To initiate the muscle action potential, several structures are necessary. These structures include t-tubules, motor end plate, ACh receptor-channels, acetylcholine, calcium, and motor neuron. The muscle fiber itself is not necessary to initiate the muscle action potential, but it is necessary for the muscle to contract after the action potential has been generated.
T-tubules are invaginations of the sarcolemma that allow for rapid transmission of the action potential throughout the muscle fiber. The motor end plate is the location where the motor neuron synapses onto the muscle fiber, and it contains ACh receptor-channels that open in response to acetylcholine released by the motor neuron.
Acetylcholine binding to the ACh receptor-channels triggers an influx of calcium ions, which leads to the release of additional calcium from the sarcoplasmic reticulum through ryanodine receptors. The calcium ions then bind to troponin, which causes tropomyosin to move and expose the myosin-binding sites on actin. Finally, the myosin heads bind to actin and initiate muscle contraction, which is powered by ATP hydrolysis and regulated by Ca2+-ATPase pumps.