ABSTRACT
Skeletal muscles are the motors for all voluntary movements of the body, from walking, to typing, to smiling. Although their functions are highly varied, all skeletal muscles have the same hierarchical structure (Figure 4.1). The fundamental force-generating unit of all skeletal muscles is the sarcomere, which combines the actions of myosin and actin motor proteins. Sarcomeres are arranged in series to form myobrils. Myobrils are arranged in parallel to form bers (or muscle cells). Muscle bers are encased in connective tissue called endomysium and are arranged in parallel to form fascicles. Muscle fascicles are encased in connective tissue called perimysium to form a whole muscle. Each muscle is encased in connective tissue called an epimysium and is attached to tendon. In the limb/joint systems, tendons transmit forces to bones, and several muscletendon units are arranged at each joint to generate torques to rotate joints and produce movement. In nonlimb systems (such as facial, speech, or eye muscles), muscle forces are transmitted via connective tissues and act to deform bodies to the appropriate conguration.
