MUSCLES AND MOVEMENT

Our muscles are bundles of fibres that alternately shorten and relax to make parts of the body move. They make up more than half your body's weight. Muscle enable you to walk, run, breathe and blink, and they keep your body in position when you sit or stand. Some muscles, such as the biceps in your arms work only when you want them to. Others, such as your heart, never stop walking.

How do muscles work?
Muscles are made up of millions of cells called muscle fibres, which contain overlapping chemical threads. When a muscle receives signals from the nervous system, the thread slide closer together, making the whole muscle shorten or contract. This moves the part of the body to which the muscle is attached. See also the muscle basic and the listing of muscles names at http://www.jdenuno.com/6~Muscles.htm