Anatomy and physiology of taste and smell

The specialized chemosensory systems of taste and smell are mediated by chemically sensitive receptors that are in a continual state of turnover and regeneration. Both systems project into the central nervous system and connect with sensory and limbic areas of the forebrain. Much has been learned recently about the nature of gustatory and olfactory transduction. Simple ion channels in gustatory cells and membrane receptors coupled to second messenger cascades in taste and olfactory receptors are involved in transducing chemical signals into neural activity. Gustatory receptors and higher-order neurons appear to be responsive to chemicals representing more than one taste quality, although their profiles of sensitivity suggest functional groups of cells. Olfactory neurons are also sensitive to a range of stimulus qualities. Recent work suggests that olfactory receptors may be encoded by a family of genes related to neurotransmitter and hormone receptors.