a voltage-gated ion channel in the presynaptic membrane of a neuron that is involved in the release of neurotransmitter (and, therefore, passage of a neural signal) at a synapse. The arrival of an action potential at the terminal buttons (see axon) of the neuron is accompanied by depolarization of the presynaptic membrane, which results in opening of the calcium channels and influx of calcium ions into the terminal buttons. This triggers fusion of the synaptic vesicles (which contain neurotransmitter) with the presynaptic membrane and the release of neurotransmitter into the synaptic cleft.