The last chapter dealt with the spread of voltage along a nerve fiber. Eventually, the signal reaches the end of the fiber and must be transmitted across the gap or synapse that separates one nerve cell from another. Nerve cells may also make synaptic connections with effector cells such as muscle cells to produce contraction, or with endocrine cells to release hormones. In line with the theme of this book, much of the discussion will be related to the synaptic connection between nerve and muscle, which is often referred to as neuromuscular transmission. Because of the accessibility of these synapses, much of our knowledge of synaptic transmission has come from studying neuromuscular synapses. In fact, the neuromuscular junction is often taken as a model of all synapses, but in recent years it has become clear that there is a great variety of synaptic connections. In addition to the example of a nerve axon releasing a chemical transmitter which can diffuse across the synaptic cleft and excite or inhibit another nerve cell or muscle cell, numerous examples of electrical connections have been found. A model of such an electrical connection is shown in Fig. 7.1, and is often referred to as a gap junction because of the continuity of an anatomical pathway from one cell to another.
KeywordsSynaptic Vesicle Neuromuscular Junction Synaptic Connection Synaptic Cleft Equilibrium Potential
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