Synaptic Transmission

Abstract

The junction of an axonal ending with a nerve cell, a muscle cell, or a glandular cell was first called a synapse by Sherrington (see also Chapter 1, p. 2). At synapses the propagated action potential is transmitted to the next cell. Originally it was wrongly believed that the axon always formed a “gap junction,” that is, was in closest contact with the cell on which it ended so that the propagated impulse could be transmitted without interruption to that cell. However, electrophysiologic and histologic investigations have shown that this form of synapse, which is now called an electrical synapse, is rare. Another type of synapse is far more common, particularly in mammals and thus in man. In this type, the axonal ending when stimulated releases a chemical substance that produces an excitatory or an inhibitory effect at the neighboring cell membrane. This type of synapse is called a chemical synapse. The structure and the function of excitatory and inhibitory chemical synapses will be explained in this chapter.