Optic nerve axon diameters measured in the cat retina: Some functional considerations

Abstract

Because of the arrangement of axon bundles in the fibre layer of the cat's retina, it is possible to obtain electronmicroscopic sections of axon bundles which contain exclusively either axons arising from the area centralis, or axons arising from peripheral retina. From electronmicrographs of such sections we have constructed axon diameter spectra for central and peripheral axon samples. The centrally originating axons are markedly smaller than peripheral axons, in good agreement with their slower conduction velocity (described in an accompanying paper). The diameter spectra of both peripheral and area centralis axon samples are unimodal, in contrast to the two conduction velocity groups known to exist within each axon population. Alternative explanations of this discrepancy between diameter and conduction velocity spectra are discussed.