Olfactory epithelium

Overview
The olfactory epithelium is a specialized epithelial tissue inside the nasal cavity that is involved in smell. In humans, it measures about 1 inch wide by 2 inches long (about 2 cm by 5 cm) and lies on the roof of the nasal cavity about 3 inches (about 7 cm) above and behind the nostrils. The olfactory epithelium is the part of the olfactory system directly responsible for detecting odors.

Olfactory epithelium consists of three distinct types of cells: Olfactory cells, supporting cells, and basal cells

The olfactory cells of the epithelium are bipolar neurons which congregate to form the olfactory nerve (cranial nerve I). The apical poles of these neurons are ciliated and coated with a serous secretion from Bowman's glands located in the lamina propria.

Analogous to neural glial cells, the supporting cells of the olfactory epithelium function as metabolic and physical support for the olfactory cells. Histologically, the supporting cells are tall columnar cells featuring microvilli and a prominent terminal web. The nuclei of supporting cells are more apically located than those of the other olfactory epithelial cells.

Resting on the basal lamina of the olfactory epithelium, basal cells are stem cells capable of division and differentiation into either supporting or olfactory cells. The constant divisions of the basal cells leads to the olfactory epithelium being replaced every 2-4 weeks.

The olfactory epithelium can be damaged by inhalation of toxic fumes, physical injury to the interior of the nose, and possibly by the use of some nasal sprays. Because of its regenerative capacity, damage to the olfactory epithelium can be temporary but in extreme cases, injury can be permanent, leading to anosmia.