ping the sarcolemma, a thin layer of connective tissue (the endomysium) separates each individual fiber from the surrounding ones (5:121). Bundles of muscle fibers are then surrounded again by a further sheet of connective tissue (the perimysium) and the entire muscle is contained within a tough outer sheet of connective tissue called the epimysium (5:122). These connective tissue sheets are continuous with the insertions and tendons which attach the muscles to the organism's skeleton (5:122).
Skeletal muscle is composed mainly of water (6:349). In fact, it is approximately 75% water (6:349). The remainder consists of protein (20%) (6:349). Inorganic salts and other substances amount to about 5% (6:349). The major proteins found within the muscle cell include myosin, actin, tropomyosin, and myoglobin (6:349). The various other materials which make the cells may include the high energy phosphates (ATP), urea, lactic acid; the minerals calcium, magnesium, and phosphorous; various enzymes and pigments; ions of sodium, potassium, and chloride; and amino acids, fats, and carbohydrates (6:349).
Muscles have an excellent blood supply (5:122). Each individual fiber is surrounded by a network of blood capillaries (5:122). During exercise, a muscle's oxygen consumption may increase nearly 70 times (6:349). To accommodate this large oxygen requirement, local vascular beds must channel large quantities of blood through exercising tissues (6:349). In rhythmic exercise such as running, swimming, or cycling, the blood flow fluctuates; it decreases during the muscle's contraction phase and increases during the relaxation period (6:349). This provides for a pulsatile flow which is complemented by the rapid dilation of previously dormant capillaries; indeed, during strenuous exercise, more than 4,000 capillaries may be delivering blood to each square millimeter of muscle cross section (6:349).
Nerve fibers typically enter a mu...