fig1
Figure 1. (A) Motor unit: an alpha motor neuron and all the fibers it innervates; (B) Anatomical structure of a skeletal muscle: muscle, fascicle, fiber, myofibril, sarcomere; (C) Sarcomere structure showing Z-lines, actin (thin) filaments and myosin (thick) filaments, and the M line (center of the sarcomere); (D) Actin thin filament segment showing the troponin-tropomyosin complex, which blocks the myosin heads from the actin-binding sites in the absence of Ca2+; a segment of a myosin thick filament, with myosin heads that interact with actin-binding sites; a cross-section of a myofibril showing actin thin filaments surrounding the myosin thick filaments.
