MEDICAL PHYSIOLOGY

Detailed explanation-1: -Once the myosin-binding sites are exposed, and if sufficient ATP is present, myosin binds to actin to begin cross-bridge cycling. Then the sarcomere shortens and the muscle contracts. In the absence of calcium, this binding does not occur, so the presence of free calcium is an important regulator of muscle contraction.

Detailed explanation-2: -Myosin binds to actin at a binding site on the globular actin protein. Myosin has another binding site for ATP at which enzymatic activity hydrolyzes ATP to ADP, releasing an inorganic phosphate molecule and energy.

Detailed explanation-3: -The myosin binding sites on actin sites are exposed after calcium enters the sarcoplasm and activates the troponin-tropomyosin complex to shift. The latching of myosin heads docking onto actin-binding sites begins the “cross bridge cycle” a process that continues as long as calcium and ATP are present.

Detailed explanation-4: -In striated muscle, calcium causes a shift in the position of the troponin complex on actin filaments, which exposes myosin-binding sites (Fig.

Detailed explanation-5: -ATP binding causes myosin to release actin, allowing actin and myosin to detach from each other. After this happens, the newly bound ATP is converted to ADP and inorganic phosphate, Pi. The enzyme at the binding site on myosin is called ATPase.