 This permissive gating is more than a matter of simple summation, however.Summation is the convergence of many EPSPs at the axon hillock (either from a single neuron firing at a high frequency or from many neurons firing at once) that depolarizes the membrane potential to the point of threshold.The membrane depolarization caused by the opening of synaptic gates causes an additional increase in intracellular calcium that facilitates the release of neurotransmitters; thus, it is able to selectively distribute information from the presynaptic cell.