Presynaptic cell

The presynaptic cell exclusively contains neurotransmitters such as acetylcholine and glutamate, stored in vesicles. When an action potential arrives in the presynaptic cell, voltage gated Ca²⁺ channels open allowing for the influx of Ca²⁺ ions  down their concentration gradient, causing the vesicles to undergo exocytosis, emptying their contents into the synaptic cleft. These can the bind to receptors on the postsynaptic membrane.