malleolus. Under the foot it splits into a thick medial part attached to the navicular
bone and a slightly weaker lateral part inserted to the three cuneiform bones. The muscle produces simultaneous
plantar flexion and supination in the non-weight-bearing leg, and approximates the heel to the calf of the leg. The
flexor hallucis longus arises distally on the fibula and on the interosseus membrane from where its relatively thick
muscle belly extends far distally. Its tendon extends beneath the flexor retinaculum to the sole of the foot and finally
attaches on the base of the last phalanx of the hallux. It plantarflexes the hallux and assists in supination. The flexor
digitorum longus, finally, has its origin on the upper part of the tibia. Its tendon runs to the sole of the foot where it
forks into four terminal tendon attached to the last phalanges of the four lateral toes. It crosses the tendon of the
tibialis posterior distally on the tibia, and the tendon of the flexor hallucis longus in the sole. Distally to its division,
the quadratus plantae radiates into it and near the middle phalanges its tendons penetrate the tendons of the flexor
digitorum brevis. In the non-weight-bearing leg, it plantar flexes the toes and foot and supinates. In the
weight-bearing leg it supports the plantar arch.[23] (For the popliteus, see above.)
Intrinsic
The intrinsic muscles of the foot, muscles whose bellies are located in the foot proper, are either dorsal (top) or
plantar (sole). On the dorsal side, two long extrinsic extensor muscles are superficial to the intrinsic muscles, and
their tendons form the dorsal aponeurosis of the toes. The short intrinsic extensors and the plantar and dorsal
interossei radiates into these aponeuroses. The extensor digitorum brevis and extensor hallucis brevis have a
common origin on the anterior side of the calcaneus, from where their tendons extend into the dorsal aponeuroses of
digits 1-4. They act to dorsiflex these digits.[30]
The plantar muscles can be subdivided into three groups associated with three regions: those of the big digit, the
little digit, and the region between these two. All these muscles are covered by the thick and dense plantar
aponeurosis, which, together with two tough septa, form the spaces of the three groups. These muscles and their fatty
tissue function as cushions that transmit the weight of the body downward. As a whole, the foot is a functional
entity.[31]
Intrinsic foot muscles
The abductor hallucis stretches along the medial edge of the foot, from the calcaneus to the base of the first phalanx
of the first digit and the medial sesamoid bone. It is an abductor and a week flexor, and also helps maintain the arch
of the foot. Lateral to the abductor hallucis is the flexor hallucis brevis, which originates from the medial cuneiform
bone and from the tendon of the tibialis posterior. The flexor hallucis has a medial and a lateral head inserted
laterally to the abductor hallucis. It is an important plantar flexor which comes into prominent use in classical ballet
(i.e. for pointe work).[31] The adductor hallucis has two heads; a stronger oblique head which arises from the cuboid
and lateral cuneiform bones and the bases of the second and third metatarsals; and a transverse head which arises
from the distal ends of the third-fifth metatarsals. Both heads are inserted on the lateral sesamoid bone of the first
digit. The muscle acts as a tensor to the arches of the foot, but can also adduct the first digit and plantar flex its first
phalanx.[32]
The opponens digiti minimi originates from the long plantar ligament and the plantar tendinous sheath of peroneus
longus and is inserted on the fifth metatarsal. When present, it acts to plantar flex the fifth digit and supports the
plantar arch. The flexor digiti minimi arises from the region of base of the fifth metatarsal and is inserted onto the
Human leg
63
base of the first phalanx of the fifth digit where it is usually merged with the abductor of the first digit. It acts to
plantar flex the last digit. The largest and longest muscles of the little toe is the abductor digiti minimi. Stretching
from the lateral process of the calcaneus, with a second attachment on the base of the fifth metatarsal, to the base of
the fifth digit's first phalanx, the muscle forms the lateral edge of the sole. Except for supporting the arch, it plantar
flexes the little toe and also acts as an abductor.[32]
The four lumbricales have their origin on the tendons of the flexor digitorum longus, from where they extend to the
medial side of the bases of the first phalanx of digits two-five. Except for reinforcing the plantar arch, they contribute
to plantar flexion and move the four digits toward the big toe. They are, in contrast to the lumbricales of the hand,
rather variable, sometimes absent and sometimes more than four are present. The quadratus plantae arises with two
slips from margins of the plantar surface of the calcaneus and is inserted into the tendon(s) of the flexor digitorum
longus, and is known as the "plantar head" of this latter muscle. The three plantar interossei arise with their single
heads on the medial side of the third-fifth metatarsals and are inserted on the bases of the first phalanges of these
digits. The two heads of the four dorsal interossei arise on two adjacent metatarsals and merge in the intermediary
spaces. Their distal attachment is on the bases of the proximal phalanges of the second-fourth digits. The interossei
are organized with the second digit as a longitudinal axis; the plantars act as adductors and pull digits 3-5 towards
the second digit; while the dorsals act as abductors. Additionally, the interossei act as plantar flexors at the
metatarsophalangeal joints. Lastly, the flexor digitorum brevis arises from underneath the calcaneus to insert its
tendons on the middle phalanges of digit 2-4. Because the tendons of the flexor digitorum longus run between these
tendons, the brevis is sometimes called perforatus. The tendons of these two muscles are surrounded by a tendinous
sheath. The brevis acts to plantar flex the middle phalanges.[33]
See also: Table of muscles
Neurovascular system
Arteries
The arteries of the leg are divided into a series of segments.
In the pelvis area, at the level of the last lumbar vertebra, the abdominal aorta, a continuation the descending aorta,
splits into a pair of common iliac arteries. These immediately split into the internal and external iliac arteries, the
latter of which descends along the medial border of the psoas major to exits the pelvis area through the vascular
lacuna under the inguinal ligament.[34]
The artery enters the thigh as the femoral artery which descends the medial side of the thigh to the adductor canal.
The canal passes from the anterior to the posterior side of the limb where the artery leaves through the adductor
hiatus and becomes the popliteal artery. On the back of the knee the popliteal artery runs through the popliteal fossa
to the popliteal muscle where it divides into anterior and posterior tibial arteries.[34]
In the lower leg, the anterior tibial enters the extensor compartment near the upper border of the interosseus
membrane to descend between the tibialis anterior and the extensor hallucis longus. Distal to the superior and
extensor retinacula of the foot it becomes the dorsal artery of the foot. The posterior tibial forms a direct continuation
of the popliteal artery which enters the flexor compartment of the lower leg to descend behind the medial malleolus
where it divides into the medial and lateral plantar arteries, of which the posterior branch gives rise to the fibular
artery.[34]
For practical reasons the lower limb is subdivided into somewhat arbitrary regions:[35]
The regions of the hip are all located in the thigh: anteriorly, the subinguinal region is bounded by the inguinal
ligament, the sartorius, and the pectineus and forms part of the femoral triangle which extends distally to the
adductor longus. Posteriorly, the gluteal region corresponds to the gluteus maximus. The anterior region of the thigh
extends distally from the femoral triangle to the region of the knee and laterally to the tensor fascia latae. The
posterior region ends distally before the popliteal fossa. The anterior and posterior regions of the knee extends from
Human leg
64
the proximal regions down to the level of the tuberosity of the tibia. In the lower leg the anterior and posterior
regions extends down to the malleoli. Behind the malleoli are the lateral and medial retromalleolar regions and
behind these is the region of the heel. Finally, the foot is subdivided into a dorsal region superiorly and a plantar
region inferiorly.[35]
Veins
The veins are subdivided into three systems. The deep or epifascial system returns approximately 85 percent of the
blood and the superficial or intermuscular system approximately 15 percent. A series of venous valves called the
perforating system interconnects the superficial and deep systems. In the standing posture, the veins of the leg have
to handle an exceptional load as they act against gravity when they return the blood to the heart. The venous valves
assist in maintaining the superficial-to-deep direction of the blood flow.[36]
•
•
•
•
•
•
•
Greater saphenous vein
Small saphenous
Femoral vein
Popliteal vein
Anterior tibial vein
Posterior tibial vein
Fibular vein
Nerves
Nerves of right leg, anterior and posterior aspects
The sensory and motor innervation to the lower limb is supplied by the lumbosacral plexus, which is formed by the
ventral rami of the lumbar and sacral spinal nerves with additional contributions from the subcostal nerve (T12) and
coccygeal nerve (Co1). Based on distribution and topography, the lumbosacral plexus is subdivided into the lumbar
plexus (T12-L4) and the Sacral plexus (L5-S4); the latter is often further subdivided into the sciatic and pudendal
plexuses:[37]
The lumbar plexus is formed lateral to the intervertebral foramina by the ventral rami of the first four lumbar spinal
nerves (L1-L4), which all pass through psoas major. The larger branches of the plexus exit the muscle to pass
sharply downward to reach the abdominal wall and the thigh (under the inguinal ligament); with the exception of the
obturator nerve which pass through the lesser pelvis to reach the medial part of the thigh through the obturator
foramen. The nerves of the lumbar plexus pass in front of the hip joint and mainly support the anterior part of the
thigh.[37] The iliohypogastric (T12-L1) and ilioinguinal nerves (L1) emerge out of the psoas major near the muscle's
origin, from where they run laterally downward to pass anteriorly above the iliac crest between the transversus
abdominis and abdominal internal oblique, and then run above the inguinal ligament. Both nerves give off muscular
branches to both these muscles. Iliohypogastric supplies sensory branches to the skin of the lateral hip region, and its
terminal branch finally pierces the aponeurosis of the abdominal external oblique above the inguinal ring to supply
sensory branches to the skin there. Ilioinguinalis exits through the inguinal ring and supplies sensory branches to the
skin above the pubic symphysis and the lateral portion of the scrotum.[38] The genitofemoral nerve (L1, L2) leaves
Human leg
65
psoas major below the two former nerves, immediately divides into two branches that descends along the muscle's
anterior side. The sensory femoral branch supplies the skin below the inguinal ligament, while the mixed genital
branch supplies the skin and muscles around the sex organ. The lateral femoral cutaneous nerve (L2, L3) leaves
psoas major laterally below the previous nerve, runs obliquely and laterally downward above the iliacus, exits the
pelvic area near the iliac spine, and supplies the skin of the anterior thigh.[38] The obturator nerve (L2-L4) passes
medially behind psoas major to exit the pelvis through the obturator canal, after which it gives off branches to
obturator externus and divides into two branches passing behind and in front of adductor brevis to supply motor
innervation to all the other adductor muscles. The anterior branch also supplies sensory nerves to the skin on a small
area on the distal medial aspect of the thigh.[39] The femoral nerve (L2-L4) is the largest and longest of the nerves of
the lumbar plexus. It supplies motor innervation to iliopsoas, pectineus, sartorius, and quadriceps; and sensory
branches to the anterior thigh, medial lower leg, and posterior foot.[39]
The nerves of the sacral plexus pass behind the hip joint to innervate the posterior part of the thigh, most of the
lower leg, and the foot.[37] The superior (L4-S1) and inferior gluteal nerves (L5-S2) innervate the gluteus muscles
and the tensor fascia latae. The posterior femoral cutaneous nerve (S1-S3) contributes sensory branches to the skin
on the posterior thigh.[40] The sciatic nerve (L4-S3), the largest and longest nerve in the human body, leaves the
pelvis through the greater sciatic foramen. In the posterior thigh if first gives off branches to the short head of the
biceps femoris and then divides into the tibial (L4-S3) and common fibular nerves (L4-S2). The fibular nerve
continues down on the medial side of biceps femoris, winds around the fibular neck and enters the front of the lower
leg. There it divides into a deep and a superficial terminal branch. The superficial branch supplies the peroneus
muscles and the deep branch enters the extensor compartment; both branches reaches into the dorsal foot. In the
thigh, the tibial nerve gives off branches to semitendinosus, semimembranosus, adductor magnus, and the long head
of the biceps femoris. The nerve then runs straight down the back of the leg, through the popliteal fossa to supply the
ankle flexors on the back of the lower leg and then continues down to supply all the muscles in the sole of the
foot.[41] The pudendal (S2-S4) and coccygeal nerves (S5-Co2) supply the muscles of the pelvic floor and the
surrounding skin.[42]
The picture on the top shows a woman's legs and the below picture a young male's legs in long shorts
The lumbosacral trunk is a communicating branch passing between the sacral and lumbar plexuses containing ventral
fibers from L4. The coccygeal nerve, the last spinal nerve, emerges from the sacral hiatus, unites with the ventral
rami of the two last sacral nerves, and forms the coccygeal plexus.[37]
Human leg
Fracture
A fracture of the leg (called "broken leg") can be classified according to the involved bone into:
• Femoral fracture (in the upper leg)
• Crus fracture (in the lower leg)
A crus fracture, in turn, can involve only the tibia (tibial fracture), only the fibula (fibular fracture) or both.
