OSMT (Ontario Society of Medical Technologists) Practice Exam

What occurs during the power stroke in muscle contraction?

1. Release of calcium ions

2. Binding of myosin to actin

3. Cross-bridge detachment

4. Myosin heads pivot, pulling actin filaments

The correct answer is: Myosin heads pivot, pulling actin filaments

The power stroke in muscle contraction specifically refers to the action where the myosin heads pivot, effectively pulling the actin filaments closer together. This process is crucial for muscle contraction and occurs after the myosin heads have attached to the actin filaments, forming cross-bridges. As ATP is hydrolyzed, it provides the energy required for this pivotal movement, resulting in the sliding of actin over myosin, which ultimately leads to muscle shortening and contraction. The other options describe different processes involved in muscle contraction. For instance, the release of calcium ions is an essential step that initiates contraction, but it occurs before the power stroke. Binding of myosin to actin describes the initial attachment needed for the power stroke but does not encompass the action itself. Cross-bridge detachment happens after the power stroke, marking the ending of one cycle of attachment and pulling, which is integral to the overall contraction mechanism but not part of the power stroke itself.