Epithelium, olfactory

Oolf nasal epithelium olfactory receptor adenylyl-cyclase [ ... 

Figure 4. Segregation of zebrafish odorant receptors within the sensory surface. Outline of a horizontal cross-section through an adult olfactory epithelium. Olfactory lamellae are depicted in white. Dots and circles indicate the approximate position of olfactory receptor neurons labeled with two different zebrafish odorant receptor probes (black dots ZOR5A, circles ZOR6A). Neurons positive for ZOR6A occupy an inner domain, while neurons labeled by ZOR5A are situated more exteriorly, with occasional overlap between expression domains. Figure taken from (Korsching et al. 1997), raw data from (Weth et al. 1996).

Although the nose houses and protects the cells that perceive odor, it does not direcdy participate in odor perception. The primary function of the nose is to direct a stream of air into the respiratory passages. While this function is occurring, a small fraction of the inhaled air passes over the olfactory epithelium, located 5—8 cm inside the nasal passages. This olfactory area occupies about 6.45 cm (one square inch) of surface in each side of the nose. 

According to the chemical theory of olfaction, the mechanism by which olfaction occurs is the emittance of particles by the odorous substances. These particles are conveyed to the olfactory epithelium by convection, diffusion, or both, and dkecdy or indkectly induce chemical changes in the olfactory receptors. 

Odors are perceived via the olfactory system, which is composed of two organs in the nose the olfactory epithelium, a very small area in the nasal system, and the trigeminal nerve endings, which are much more widely distributed in the nasal cavity (11). The olfactory epithelium is extremely sensitive, and humans often sniff to bring more odorant in contact with this area. The trigeminal nerves initiate protective reflexes, such as sneezing or interruption of irrhalation, with exposure to noxious odorants. 

The epithelium covering the nasal cavity. This epithelium contains numerous cell types including the specialized olfactory sensory neurons which detect the chemical stimuli derived from smells by a specific family of G protein-coupled receptors known as olfactory receptors. 

Sensory receptors that structurally and functionally belong to the G protein coupled receptor superfamily. Olfactory receptors are a large GPCR family with >300 members in human that are expressed in neurons of the nasal olfactory epithelium where they sense mostly volatile olfactory molecule. The overall number of olfactory receptors differs widely between species and an expansion of different recqrtors is in particular obvious in species that depend on their olfactory sense for survival. 

Liberies SD, Buck LB (2006) A second class of chemosensory receptors in the olfactory epithelium. Nature 442 645-650... 

The mechanisms by which the taste (and also the olfactory) system senses chemical compounds is assumed to occur by way of a chemoreceptory system that interacts effectively with a broad, structural variety of stimulant molecules, by means of a receptor epithelium consisting of the mosaic of adjacent, peripheral membranes of many receptor cells, exposed to a medium carrying stimulus molecules. A receptor cell is conveniently and, for our present purpose, sufficiently defined as a cell equipped to interact, according to some mechanism, with stimulus molecules, to convert the effect of this interaction into a signal, and to project this signal into the system. The taste receptor is thus a differentiated, epithelial cell synaptically contact-... 

Fig. 2.7 Salamander nasal cavity TS — anterior to entry of naso-lacrimal duct. LD = lateral diverticulum NSE = non-sensory epithelium VNE = vomeronasal epithelium MOE = olfactory epithelium and RP = reflective pigment (after Dawley, 1988).

In the squamous/stratified epithelium covering, the palatal aperture of the N-P canals and the dorso-lateral surfaces of the papilla, there are occasional clusters of taste buds. These non-olfactory chemosensory elements are positioned at or near to the entrance to the AOS, suggesting that some initial chemosensation may arise from the sampling of material... 

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