Anatomy & Physiology

Anatomy & Physiology Study Guide Muscle fiber type and physical conditioning determine muscle performance capabilities: • The three types of skeletal muscle fibers are fast fibers, slow fibers, and intermediate fibers. o Fast fibers, which are large in diameter, contain densely packed myofibrils, large glycogen reserves, and relatively few mitochondria. They produce rapid and powerful contractions of relatively brief duration. o Slow fibers are about half the diameter of fast fibers and take three times as long to contract after stimulation. Specializations, such as abundant mitochondria, an extensive capillary supply, and high concentrations of myoglobin, enable slow fibers to continue contracting for extended periods. o Intermediate fibers are very similar to fast fibers but have a greater resistance to fatigue. • Muscles dominated by fast fibers appear pale and are called white muscles. • Muscles dominated by slow fibers are rich in myoglobin and appear as red muscles. • Anaerobic endurance is the time over which muscular contractions can be sustained by glycolysis and reserves of ATP and CP. • Aerobic endurance is the time over which a muscle can continue to contract while supported by mitochondrial activities. Cardiac muscle tissue differs structurally and functionally from skeletal muscle tissue: • Since cardiac muscle twitches do not exhibit wave summation, cardiac muscle tissue cannot produce tetanic contractions. • Cardiac muscle cells contract without neural stimulation (automaticity), and their contractions last longer than those of skeletal muscle. • Cardiac muscle tissue is located only in the heart. Cardiac muscle cells are small, have one centrally located nucleus, have short, broad T tubules, and are dependent on aerobic metabolism. Intercalated discs are found where neighboring plasma membranes connect. Smooth muscle tissue differs structurally and functionally from skeletal muscle tissue: • Smooth muscle tissue is non-striated, involuntary muscle tissue. • Smooth muscle cells lack sarcomeres and the resulting striations. The thin filaments are anchored to dense bodies. • Smooth muscle contracts when calcium ions interact with calmodulin, which activates myosin light chain kinase. • Smooth muscle functions over a wide range of lengths (plasticity). • In multiunit smooth muscle cells, each smooth muscle cell acts relatively independently of other smooth muscle cells in the organ. Visceral smooth muscle cells are not always innervated by motor neurons. Neurons that innervate smooth muscle cells are not under voluntary control.

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