Figure 12.1 Microscopic anatomy of skeletal muscle. Dark A band Light I band Nuclei Fiber Fiber Sarcolemma Mitochondrion Myofibril Dark A band Light I band Nucleus Z disc H zone Z disc Thin (actin) filament Thick (myosin) filament I band A band I band M line Sarcomere M line Z disc Z disc Thin (actin) filament Elastic (titin) filaments Thick (myosin) filament I band thin filaments only H zone thick filaments only M line thick filaments linked by accessory proteins Outer edge of A band thick and thin filaments overlap

Figure 12.2 Relationship of the sarcoplasmic reticulum and T tubules to the myofibrils of skeletal muscle. Part of a skeletal muscle fiber (cell) I band A band I band Z disc H zone Z disc M line Sarcolemma Myofibril Triad: T tubule Terminal cisterns of the SR (2) Sarcolemma Tubules of the SR Myofibrils Mitochondria

Nuclei of muscle fibers Figure 12.3 Photomicrograph of muscle fibers, longitudinal and cross sections (800). Nuclei of muscle fibers Muscle fibers, longitudinal view Muscle fibers, cross-sectional view 3

Figure 12.4 Connective tissue coverings of skeletal muscle. Epimysium Perimysium Epimysium Bone Endomysium Tendon Muscle fiber within a fascicle Blood vessel Perimysium wrapping a fascicle Endomysium (between individual muscle fibers) Muscle fiber Fascicle Perimysium 4

Figure 12.5 The neuromuscular junction. Synaptic vesicle containing ACh Sarcolemma Mitochondrion Synaptic cleft Axon terminal of motor neuron Fusing synaptic vesicles ACh Sarcoplasm of muscle fiber ACh receptors Junctional folds of sarcolemma 5

Figure 12.6 Photomicrograph of neuromuscular junctions (750). Terminal branch of an axon Axon terminal at neuromuscular junction Muscle fibers 6