The<unk>  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<unk>  is the part of the<unk>  system directly responsible for detecting odors.<unk>  consists of three distinct types of cells:<unk>  cells, supporting cells, and basal cells
The<unk>  cells of the<unk>  are bipolar neurons which congregate to form the<unk>  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<unk>  function as metabolic and physical support for the<unk>  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<unk>  epithelial cells.
Resting on the basal lamina of the<unk> , basal cells are stem cells capable of division and differentiation into either supporting or<unk>  cells.  The constant divisions of the basal cells leads to the<unk>  being replaced every 2-4 weeks.
The<unk>  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<unk>  can be temporary but in extreme cases, injury can be permanent, leading to anosmia.
Olfactory epithelium
Vomeronasal organ
Cochlear nuclei
Olivary body
Olfactory bulb
Optic stalk
Olfactory receptor neuron
Fundic glands