Chapter 6: The Muscular System

Because flexing muscles look like mice scurrying beneath the skin, some scientist long ago dubbed them muscles, from the Latin word mus meaning "little mouse." Indeed, the rippling muscles of professional boxers or weight lifters is often the first thing that comes to mind when one hears the word muscle. But muscle is also the dominant tissue in the heart and in the walls of other hollow organs of the body. In all its forms, it makes up nearly half the body's mass.

The essential function of muscle is contraction, or shortening-a unique characteristic that sets it apart from any other body tissue. As a result of this ability, muscles are responsible for essentially all body movement and can be viewed as the "machines" of the body.