The Corpus Callosum as a Model System in the Study of Mammalian Cerebral Axons
A large body of information is now available regarding the mechanism and the phenomonology of impulse conduction in invertebrate axons and in mammalian peripheral axons. Such axons, however, are of relatively large diameter when contrasted with their counterparts in the mammalian brain. Bishop (1966) has estimated that more than 80% of the fibers in the mammalian cortex are less than 3 μm in diameter, and in the pyramidal tract of the cat (Hildebrand and Skoglund, 1971) approximately 50% of the axons are less than 1 μm in diameter. The finest myelinated axons in the central nervous system are 0.2–0.3 μm in diameter (Bishop and Smith, 1964; Waxman and Bennett, 1972; Waxman and Swadlow, 1976a) while nonmyelinated axons may be as fine as 0.08 μm in diameter (Swadlow et al, 1980b; Waxman and Swadlow, 1976a).
KeywordsNeurol Rosene Stim Identical Diameter
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- Bishop, G. H., 1966, Fiber size and myelination in afferent systems, in:Pain( R. S. Knighton and P. R. Dunke, eds.), Churchill, London.Google Scholar
- Bishop, P. O., Burke, W., and Davis, R., 1962, Single-unit recording from antidromically activated optic radiation neurons, J. Physiol. (Lond.) 162:232–250.Google Scholar
- Boyd, I. A., 1964, The relation between conduction velocity and diameter for the three groups of efferent fibres in nerves in mammalian skeletal muscle, J. Physiol. (Lond.) 175:33–35.Google Scholar
- Chiu, S. Y., Ritchie, J. M., Robart, R. B., and Stagg, D., 1979, A quantitative description of membrane currents in rabbit myelinated nerve, J. Physiol. (Lond.) 292:149–166.Google Scholar
- Chung, S., Raymond, S. A., and Lettvin, J. Y., 1970, Multiple meaning in single visual units, Brain Behav. Evol. 3:73–101.Google Scholar
- Hodgkin, A. L., and Huxley, A. F., 1952, A quantitatve description of membrane current and its application to conduction and excitation in nerve, J. Physiol (Lond.) 117:500–544.Google Scholar
- Paintal, A. S., 1967, A comparison of the nerve impulses of mammalian nonmedullated nerve fibers with those of the smallest diameter medullated fibers, J. Physiol (Lond.) 193:523–533.Google Scholar
- Rushton, W. A. H., 1951, A theory of the effects of fibre size in medullated nerve, J. Physiol (Lond.) 115:101–121.Google Scholar
- Swadlow, H. A., Waxman, S. G., and Geschwind, N., 1980b, Small-diameter non-myelinated axons in the primate corpus callosum, Arch. Neurol. 37:114–115.Google Scholar
- Tasaki, I., 1959, Conduction of the nerve impulse, in:Handbook of Physiology(J. Field and H. W. Magoun, eds.), American Physiological Society, Washington, D. C., Vol. I, pp. 75–122.Google Scholar