APA Dictionary of Psychology

a type of specialized junction through which a signal is transmitted from one neuron to another across the narrow gap (synaptic cleft) separating them through the release and diffusion of neurotransmitter. Though slower than electrical synapses, chemical synapses are more flexible and comprise the majority of neuronal junctions within the body. Because of this prevalence, the qualifier generally is omitted and synapse used alone to denote a chemical junction.