Cultural aspects
Adolescent and adult women in many Western cultures often remove the hair from their legs. Toned, tanned, shaved
legs are sometimes perceived as a sign of youthfulness and are often considered attractive in these cultures.
Men generally do not shave their legs in any culture. However, leg-shaving is a generally accepted practice in
modeling. It is also fairly common in sports where the hair removal makes the athlete appreciably faster by reducing
drag; the most common case of this is competitive swimming. It is also practised in many other sports, in which skin
injuries are common: the absence of grown hair makes nicks, scratches and bruises heal faster because of the reduced
microbial population on shaved skin.
Legs are often used metaphorically in many cultures to indicate either strength or mobility. The supporting columns
of an object may be referred to as legs as well, as in chair legs.
Notes
[1] http:/ / www. nlm. nih. gov/ cgi/ mesh/ 2011/ MB_cgi?mode=& term=Leg
[2] http:/ / www. mercksource. com/ pp/ us/ cns/ cns_hl_dorlands_split. jsp?pg=/ ppdocs/ us/ common/ dorlands/ dorland/ five/ 000058188. htm
[3] "Lower Extremity" (http:/ / www. nlm. nih. gov/ cgi/ mesh/ 2007/ MB_cgi?mode=& term=Lower+ Extremity& field=entry). Medical Subject
Headings (MeSH). National Library of Medicine. . Retrieved 2009-04-18.
[4] "lower limb" (http:/ / www. mercksource. com/ pp/ us/ cns/ cns_hl_dorlands_split. jsp?pg=/ ppdocs/ us/ common/ dorlands/ dorland/ five/
000060202. htm#000060202). Dorland's Medical Dictionary for Healthcare Consumers. Elsevier. . Retrieved 2009-04-18.
[5] "Leg" (http:/ / www. nlm. nih. gov/ cgi/ mesh/ 2007/ MB_cgi?mode=& term=Leg& field=entry). Medical Subject Headings (MeSH).
National Library of Medicine. . Retrieved 2009-04-18.
[6] "leg" (http:/ / www. mercksource. com/ pp/ us/ cns/ cns_hl_dorlands_split. jsp?pg=/ ppdocs/ us/ common/ dorlands/ dorland/ five/
000058188. htm). Dorland's Medical Dictionary for Healthcare Consumers. Elsevier. . Retrieved 2009-04-18.
[7] Merriam-Webster Dictionary leg (http:/ / www. m-w. com/ dictionary/ leg)
[8] leg (http:/ / www. emedicinehealth. com/ script/ main/ srchcont_dict. asp?src=leg) at eMedicine Dictionary
[9] Thieme Atlas of Anatomy (2006), p 360
[10] Thieme Atlas of Anatomy (2006), p 361
[11] Thieme Atlas of Anatomy (2006), p 362
[12] Platzer (2004), p 196
[13] Platzer (2004), pp 244-247
[14] Platzer, (2004), p 232
[15] Platzer (2004), p 234
[16] Platzer (2004), p 236
[17] Platzer (2004), p 238
[18] Platzer (2004), p 240
[19] Platzer (2004), p 242
[20] Platzer (2004), p 252
[21] Platzer (2004), p 248
[22] Platzer (2004), p 250
[23] Platzer (2004), p 264
[24] Platzer (2004), p 266
[25] Platzer (2004), p 256
[26] Platzer (2004), p 258
[27] Platzer (2004), p 260
[28] Chaitow (2000), p 554
[29] Platzer (2004), p 262
[30] Platzer (2004), p 268
66
Human leg
[31]
[32]
[33]
[34]
Platzer (2004), p 270
Platzer (2004), p 272
Platzer (2004), p 274
Thieme Atlas of Anatomy (2006), p 464
[35]
[36]
[37]
[38]
[39]
[40]
[41]
[42]
Platzer (2004), p 412
Thieme Atlas of Anatomy (2006), pp 466-467
Thieme Atlas of anatomy (2006), pp 470-471
Thieme Atlas of anatomy (2006), pp 472-473
Thieme Atlas of anatomy (2006), pp 474-475
Thieme Atlas of Anatomy (2006), p 476
Thieme Atlas of Anatomy (2006), pp 480-481
Thieme Atlas of Anatomy (2006), pp 482-483
References
• Chaitow, Leon; Walker DeLany, Judith (2000). Clinical Application of Neuromuscular Techniques: The Lower
Body (http://books.google.com/?id=09fssXGvlrIC&pg=PA554). Elsevier Health Sciences. ISBN 0443062846.
• consulting editors, Lawrence M. Ross, Edward D. Lamperti; authors, Michael Schuenke, Erik Schulte, Udo
Schumacher. (2006). Thieme Atlas of Anatomy: General Anatomy and Musculoskeletal System. Thieme.
ISBN 1-58890-419-9.
• Platzer, Werner (2004). Color Atlas of Human Anatomy, Vol. 1: Locomotor System (5th ed.). Thieme.
ISBN 3-13-533305-1.
External links
• Interactive Rotation of Leg Arteries and Veins (http://www.landholt.com/Interactive/Rotation_AV)
67
Knee
68
Knee
Knee
Right knee
Latin
articulatio genus
Gray's
subject #93 339
Nerve
femoral, obturator, sciatic
MeSH
Knee
[1]
[2]
Dorlands/Elsevier Knee [3]
The knee joint joins the thigh with the leg and consists of two articulations: one between the femur and tibia, and
[4]
[5]
one between the femur and patella. It is the largest joint in the human body and is very complicated. The knee is
[6]
a mobile trocho-ginglymus (i.e. a pivotal hinge joint), which permits flexion and extension as well as a slight
medial and lateral rotation. Since in humans the knee supports nearly the whole weight of the body, it is vulnerable
to both acute injury and the development of osteoarthritis.
It is often grouped into tibiofemoral and patellofemoral components.[7]
considered with tibiofemoral components.)[9]
[8]
(The fibular collateral ligament is often
Human anatomy
The knee is a complex, compound, condyloid variety of a synovial
joint. It actually comprises three functional compartments: the
femoropatellar articulation consists of the patella, or "kneecap", and
the patellar groove on the front of the femur through which it slides;
and the medial and lateral femorotibial articulations linking the femur,
or thigh bone, with the tibia, the main bone of the lower leg.[10] The
joint is bathed in synovial fluid which is contained inside the synovial
membrane called the joint capsule.
Articular surfaces of femur.
Upon birth, a baby will not have a conventional knee cap, but a growth formed of cartilage. In females this turns to a
normal bone knee cap by the age of 3, in males the age of 5.
Knee
69
Articular bodies
The articular bodies of the femur are its lateral and medial condyles.
These diverge slightly distally and posteriorly, with the lateral condyle
being wider in front than at the back while the medial condyle is of
more constant width.[11] The radius of the condyles' curvature in the
sagittal plane becomes smaller toward the back. This diminishing
radius produces a series of involute midpoints (i.e. located on a spiral).
The resulting series of transverse axes permit the sliding and rolling
motion in the flexing knee while ensuring the collateral ligaments are
sufficiently lax to permit the rotation associated with the curvature of
the medial condyle about a vertical axis.[12]
Articular surfaces of tibia.
The pair of tibial condyles are separated by the intercondylar eminence[11] composed of a lateral and a medial
[13]
tubercle.
The patella is inserted into the thin anterior wall of the joint capsule.[11] On its posterior surface is a lateral and a
medial articular surface,[12] both of which communicate with the patellar surface which unites the two femoral
condyles on the anterior side of the bone's distal end.[14] A common disease found in the knee is "Tartas".
Articular capsule
Lateral and posterior aspects of right knee
The articular capsule has a synovial and a fibrous membrane separated by fatty deposits. Anteriorly, the synovial
membrane is attached on the margin of the cartilage both on the femur and the tibia, but on the femur, the
[15]
The suprapatellar bursa is prevented from being
suprapatellar bursa or recess extends the joint space proximally.
[16]
pinched during extension by the articularis genu muscle.
Behind, the synovial membrane is attached to the
margins of the two femoral condyles which produces two extensions similar to the anterior recess. Between these
two extensions, the synovial membrane passes in front of the two cruciate ligaments at the center of the joint, thus
forming a pocket direct inward.[15]
Bursae
Numerous bursae surround the knee joint. The largest communicative bursa is the suprapatellar bursa described
above. Four considerably smaller bursae are located on the back of the knee. Two non-communicative bursae are
located in front of the patella and below the patellar tendon, and others are sometimes present. [15]
Cartilage
Cartilage is a thin, elastic tissue that protects the bone and makes certain that the joint surfaces can slide easily over
each other. Cartilage ensures supple knee movement. There are two types of joint cartilage in the knees: fibrous
cartilage (the meniscus) and hyaline cartilage. Fibrous cartilage has tensile strength and can resist pressure. Hyaline
cartilage covers the surface along which the joints move. Cartilage will wear over the years. Cartilage has a very
Knee
70
limited capacity for self-restoration. The newly formed tissue will generally consist for a large part of fibrous
cartilage of lesser quality than the original hyaline cartilage. As a result, new cracks and tears will form in the
cartilage over time.
Menisci
The articular disks of the knee-joint are called menisci because they only partly divide the joint space.[17] These two
disks, the medial meniscus and the lateral meniscus, consist of connective tissue with extensive collagen fibers
containing cartilage-like cells. Strong fibers run along the menisci from one attachment to the other, while weaker
radial fibers are interlaced with the former. The menisci are flattened at the center of the knee joint, fused with the
synovial membrane laterally, and can move over the tibial surface. [18]
The menisci serve to protect the ends of the bones from rubbing on each other and to effectively deepen the tibial
sockets into which the femur attaches. They also play a role in shock absorption, and may be cracked, or torn, when
the knee is forcefully rotated and/or bent.
Ligaments
The ligaments surrounding the knee joint offer stability by limiting
movements and, together with several menisci and bursae, protect the
articular capsule.
