the time necessary for the conduction of a signal across a synapse; the interval between the arrival of a nerve impulse at the ending of a presynaptic fiber and the start of the postsynaptic potential. In synapses with a chemical transmission mechanism a synaptic delay lasts from 0.3–0.5 milliseconds to several milliseconds. During most of this period mediators are released by presynaptic endings under the influence of nerve impulses. Synaptic delay is practically absent in synapses with electrotonic transmission.