Growth pattern of axons in the optic nerve of chick during myelogenesis
- 1 July 1978
- journal article
- research article
- Published by Wiley in Journal of Comparative Neurology
- Vol. 180 (1), 73-84
- https://doi.org/10.1002/cne.901800106
Abstract
The purpose of this experiment was to study the diameter of axons at the time of the initiation of myelin and the pattern of growth of axons in the optic nerve of the chick. Embryos between 15 and 20 days and chicks 3, 5, 22 and 60 days of age were studied on the electron microscopic level. Based on axon diameter a unimodal distribution of unmyelinated axons is present through day 20 of incubation with a mean of approximately 0.35 μ. This population is represented through 22 days of age but from day 3 on, a second distinct population of unmyelinated axons is present which has a mean diameter that is approximately twice that of the smaller unmyelinated axons. All axons do not increase simultaneously in diameter but once growth starts, the unmyelinated axons apparently double in diameter at a relatively rapid rate prior to myelination. On incubation day 17 less than 1% of the axons in the optic nerve is myelinated. The number of axons in this group and their diameter (mean approximately 1.2 μ) remain relatively constant through day 3 but from days 5 through 22, two distinct populations of myelinated axons are present with mean diameters of 0.51 μ, 1.76 μ, and 3.90 μ. These populations represent approximately 20%, 67%, and 13% respectively of the total fiber population. As age increases the diameter of some myelinated axons is as small as or smaller than the unmyelinated axons at an earlier period in development. This suggests that factors other than axon diameter might be involved in the start of myelination. It appears that the increase in axon diameter does not occur in a continuous manner but in a saltatory manner from one size to another.This publication has 16 references indexed in Scilit:
- Specific projection of displaced retinal ganglion cells upon the accessory optic system in the pigeon (Columbia livia).Proceedings of the National Academy of Sciences of the United States of America, 1977
- The development of the isthmo‐optic tract in the chick, with special reference to the occurrence and correction of developmental errors in the location and connections of isthmo‐optic neuronsJournal of Comparative Neurology, 1976
- The time of origin and the pattern of survival of neurons in the isthmo‐optic nucleus of the chickJournal of Comparative Neurology, 1976
- Ganglion cell formation in the chick neural retinaBrain Research, 1973
- Lhermitte-Duclos Disease (Granule Cell Hypertrophy of the Cerebellum) Pathological Analysis of the First Familial CasesJournal of Neuropathology and Experimental Neurology, 1969
- The pigeon retina: Quantitative aspects of the optic nerve and ganglion cell layerJournal of Comparative Neurology, 1969
- Relation between the number of myelin lamellae and axon circumference in fibers of vagus and sciatic nerves of miceJournal of Comparative Neurology, 1967
- The optic nerve. Properties of a central tract*The Journal of Physiology, 1953
- DIFFUSE HYPERTROPHY OF THE CEREBELLAR CORTEX (MYELINATED NEUROCYTOMA)Archives of Neurology & Psychiatry, 1943
- A relation between axone diameter and myelination determined by measurement of myelinated spinal root fibersJournal of Comparative Neurology, 1934