The normative neurophysiologic data relating to the maturation of peripheral nerves and muscle in children have been greatly expanded in the recent past (1-10).

The reader is referred to the volume by Jones, Bolton, and Harper (8) for an excellent review of neurophysio­logic norms in pediatric populations. Peripheral nerve myelination begins at about the 15th week of gesta­tion and continues throughout the first 3-5 years after birth (11).

Conduction velocities are determined by myelination, diameter of the fiber, and internodal dif­ferences. Myelination occurs at the same rate, whether intrauterine or extrauterine. Conduction velocities are directly related to gestational and postconceptual age, and are unrelated to birth weight (12,13). Conduction velocities increase in direct proportion to the increase in diameter of fibers during growth. A direct rela­tionship also exists between the diameter of the axon and the thickness of the myelin sheath. The diameter of the fibers at the time of birth has been shown to be one-half of that in the adult. No unusual acceler­ation of myelination occurs subsequent to birth (14). Peripheral fibers reach their maximum diameter at 2-5 years after birth (14,15). The nodes of Ranvier con­tinue to remodel, with peak internodal distances being reached at 5 years of age.

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