Ligaments, tendons and the kinds of movement in living things
Ligaments are separate bundles of fibrous connective tissue. Each end is fixed to one of the two bones of a joint, so a ligament ties the bones together and limits the directions in which the joint can move. Its fibres are very strong and slightly elastic, so a sudden push stretches them a little instead of tearing them. Even so, twisting a joint can tear a ligament, for example the cruciate ligament of the knee. Tendons are strong connective tissue joining a muscle to a bone. When the muscle contracts, the tendon pulls the bone, so the bone moves. The Achilles tendon joins the calf muscle (gastrocnemius) to the heel bone. A tendon can tear after hard effort or a sudden contraction; sudden pain in a joint, tendon or muscle should be looked at by a doctor, who decides what to do. The rule is simple: a ligament joins bone to bone, and a tendon joins muscle to bone. Movement itself is a sign of life, and it happens at three levels: inside each cell, as in cytoplasmic streaming; in a part of the organism, as in peristalsis in the intestine of a vertebrate; and of the whole organism, which moves from place to place to find food or a mate or to escape danger.
| Ligament | Tendon | |
|---|---|---|
| Joins | bone to bone | muscle to bone |
| Job | holds a joint together and limits its movement | passes the pull of a muscle to a bone |
| Property | strong, a little elastic | strong |
| Example | cruciate ligament of the knee | Achilles tendon of the heel |
| Level | Example | What moves |
|---|---|---|
| Inside a cell | cytoplasmic streaming | the cytoplasm and the chloroplasts in it |
| A part of the organism | peristalsis | food along the intestine |
| The whole organism | a fish swimming to food | the whole body, from place to place |
Find your Achilles tendon, with a grown-up. Sit and place two fingers lightly on the thick cord just above your heel, behind the ankle. Rise slowly onto your toes and feel the cord tighten. Write which muscle pulls on it and which bone it moves. Press only lightly, and if there is ever pain there, ask a doctor instead of testing it. Then draw a simple diagram: a muscle, a tendon, a bone, a joint and a ligament, and write bone to bone or muscle to bone beside each connector.