DEVELOPMENT OF CUTANEOUS INNERVATION IN THE CHICK - ULTRASTRUCTURAL AND QUANTITATIVE-ANALYSIS

  • 1 January 1979
    • journal article
    • research article
    • Vol. 68  (1) , 1-16
Abstract
In the chick, at the thoracic level, the dorsal branches of spinal nerves form at 4 days of incubation (stage 25) and reach the skin from 5 1/2-6 days (stages 28-29). At 6 days, the growing nervous peripheral processes, axons, form large bundles (200-1000 fibers). At 10 days, young Schwann cells divide the bundles into groups of axons. The perineurium and endoneurium differentiate from 10-14 days (but epineurium is formed after hatching). At 14 days of incubation, the adult pattern of cutaneous innervation is established. At this same stage, myelogenesis begins but develops mainly after hatching:1% of the axons is myelinated at 16 days of incubation, 4% at hatching, 40% in 6-wk old chickens and 60% in adults. Less than 10% of myelinated axons of the adult are already myelinated at hatching. Two modes of myelogenesis were observed: early myelination, starting in the embryo around axons measuring about 1 .mu.m in diameter and delayed myelination, occurring in the older chickens after an increase in axon diameter. Evidently there is, in the development of chick skin innervation, a critical stage (14-15 days of incubation) apparently corresponding to the stabilization of cutaneous nerve supply.

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