ABSTRACT
The sense of taste, gustation, provides a means of avoiding potentially noxious foodstuffs or selecting for foods which have a high energy content. Classically, four tastes are described, salty, sour, sweet and bitter, on the basis that no cross-adaptation occurs between them. A fifth taste, umami, produced by monosodium glutamate, is now recognised. Plant alkaloids, some of which are toxic in high concentrations, are extremely bitter. Taste buds are located in the epithelium of the tongue, palate, pharynx, epiglottis and the upper part of the esophagus. Many of the ions or molecules responsible for taste sensation are hydrophilic and freely diffusible. Those which are hydrophobic include plant alkaloids which may bind to proteins in the saliva, equivalent to odorant binding proteins, for presentation to gustatory receptor cells. Transduction involves changes in membrane conductance which causes a depolarizing generator potential, triggering action potentials, calcium influx and so neurotransmitter release.
