Branchings at the central node of Ranvier, observed in the anterior horn and Clarke's nucleus of the cat. An electron microscopic study

Abstract

A total of 246 nodes of Ranvier were observed in the spinal gray matter (the anterior horn of C 6–7 and the nucleus dorsalis at L 3) of the cat by electron microscopy. About 55% of the total nodes of Ranvier had axonal branchings (30%) or nodal boutons (25%) of various types which were designated here as specialized nodes of Ranvier, and the rest (45%) were of conventional types. The axonal branchings consisted of bifurcations (14%), or collaterals (2%), trifurcations (12%) and multiple furcations (2%). Except for a few cases, most of them occurred at the nodes of Ranvier. The nodal boutons were found only in axons of small diameters (less than 3.0 μm) at the nodes of Ranvier, and some nodes had long processes (more than 7 μm) which formed multiple synaptic contacts with soma or dendrites. There was no linear relationship between the diameter and the length of the axons at the nodes of Ranvier. The non-conventional nodes of Ranvier are common both in the anterior horn and in Clarke's nucleus, but their occurrence is more frequent in Clarke's nucleus. It is suggested that this may reflect differences in axonal architectonics.