SYSTEMIC ANATOMY
General anatomy of the skeletal muscles
The skeletal muscles are attached to bones and contracting muscles causes them to move (Figs. 126-128). Muscles participate in formation of body cavities and have influence upon organs of sight, hearing and equilibrium. They help to retain the body in balance, provide support and movement, accomplish respiration and swallowing and perform facial gestures. The human body contains about 400 muscles, which contract voluntarily when a person wills them to.
Structure of the skeletal muscles
The principle elements of the skeletal muscles are striated muscles fibres. These fibres are sur-
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rounded by loose connective tissue called endomi-sium. Bundles, or fascicles, of fibers are separated from one another by connective tissue layers called perimysium, and the whole muscle is surrounded by the epimisium (outer perimysium). Loose connective tissue found in muscles perform functions of support and demarcation between functional elements. It also holds the blood vessels, which nourish muscle fibers, and nerves.
Classification of the muscles
There are several classification of skeletal muscles. Muscles can be classified according to topography, shape, orientation of fibers, function and position relative to joints. They are divided into superficial and deep, lateral and medial, internal and external. Muscles can be of many possible shapes. Walls of the abdomen are formed by broad strap muscles. They attach to bones and move them like levers. Fascicles in a fusiform muscle are oriented parallel to its longitudinal axis. Muscles in which fiber fascicles are situated only on one side of the tendon are called unipennate. If they are situated on two sides, the muscle is called bipennate. And if fascicles extend from several sides of the tendon, the muscle is called multipennate (Fig. 129).