Morphology of the human olfactory epithelium.

The human olfactory epithelium has been previously studied with scanning electron microscopy; however, most studies have been limited to examining the epithelial surface. In an attempt to examine structures below the surface, we scanned epithelial fractures that occurred during tissue preparation. This made it possible to obtain unique three-dimensional images of cell profiles from the mucosal surface through the full depth of the epithelium. We examined supporting cells, olfactory neurons, basal cells, and a fourth cell type, the microvillar cell. Supporting cells had a microvillar surface and were in close contact with olfactory neurons and their processes. Olfactory neurons were primarily located in the middle and lower epithelial regions. Basal cells occurred alone or in clusters adjacent to the basal lamina. Microvillar cells were always observed in the upper epithelial region. They were flask- or pear-shaped, had a tuft of microvilli that extended into the nasal cavity, and a thin axon-like process that passed basally towards the lamina propria. This study represents the first comprehensive scanning electron microscopy examination of the human olfactory epithelium. Three-dimensional images obtained for each epithelial cell type allowed us to examine cell processes and their close contacts, especially between supporting cells and olfactory neurons. These results also revealed the irregular and patchy distribution of olfactory receptors within the human nasal cavity. Further studies that examine the detailed morphology of the human olfactory epithelium should provide a better understanding of the physiological mechanism and clinical disorders that affect olfactory function in humans.