A two-component positive single unit spike could be recorded extracellularly from neurones in the acoustic ganglion of the guinea pig cochlea. Light and electron microscopy showed that the bipolar afferent neurones and their processes were myelinated except at nodes of Ranvier on either side of the cell soma, about 40 μm from the point of emergence of the myelinated processes. This anatomical finding and the properties of the two-component spike suggest that impulse conduction in these cells is achieved by rapid successive activation of the low threshold nodes on either side of the cell soma. The possible advantages of such a conduction system are discussed.
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