What role does calcium play in neurotransmitter release?

Calcium plays a major role in triggering synaptic vesicle exocytosis and the release of neurotransmitters. When an action potential propagates down the axon of a nerve and arrives at the axon nerve terminal it activates voltage-gated calcium channels causing an increase in intracellular calcium at the active zone. Calcium-sensitive synaptotagmin proteins then bind to calcium which promotes the interactions between v-SNARE protein complexes on the vesicle membrane and t-SNARE protein complexes on the presynaptic membrane. This causes the two membranes to fuse together and the release of neurotransmitters into the synaptic cleft.