Detachment of myosin cross-bridges from actin filaments occurs during which phase of muscle contraction?

• A. Release of ADP from myosin head
• B. Power stroke
• C. Binding of ATP to myosin head
• D. Hydrolysis of ATP to ADP and Pi

Answer: (C)

Verified step by step guidance

1. Understand the role of myosin and actin in muscle contraction: Myosin heads form cross-bridges with actin filaments, which are essential for the sliding filament mechanism of muscle contraction.
2. Recall the ATP cycle in muscle contraction: ATP binding, hydrolysis, and release of ADP and Pi are critical steps in the myosin-actin interaction cycle.
3. Focus on the detachment phase: Detachment of the myosin head from the actin filament occurs when ATP binds to the myosin head. This binding reduces the affinity of myosin for actin, causing the cross-bridge to break.
4. Differentiate between the phases: The power stroke occurs when ADP and Pi are released, causing the myosin head to pull the actin filament. Hydrolysis of ATP to ADP and Pi re-cocks the myosin head for the next cycle, but detachment specifically requires ATP binding.
5. Conclude that the correct answer is 'Binding of ATP to myosin head,' as this is the step that directly causes the detachment of the myosin cross-bridge from the actin filament.