Three layers of connective tissue are part of each muscle: (1) an outer epimysium, (2) a central perimysium, and (3) an inner endomysium. These layers and the relationships among them are diagrammed in Figure 10-1.

The entire muscle is surrounded by the epimysium, a dense layer of collagen fibers. The epimysium separates the muscle from surrounding tissues and organs. It is connected to the deep fascia, a dense connective tissue layer (see Figure 4-17).

The connective tissue fibers of the perimysium divide the skeletal muscle into a series of compartments, each containing a bundle of muscle fibers called a fascicle. In addition to collagen and elastic fibers, the perimysium contains blood vessels and nerves that maintain blood flow and innervate the fascicles. Each fascicle receives branches of these blood vessels and nerves.

Within a fascicle, the delicate connective tissue of the endomysium  surrounds the individual skeletal muscle fibers and interconnects adjacent muscle fibers. Scattered between the endomysium and the muscle fibers are satellite cells, embryonic stem cells that function in the repair of damaged muscle tissue.   Disruption of Normal Muscle Organization

The collagen fibers of the endomysium and perimysium are interwoven and blend into one another. At each end of the muscle, the collagen fibers of the epimysium, perimysium, and endomysium come together to form a bundle known as a tendon or a broad sheet called an aponeurosis. Tendons and aponeuroses usually attach skeletal muscles to bones. Where a tendon attaches to a bone, the tendon fibers extend into the bone matrix, providing a firm attachment. As a result, any contraction of the muscle will exert a pull on its tendon and thereby on the attached bone (or bones).