Final answer:
Acetylcholine is synthesized and stored in vesicles within the presynaptic neuron. When the neuron is stimulated, the vesicles release acetylcholine into the synaptic cleft.
Step-by-step explanation:
The 3 stores of vesicles of acetylcholine are located in the presynaptic neuron. Acetylcholine is synthesized and stored in small, membrane-bound vesicles within the presynaptic neuron. When an action potential reaches the presynaptic neuron, the vesicles fuse with the presynaptic membrane and release acetylcholine into the synaptic cleft, where it can bind to receptors on the postsynaptic membrane.