The term applied to the anatomical relation of one NEURON(E) (nerve cell) with another which is effected at various points by contact of their branching processes. The two neurons do not come directly into contact, but the release of a chemical NEUROTRANSMITTER by one neuronal AXON results in this chemical travelling across the synapse and firing off the signal along another nerve. A signal can be sent across a synapse in one direction only, from presynaptic or postsynaptic membranes. Synapses are divided into excitatory and inhibitory types. When a neurotransmitter travels across an excitatory synapse it usually provokes the receptor neuron into initiating an electrical impulse. Inhibitory synapses cool down the excitation of the adjacent neurons. Drugs that influence the NERVOUS SYSTEM usually do so by affecting the release or modification of the neurotransmitters passing across the synapse.