Fiber Size and Organization of Afferent Pathways

Abstract

Concepts of the organization and functional characteristics of afferent pathways in the central nervous system have been derived from anatomical studies of large fiber myelin sheath degeneration by the Marchi method; observation of centrally recorded, electronically amplified potentials resulting from peripheral nerve stimulation; and clinical observation of the sensory deficit attributed to disruption incident to disease and surgical procedures in man. There has been little evidence, either physiological or anatomical, of any consistent relationship between the central afferent systems and peripheral nerve fiber size. The compound peripheral nerve action potential was described by Gasser and Erlanger.¹⁶ They delineated A, B, and C responses which were oscillographically recorded, and related to large, intermediate, and small-sized fiber groups. Subsequent studies by Erlanger and Gasser,¹³ by Bishop and Heinbecker,⁵ and Gasser and Grundfest¹⁸ further demonstrated the relationship of fiber size in peripheral nerves to threshold for excitation, velocity of