Dear student, acetyl choline is a neurotransmitter which is stored in the synaptic vesicles at the end of the acetyl choline producing neurons. When a nerve impulse arrives at the neuron terminal than the depolarisation (causing influx of calcium ions) leads to the release of the acetyl choline in the neuro muscular junctions. Acetyl choline is a cheif neurotransmitter of the parasympathetic nervous system. Regards