4.6 - The Chemical Senses

Abstract

This chapter describes the olfactory receptors and chemical senses. The chemical senses include the sense of taste and smell. Both detect foreign chemicals when they interact with receptors at surfaces of the body. Smell detects volatile chemicals in the inhaled air, and taste detects dissolved chemicals in food and drink. Olfactory receptor cells have long cilia that protrude into a mucus layer that is secreted by Bowman's glands in the olfactory epithelium. Odorant binding proteins on the cilia membrane bind odorants and couple to a G s protein that stimulates adenylyl cyclase and increases cyclic adenosine monophosphate in the olfactory cells. Taste receptors are located in taste buds—conglomerates of about 50–100 cells—on taste papillae on the tongue and elsewhere in the pharynx and palate. The facial nerve innervates the front of the tongue, the glossopharyngeal innervates the back of the tongue, and the vagus nerve innervates the palate, pharynx, and epiglottis. Sour taste detects the receptor cell's intracellular [H + ] and this is coupled to Ca 2+ entry that releases neurotransmitter onto the afferent sensory nerve. It is found that the increase in cytosolic [Ca 2+ ] activates a transient receptor protein that increases Na + influx thereby, depolarizing the taste receptor cells.