title: Observations on the morphology at the transition between the peripheral and the central nervous system in the cat. IV. Unmyelinated fibres in S1 dorsal rootlets.
abstract: Unmyelinated (d.r.C) fibres have been investigated electronmicroscopically at their passage from the peripheral to the central nervous system in feline S1 dorsal rootlets. The earlier demonstrated rearrangement of C-fibres during their passage along the transitional region (TR) was confirmed by the observation of extensive fibre divergence. The transitional region Schwann cells was calculated to be 10-20 times as high in the TR as in the more distal parts of the rootlets. Analysis of consecutive ultra-thin sections showed that PNS unmyelinated axons 0.8 micrometer or more acquired a myelin sheath as they entered the CNS. Fibres 0.6-0.8 micrometer in diameter appeared to be segmentally myelinated in the CNS. Fibres less than 0.6 micrometer remained unmyelinated at their CNS entrance. A few fibres showed degenerative signs and terminated in the transitional region.
mesh_terms: D000818:Animals; D002415:Cats; D009186:Myelin Sheath / Q000648:ultrastructure; D009412:Nerve Fibers / Q000648:ultrastructure*; D010525:Peripheral Nerves / Q000648:ultrastructure*; D012583:Schwann Cells / Q000648:ultrastructure; D013126:Spinal Nerve Roots / Q000648:ultrastructure*