Figure 1.

The synaptic vesicle cycle. Prepared synaptic vesicles are marked with a dark color, while unprepared ones are marked with a light color. Once action potentials arrive at synaptic terminals, vesicles in RRP successively move to presynaptic membrane to fuse with release sites and release neurotransmitters into the cleft. Meanwhile, vesicles from the recycling pool quickly move to refill the RRP. Then, the released neurotransmitters bind to receptors on the postsynaptic membrane to complete signal transmission. Finally, most of the released neurotransmitters are transported back to the presynaptic terminals directly or via astrocytes (blue arrows) and taken up into synaptic vesicles for a new round of exocytosis.