In the cross-bridge cycle, what happens when a new ATP binds to myosin?

• A. Cross-bridge forms with actin
• B. Cross-bridge releases and myosin returns to original position
• C. Calcium release stops
• D. Actin slides past myosin without detachment

Answer: (B)

Binding of ATP to the myosin head causes the cross-bridge to detach from actin. This detachment resets the cycle: the bound ATP is then hydrolyzed to ADP and Pi, which re-energizes and re-cocks the myosin head into a high-energy position. A new attachment to actin can then form further along the filament, allowing another round of the power stroke. This detachment and re-cocking is what allows continuous cycling and muscle shortening.