the contraction of a muscle cell
6.4 Contraction of Muscle Cells. The contractile apparatus in skeletal and cardiac muscles is a specialized structure for contraction, and consists of basic unit called sarcomere (Fig. 6-10A). These are mainly composed of thick myosin filaments, consisting of polymerized myosins, and thin actin filaments.he protein complex that regulates this contraction exists in the contractile apparatus (Fig. 6-11B). Regulatory proteins bind to actin filaments to keep myosin heads from binding to them. In this condition, actin filaments and myosin heads cannot interact, thus disabling the contraction of muscle cells.