Olfactory epithelium

Recommended video: Olfactory nerve [16:16]

Course of the olfactory nerve viewed from the left side of a parasagittal section.

The olfactory epithelium is a type of pseudostratified columnar epithelium involved in sensing smell. It lines the olfactory cleft of the nasal cavity and forms one of the major components of the olfactory mucosa, with the other being the lamina propria. 

The olfactory epithelium is approximately 60μm thick and lies external to the lamina propria of the olfactory mucosa. It is highly disorganized and is composed of three main cell types:

• basal cells
• non-neuronal supporting cells
• olfactory cells

The olfactory cells, or more specifically the olfactory sensory neurons (olfactory receptor cells) are regarded as the most important cell type as they are directly involved with transmitting olfactory information centrally. The apical end of these cells are covered in long and short microvilli which function to trap odor molecules as they travel through the nasal cavity and therefore contribute to the perception of smell. The olfactory sensory neuron, a bipolar cell, gives rise to an unmyelinated axon, which congregates with similar axons to form the olfactory nerve (CN I). It is surrounded and supported by the non-neuronal supporting cells of the olfactory epithelium.

Non-neuronal supporting cells are analogous to neural glial cells and function as metabolic and physical support for the olfactory sensory neurons. This group of cells also act as epithelial cells and function to create a barrier from the external environment.

Basal cells support lifelong renewal of the olfactory epithelium and are divided into globose basal cells (reserve and active progenitors) and horizontal basal cells (reserve, activated by injury). Basal cells are stem and progenitor cells which can be differentiated into olfactory sensory neurons. This group of cells, therefore allow for the olfactory epithelium to be replaced and regenerated every 2-4 weeks.