What is the role of actin and myosin in muscle contraction?

Actin and myosin are key proteins found in muscle fibers and are central to the muscle contraction process. When a muscle contracts, it is primarily due to the interaction between these two proteins within the muscle cells.

In a sarcomere, which is the basic unit of a muscle, actin filaments and myosin filaments work together through a process known as the sliding filament theory. During contraction, myosin heads attach to binding sites on the actin filaments, forming cross-bridges. Through a series of molecular interactions, the myosin heads pull the actin filaments toward the center of the sarcomere, resulting in shortening of the sarcomere and thus muscle contraction.

This dynamic interaction and the subsequent shortening of the sarcomere is what enables muscles to contract effectively, facilitating movement. Therefore, the role of actin and myosin in muscle contraction specifically illustrates how they allow the sarcomere to contract, making the correct choice clearly aligned with the fundamental mechanisms of muscle physiology.