Which sequence describes the cross-bridge cycle during skeletal muscle contraction?

• A. Resting state with myosin heads hydrolyzed to high-energy state; Ca2+ allows cross-bridge formation; power stroke occurs moving actin; ADP and Pi are released; cross-bridge detaches when new ATP binds; ATP is hydrolyzed to re-cock the head for next cycle.
• B. Cross-bridge formation occurs before Ca2+ release; ATP binds to actin to detach; Ca2+ binds myosin; contraction occurs.
• C. Myosin head remains bound to actin while Ca2+ levels drop; ATP is not required for detachment.
• D. Calcium ions cause immediate detachment of myosin from actin without ATP involvement.

Answer: (A)