abstract:A synaptic potential (also known as a postsynaptic potential) in short is a change in the potential, voltage, of the post synaptic cell. In other words, it is an alteration in the membrane potential of a cell resulting from activation of a synaptic input.
When an action potential comes down this pre-synaptic axon, when it reaches this point here, it sets off the process of these vesicles dumping their content into the synaptic cleft.