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The Human Body

Author(s): Deanne Erdmann MS

Skeletal Muscle Contraction

A whole muscle is composed of bundles made of muscle fibers or cells. Actin and myosin are proteins which are found in muscle cells. During a contraction, the knoblike head of a myosin filament attaches to a binding site on actin to form a "crossbridge." Powered by ATP, the crossbridge changes shape, pulling the actin filament toward the center of the sarcomere.