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Human Body Study

Tendons

Tough, fibrous cords of dense connective tissue that anchor muscle to bone — the cables through which a muscle’s pull becomes skeletal movement.

The three muscle types and the tendons that anchor them A four-panel plate: three comparative panels of skeletal, cardiac and smooth muscle drawn so the visual differences carry the classification, plus a fourth panel showing skeletal muscle attaching to bone via a tendon. Each panel links to that subject's article. Skeletal muscle long striated multinucleate fibres, attached to bones Cardiac muscle branched cells joined by intercalated discs, with a central nucleus Smooth muscle spindle-shaped cells with a single central nucleus; no striations Tendon — connection to bone a skeletal muscle's belly tapers into a cord of parallel collagen fibres, anchored into bone muscle tendon bone Three muscle types — one mechanism, three cell forms — plus the tendon, by which a skeletal muscle pulls on bone.

Structure

Section titled “Structure”

Tendons are built almost entirely of tightly packed parallel collagen fibres (mostly type I collagen), with a sparse population of tendon cells (tenocytes) tucked between the bundles. The fibres are organised hierarchically — collagen molecules into fibrils, fibrils into fibres, fibres into fascicles, fascicles into the whole tendon — and the whole structure is wrapped in connective-tissue sheaths. In places where a tendon must glide past bone or other tendons (the wrist, the ankle), it runs inside a lubricated synovial sheath.

What they do

Section titled “What they do”
  • Transmit muscle force to the skeleton — the muscle contracts, the tendon pulls, the bone moves.
  • Store and release elastic energy — tendons stretch slightly under load and recoil, which makes walking and running more efficient.
  • Concentrate a wide muscle’s pull onto a small bony attachment, and let muscles act at a distance from their target (the long tendons of the forearm operate the fingers).

Notable tendons

Section titled “Notable tendons”
  • Achilles tendon — the body’s thickest and strongest; joins the calf muscles to the heel bone.
  • Patellar tendon — links the quadriceps (via the kneecap) to the shinbone.
  • Rotator cuff tendons — four short tendons binding shoulder muscles to the head of the humerus.
  • Long flexor and extensor tendons of the forearm — operate the fingers from muscles in the forearm.

Key idea

Section titled “Key idea”

Tendons are tough but slow to heal — like ligaments, their blood supply is sparse. The two are often confused, but the distinction is simple: a tendon connects muscle to bone; a ligament connects bone to bone.