Vesicular release

Most of the neurotransmitter release takes place by transmitter-loaded synaptic vesicles fusing with presynaptic membrane and discharging their contents into the synaptic cleft. This is exocytosis. It is triggered by the entrance at the nerve terminal of an action potential that causes a transient and highly localized influx of Ca2+. After releasing the vesicle membrane, it is recycled from the presynaptic membrane to form new vesicles by endocytosis. The vesicles are consequently loaded with transmitter through active transporters restricted in the vesicle membrane.