OSMT (Ontario Society of Medical Technologists) Practice Exam

The main component of thick filaments in muscle cells is myosin. Myosin is a motor protein that plays a critical role in muscle contraction. It consists of long fibrous tails and globular heads, which can bind to actin, the primary component of thin filaments. During muscle contraction, the myosin heads attach to the actin filaments and pull them toward the center of the sarcomere, the basic unit of muscle fiber, resulting in muscle shortening and contraction.

In contrast, tropomyosin and troponin are regulatory proteins associated with the thin filaments. Tropomyosin covers the binding sites on actin and prevents myosin from binding in a relaxed muscle state. Troponin is a complex that interacts with tropomyosin and is responsive to calcium ions, which trigger muscle contraction by causing tropomyosin to shift and expose the binding sites on actin. While actin is crucial for the structure and function of thin filaments, myosin is specifically responsible for the formation of thick filaments and the contraction mechanics in muscle cells. Thus, myosin is rightly identified as the main component of thick filaments.