Introduction

The activity of different cells, tissues and organs in an animal is coordinated by means of specialized communication systems and these systems may be either chemical or electrical. Hormones and neurotransmitters are chemical communicators, that is, they act at a point different from that at which they were produced and released. Electrical communication is by means of excitable cells and the message is carried by action potentials. Because each excitable cell usually produces action potentials of fixed waveforms, information is transmitted by the number of action potentials per unit time (frequency), rather than by the shape of the waveforms. In this chapter we will discuss how these electrical signals are transmitted from one excitable cell to another (Synaptic Transmission) and this is often by a chemical communicator.

The neuromuscular junction

The experimental model used probably most frequently to study synaptic transmission is the nerve-muscle preparation. Electrical stimulation of a nerve results in action potentials being recorded by microelectrodes that are inserted in the muscle fibre. The nerve fibre when it reaches the surface of the muscle fibre splits into a number of different branches, and a recording microelectrode in the muscle fibre in the vicinity of one of these branches shows a slightly unusual action potential in that the action potential has a small hump on its rising edge (see Figure 9.1).