The term 'synapse' comes from the Greek words 'syn', which means 'together' and 'haptein' meaning 'to clasp'. Action potential do not cease at the end of a single neuron. They are passed on to another excitable cell. The junction between two neurons is called a synapse (Sai- naps). Actually, the neurons are not in direct contact at a synapse. There is a gap called synaptic cleft between them. For an impulse to continue along a nerve pathway, it must cross this gap. The process of crossing the gap at a synapse is called synaptic transmission.
Action potentials can cross a synapse in one direction only. A fiber which carries an impulse toward a synapse is called presynaptic fiber. A fiber which receives the impulse after it crosses the synapse is a postsynaptic fiber. It serves as structural basis of communication between the neurons in the CNS and between muscle cells and neurons in the PNS.