Skeletal muscles are voluntary muscles which contract in order tomove the bones they connect. Located throughout the body, thesemuscles form a layer between the bones of the skeleton and subcutaneousfatty tissue.Structurally, skeletal muscles consist of a contractile belly andtwo extremities, often tendinous, called the origin and the insertion.The origin is usually the more stationary end of a contractingmuscle, and the insertion the more movable. Skeletal muscles consistof elongated muscle fibers and fibrous connective tissue whichanchors the muscles to the underlying skeleton. The composition ofmuscle fibers in a muscle determines the potential strength of musclecontraction and the possible range of motion due to contraction.The shapes of muscles often reveal their function.Anatomists distinguish between two types of muscle contraction.In isotonic contraction, the length of a muscle changes and the muscleproduces movement, while in isometric contraction, themusclecontracts or tenses without producing movement or undergoing achange in length.Skeletal muscles act across one or more movable joints, workingtogether in groups to produce movement or to modify the actionsof other muscles. Depending on the types of joints involved andthe points of attachment of the muscle , a standard name can begiven to any movement so produced, for example flexion/extensionor protraction/retraction .
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