A freeze-fracture study of receptor axons and Schwann cells in the human olfactory mucosa.

Electron micrographs of freeze-fracture replicas from the human olfactory mucosa were analysed regarding the structure of the axons of the olfactory receptor cells. In the lamina propria, numerous axons were generally invested with one Schwann cell. The ensheathed axons were often found in close contact with one another. Membrane specializations were not found at these sites, nor were tightening membrane junctions observed in the mesaxons. The Schwann cell plasmalemma exhibited caveolae, whose neck was surrounded by uniformly sized intramembranous particles evenly distributed over the axolemmal fracture planes. There was a marked difference in particle density between the P face (about 850/micron 2) and the E face (about 180/micron 2).