Freeze-fracture electron microscopy of non-myelinated nerve fibres in the human dental pulp.
Freeze-fracture replicas from the subodontoblast region gave a good three-dimensional comprehension of the structure of non-myelinated nerve fibres. Each Schwann cell ensheathed 1-15 axons with a mean diameter of 0.4 micron (0.1-1.2 micron). Many axons were not entirely ensheathed but were exposed to the extracellular space to various degrees. Tightening membrane specializations were not found in the mesaxons. The Schwann-cell plasmalemma exhibited caveolae with necks surrounded by evenly-sized intramembranous particles, typical of endocytosis. The nuclear envelope of Schwann cells showed a few typical pores and perinuclear cisterna. In tangential fractures, the axolemma displayed intramembranous particles evenly distributed over the axolemmal fracture planes. There was a marked difference in particle density between the P (600-650/micron2) and E (150-200/micron2) faces.
D000293:Adolescent; D000328:Adult; D001369:Axons / Q000648:ultrastructure; D001641:Bicuspid / Q000294:innervation; D003782:Dental Pulp / Q000294:innervation* / Q000648:ultrastructure; D005614:Freeze Fracturing; D006801:Humans; D008854:Microscopy, Electron; D008963:Molar / Q000294:innervation; D009186:Myelin Sheath / Q000502:physiology; D009412:Nerve Fibers / Q000648:ultrastructure*; D012583:Schwann Cells / Q000648:ultrastructure