Differences between the nodes of Ranvier of large and small diameter fibres in the P.N.S.

Abstract

The architecture of nodes of Ranvier in the spinal nerve roots of the rabbit has been examined. It has been shown that the nodes of large diameter fibres (mean 12 μm) are structurally different from those of small diameter fibres (mean 3 μm) on the basis of differences in the degree of axonal constriction, the frequent packing of axoplasmic constituents on one side of the node in large fibres, and the complexity of the arrangement of Schwann cell fingers which abut the nodal axolemma. Schwann cell fingers were seen to traverse a granular nodal gap substance which was web-like and came to rest upon a supra-axonal granular layer. Fine strands (5–6 nm in diameter) apparently formed bridges between some Schwann cell fingers and the nodal axolemma. The picture which emerges from this study is that the nodal apparatus might have orientation and structural stability which contribute to its efficiency as an electrogenic pump and is structurally distinct in small and large diameter fibres.