Intracapsular
The knee is stabilized by a pair of cruciate ligaments. The anterior
cruciate ligament (ACL) stretches from the lateral condyle of femur to
the anterior intercondylar area. The ACL is critically important
because it prevents the tibia from being pushed too far anterior relative
to the femur. It is often torn during twisting or bending of the knee.
The posterior cruciate ligament (PCL) stretches from medial condyle
of femur to the posterior intercondylar area. Injury to this ligament is
uncommon but can occur as a direct result of forced trauma to the
ligament. This ligament prevents posterior displacement of the tibia
relative to the femur.
The transverse ligament stretches from the lateral meniscus to the
medial meniscus. It passes in front of the menisci. Is divided into
several strips in 10% of cases.[18] The two menisci are attached to each
others anteriorly by the ligament.[19] The posterior and anterior
meniscofemoral ligaments stretch from posterior horn of lateral
meniscus to the medial femoral condyle. They pass posteriorly behind
the posterior cruciate ligament. The posterior meniscofemoral ligament
is more commonly present (30%); both ligaments are present less
often.[18] The meniscotibial ligaments (or "coronary") stretches from
inferior edges of the mensici to the periphery of the tibial plateaus.
Anterolateral aspect of right knee.
Anteromedial aspect of knee
Extracapsular
The patellar ligament connects the patella to the tuberosity of the tibia. It is also occasionally called the patellar
tendon because there is no definite separation between the quadriceps tendon (which surrounds the patella) and the
Knee
71
area connecting the patella to the tibia.[20] This very strong ligament helps give the patella its mechanical leverage[21]
and also functions as a cap for the condyles of the femur. Laterally and medially to the patellar ligament the lateral
and medial patellar retinacula connect fibers from the vasti lateralis and medialis muscles to the tibia. Some fibers
from the iliotibial tract radiate into the lateral retinaculum and the medial retinaculum receives some transverse
fibers arising on the medial femoral epicondyle. [11]
The medial collateral ligament (MCL a.k.a. "tibial") stretches from the medial epicondyle of the femur to the medial
tibial condyle. It is composed of three groups of fibers, one stretching between the two bones, and two fused with the
medial meniscus. The MCL is partly covered by the pes anserinus and the tendon of the semimembranosus passes
under it.[11] It protects the medial side of the knee from being bent open by a stress applied to the lateral side of the
knee (a valgus force). The lateral collateral ligament (LCL a.k.a. "fibular") stretches from the lateral epicondyle of
the femur to the head of fibula. It is separate from both the joint capsule and the lateral meniscus.[11] It protects the
lateral side from an inside bending force (a varus force).
Lastly, there are two ligaments on the dorsal side of the knee. The oblique popliteal ligament is a radiation of the
tendon of the semimembranosus on the medial side, from where it is direct laterally and proximally. The arcuate
popliteal ligament originates on the apex of the head of the fibula to stretch proximally, crosses the tendon of the
popliteus muscle, and passes into the capsule.[11]
Movements
Maximum movements[22] and muscles[23]
Extension 5-10°
Flexion 120-150°
(In order of importance)
Quadriceps (with
Semimembranosus
some assistance from
the Tensor fasciae latae) Semitendinosus
Biceps femoris
Gracilis
Sartorius
Popliteus
Gastrocnemius
Internal rotation* 10°
External rotation* 30-40°
(In order of importance) Biceps femoris
Semimembranosus
Semitendinosus
Gracilis Sartorius
Popliteus
*(knee flexed 90°)
The knee permits flexion and extension about a virtual transverse axis, as well as a slight medial and lateral rotation
about the axis of the lower leg in the flexed position. The knee joint is called "mobile" because the femur and lateral
meniscus move[24] over the tibia during rotation, while the femur rolls and glides over both menisci during
extension-flexion.[25]
The center of the transverse axis of the extension/flexion movements is located where both collateral ligaments and
both cruciate ligaments intersect. This center moves upward and backward during flexion, while the distance
between the center and the articular surfaces of the femur changes dynamically with the decreasing curvature of the
femoral condyles. The total range of motion is dependent on several parameters such as soft-tissue restraints, active
insufficiency, and hamstring tightness.[22]
Knee
72
Extended position
With the knee extended both the lateral and medial collateral ligaments, as well as the anterior part of the anterior
cruciate ligament, are taut. During extension, the femoral condyles glide into a position which causes the complete
unfolding of the tibial collateral ligament. During the last 10° of extension, an obligatory terminal rotation is
triggered in which the knee is rotated medially 5°. The final rotation is produced by a lateral rotation of the tibia in
the non-weight-bearing leg, and by a medial rotation of the femur in the weight-bearing leg. This terminal rotation is
made possible by the shape of the medial femoral condyle, assisted by contraction of the popliteus muscle and the
iliotibial tract and is caused by the stretching of the anterior cruciate ligament. Both cruciate ligaments are slightly
unwinded and both lateral ligaments become taut.[25]
Flexed position
In the flexed position, the collateral ligaments are relaxed while the cruciate ligaments are taut. Rotation is controlled
by the twisted cruciate ligaments; the two ligaments get twisted around each other during medial rotation of the tibia
— which reduces the amount of rotation possible — while they become unwounded during lateral rotation of the
tibia. Because of the oblique position of the cruciate ligaments at least a part of one of them is always tense and these
ligaments control the joint as the collateral ligaments are relaxed. Furthermore, the dorsal fibers of the tibial
collateral ligament become tensed during extreme medial rotation and the ligament also reduces the lateral rotation
to 45-60°.[25]
Blood supply
The femoral artery and the popliteal artery help form the arterial
network surrounding the knee joint (articular rete). There are 6 main
branches:
• 1. Superior medial genicular artery
• 2. Superior lateral genicular artery
• 3. Inferior medial genicular artery
• 4. Inferior lateral genicular artery
• 5. Descending genicular artery
• 6. Recurrent branch of anterior tibial artery
The medial genicular arteries penetrate the knee joint.
Arteries of the knee
Disorders and injury
Knee pain is caused by trauma, misalignment, and degeneration as well as by conditions like arthritis.[26] The most
common knee disorder is generally known as patellofemoral syndrome.The majority of minor cases of knee pain can
be treated at home with rest and ice but more serious injuries do require surgical care.[27]
One form of patellofemoral syndrome involves a tissue-related problem that creates pressure and irritation in the
knee between the patella and the trochlea (patellar compression syndrome), which causes pain. The second major
class of knee disorder involves a tear, slippage, or dislocation that impairs the structural ability of the knee to balance
the leg (patellofemoral instability syndrome). Patellofemoral instability syndrome may cause either pain, a sense of
poor balance, or both.[28]
Age also contributes to disorders of the knee. Particularly in older people, knee pain frequently arises due to
osteoarthritis. In addition, weakening of tissues around the knee may contribute to the problem.[29] Patellofemoral
instability may relate to hip abnormalities or to tightness of surrounding ligaments.[28]
Knee
73
Cartilage lesions can be caused by:
•
•
•
•
•
•
Accidents (fractures)
Injuries
The removal of a meniscus
Anterior cruciate ligament injury
Posterior cruciate ligament injury
Considerable strain on the knee.
Any kind of work during which the knees undergo heavy stress may also be detrimental to cartilage. This is
especially the case in professions in which people frequently have to walk, lift, or squat. Other causes of pain may be
excessive on, and wear of, the knees, in combination with such things as muscle weakness and overweight.
Common complaints:
• A painful, blocked, locked or swollen knee.
• Sufferers sometimes feel as if their knees are about to give way, or may feel uncertain about their movement.
The pain felt by people with cartilage injury does not come from the cartilage itself, but from the irritated tissue
surrounding the cartilage, or from pieces of cartilage that have come loose. If cartilage injury goes untreated, the
layer of cartilage will continue to gradually wear away, causing arthrosis and gradual immobility.
Overall fitness and knee injury
Physical fitness is related integrally to the development of knee problems. The same activity such as climbing stairs
may cause pain from patellofemoral compression for someone who is physically unfit, but not for someone else (or
even for that person at a different time). Obesity is another major contributor to knee pain. For instance, a
30-year-old woman who weighed 120 lb at age 18 years, before her three pregnancies, and now weighs 285 lb, had
added 660 lb of force across her patellofemoral joint with each step.[30]
Common injuries due to physical activity
In sports that place great pressure on the knees, especially with
twisting forces, it is common to tear one or more ligaments or
cartilages.
Anterior cruciate ligament injury
ACL is the most commonly injured ligament of the knee. The injury is
common during sports. Twisting of the knee is a common cause of
over-stretching or tearing the ACL. When the ACL is injured one may
hear a popping sound and the leg may suddenly give out. Besides
swelling and pain, walking may be painful and the knee will feel
unstable. Minor tears of the anterior cruciate ligament may heal over
time, but a torn ACL requires surgery. After surgery, recovery is
prolonged and low impact exercises are recommended to strengthen
the joint.[31]
Model demonstrating parts of an artificial knee
Torn meniscus injury
Knee
74
The menisci act as shock absorbers and separate the two ends of bone in the knee joint. There are two menisci in the
knee, the medial (inner) and the lateral (outer). When there is torn cartilage, it means that the meniscus has been
injured. Meniscus tears occur during sports often when the knee is twisted. Menisci injury may be innocuous and one
may be able to walk after a tear, but soon swelling and pain set in. Sometimes the knee will lock while bending. Pain
often occurs when one squats. Small meniscus tears are treated conservatively but most large tears require
surgery.[32]
Fractures
Knee fractures are rare but do occur, especially as a result of motor vehicle accidents. There is usually immediate
pain; swelling and one may not be able to stand on the leg. The muscles go into spasm and even the slightest
movements are painful. X-rays can easily confirm the injury and surgery depends on the degree of displacement and
type of fracture.
Ruptured tendon
Tendons usually attach muscle to bone. In the knee the quadriceps and patellar tendon can sometimes tear. The
injuries to these tendons occur when there is forceful contraction of the knee. If the tendon is completely torn,
bending or extending the leg is impossible. A completely torn tendon requires surgery but a partially torn tendon can
be treated with leg immobilization followed by physical therapy.
Overuse
Overuse injuries of the knee include tendonitis, bursitis, muscle strains and iliotibial band syndrome. These injuries
often develop slowly over weeks or months. Activities that induce pain usually delay healing. Rest, ice and
compression do help in most cases. Once the swelling has diminished, heat packs can increase blood supply and
promote healing. Most overuse injuries subside with time but can flare up if the activities are quickly resumed.[33] To
prevent overuse injuries, warm up prior to exercise, limit high impact activities and keep your weight under control.
Surgical interventions
Before the advent of arthroscopy and arthroscopic surgery, patients having surgery for a torn ACL required at least
nine months of rehabilitation, having initially spent several weeks in a full-length plaster cast. With current
techniques, such patients may be walking without crutches in two weeks, and playing some sports in a few months.
In addition to developing new surgical procedures, ongoing research is looking into underlying problems which may
increase the likelihood of an athlete suffering a severe knee injury. These findings may lead to effective preventive
measures, especially in female athletes, who have been shown to be especially vulnerable to ACL tears from
relatively minor trauma.
Articular cartilage repair treatment :
•
•
•
•
•
Arthroscopic debriment of the knee (arthroscopic lavage).
Mosaïc-plasty.
Microfracture (Ice-picking).
Autologous Chondrocyte Implantation.
