The propagation of the action potential along the axon reaches the region immediately anterior to the presynaptic membrane causing its permeability to calcium ions to change and these ions to enter the cell. In the presynaptic area of the axon there are many neuro transmitter-repleted vesicles that by means of exocytosis activated by the calcium influx release the neurotransmitters into the synaptic cleft. The neurotransmitters then bind to specific receptors of the postsynaptic membrane. (The binding of neurotransmitters to their receptors is reversible, i.e., the neurotransmitters are not consumed after the process.) With the binding of neurotransmitters to the postsynaptic receptors the permeability of the postsynaptic membrane is altered and the depolarization that will lead to the first action potential of the postsynaptic cell begins.   _{Your Comment}