The specialized olfactory epithelial cells characterize the only group of neurons capable of regeneration. Activation occurs when odiferous molecules come in contact with specialized processes known as the olfactory vesicles. Within the nasal cavity, the turbinates or nasal conchae serve to direct the inspired air toward the olfactory epithelium in the upper posterior region. These specialized epithelial cells give rise to the olfactory vesicles containing kinocilia, which serve as sites of stimulus transduction. The olfactory epithelium consists of 3 cell types including basal, supporting, and olfactory receptor cells.
Basal cells are stem cells that give rise to the olfactory receptor cells.
The continuous turnover and new supply of these neurons is unique to the olfactory system. No other location in the mature nervous system exists wherein less differentiated stem cells replace neurons. Supporting cells are scattered among the receptor cells and have numerous microvilli and secretory granules, which empty their contents onto the mucosal surface. The receptor cells are actually bipolar neurons, each possessing a thin dendritic rod that contains specialized cilia extending from the olfactory vesicle and a long central process that forms the fila olfactoria. The cilia provide the transduction surface for odorous stimuli.