Fine structure of unmyelinated nerves in neonatal skin.

The fine structure of unmyelinated cutaneous nerve fibers in newborns was examined in lesions of adnexal polyp of neonatal skin. In the neonatal cutaneous nerves, unmyelinated fibers outnumbered myelinated ones. The unmyelinated fibers consisted of Schwann cells, axons and basal lamina. Their ultrastructural organization was basically similar to that in the adult skin. However, some of the unmyelinated fibers contained axonal bundles which suggested a state of cytoarchitectual immaturity or incomplete growth. Phagocytosis of melanosomes by Schwann cells was also observed.