Osteochondral Autograft and Allografts.
Knee
75
Diagnostics
The ideal diagnostic test for assessing knee pain are the standard AP and lateral views of plain x-rays as a person in
knee pain may not be able to stand. Magnetic resonance imaging is often used for diagnosing soft tissue injuries of
the knee. But sometimes it can be overly sensitive; and can even detect tears and signs of inflammation in people
who have no pain in their knees. Arthroscopy may be used to examine the knee as well as perform surgical tasks like
removal of free fragments and repair of meniscal and ligament injuries.
Several diagnostic maneuvers help clinicians diagnose an injured ACL. In the anterior drawer test, the examiner
applies an anterior force on the proximal tibia with the knee in 90 degrees of flexion. The Lachman test is similar,
but performed with the knee in only about twenty degrees of flexion, which is more comfortable to a patient in acute
pain. The pivot-shift test adds a valgus (outside-in) force to the knee while it is moved from flexion to extension.
Any abnormal motion in these maneuvers, suggests a tear of the collateral or cruciate ligaments of the knee.
The diagnosis of soft tissue injuries is usually confirmed by MRI, while that of bone injuries by a CT Scan. The
availability of sophisticated investigations, like CT Scan with 3D reconstruction, has greatly decreased the number of
purely diagnostic arthroscopies performed.
Animal anatomy
In humans the knee refers to the joints between the femur, tibia and patella. In quadrupeds, particularly horses and
ungulates the term is commonly used to refer to the carpus, probably because of its similar hinge or ginglymus
action. The joints between the femur, tibia and patella are known as the stifle in quadrupeds. In insects and other
animals the term knee is used widely to refer to any ginglymus joint.
Additional images
Knee MR Knee
76
Knee MR Knee X-ray Knee
77
Cruciate ligaments Left knee-joint from behind, showing
interior ligaments. Knee
78
Capsule of right knee-joint (distended).
Lateral aspect. Anterior and lateral view of knee. Notes
[1] http:/ / education. yahoo. com/ reference/ gray/ subjects/ subject?id=93#p339
[2]
[3]
[4]
[5]
[6]
[7]
http:/ / www. nlm. nih. gov/ cgi/ mesh/ 2011/ MB_cgi?mode=& term=Knee
http:/ / www. mercksource. com/ pp/ us/ cns/ cns_hl_dorlands_split. jsp?pg=/ ppdocs/ us/ common/ dorlands/ dorland/ five/ 000056558. htm
knee+joint (http:/ / www. emedicinehealth. com/ script/ main/ srchcont_dict. asp?src=knee+ joint) at eMedicine Dictionary
Kulowski (1932), p 618
See trochoid and ginglymus.
Rytter S, Egund N, Jensen LK, Bonde JP (2009). "Occupational kneeling and radiographic tibiofemoral and patellofemoral osteoarthritis"
(http:/ / www. occup-med. com/ content/ 4/ / 19). J Occup Med Toxicol 4: 19. doi:10.1186/1745-6673-4-19. PMC 2726153. PMID 19594940.
.
[8] Gill TJ, Van de Velde SK, Wing DW, Oh LS, Hosseini A, Li G (December 2009). "Tibiofemoral and patellofemoral kinematics after
reconstruction of an isolated posterior cruciate ligament injury: in vivo analysis during lunge" (http:/ / ajs. sagepub. com/ cgi/
pmidlookup?view=long& pmid=19726621). Am J Sports Med 37 (12): 2377–85. doi:10.1177/0363546509341829. PMID 19726621. .
[9] Scott J, Lee H, Barsoum W, van den Bogert AJ (November 2007). "The effect of tibiofemoral loading on proximal tibiofibular joint motion"
(http:/ / www3. interscience. wiley. com/ resolve/ openurl?genre=article& sid=nlm:pubmed& issn=0021-8782& date=2007& volume=211&
issue=5& spage=647). J. Anat. 211 (5): 647–53. doi:10.1111/j.1469-7580.2007.00803.x. PMC 2375777. PMID 17764523. .
[10] Burgener (2002), p 390
[11] Platzer (2004), p 206
[12] Platzer (2004), pp 194-195
[13] Platzer (2004), p 202
[14] Platzer (2004), p 192
[15] Platzer (2004), p 210
Knee
[16] B Reider, JL Marshall, B Koslin, B Ring and FG Girgis (1981). "The anterior aspect of the knee joint" (http:/ / www. ejbjs. org/ cgi/ reprint/
63/ 3/ 351. pdf). J Bone Joint Surg Am. 1981;63:351-356.. . Retrieved 2010-08-17.
[17] Platzer (2004), p 26
[18] Platzer (2004), p 208
[19] Diab (1999), p 200
[20] MedicineNet.com, Definition of Patellar tendon
[21] Moore (2006), p 194
[22] Thieme Atlas of Anatomy (2006), pp 398-399
[23] Platzer (2004), p 252
[24] Thieme Atlas of Anatomy (2006), p 399
[25] Platzer (2004), pp 212-213
[26] " Back of Knee Pain Causes (http:/ / healthlifeandstuff. com/ 2009/ 07/ back-of-knee-pain-causes/ )
[27] Knee anatomy facts and myths (http:/ / www. kneeanatomy. net/ ) 2010-01-26
[28] Afra R and Schepsis A (May 28, 2008). "Addressing patellofemoral pathology: Biomechanics and classification" (http:/ / jmm.
consultantlive. com/ article/ 1145622/ 1403741). The Journal of Musculoskeletal Medicine. .
[29] Pill SG, Khoury LD, Chin GC et al. (October 29, 2008). "MRI for evaluating knee pain in older patients: How useful is it?" (http:/ / jmm.
consultantlive. com/ display/ article/ 1145622/ 1404837). The Journal of Musculoskeletal Medicine. .
[30] Andrish JT (May 8, 2009). "Sports injuries in weekend warriors: 20 Clinical pearls" (http:/ / jmm. consultantlive. com/ display/ article/
1145622/ 1412245). The Journal of Musculoskeletal Medicine 26 (5). .
[31] Knee pain and injuries (http:/ / sportsmedicine. about. com/ od/ kneepainandinjuries/ Knee_Pain_and_Injuries. htm) About sports online
portal. 2010-01-26
[32] Tandeter, Howard B. "Acute Knee Injuries: Use of Decision Rules for Selective Radiograph Ordering" (http:/ / www. aafp. org/ afp/
991201ap/ 2599. html) 2010-01-26.
[33] Knee injuries and disorders (http:/ / www. nlm. nih. gov/ medlineplus/ kneeinjuriesanddisorders. html) MedLine Plus. 2010-01-26
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Resonance Imaging (http://books.google.com/?id=brsH_IqPzzoC&pg=PA390). Thieme. ISBN 1588900851.
• Diab, Mohammad (1999). Lexicon of Orthopaedic Etymology (http://books.google.com/?id=fstFQVnw8-wC&
pg=PA200). Taylor & Francis. ISBN 9057025973.
• Kulowski, Jacob (1932). Flexion Contracture of the Knee: The Mechanics of the Muscular Contracture and the
Turnbuckle Cast Method of Treatment (http://www.ejbjs.org/cgi/reprint/14/3/618.pdf). Journal of Bone and
Joint Surgery.
• Moore, Keith L.; Dalley, Arthur F.: Agur, A. M. R. (2006). Clinically Oriented Anatomy (http://books.google.
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• Platzer, Werner (2004). Color Atlas of Human Anatomy, Vol. 1: Locomotor System (5th ed.). Thieme.
pp. 206–213. ISBN 3-13-533305-1.
• "Definition of patellar tendon" (http://www.medterms.com/script/main/art.asp?articlekey=34200).
MedicineNet.com. Retrieved 2008-12-11.
• Thieme Atlas of Anatomy: General Anatomy and Musculoskeletal System. Thieme. 2006. ISBN 1-58890-419-9.
79
Ladle (spoon)
80
Ladle (spoon)
A ladle is a type of spoon used to scoop up and serve
soup, lasagne, or other foods. Although designs vary,
a typical ladle has a long handle terminating in a
deep bowl, frequently with the bowl oriented at an
angle to the handle to facilitate lifting liquid out of a
pot or other vessel and conveying it to a bowl. Some
ladles involve a point on the side of the basin to
allow for finer stream when pouring the liquid;
however, this can create difficulty for left handed
users, as it is easier to pour towards one's self. Thus,
many of these ladles feature such pinches on both
sides. Ladles are usually made of the same stainless
steel alloys as other kitchen utensils; however, they
can be made of aluminium, silver, plastics, melamine
resin, wood, bamboo or other materials. Ladles are
made in a variety of sizes, the larger ones being
about 1 foot (30 cm) in length, with the different
sizes tailored to the intended use.
Sterling silver ladle - hallmarked London silver 1876-7 (on 5cm
squares)
Aluminium ladle (on 5cm squares)
Melamine ladle (on 5cm squares)
Stainless steel ladle (on 5cm squares)
Ladle (spoon)
81
Copper alloy ladle
Meat slicer
A meat slicer, also called a slicing machine, deli
slicer or simply a slicer, is a tool used in butcher
shops and delicatessens to slice meats and cheeses.
The first meat slicer was invented by Wilhelm van
Berkel in Rotterdam in 1898.[1] [2] [3] Older models of
meat slicer may be operated by crank, while newer
ones generally use an electric motor.[4]
More recently, meat slicers have become available in
the home market for people wanting to slice their own
meats and cheeses.[5]
References
[1] Feith, Jan (1922). Modern Holland. Nijgh & van Ditmar's
Publishing Co.,ltd. pp. 245.
Antique meat slicer.
[2] "Berkel" (http:/ / www. averyberkel. com/ main. aspx?p=1. 1.
3. 7). Avery Berkel. . Retrieved 2008-10-05.
[3] "Company history" (http:/ / www. berkelcompany. com/ details. cfm?id=61). Berkel. . Retrieved 2008-10-05.
[4] "Vintage Hand-cranked Meat Slicers Popular Among ‘Green’ Chefs and Restaurants" (http:/ / www. emiliomiti. com/ restaurant-news/
vintage-hand-cranked-meat-slicers-popular-among-green-chefs-and-restaurants/ ). Emiliomiti LLC. . Retrieved 2008-10-05.
[5] Chu, Louisa. "Ultimate Boy Toy Meat slicers come out from behind the butcher counter" (http:/ / www. chow. com/ stories/ 10197). Chow. .
Retrieved 2008-10-05.
Nail (anatomy)
82
Nail (anatomy)
Fingernails
Toenails
A nail is a horn-like envelope covering the dorsal aspect of the terminal phalanges of fingers and toes in humans,
most non-human primates, and a few other mammals. Nails are similar to claws, which are found on numerous other
animals. Fingernails and toenails are made of a tough protein called keratin, as are animals' hooves and horns. The
mammalian nail, claw, and hoof are all examples of unguis [plural ungues].
