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The muscular system is composed of muscle tissue that is highly specialized to contract, or shorten when stimulated. Muscles move the bones. 40-50% of the mass of the human body is muscle. Muscle is found almost everywhere in and on the body. It is found not only beneath the skin, but also deep inside of the body.

    There are three different kinds of muscles: Skeletal, smoot and cardiac.

  Skeletal muscles are attached mostly to bones. These muscles are used for most physical movement. They are responsible for voluntary movement. Most skeletal muscles are consciously controlled by the central nervous system. Skeletal muscle cells are large. They have more than one nucleus. Because of their length, they are often called muscle fibers.

    Smooth muscles are involved in involuntary movement. These cells are spindle shaped with separate nuclei and are not stiated (in lines) like skeletal muscles. Most cells contract without stimulation from the nervous system. The movement of these muscles move food hrough our digestive track and control blood flow through our circulatory system.

    Cardiac muscles are only found in the heart. Although they are striated, they are moved involuntarily. Adjacent cells from branching fibers allow nerve impulses to pass from cell to cell and move the muscle.