Electron-microscopic observations on preterminal fibers in the oculomotor nucleus of the cat: With special reference to the relation between axon diameter and myelin thickness in mammalian gray matter

Abstract

Electron microscopy of myelinated fibers in main lateral cell groups of the cat oculomotor nucleus reveals the majority to have diameters of les than 3 μm, with more than one-half less than 1 μm in diameter. The values of the ratio g (axon diameter/total fiber diameter) range between 0.58 and 0.88, with a mean of 0.74. There is no definite relation between g and fiber diameter. The morphological data are consistent with physiological data on preterminal conduction velocities in the oculomotor nucleus, and extend the dimensional analysis of myelinated fibers in gray matter, which has previously been confined to lower vertebrates, to the mammalian central nervous system.