chemoreceptor
n. a sensory nerve ending, such as any of those in the taste buds or olfactory epithelium, that is capable of reacting to certain chemical stimuli. The chemical molecule or electrolyte generally must be in a solution to be detected by the chemoreceptors for taste; it must be volatile to be detected by those involved in smell. In humans, there are hundreds of different taste receptor proteins and a total of about 300,000 taste cells, with some taste receptors reacting only to certain stimuli, such as those producing a bitter taste. Humans also have about 1,000 types of olfactory receptors and about 1,000 receptors of each type, giving a total of one million olfactory receptors; other mammals (e.g., dogs) may have ten times that number. The relation between specific olfactory stimuli and particular olfactory receptors is still being debated.