Human anatomy
The nail consists of the nail plate, the nail matrix and the nail bed below it, and the grooves surrounding it.[1]
Parts of the nail
Nail
Basic nail anatomy
Latin
unguis
Code
TH H3.12.00.3.02001
The matrix (synonyms:[2] matrix unguis, keratogenous membrane, nail matrix, onychostroma) is the tissue (or
germinal matrix) upon which the nail rests,[3] the part of the nail bed that extends beneath the nail root and contains
nerves, lymph and blood vessels.[4] The matrix is responsible for the production of the cells that become the nail
plate. The width and thickness of the nail plate is determined by the size, length, and thickness of the matrix, while
the shape of the fingertip itself determines if the nail plate is flat, arched, or hooked.[5] The matrix will continue to
grow as long as it receives nutrition and remains in a healthy condition.[4] As new nail plate cells are incubated, they
emerge from the matrix round and white to push older nail plate cells forward; and in this way yet older cells become
compressed, flat, and translucent, making the pink colour of the capillaries in the nail bed below visible.[6]
The lunula (occasionally called simply "the moon") is the visible part of the matrix, the whitish crescent-shaped base
[7]
of the visible nail. The lunula is largest in the thumb and often absent in the little finger.
Nail (anatomy)
The nail bed is the skin beneath the nail plate.[7] Like all skin, it is composed of two types of tissues: the deeper
dermis, the living tissue fixed to the bone which contains capillaries and glands,[8] and the superficial epidermis, the
layer just beneath the nail plate which moves forward with the plate. The epidermis is attached to the dermis by tiny
longitudinal "grooves"[5] known as the matrix crests or crests of nail matrix (cristae matricis unguis).[3] [8] As we
age, the plate grows thinner and these ridges become evident in the plate itself.[5]
The nail sinus (sinus unguis) is the deep furrow into which the nail root is inserted.[3]
The nail root (radix unguis) is the part of nail situated in the nail sinus,[3] i.e. the base of the nail embedded
underneath the skin. It originates from the actively growing tissue below, the matrix.[4]
The nail plate or body of nail (corpus unguis)[3] is the actual nail, and like hair and skin, made of translucent keratin
protein made of amino acids. In the nail it forms a strong flexible material made of several layers of dead, flattened
cells.[5] The plate appears pink because of the underlying capillaries.[7] Its (transversal) shape is determined by the
form of the underlying bone.[5] In common usage, the word nail often refers to the this part only.
The free margin (margo liber) or distal edge is the anterior margin of the nail plate corresponding to the abrasive or
cutting edge of the nail.[3] The hyponychium (informally known as the "quick")[9] is the epithelium located beneath
the nail plate at the junction between the free edge and the skin of the fingertip. It forms a seal that protects the nail
bed.[4] The onychodermal band is the seal between the nail plate and the hyponychium. It is found just under the
free edge, in that portion of the nail where the nail bed ends and can be recognized by its glassy, greyish colour (in
fair-skinned people). It is not perceptible in some individuals while it is highly prominent on others.[5]
The eponychium is the small band of epithelium that extends from the posterior nail wall onto the base of the nail.[3]
Often and erroneously called the "proximal fold" or "cuticle", the eponychium is the end of the proximal fold that
folds back upon itself to shed an epidermal layer of skin onto the newly formed nail plate. This layer of non-living,
almost invisible skin is the cuticle that "rides out" on the surface of the nail plate. Together, the eponychium and the
cuticle form a protective seal. The cuticle on the nail plate is dead cells and is often removed during manicure, but
the eponychium is living cells and should not be touched.[6] The perionyx is the projecting edge of the eponychium
covering the proximal strip of the lunula.[3]
The nail wall (vallum unguis) is the cutaneous fold overlapping the sides and proximal end of the nail. The lateral
margin (margo lateralis) is lying beneath the nail wall on the sides of the nail and the nail groove or fold (sulcus
matricis unguis) are the cutaneous slits into which the lateral margins are embedded.[3]
The paronychium is the border tissue around the nail[10] and paronychia is an infection in this area.
Function
Aesthetics aside, a healthy (finger)nail has the function of protecting the distal phalanx, the fingertip, and the
surrounding soft tissues from injuries. It also serves to enhance precise delicate movements of the distal digits
through counter-pressure exerted on the pulp of the finger. [1] The nail then acts as a counterforce when the end of
the finger touches an object, thereby enhancing the sensitivity of the fingertip,[11] even though there are no nerve
endings in the nail itself. Finally, the nail functions as a tool, enabling for instance a so called "extended precision
grip" (e.g. pulling out a splinter in one's finger).
83
Nail (anatomy)
84
Growth
The growing part of the nail is the part still under the skin at the nail's proximal end under the epidermis, which is the
only living part of a nail.
In mammals, the length and growth rate of nails is related to the length of the terminal phalanges (outermost finger
bones). Thus, in humans, the nail of the index finger grows faster than that of the little finger; and fingernails grow
up to four times faster than toenails. [12]
In humans, nails grow at an average rate of 3 mm (0.12 in) a month (as they are a form of hair).[13] Fingernails
require 3 to 6 months to regrow completely, and toenails require 12 to 18 months. Actual growth rate is dependent
upon age, gender, season, exercise level, diet, and hereditary factors. Nails grow faster in the summer than in any
other season.[14] Contrary to popular belief, nails do not continue to grow after death; the skin dehydrates and
tightens, making the nails (and hair) appear to grow.[15]
Medical aspects
Healthcare and pre-hospital-care providers (EMTs or paramedics)
often use the fingernail beds as a cursory indicator of distal tissue
perfusion of individuals that may be dehydrated or in shock.[16]
However, this test is not considered reliable in adults.[17] This is known
as the CRT or blanch test.
WEJ Procedure: briefly depress the fingernail bed gently with a finger.
This will briefly turn the nailbed white; the normal pink colour should
be restored within a second or two. Delayed return to pink colour can
be an indicator of certain shock states such as hypovolemia [18] [19]
Thumbnail of the right hand with cuticle (left)
and hangnail (top)
Nail growth record can show the history of recent health and
physiological imbalances, and has been used as a diagnostic tool since
ancient times.[20] Deep transverse grooves known as Beau's lines may
form across the nails (not along the nail from cuticle to tip) and are
usually a natural consequence of aging, though they may result from
disease. Discoloration, thinning, thickening, brittleness, splitting,
grooves, Mees' lines, small white spots, receded lunula, clubbing
(convex), flatness, spooning (concave) can indicate illness in other
areas of the body, nutrient deficiencies, drug reaction or poisoning, or
Mechanical injury can result in the nail being
merely local injury. Nails can also become thickened
dropped.
(onychogryphosis), loosened (onycholysis), infected with fungus
(onychomycosis) or degenerate (onychodystrophy); for further information see nail diseases.
Health and care
Bluish or purple fingernail beds may be a symptom of peripheral cyanosis, which indicates oxygen deprivation.
Nails can dry out, just like skin. They can also peel, break, and be infected. Toe infections, for instance, can be
caused or exacerbated by dirty socks, specific types of aggressive exercise, tight footwear, and walking unprotected
in an unclean environment.
Nail tools used by different people may transmit infections. Nail files, "if ... used on different people, ... may spread
nail fungi, staph bacteria or viruses," warns Ted Dischman, a spokesperson for the California Board of Barbering and
Cosmetology.germs In fact, over 100 bacterial skin infections in 2000 were traced to footbaths in nail salons. To avoid
this, new improved contactless tools can be used, for example, gel and cream cuticle removers instead of cuticle
Nail (anatomy)
scissors.
Many people also compulsively bite their nails.
Nail disease can be very subtle and should be evaluated by a
dermatologist with a focus in this particular area of medicine.[21]
However, most times it is a nail technician who will note a subtle
change in nail disease.
Inherited accessory nail of the fifth toe occurs where the toenail of the
smallest toe is separated, forming a smaller, "sixth toenail" in the outer
corner of the nail. Like any other nail, it can be cut using a nail clipper.
Nutrition for healthy nails
Vitamin A is an essential micronutrient for vision, reproduction, cell
and tissue differentiation, and immune function. Vitamin D and
calcium work together in cases of maintaining homeostasis, creating
muscle contraction, transmission of nerve pulses, blood clotting, and
membrane structure. A lack of vitamin A, vitamin D, and calcium can
cause dryness and brittleness. Sources of these micronutrients include
fortified milk, cereal, and juices, salt-water fish, fish-liver oils, and
Damaged thumbnail
some vegetables. Vitamin B12 can only be found in animal sources
such as liver and kidney, fish, chicken, and dairy products and
therefore can cause intake issues in vegetarian and vegan populations. Not enough B12 vitamin can lead to excessive
dryness, darkened nails, and rounded or curved nail ends. Insufficient intake of both vitamin A and B, as previously
described, results in fragile nails with horizontal and vertical ridges.[22] Protein is a building material for new nails,
therefore low dietary protein intake may cause white nail beds. Dietary sources of this macronutrient include eggs,
milk, cheese, meat, beans and legumes. A lack of protein combined with deficiencies in folic acid and vitamin C
produce ‘hangnails’. Essential fatty acids play a large role in healthy skin as well as nails. As touched upon
previously, essential fatty acids can be obtained through consumption of fish, flaxseed, canola oil, seeds, leafy
vegetables, and nuts. Splitting and flaking of nails may be due to a lack of linoleic acid. Iron-deficiency anemia can
lead to a pale color along with a thin, brittle, ridged texture. Iron deficiency in general may cause the nails to become
flat or concave, rather than convex. Iron can be found in animal sources, called heme iron, such as meat, fish, and
poultry, and can also be found in fruits, vegetables, dried beans, nuts, and grain products, also known as non-heme
iron. Heme iron is absorbed fairly easily in comparison to non-heme iron, however both types provide the necessary
bodily functions.[23]
Fashion
Manicures and pedicures are health and cosmetic procedures to groom, trim, and paint the nails and manage calluses.
They require various tools such as cuticle scissors, nail scissors, nail clippers, and nail files. Artificial nails can also
be appended onto real nails for cosmetic purposes.
A person whose occupation is to cut, shape and care for nails as well as to apply overlays such as acrylic and UV Gel
is sometimes called a nail technician[24] . The place where a nail technician works may be a nail salon or nail shop or
nail bar.
Painting the nails with nail polish (also called nail lacquer and nail varnish) is a common practice dating back to at
least 3000 B.C.
85
Nail (anatomy)
Non-human anatomy
The nails of primates and the hooves of running mammals evolved from the
claws of reptiles.[25]
In contrast to nails, claws are typically curved ventrally (downwards in animals)
and compressed sideways. They serve a multitude of functions — including
climbing, digging, and fighting — and have undergone numerous adaptive
changes in different animal taxa. Claws are pointed at their ends and are
composed of two layers: a thick, deep layer and a superficial, hardened layer
which serves a protective function. The underlying bone is a virtual mould of the
overlying horny structure and therefore has the same shape as the claw or nail.
Compared to claws, nails are flat, less curved, and do not extend far beyond the
tip of the digits. The ends of the nails usually consist only of the "superficial",
hardened layer and are not pointed like claws.[25]
With only a few exceptions, primates retain plesiomorphic (original, "primitive")
Nails are a distinguishing feature in
hands with five digits, each equipped with either a nail or a claw. For example,
the primate order.
all prosimians (i.e. "primitive" primates or "proto-primates") have nails on all
digits except the second toe which is equipped with a so called toilet-claw (i.e.
important for grooming activities). The needle-clawed bushbaby (Euoticus) have keeled nails (the thumb and the first
and the second toes have claws) featuring a central ridge that ends in a needle-like tip. In tree shrews all digits have
claws and, unlike most primates, the digits of their feet are positioned close together, and therefore the thumb cannot
be brought into opposition (another distinguishing feature of primates).[25]
A study of the fingertip morphology of four small-bodied New World monkey species indicated a correlation
between increasing small-branch foraging and
1. expanded apical pads,
2. developed epidermal ridges (fingerprints),
3. broadened distal parts of distal phalanges (fingertip bone), and
4. reduced flexor and extensor tubercles.
