Tuesday, February 20, 2007

HYBW #7 - Joints

Joints are the bits that hold our bodies together. Some joints act as hinges (such as knees and elbows), while others allow for more complicated movement - a shoulder or hip joint, for example, allows for backward, forward, sideways, and rotating movements. And some don't move much at all.

Fibrous joints are the ones that don't move much. The dome of the skull is made of a number of bony plates. Between the edges of these plates are joints of fibrous tissue. Fibrous joints also hold the teeth in the jawbone.

Cartilaginous joints allow very limited movement. Each of the vertebrae in the spine is held together by cartilaginous joints. They give the spine its combination of strength and flexibility.

Synovial joints are filled with synovial fluid, which acts as a lubricant to help the joints move easily. There are three kinds of synovial joints that play a big part in voluntary movement:

Hinge joints allow movement in one direction, as seen in the knees and elbows.

Pivot joints allow a rotating or twisting motion, like the ones that support our head.

Ball-and-socket joints allow the greatest freedom of movement. The hips and shoulders have this type of joint, in which the round end of a long bone fits into the hollow of another bone.