The Nerve Impulse

Abstract

The morphological and biochemical heterogeneity of CNS neurons means that these cells cannot be conceptualized simply as conductors that generate impulses according to some fixed percentage of activated synapses. Neurons differ from one another in a variety of ways. To a greater or lesser extent, each is biochemically unique and exhibits differences in cytoplasmic and membrane characteristics and the duration of sodium, potassium and calcium currents. Some cells have a low excitability, requiring a relatively intense stimulus to produce one or two spikes. Certain ones fire without apparent synaptic input, while others typically fire in bursts (Byrne, 1979). Moreover, the locus of generation of the impulse may vary. In pacemaker neurons, for example, the nerve spike is generally initiated in the cell body, while in nonpacemaker cells the locus may be the axon or axon hillock.