This suggests that whereas claws are useful on large-diameter branches, wide fingertips with nails and epidermal
ridges were required for habitual locomotion on small-diameter branches. It also indicates keel-shaped nails of
Callitrichines (a family of New World monkeys) is a derived postural adaptation rather than retained ancestral
condition. [26]
References
[1] Onumah, Neh; Scher, Richard K (May 2009). "Nail Surgery" (http:/ / emedicine. medscape. com/ article/ 1126725-overview). eMedicine. .
Retrieved March 2010.
[2] "Nail matrix" (http:/ / www. biology-online. org/ dictionary/ Nail_matrix). Biology Online. 2005. . Retrieved February 2010.
[3] Feneis, Heinz (2000). Pocket Atlas of Human Anatomy (4th ed.). Thieme. pp. 392–95. ISBN 3-13-511204-7.
[4] "Glossary of Nail Technology Terminology" (https:/ / www. nailsuperstore. com/ tips/ view. aspx?TipId=81). 2008. . Retrieved February
2010.
[5] Preuss, Marti (2000). "Understanding Your Natural Nails" (http:/ / hooked-on-nails. com/ naturalnails. html). Hooked on Nails. . Retrieved
February 2010.
[6] Lellipop (August 2006). "Anatomy of the nail" (http:/ / www. salongeek. com/ health-safety-unatural/ 40362-anatomy-nail. html). Salon
Geek. . Retrieved February 2010.
[7] "Nail Anatomy" (http:/ / www. naildoctors. com/ nail_anatomy. html). Nail Doctors. 2005. . Retrieved February 2010.
[8] "Glossary fo Nail Conditions" (http:/ / www. footdoc. ca/ Website Nail Conditions (A Glossary). htm). The Achilles Foot Health Centre. .
[9] http:/ / books. google. com/ books?id=p8VqAAAAMAAJ& q=hyponychium+ quick& dq=hyponychium+ quick& hl=en&
ei=0oSuTMSqA4O88gao4PTcBA& sa=X& oi=book_result& ct=result& resnum=1& ved=0CCUQ6AEwAA
86
Nail (anatomy)
[10] Jordan, Christopher; Mirzabeigi, Edwin (2000-04-01). Atlas of orthopaedic surgical exposures (http:/ / books. google. com/
?id=gMSW59keA4UC& pg=PA101). Thieme. p. 101. ISBN 0865777764. .
[11] Wang, Quincy C; Johnson, Brett A (May 2001). "Fingertip Injuries" (http:/ / www. aafp. org/ afp/ 20010515/ 1961. html). American Family
Physician. . Retrieved March 2010.
[12] Ravosa, Matthew J.; Dagosto, Marian (2007). Primate origins: adaptations and evolution (http:/ / books. google. com/
?id=C8RAGvdzedoC& pg=PA416). Springer. pp. 389–90. ISBN 0387303359. .
[13] Toenail Definition - Medicine.net (http:/ / www. medterms. com/ script/ main/ art. asp?articlekey=7740)
[14] Hunter, J. A. A., Savin, J., & Dahl, M. V. (2002). Clinical dermatology. Malden, Mass: Blackwell Science. p. 173. ISBN 0632059168
[15] BMJ 2007;335(7633):1288 (22 December), doi:10.1136/bmj.39420.420370.25 (http:/ / www. bmj. com/ cgi/ content/ full/ 335/ 7633/ 1288)
[16] Monterey County EMS Manual (http:/ / www. co. monterey. ca. us/ health/ EMS/ pdfs/ EMSManual. pdf). Chapter XI, Patient assessment.
[17] Schriger DL, Baraff LJ (Jun 1991). "Capillary refill—is it a useful predictor of hypovolemic states?" (http:/ / linkinghub. elsevier. com/
retrieve/ pii/ S0196-0644(05)82375-3). Ann Emerg Med 20 (6): 601–5. doi:10.1016/S0196-0644(05)82375-3. PMID 2039096. .
[18] MedlinePlus Encyclopedia Capillary nail refill test (http:/ / www. nlm. nih. gov/ medlineplus/ ency/ article/ 003394. htm)
[19] St. Luke's Hospital (http:/ / www. stlukes-stl. com/ health_content/ health_ency/ 1/ 003394. htm). Capillary nail refill test.
[20] American Academy of Dermatology - Nail Health (http:/ / www. aad. org/ public/ Publications/ pamphlets/ NailHealth. htm)
[21] http:/ / www. nailsmag. com/ feature. aspx?fid=762& ft=1
[22] Zempleni, J; R.B. Rucker, D.B. McCormick, J.W. Suttie (2007). Handbook of vitamins (http:/ / linus. lmu. edu) (4th ed.). .
[23] Cashman MW, Sloan SB (2010). "Nutrition and nail disease". Clinics in Dermatology 28 (4): 420–425.
doi:10.1016/j.clindermatol.2010.03.037. PMID 20620759.
[24] "Nails and Beauty Academy Training" (http:/ / www. nailsandbeautyacademy. co. uk). 2008. . Retrieved February 2010.
[25] Ankel-Simons, Friderun (2007). Primate anatomy: an introduction (3rd ed.). pp. 342–44. ISBN 0-12-372576-3.
[26] Hamrick, Mark W. (1998). "Functional and adaptive significance of primate pads and claws: Evidence from New World anthropoids" (http:/
/ www3. interscience. wiley. com/ journal/ 28218/ abstract). American Journal of Physical Anthropology (Wiley-Liss) 106 (2): 113–127.
doi:10.1002/(SICI)1096-8644(199806)106:2<113::AID-AJPA2>3.0.CO;2-R. PMID 9637179. . (Abstract)
External links
• Nail Disorders and Diseases (http://www.uspedicurespa.com/blog.aspx?tag=nail disorders) - types of nail
disorders: Paronychia, Onychogryphosis, Melanonychia
87
Peel (tool)
88
Peel (tool)
A peel is a shovel-like tool used by bakers to slide loaves of bread, pizzas, pastries, and
other baked goods into and out of an oven.[1] It is usually made of wood, with a flat
carrying surface (like a shovel's blade) for holding the baked good and a handle extending
from one side of that surface. Alternatively, the carrying surface may be made of sheet
metal, which is attached to a wooden handle.
A peel's intended functions are to:
• Transfer delicate breads, pastries, et cetera into an oven where transferring them directly
by hand could deform their delicate structure.
• Allow food to be placed further back in an oven than could normally be reached by the
baker.
• Keep the baker's hands out of the hottest part of an oven, or prevent the baker from
burning their hands on the hot baked goods.
A peel, in this case used
for pizza and also
sometimes called a
pizza shovel
Peel (tool)
89
Prior to use, peels are often sprinkled with flour, cornmeal, or milled wheat bran, to allow
baked goods to easily slide onto and off them.
There are peels of many sizes, with the length of the handle suited to the depth of the
oven, and the size of the carrying surface suited to the size of the food it is meant to carry
(for instance, slightly larger than the diameter of a pizza). Household peels commonly
have handles around 15 cm long and carrying surfaces around 35 cm square, though
handles range in length from vestigial (~6 centimeters) to extensive (~1.5 meters or more),
and carrying surfaces range in size from miniature (~12 centimeters square) to
considerably wide (1 meter square or more).
Other tools
An alternative, and related, meaning of the word "peel" is a wooden pole with a smooth
cross-piece at one end, which was used in printing houses of the hand-press period (before
around 1850) to raise printed sheets onto a line to dry, and to take them down again once
dried. The term is also sometimes used for the blade of an oar. All three meanings derive
ultimately from the Latin pala, a spade.
Small utensil the size of a
spatula.
References
[1] Simmons, Marie (2008). Things Cooks Love: Implements, Ingredients, Recipes. Ben Fink photographs. Andrews McMeel. p. 283.
ISBN 0740769766.
Scraper (kitchen)
There are several types of kitchen implements which are termed scrapers. They can be made of metal, plastics such
as polyethylene, nylon, or polypropylene, wood, rubber or silicone rubber. In practice, one type of scraper is often
interchanged with another or with a spatula (thus scrapers are often called spatulas) for some of the various uses.
Kitchen scrapers
Scraper (kitchen)
90
Bowl scraper
Bowl scrapers are, as the name suggests, used to remove material
from mixing bowls. Often, a plate scraper is used for this purpose,
particularly since the long handle allows it to be used to remove
contents of bowls as well as jars, such as mayonnaise jars; however,
Long-handled scraper can be used as a bowl
for bowls, dedicated scrapers are available, lacking the handle, and
scraper
consisting of a flat, flexible piece of plastic or silicone rubber sized for
convenient holding with the palm and fingers, with a curved edge to
match the curvature of the average bowl. The degree of curvature can vary from a slight curvature along one edge of
a rectangle, to a complex shape composed of changing radii to adapt better to bowls of different sizes. Sometimes a
hole is provided in one corner, to allow for hanging the utensil, as well as for placement of the thumb to allow for
more secure grip. Prices vary from below one American dollar, to as much as $20 American. [1]
The technique for use of either form of bowl scraper is essentially intuitive.
Dough scraper
Dough scrapers, or pastry scrapers, are more rigid implements, often
made of a metal rectangle with a wooden, plastic, or metal handle
running along one long edge not only for more comfortable grip, but
also to add rigidity; some bowl scrapers, however, are designed to be
stiff enough to serve a dual purpose and are sold as such. Occasionally,
an implement resembling a putty knife is sold for this purpose.[2] ,[3]
This implement is used to manipulate raw dough, by scraping it from a
Dough scraper
surface on which it has been rolled, as well as to slice it. It can also be
called a spatula.
Grill scraper
A grill scraper is a device used to clean cooking grills by scraping stuck particles of food from their surface. For flat
surfaced grills, their design can vary from similar to a putty knife, to a more complex device with provision to
protect the hands from the hot grill surface, targeted to professional cooks and chefs[4] , to even more complex
models[5] costing $100 American. Varieties sold for cleaning wire grills are also available, with notches in the edge
of the blade to match the wires of the grill.
Plate scraper
A plate scraper consists of a plastic, wooden, or metal handle attached
to a flexible rubber head. Although the original use of the implement
was to remove food from plates before washing [6] , its use has evolved
to more of a utilitarian implement, the bowl scraper.
Plate scraper
Scraper (kitchen)
91
Pan scraper
The pan scraper is, as the name suggests, an implement designed for
the forcible removal of tightly stuck or burned food from the bottom of
pots and pans before washing. They usually resemble a putty knife
with a metal blade and a metal, wood, or plastic handle, sometimes
with the handle mounted at an angle to the blade to allow for more
vigorous scraping parallel to the surface; others, however, are a wedge
shaped piece of hard plastic molded to fit the hand and with a slightly
rounded sharp edge.[7]
A spatula may be used as a pan scraper
Shellfish scraper
A shellfish scraper is a specialized utensil used for removing meat from cooked shellfish at the dining table. It
consists of a stainless steel rod about ten inches in length, with a flattened tip at one end and a forked tip at the other.
