ELECTROPHYSIOLOGICAL EVIDENCE OF RANVIER NODE CLUSTERING IN HUMAN SENSORY NERVE FASCICLES

Thin concentric needle electrodes were used to explore intact median n erve fascicles in human subjects. In particular, the presence of singl e units, probably recorded from nodes of Ranvier, was studied in diffe rent parts of a fascicle. Single-unit activity in myelinated fibers wa s rarely found at numerous sites. In many other intrafascicular areas, a substantial number of single units could be discriminated in the sa me or nearby recording sites with the same technique. To account for t he neurophysiological results, stochastic models and statistical tests were developed to test various hypotheses concerning intrafascicular nerve fiber arrangements. The acquired data suggested both an intrafas cicular modality grouping of nerve fibers and a simultaneous clusterin g of the Ranvier nodes of these fibers within very restricted areas of a fascicle. It was further concluded that the yield when searching fo r units in different types of nerve preparations may depend upon the u ltrastructure of the explored nerve segments.