w8pedia:Physiology:Tendon

A tendon or sinew is a tough band of fibrous connective tissue that connects muscle to bone. They are similar to ligaments except that ligaments join one bone to another.

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 parallel, hierarchical arrangement of densely-packed collagen fibrils. Tenocytes are specialised fibroblasts responsible for the maintenance of collagen structure.

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 fibres 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.

Tendonitis refers to swelling of a tendon.

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.

References

Tendons & Ligaments in Journal of Musculoskeletal & Neuronal Interactions; 2005, 5(1): Eds. Lyritis GP & Jee WSS

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