<Li> The electrical depolarization of the membrane at the synapse causes channels to open that are permeable to calcium ions . </Li> <Li> Calcium ions flow through the presynaptic membrane, rapidly increasing the calcium concentration in the interior . </Li> <Li> The high calcium concentration activates a set of calcium - sensitive proteins attached to vesicles that contain a neurotransmitter chemical . </Li> <Li> These proteins change shape, causing the membranes of some "docked" vesicles to fuse with the membrane of the presynaptic cell, thereby opening the vesicles and dumping their neurotransmitter contents into the synaptic cleft, the narrow space between the membranes of the pre - and postsynaptic cells . </Li>

Who is credited with demonstrating the existence of chemical synapses