Tendon
From Wikipedia, the free encyclopedia
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For other uses, see Tendon (disambiguation).
A tendon (or sinew) is a tough band of fibrous connective tissue that connects muscle to bone, or muscle to muscle. They are similar to ligaments except that ligaments join one bone to another. Tendons are designed to withstand tension. Typically tendons connect muscles to bones; together, a combination of tendons and muscles can only exert a pulling force.
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[edit] Composition
Tendons are composed mainly of water, type-I collagen and cells called tenocytes. Minor fibrillar collagens, fibril-associated collagens and proteoglycans are present in small quantities and are critical for tendon structure. Most of the strength of tendon is due to the vertical, hierarchical arrangement of densely-packed collagen fibrils. Tenocytes are specialized fibroblasts responsible for the maintenance of collagen structure.
[edit] Anatomy
The origin of a tendon is where it joins to a muscle. Collagen fibers from within the muscle organ are continuous with those of the tendon. A tendon inserts into bone at an enthesis where the collagen fibers are mineralised and integrated into bone tissue.
Tenocytes produce collagen molecules which aggregate end-to-end and side-to-side to produce collagen fibrils. Fibril bundles are organised by tenocytes to form fibres. Collagen fibres coalesce into macroaggregates. Groups of macroaggregates are bounded by connective tissue endotendon and are termed fascicles. Groups of fascicles are bounded by the epitendon and peritendon to form the tendon organ.
Blood vessels may be visualised within the endotendon running parallel to collagen fibres, with occasional branching transverse anastomoses.
The internal tendon bulk is thought to contain no nerve fibres, however the epi- and peritendon contain nerve endings, while Golgi tendon organs are present at the junction between tendon and muscle.
Tendon length varies in all major groups and from monkey to person. Tendon length is practically the discerning factor where muscle size and potential muscle size is concerned. For example, a man with a 1 centimetre biceps tendon will have greater potential for muscle mass than a man with a longer tendon. Cases in point: Bodybuilders will generally have short tendons and are said to have 'great genetics', however not all bodybuilders are blessed with short tendons. Examples of people with short tendons (in particular the upper arms) are Casey Viator and Arnold Schwarzenegger. Tendon length is determined exclusively by genetics.
[edit] Other information
Tendonitis refers to inflammation of a tendon.
The Achilles tendon is a particularly large tendon connecting the heel to the muscles of the calf. It is so named because the mythic hero Achilles was said to have been killed due to an injury at this spot.
Sinew was also widely used in the medieval times as a form of ancient elastic. Some specific uses include using sinew as thread for sewing, attaching feathers to arrows (see fletch), lashing tool blades to hafts, etc. It also recommended in survival guides as a material from which strong ropes can be made for items like traps or living structures.
Tendon (particularly beef tendon) is used as a food in some cuisines.
[edit] See also
[edit] References
Tendons & Ligaments in Journal of Musculoskeletal & Neuronal Interactions; 2005, 5(1): Eds. Lyritis GP & Jee WSS
