VERTEBRATE NERVES: SOME CORRELATIONS BETWEEN FIBER SIZE AND ACTION POTENTIALS

Abstract

Unmye-linated fibers were counted and myelinated fibers counted and measured in a saphenous, phrenic and sympathetic nerve of a cat; a phrenic, sympathetic and depressor nerve of rabbit; and 2 vagi of turtle. A classification of fiber sizes was plotted and compared with action potential waves. Although, in general, maximum in the fiber size distribution corresponded with an equal no. of the potential max. and had a comparable order of magnitude, no function of fiber size was found from which potential waves could be predicted accurately. Conduction rate diminished more rapidly in the smaller size of fibers than would be expected if the conduction rate bore a linear relationship to the size of fiber. The presence of C waves in the action potential of all nerves investigated, except the phrenic, seems to confirm previous conclusions that the C wave is due to unmyelinated fibers. The isolated group of fibers with diam. 2.6-5.2[mu] in the depressor of the rabbit, together with the appearance of a large B1 wave, seemed to indicate that this wave is due to fibers between these sizes. As a corollary, the large B2 wave observed in the combined svmpathetic and depressor was produced by fibers less than 2.6[mu] in diam. The large amplitude of C waves in turtle vagi was associated with large size unmyelinated fibers.