Answer:
The action potential in an alpha motor neuron is propagated by saltatory conduction that, when it reaches the terminal bouton, causes a Ca2+ influx which leads to the fusing of acetylcholine-containing synaptic vesicles with the plasma membrane, and the release of said neurotransmitter in the neuromuscular junction. Acetylcholine activates the nicotinic receptors that open the sodium / potassium channel and causes the sarcolemma to reverse its polarity.
Depolarization will reach the sarcoplasmic reticulum and thanks to the T Tubules the potential for intracellular release of accumulated Ca2+ will be approximated. To make the concentration of this ion sufficient to produce the contraction there will also be an extracellular calcium entry through the Ca2+ channels. At this moment, the myosin-actin junction points are free and when binding occurs the contraction. When the moment of relaxation arrives, the links must be broken so that the muscle is not contracted. These bonds are broken thanks to the action of myosin as ATP, which breaks the bond by ATP hydrolysis. This process will be favored only when the Ca2+ decrease.