The Muscular System
The muscular system is the body's network of tissues that controls movement both of the body and within it. Walking, running, jumping: all these actions propelling the body through space are possible only because of the contraction (shortening) and relaxation of muscles. These major movements, however, are not the only ones directed by muscular activity. Muscles make it possible to stand, sit, speak, and blink. Even more, were it not for muscles, blood would not rush through blood vessels, air would not fill lungs, and food would not move through the digestive system. In short, muscles are the machines of the body, allowing it to work.
Design: Parts of the Muscular System
The muscles of the body are divided into three main types: skeletal, smooth, and cardiac. As their name implies, skeletal muscles are attached to the skeleton and move various parts of the body. They are composed of tissue fibers that are striated or striped. The alternating bands of light and dark result from the pattern of the filaments (threadlike proteins) within each muscle cell. Skeletal muscles are called voluntary muscles because a person controls their use, such as in the flexing of an arm or the raising of a foot.
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