Pharmocology and Physiology of the Synaptic Transmission of Excitation

Abstract

This chapter discusses the pharmocology and physiology of the synaptic transmission of excitation. The activity of the nervous system would not exist without the transmission of signals between the interneuronal connections as well as between nervous elements and effector organs. The transmitter substance in presynaptic endings must be stored in special structural inclusions, the vesicles localized in the immediate neighborhood of the postsynaptic membrane. Electron microscopical investigations have disclosed the existence of such vesicles in nearly all synapses. The immediate stimulus for the transmitter release is evidently the depolarization of the nerve ending by the action potential, as the delivery of depolarizing current highly increases the frequency of miniature potentials. It is found that as the level of polarization of the membrane determines the amplitude of the action potential generated, a decrease in polarization of the presynaptic endings is accompanied by a diminution of the amplitude of the action potential and of the quantity of transmitter substance released. It is observed that a lack of calcium ions or a surplus of magnesium ions interferes with the release of transmitter from presynaptic nerve endings, without notably influencing the susceptibility of the postsynaptic membrane to the transmitter.