MUSCLE PHYSIOLOGY

Detailed explanation-1: -The motion of muscle shortening occurs as myosin heads bind to actin and pull the actin inwards. This action requires energy, which is provided by ATP. Myosin binds to actin at a binding site on the globular actin protein.

Detailed explanation-2: -As discussed later, the motor activity of myosin moves its head groups along the actin filament in the direction of the plus end. This movement slides the actin filaments from both sides of the sarcomere toward the M line, shortening the sarcomere and resulting in muscle contraction.

Detailed explanation-3: -In muscle contraction, the actin filaments slide along the myosin filaments. This is driven by the heads of the myosin molecules, which bind to actin and, in a sequence of binding and release movements, ‘walk’ along the actin filament. This repetitive binding and release is powered by the hydrolysis of ATP (Fig.

Detailed explanation-4: -Within the sarcomere, myosin slides along actin to contract the muscle fiber in a process that requires ATP. Scientists have also identified many of the molecules involved in regulating muscle contractions and motor behaviors, including calcium, troponin, and tropomyosin.

Detailed explanation-5: -The sliding can only occur when myosin-binding sites on the actin filaments are exposed by a series of steps that begins with Ca++ entry into the sarcoplasm. Tropomyosin is a protein that winds around the chains of the actin filament and covers the myosin-binding sites to prevent actin from binding to myosin.