Answer:
An action potential stimulates muscle into contraction by propagating down a motor neuron. It will traverse down to the terminal end of the axon. In the terminal bouton there is a rapid influx of calcium ions which push vesicles containing neurotransmitters (ACh) outside. These little vesicles will travel across a small space (called synaptic cleft) and bind to nicotinic recepters on the motor end plate. This will cause an motor end plate potential that will continue the action potential into the T-tubules to spread the action potential throughout your muscle. The action potential activates DHPR which is a voltage gated Ca++ channel, however, it is blocked by RyR. When this happens it produces a conformational change in RyR to open and allow Ca++ out from the sarcoplasmic reticulum. Additional RyR channels that are not coupled with DHPR will also open to allow even more Ca++ out. This calcium released initiates contraction of myofibrils and are quickly pumped back into the SR.