When a skeletal muscle relaxes, what causes the myosin cross-bridges to separate and the thin filaments to return to their original position?

When a skeletal muscle relaxes,myosin head attach to actin by breaking down ATP to ADP and phosphate with the help of myosin ATPase. The myosin head forms the cross -bridges on the active site of the actin.The cross-bridge pulls the actin which slide over the myosin. The release of ADP completes the cross-bridge movements . ATP attaches to myosin, and break the actin -myosin cross-bridge. Thus breaking of ATP into ADP and phosphate help the thin filament to return to their original position.

A loss of calcium.

Explanation:

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