MUSCLE PHYSIOLOGY

Detailed explanation-1: -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-2: -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-3: -This process is known as myosin-actin cycling. As the myosin S1 segment binds and releases actin, it forms what are called cross bridges, which extend from the thick myosin filaments to the thin actin filaments. The contraction of myosin’s S1 region is called the power stroke (Figure 3).

Detailed explanation-4: -According to this theory, myosin filaments use energy from ATP to “walk” along the actin filaments with their cross bridges. This pulls the actin filaments closer together. The movement of the actin filaments also pulls the Z lines closer together, thus shortening the sarcomere.

Detailed explanation-5: -Myosin pulls on actin filaments by performing a power stroke, in which the head of the molecule cocks itself backward. To perform this movement, myosin must use energy from adenosine triphosphate (ATP). It does so by acting as an ATPase, which causes the hydrolysis of ATP to form adenosine diphosphate (ADP).