Each food contains many chemicals, which are able to activate a range of taste receptors, thereby providing the unique experiences of taste. Of course the sensory organs of taste are found in the mouth, and include the tongue, palate, pharynx and epiglottis. The tip of the tongue is particularly sensitive to sweetness, the sides to saltiness and sourness, and the back of the tongue to bitterness. The sensory elements are papillae, which are small projections containing the taste buds. Taste buds contain the taste receptor cells, which sense the presence of chemicals in the mouth.
Afferent axons relay the information to the brain via the cranial nerves.
The taste cells are not really neurons, but do synapse upon the axons that relay information to the brain. Some taste receptors directly activate ion channels, while others are similar to G protein-coupled receptors in structure. For example, small molecules such as NaCl and HCl can directly pass through ion channels. Increases in sodium concentrations can lead to increased sodium conductance through an amiloride-sensitive sodium channel. Other chemicals may activate or block ion channels directly, or bind to receptors similar to G protein-coupled receptors.