[8]
Crumb scraper
Although not a cooking utensil, a crumb scraper is used during a meal to remove crumbs and other unwanted small
debris from the surface of table, for cleanliness. Although historically, when crumb scrapers were mostly used in
[9]
homes, ornate designs were used , the variety most often seen currently is sized and shaped for a waiter to carry in
a breast pocket, and consists of a piece of sheet metal bent into a semi-cylindrical shape closely resembling a
laboratory scoopula, which is dragged across the table so that the debris is dragged towards the edge, where it can be
disposed of.[10]
References
[1] Bowl scrapers sorted by price (http:/ / www. amazon. com/ s?keywords=bowl+ scraper& rs=284507& rh=i:aps,k:bowl+
scraper,i:garden,n:1055398,n:284507& sort=-price), Amazon.com
[2] Triangular Spatula (http:/ / www. ablekitchen. com/ ProductDetails. asp?ProductCode=WC-64510)
[3] Pan Scraper (http:/ / www. amazon. com/ dp/ B000638HOC)
[4] Grill scrapers (http:/ / www. princecastle. com/ products/ grill_tools_161-173_scrapers. asp)
[5] Ergonomic Grill Scraper (http:/ / www. princecastle. com/ products/ grill_tools_613_scraper. asp)
[6] Plate Scraper (http:/ / digital. lib. msu. edu/ projects/ cookbooks/ html/ museum/ object_074. html), "Feeding America"
[7] Pot or Pan Scraper (http:/ / www. recipetips. com/ glossary-term/ t--38311/ pot-or-pan-scraper. asp), Recipetips.com
[8] Shellfish Scraper (http:/ / www. instawares. com/ shellfish-scraper-l-stainless. mtg-62130. 0. 7. htm#gallery)
[9] Crumb Scraper (http:/ / digital. lib. msu. edu/ projects/ cookbooks/ html/ museum/ object_024. html), "Feeding America"
[10] patent for a crumb scraper (http:/ / www. freepatentsonline. com/ D473988. html?highlight=crumb,scraper& stemming=on)
Skin
92
Skin
Skin
A diagram of human skin.
Skin is a soft outer covering of an animal, in particular a
vertebrate. Other animal coverings such as the arthropod
exoskeleton or the seashell have different developmental origin,
structure and chemical composition. The adjective cutaneous
means "of the skin" (from Latin cutis, skin). In mammals, the skin
is the largest organ of the integumentary system made up of
multiple layers of ectodermal tissue, and guards the underlying
muscles, bones, ligaments and internal organs.[1] Skin of a
different nature exists in amphibians, reptiles, and birds.[2] All
A close up picture of a rhinoceros skin.
mammals have some hair on their skin, even marine mammals
which appear to be hairless. Because it interfaces with the
environment, skin plays a key role in protecting (the body) against pathogens[3] and excessive water loss.[4] Its other
functions are insulation, temperature regulation, sensation, and the protection of vitamin D folates. Severely
damaged skin will try to heal by forming scar tissue. This is often discoloured and depigmented.
Hair with sufficient density is called fur. The fur mainly serves to augment the insulation the skin provides, but can
also serve as a secondary sexual characteristic or as camouflage. On some animals, the skin is very hard and thick,
and can be processed to create leather. Reptiles and fish have hard protective scales on their skin for protection, and
birds have hard feathers, all made of tough β-keratins. Amphibian skin is not a strong barrier to passage of chemicals
and is often subject to osmosis. For example, a frog sitting in an anesthetic solution could quickly go to sleep.
Functions
Skin performs the following functions:
1. Protection: an anatomical barrier from pathogens and damage between the internal and external environment in
[3] [4]
bodily defense; Langerhans cells in the skin are part of the adaptive immune system.
2. Sensation: contains a variety of nerve endings that jump to heat and cold, touch, pressure, vibration, and tissue
injury; see somatosensory system and haptic perception.
3. Heat regulation: increase perfusion and heatloss, while constricted vessels greatly reduce cutaneous blood flow
and conserve heat. Erector pili muscles are significant in animals.
4. Control of evaporation: the skin provides a relatively dry and semi-impermeable barrier to fluid loss.[4]
5. Storage and synthesis: acts as a storage center for lipids and water
6. Absorption: oxygen, nitrogen and carbon dioxide can diffuse into the epidermis in small amounts; some animals
use their skin as their sole respiration organ (in humans, the cells comprising the outermost 0.25–0.40 mm of the
skin are "almost exclusively supplied by external oxygen", although the "contribution to total respiration is
Skin
93
negligible")[5]
7. Water resistance: The skin acts as a water resistant barrier so essential nutrients aren't washed out of the body.
Mammalian skin layers
Mammalian skin is composed of two primary layers:
• the epidermis, which provides waterproofing and serves as a barrier to infection; and
• the dermis, which serves as a location for the appendages of skin;
Epidermis
Epidermis, "epi" coming from the Greek meaning "over" or "upon", is the outermost layer of the skin. It forms the
waterproof, protective wrap over the body's surface and is made up of stratified squamous epithelium with an
underlying basal lamina.
The epidermis contains no blood vessels, and cells in the deepest layers are nourished by diffusion from blood
capillaries extending to the upper layers of the dermis. The main type of cells which make up the epidermis are
Merkel cells, keratinocytes, with melanocytes and Langerhans cells also present. The epidermis can be further
subdivided into the following strata (beginning with the outermost layer): corneum, lucidum (only in palms of hands
and bottoms of feet), granulosum, spinosum, basale. Cells are formed through mitosis at the basale layer. The
daughter cells (see cell division) move up the strata changing shape and composition as they die due to isolation
from their blood source. The cytoplasm is released and the protein keratin is inserted. They eventually reach the
corneum and slough off (desquamation). This process is called keratinization and takes place within about 27 days.
This keratinized layer of skin is responsible for keeping water in the body and keeping other harmful chemicals and
pathogens out, making skin a natural barrier to infection. The epidermis helps the skin to regulate body temperature.
Layers
The epidermis is divided into several layers where cells are
formed through mitosis at the innermost layers. They move up
the strata, changing shape and composition as they differentiate
and become filled with keratin. They eventually reach the top
layer, called the stratum corneum, consisting of approximately
15-350 layers of dead cells strengthened and made
water-resistant by the keratin. This process is called
keratinization. The dead cells are then sloughed off, or
desquamated, which takes place within weeks.
Sublayers
Epidermis is divided into the following 5 sublayers or strata:[6]
•
•
•
•
•
Stratum corneum
Stratum lucidum
Stratum granulosum
Stratum spinosum
Stratum germinativum (also called the"stratum basale")
[also see: image rotating (1.1 mb) ]
Optical coherence tomogram of fingertip, depicting
stratum corneum (~500 µm thick) with stratum
disjunctum on top and stratum lucidum (connection to
stratum spinosum) in the middle. At the bottom
superficial parts of the dermis. Sweatducts are clearly
visible.
Blood capillaries are found beneath the epidermis, and are linked
to an arteriole and a venule. Arterial shunt vessels may bypass the network in ears, the nose and fingertips.
Skin
94
Dermis
The distribution of the bloodvessels in the skin of the sole of the foot. (Corium - TA alternate term for dermis - is labeled at upper
right.)
A diagrammatic sectional view of the skin (click on image to magnify). (Dermis labeled at center right.)
Gray's
subject #234 1065
MeSH
Dermis
Dorlands/Elsevier
Skin
[7]
[8]
[9]
Dermis
The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from
stress and strain. The dermis is tightly connected to the epidermis by a basement membrane. It also harbors many
Mechanoreceptors (nerve endings) that provide the sense of touch and heat. It contains the hair follicles, sweat
glands, sebaceous glands, apocrine glands, lymphatic vessels and blood vessels. The blood vessels in the dermis
provide nourishment and waste removal from its own cells as well as from the Stratum basale of the epidermis.
The dermis is structurally divided into two areas: a superficial area adjacent to the epidermis, called the papillary
region, and a deep thicker area known as the reticular region.
Papillary region
The papillary region is composed of loose areolar connective tissue. This is named for its fingerlike projections
called papillae, that extend toward the epidermis. The papillae provide the dermis with a "bumpy" surface that
interdigitates with the epidermis, strengthening the connection between the two layers of skin.
Reticular region
The reticular region lies deep in the papillary region and is usually much thicker. It is composed of dense irregular
connective tissue, and receives its name from the dense concentration of collagenous, elastic, and reticular fibres that
weave throughout it. These protein fibres give the dermis its properties of strength, extensibility, and elasticity. Also
located within the reticular region are the roots of the hair, sebaceous glands, sweat glands, receptors, nails, and
blood vessels.
Skin
95
Hypodermis
The hypodermis is not part of the skin, and lies below the dermis. Its purpose is to attach the skin to underlying bone
and muscle as well as supplying it with blood vessels and nerves. It consists of loose connective tissue and elastin.
The main cell types are fibroblasts, macrophages and adipocytes (the hypodermis contains 50% of body fat). Fat
serves as padding and insulation for the body. Another name for the hypodermis is the subcutaneous tissue.
Microorganisms like Staphylococcus epidermidis colonize the skin surface. The density of skin flora depends on
region of the skin. The disinfected skin surface gets recolonized from bacteria residing in the deeper areas of the hair
follicle, gut and urogenital openings.
In fish and amphibians
The epidermis of fish and of most amphibians consists entirely of live cells, with only minimal quantities of keratin
in the cells of the superficial layer. It is generally permeable, and, in the case of many amphibians, may actually be a
major respiratory organ. The dermis of bony fish typically contains relatively little of the connective tissue found in
tetrapods. Instead, in most species, it is largely replaced by solid, protective bony scales. Apart from some
particularly large dermal bones that form parts of the skull, these scales are lost in tetrapods, although many reptiles
do have scales of a different kind, as do pangolins. Cartilaginous fish have numerous tooth-like denticles embedded
in their skin, in place of true scales.
Sweat glands and sebaceous glands are both unique to mammals, but other types of skin gland are found in other
vertebrates. Fish typically have a numerous individual mucus-secreting skin cells that aid in insulation and
protection, but may also have poison glands, photophores, or cells that produce a more watery, serous fluid. In
amphibians, the mucus cells are gathered together to form sac-like glands. Most living amphibians also possess
granular glands in the skin, that secrete irritating or toxic compounds.[10]
Although melanin is found in the skin of many species, in reptiles, amphibians, and fish, the epidermis is often
relatively colourless. Instead, the colour of the skin is largely due to chromatophores in the dermis, which, in
addition to melanin, may contain guanine or carotenoid pigments. Many species, such as chameleons and flounders
may be able to change the colour of their skin by adjusting the relative size of their chromatophores.[10]
In birds and reptiles
The epidermis of birds and reptiles is closer to that of mammals, with a layer of dead keratin-filled cells at the
surface, to help reduce water loss. A similar pattern is also seen in some of the more terrestrial amphibians, such as
toads. However, in all of these animals there is no clear differentiation of the epidermis into distinct layers, as occurs
in humans, with the change in cell type being relatively gradual. The mammalian epidermis always possesses at least
a stratum germinativum and stratum corneum, but the other intermediate layers found in humans are not always
distinguishable. Hair is a distinctive feature of mammalian skin, while feathers are (at least among living species)
similarly unique to birds.[10]
Birds and reptiles have relatively few skin glands, although there may be a few structures for specific purposes, such
as pheromone-secreting cells in some reptiles, or the uropygial gland of most birds.[10]
Skin
96
Mechanics
Skin has a soft tissue mechanical behavior when stretched. The intact skin is prestreched (i.e. has residual stress) like
neoprene wetsuits around the diver's body. When deep cuts are made on the skin, it retracts, widening the slice hole.
