How a Sarcomere Works (pt. 2)
After the myosin filament heads bind to the actin, ADP and P are released from the myosin heads, creating a power stroke-like movement and thus change the position of the filaments.
The last part of the cycle occurs when the heads of myosin molecules detach from the actin due to binding between ATP molecules and myosin heads.
This cycle repeats until nerve impulses stop sending signals to contract. Once this has happened, calcium ions return to their storage sites in the sarcoplasmic reticulum until the next impulse comes.
Here's a quick summary of the whole process.