Normally the resting membrane potential of a motor neuron is kept at -70mV to -50 with a higher concentration of sodium outside and a higher concentration of potassium inside. When an action potential propagates down a nerve and reaches the axon terminal of the motor neuron, the change in membrane voltage causes the calcium voltage gated ion channels to open allowing for an influx of calcium ions. These calcium ions cause the acetylcholine vesicles attached to the presynaptic membrane to release acetylcholine via exocytosis into the synaptic cleft.
