Answer: Neurotransmitters are being produced by neuron and stored in vesicles.
Explanation:
Neurotransmitters are secreted into the synaptic gap by exocytosis process, where the vesicles membranes fuse with the presynaptic button. The synaptic gap is usually in the order of 0.02 micron.
Several neurotransmitters include Acetylcholine, Dopamine, GABA (gamma-aminobutyric acid), Glutamate, Norepinephrine, and Serotonin.