Unmyelinated fibres in the sacral 3 and caudal 1 ventral roots of the cat.

Abstract

Of the axons in the S[sacral]3 and caudal (Ca)1 ventral roots of the cat, 29% were unmyelinated. Approximately 1/2 of these unmyelinated axons survived in the proximal stump of a sectioned ventral root and were regarded as unmyelinated preganglionic efferents. At least 27% of the preganglionic efferents in segments S3 and Ca 1 were unmyelinated. The other half of the ventral root unmyelinated axons arose from dorsal root ganglion cells and survived in the distal stump of a sectioned ventral root. These data and the receptive field data in the companion paper, showed that these unmyelinated fibers were sensory. Since 15% of the ventral root axons are sensory, the Law of Bell and Magendie cannot be regarded as an accurate description of the organization of these ventral roots.