During which step does the myosin head enter the "cocked" position?

The "cocked" position of the myosin head is reached during the second step of the contraction cycle in muscle physiology. This stage is characterized by the binding of ATP to the myosin head, which causes the myosin to detach from the actin filament after the power stroke. Hydrolysis of ATP occurs in this step, leading to the reconfiguration of the myosin head into the cocked position. In this state, the myosin head is ready for the next interaction with actin, as it is in an energized state that is crucial for muscle contraction.

Understanding this sequence is vital for comprehending how muscles contract, as it highlights the intricate interactions between myosin and actin mediated by energy provided from ATP. The process involves multiple steps, but the cocked positioning is specifically critical for preparing myosin for the subsequent power stroke that drives contraction.