Medicina

8 Synaptic Transmission and the Neuromuscular Junction
Edward G. Moczydlowski

The ionic gradients that cells maintain across their membranes provide a form of storedelectrochemical energy cells can use for electrical signalling. The combination of a resting membrane potential of -60 to -90 mV and a diverse array of voltage-gated ionchannels allows excitable cells to generate action potentials that propagate over long distances along the surface membrane of a single nerve axon or muscle fiber. However,another class of mechanisms is necessary to transmit such electrical information from cell to cell throughout the myriad of neuronal networks that link the brain with sensory andeffector organs. Electrical signals must pass across the specialized gap region between two apposing cell membranes that is called a synapse. The process underlying thiscell-to-cell transfer of electrical signals is termed synaptic transmission. Communication between cells at a synapse can be either electrical or chemical. Electrical synapsesprovide direct electrical continuity between cells by means of gap junctions, whereas chemical synapses link two cells together by a chemical neuro-transmitter that isreleased from one cell and diffuses to another. In this chapter we discuss the general properties of synaptic transmission and then focus mainly on synaptic transmission betweena motor neuron and a skeletal muscle fiber. This interface between the motor neuron and the muscle cell is called the neuromuscular junction. In Chapter 12, the focus is onsynaptic transmission between neurons in the central nervous system (CNS).
Printed from STUDENT CONSULT: Medical Physiology (on 08 August 2006) © 2006 Elsevier