Human uses and culture
The term "skin" may also refer to the covering of a small animal, such as a sheep, goat (goatskin), pig, snake
(snakeskin) etc. or the young of a large animal.
The term hides or rawhide refers to the covering of a large adult animal such as a cow, buffalo, horse etc.
Skins and hides from different animals are used for clothing, bags and other consumer products, usually in the form
of leather, but also furs.
Skin from sheep, goat and cattle was used to make parchment for manuscripts.
Skin can also be cooked to make pork rind or crackling.
Detailed cross section
Skin layers, of both hairy and hairless skin
Skin
97
References
[1] "Skin care" (analysis), Health-Cares.net, 2007, webpage: HCcare (http:/ / skin-care. health-cares. net/ oily-skin-care. php).
[2] Alibardi L. (2003). Adaptation to the land: The skin of reptiles in comparison to that of amphibians and endotherm amniotes. J Exp Zoolog B
Mol Dev Evol. 298(1):12-41. PMID 12949767
[3] Proksch E, Brandner JM, Jensen JM. (2008).The skin: an indispensable barrier. Exp Dermatol. 17(12):1063-72. PMID 19043850
[4] Madison KC. (2003). Barrier function of the skin: "la raison d'être" of the epidermis (http:/ / www. nature. com/ jid/ journal/ v121/ n2/ pdf/
5601872a. pdf). J Invest Dermatol. 121(2):231-41. doi:10.1046/j.1523-1747.2003.12359.x PMID 12880413
[5] Stücker, M., A. Struk, P. Altmeyer, M. Herde, H. Baumgärtl & D.W. Lübbers (2002). The cutaneous uptake of atmospheric oxygen
contributes significantly to the oxygen supply of human dermis and epidermis. (http:/ / jp. physoc. org/ content/ 538/ 3/ 985. full. pdf)PDF
Journal of Physiology 538(3): 985–994. doi:10.1113/jphysiol.2001.013067
[6] The Ageing Skin - Structure (http:/ / pharmaxchange. info/ press/ 2011/ 03/ the-ageing-skin-part-1-structure-of-skin-and-introduction/ )
[7] http:/ / education. yahoo. com/ reference/ gray/ subjects/ subject?id=234#p1065
[8] http:/ / www. nlm. nih. gov/ cgi/ mesh/ 2011/ MB_cgi?mode=& term=Dermis
[9] http:/ / www. mercksource. com/ pp/ us/ cns/ cns_hl_dorlands_split. jsp?pg=/ ppdocs/ us/ common/ dorlands/ dorland/ seven/ 000097765. htm
[10] Romer, Alfred Sherwood; Parsons, Thomas S. (1977). The Vertebrate Body. Philadelphia, PA: Holt-Saunders International. pp. 129–145.
ISBN 0-03-910284-X.
Spatula
The term spatula is used to refer to various small implements with a broad, flat, flexible blade used to mix, spread
and lift materials including foods, drugs, plaster and paints. The term derives from the Latin word for a flat piece of
wood or splint (a diminutive form of the Latin spatha, meaning broadsword), hence its use also for the small, flat
device, often made of wood, used to depress the tongue during medical examinations of the mouth and throat. The
words spade (digging tool) and spathe are similarly derived. The word spatula is known to have been used in English
since 1525.[1]
Design
Spatulas have a handle long enough to keep the holder's hand away from what is being lifted, or flipped. The blade
often has one side longer than the other. The right side (as used) tends to be longer than the left, as this is more
effective for right-handed people. Left-handed spatulas exist, but are rare. The blade may be perforated with holes or
slots allowing liquids to flow through.
Kitchen spatula
The kitchen spatula, also called a rubber scraper is a utensil
with a long handle and a broad flat edge, used for mixing and
scraping bowls.[2] [3] [4]
Kitchen spatulas are usually made of plastic, with a wooden or
plastic handle to insulate them from heat.
In American English, the word spatula is often used to refer to a
scraper.
In popular culture
The "Weird Al" Yankovic comedy film UHF features an ad for a
fictional outlet store called Spatula City that sells nothing but
A common kitchen spatula design
spatulas. The ad features people getting very excited over
receiving spatulas, including children at Christmas and wives getting them as romantic gifts.
Spatula
98
Related utensils
•
•
•
•
Peel
Putty knife
Scraper
Scoopula
References
[1] "Etymology OnLine" (http:/ / www. etymonline. com/ index. php?search=spatula& searchmode=none). . Retrieved 2007-05-24.
[2] "AskOxford.com".
[3] "Merriam-Webster Online Dictionary" (http:/ / www. m-w. com/ cgi-bin/ dictionary?va=spatula). . Retrieved 2007-06-20.
[4] "AskOxford.com" (http:/ / www. askoxford. com/ concise_oed/ spatula?view=uk). . Retrieved 2010-03-14.
Tongs
Tongs are gripping and lifting tools, of which there are many forms
adapted to their specific use. Some are merely large pincers or nippers,
but the greatest number fall into three classes:
1. Tongs which have long arms terminating in small flat circular ends
of tongs and are pivoted close to the handle, as in the common
fire-tongs, used for picking up pieces of coal and placing them on a
fire.
2. Tongs consisting of a single band of metal bent round one or two
bands joined at the head by a spring, as in sugar-tongs (a pair of
usually silver tongs with claw-shaped or spoon-shaped ends for
serving lump sugar), asparagus-tongs and the like.
Silicone-tipped locking tongs designed to
withstand temperatures up to 500 degrees
fahrenheit
3. Tongs in which the pivot or joint is placed close to the gripping
ends, such as a driller's round tongs, blacksmith's tongs or
crucible-tongs.
The tongs are the most-used cooking utensil when grilling, as they
provide a way to move, rotate and turn the food with delicate precision.
Long handled locking tongs designed for outdoor
grilling
Wedge (mechanical device)
Wedge (mechanical device)
A wedge is a triangular shaped tool, a compound and portable inclined
plane, and one of the six classical simple machines. It can be used to
separate two objects or portions of an object, lift an object, or hold an
object in place. It functions by converting a force applied to its blunt
A wood splitting wedge
end into forces perpendicular (normal) to its inclined surfaces.[1] The
mechanical advantage of a wedge is given by the ratio of the length of
its slope to its width.[2] [3] Although a short wedge with a wide angle may do a job faster, it requires more force than
a long wedge with a narrow angle.
History
The origin of the wedge is unknown likely because it has been in use for over 9000 years. In ancient Egyptian
quarries, bronze wedges were used to break away blocks of stone used in construction. Wooden wedges, that swelled
after being saturated with water, were also used. Some indigenous peoples of the Americas used antler wedges for
splitting and working wood to make canoes, dwellings and other objects.
Examples for lifting and separating
Wedges can be used to lift heavy objects, separating them from the surface upon which they rest. They can also be
used to separate objects, such as blocks of cut stone. Splitting mauls and splitting wedges are used to split wood
along the grain. A narrow wedge with a relatively long taper used to finely adjust the distance between objects is
called a shim, and is commonly used in carpentry.
The tips of forks and nails are also wedges, as they split and separate the material into which they are pushed or
driven; the shafts may then hold fast due to friction.
99
Wedge (mechanical device)
100
Examples for holding fast
Wedges can also be used to hold objects in place, such as engine parts (poppet valves), bicycle parts (stems and
eccentric bottom brackets), and doors.
A wedge-type door stop (door wedge) functions largely because of the friction generated between the bottom of the
door and the wedge, and the wedge and the floor (or other surface).
Mechanical advantage
The mechanical advantage of a wedge can be calculated by dividing the length of the
slope by the wedge's width:[2]
Cross-section of a splitting
wedge with its length
oriented vertically. A
downward force produces
forces perpendicular to its
inclined surfaces.
The more acute, or narrow, the angle of a wedge, the greater the ratio of the length of its slope to its width, and thus
[3]
the more mechanical advantage it will yield.
However, in an elastic material such as wood, friction may bind a narrow wedge more easily than a wide one. This is
why the head of a splitting maul has a much wider angle than that of an axe.
References
[1] Wedges and screws (http:/ / em-ntserver. unl. edu/ Negahban/ em223/ note16/ note16. htm), , retrieved 2009-07-29.
[2] Bowser, Edward Albert (1920), An elementary treatise on analytic mechanics: with numerous examples (http:/ / books. google. com/
?id=mE4GAQAAIAAJ) (25th ed.), D. Van Nostrand Company, pp. 202–203, .
[3] McGraw-Hill Concise Encyclopedia of Science & Technology, Third Ed., Sybil P. Parker, ed., McGraw-Hill, Inc., 1992, p. 2041.
Zester
101
Zester
A zester (also, citrus zester or lemon zester) is a kitchen utensil
for obtaining zest from lemons and other citrus fruit. A kitchen
zester is approximately four inches long, with a handle and a
curved metal end, the top of which is perforated with a row of
round holes with sharpened rims. To operate, the zester is pressed
with moderate force against the fruit and drawn across its peel.
The rims cut the zest from the pith underneath. The zest is cut into
ribbons, one drawn through each hole.[1]
Other tools are also sometimes called zesters because they too are
able to separate the zest from a citrus fruit. For example, when
Microplane discovered that its surform type wood rasps had
become popular as food graters and zesters, it adapted the
woodworking tools and marketed them as "zester / graters". An
additional form of zesting or zester is called "spin zesting" adopted
from the tool known as the Zip Zester. "Spin Zesting" allows
perfect abstraction of the citrus in seconds without sacrificing
safety of having the blade close to your fingers. 95% of the zest is
abstracted leaving out the bitter pith matter.[2]
A zester zests an orange
References
Notes
[1] James A. Beard (1970-02-16). "Man's Best Friends:Stripper and Zester" (http:/
A Microplane grater / zester in use
/ news. google. com/ newspapers?id=2gAOAAAAIBAJ&
sjid=KHwDAAAAIBAJ& pg=7282,4788177& dq=zester). Saint Petersburg
Times. .
[2] "A potpourri of unusual holiday gifts for your favorite chef" (http:/ / edition. cnn. com/ 2000/ FOOD/ news/ 12/ 11/ holiday. shopping/ ).
CNN. 2000-12-11. .
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Mark-mitchell-aldershot, N2e, Nczempin, Nono64, Pinethicket, Prashanthns, Proton donor, Quickos, RJ Reyes, Renicrew, Shyamal, Silvonen, Snigbrook, Stemonitis, Tanzania, Tide rolls, Timo
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Bishonen, Blackdog182, Blahblah1992, Bobo192, Brandon, COMPFUNK2, CTZMSC3, Calor, Can't sleep, clown will eat me, Capricorn42, Carbonrodney, Carlosguitar, Cartire1,
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105
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Image Sources, Licenses and Contributors
Image Sources, Licenses and Contributors
File:Vespula vulgaris SEM Antenna 03.jpg Source: http://en.wikipedia.org/w/index.php?title=File:Vespula_vulgaris_SEM_Antenna_03.jpg License: Public Domain Contributors: MyName
(SecretDisc)
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Kerry7374, Liné1, Miketsukunibito, Petwoe, 2 anonymous edits
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Villarreal
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