Segregation by modality of myelinated and unmyelinated fibers in human sensory nerve fascicles.

Thin diameter concentric needle electrodes with a small recording surface were used to explore the characteristics of neighboring fibers in sensory median nerve fascicles. Fibers which were close neighbors in the fascicle, were not randomly distributed intraneurally. Instead there was an intrafascicular segregation by modality of both myelinated and unmyelinated fibers. In addition, evidence was obtained which suggested that the contents of different Schwann cells vary. Some Schwann cell systems envelop afferent C fibers whereas others hold efferent sympathetic C axons. The results imply a modality segregation amongst both A and C fibers in human peripheral sensory nerve fascicles.