Resting Phase
During the Resting Phrase, the muscle is not being stimulated by the motor neuron so the muscle is at rest.
Excitation-Contraction Coupling Phase
This is when Calcium is released into the myofibril. Calcium attaches to troponin, which causes the moving of tropomyosin and exposing the binding sites on the actin molecule.Myosin cross-bridge heads act us couples by attaching to actin filaments.
Contraction Phase
Myosin cross-bridges flex by using the energy released by the breakdown of ATP.ATP is needed for myosin cross-bridge flexion
For the myosin to detach from actin
Recharge Phase
Muscular contraction is a process that can be repeated over and over depending on factors such as Calcium is being available to bind to troponin,ATP is being available to provide the energy for cross-bridge flexion and to detach the myosin from the actin and Myosin ATPase has available ultimately breakdown ATP.
Relaxation Phase
When the motor neuron stops firing impulse, this allows calcium to be removed from the myofibril and back into the sarcoplasmic reticulum. This means tropomyosin movies back to cover and block the active binding sites on actin. This results in Myosin cross-bridges not longer having the ability to attach to actin. Finally the muscle relaxes and returns to its resting length.