FIGURE 19.4 • Diagram of olfactory transduction pathway. This diagram shows interactions of the odorant molecules with proteins associated with olfactory receptor cell. Incoming in inhaled air odorant molecules are solubilized in the olfactory mucus and bind to olfactory binding proteins, which deliver them to the olfactory receptors. Note that different odorant molecules bind with different affinity to the olfactory receptors. Strong signal (see green G protein–coupled olfactory receptor) is produced by high affinity binding where odorant molecule (green) matches perfectly the binging site on the receptor. Other olfactory receptors (yellow and pink) show less affinity binding, thus producing weaker signals. Stimulated by odorant molecules olfactory receptors activate enzyme adenylyl cyclase and initiate the cAMP cascade of evens leading to opening of specific Na and Ca2channels. Influx of Na and Ca2 is responsible for cell depolarization. Generated action potential travels on axons of olfactory receptor cells from nasal cavity passing through the ethmoid bone and surrounding brain coverings to the olfactory bulb of the brain.
processes in some basal cells that partially ensheathe the first portion of the olfactory receptor cell axon. They thus maintain a relationship to the olfactory receptor cell even in their undifferentiated state.
Olfactory glands are a characteristic feature of the olfactory mucosa.
The olfactory glands (Bowman’s glands), a characteristic feature of the mucosa, are branched tubuloalveolar serous glands that deliver their proteinaceous secretions via ducts onto the olfactory surface (see Fig. 19.3 and Plate 69, page 688). Lipofuscin granules are prevalent in the gland cells, and in combination with the lipofuscin granules in the supporting cells of the olfactory epithelium, they give the mucosa its natural yellow-brown coloration. Short ducts composed of cuboidal cells lead from the glands and pass through the basal lamina into the olfactory epithelium, where they continue to the epithelial surface to discharge their contents.
The serous secretion of the olfactory glands serves as a trap and solvent for odoriferous substances. Constant flow from the glands rids the mucosa of remnants of detected odoriferous substances so that new scents can be continuously detected as they arise.
The identifying feature of the olfactory region of the nasal mucosa in a histologic preparation is the presence of the olfactory nerves in combination with olfactory glands in the lamina propria. The nerves are particularly conspicuous because of the relatively large diameter of the individual unmyelinated fibers that they contain (see Figs. 19.3 and 19.4).
Paranasal sinuses are air-filled spaces in the bones of the walls of the nasal cavity.
The paranasal sinuses are extensions of the respiratory region of the nasal cavity and are lined by respiratory epithelium. The sinuses are named for the bone in which they are found (i.e., the ethmoid, frontal, sphenoid, and maxillary bones). The sinuses communicate with the nasal cavities via narrow openings onto the respiratory mucosa. The mucosal surface of the sinuses is a thin, ciliated, pseudostratified columnar epithelium with numerous goblet cells. Mucus produced in the sinuses is swept into the nasal cavities by coordinated ciliary movements. The sinuses are often subject to acute infection after viral infection of the upper respiratory tract. Severe infections may require physical drainage.