DIFFERENTIATION OF AXON TYPES IN VISCERAL NERVES BY MEANS OF THE POTENTIAL RECORD

Abstract

By means of the cathode ray oscillograph technique, 4 components of potential can be recognized in certain autonomic nerves. The vagus and the genital branch of the genito-crural contain all 4 components. Other nerves lack certain of these elements. The potentials are termed for convenience the A, B1, B2 and C components. Determinations have been made of the properties of the fiber groups which contribute to these potentials. The first 2 groups are similar to each other, the last 2 likewise resemble each other, the major differences in certain properties occurring between the 2nd and 3rd (B1 and B2) components. The properties which change more abruptly from the B1 group to the B2 are threshold, duration of axon potential response, chronaxie and absolutely refractory period, indicating a lower irritability and a slower activity and recovery in the last 2 groups, as compared to the first 2, in the ratio of at least 4 to 1. Histological cross sections of tested nerves lead to the inference that the first or A potential arises from large myelinated fibers of the type supplying skeletal muscle and peripheral afferent endings, i.e., somatic, motor and sensory. The B1 potential arises from fibers of the type usually assigned to visceral afferent function, passing through autonomic nerves. The B2 and C potentials arise from fibers which in certain nerves can be identified as autonomic effer-ents. Of these 2 groups the B2 is inferred to contain the small thinly myelinated axons present in the autonomic system, the C the unmyelinated.