Taste buds are present on fungiform, foliate, and circumvallate papillae.
In histologic sections, taste buds appear as oval, pale-staining bodies that extend through the thickness of the epithelium (Fig. 16.5). A small opening onto the epithelial surface at the apex of the taste bud is called the taste pore.
Three principal cell types are found in taste buds:  Neuroepithelial (sensory) cells are the most numerous cells in the taste bud. These elongated cells extend from the basal lamina of the epithelium to the taste pore, through which the tapered apical surface of each cell extends microvilli (see Fig. 16.5). Near their apical surface they are connected to neighboring neuroepithelial or supporting cells by tight junctions. At their base they form a synapse with the processes of afferent sensory neurons of the facial (cranial nerve VII), glossopharyngeal (cranial nerve IX), or vagus (cranial nerve X) nerves. The turnover time of neuroepithelial cells is about 10 days.
 Supporting cells are less numerous. They are also elongated cells that extend from the basal lamina to the taste pore. Like neuroepithelial cells, they contain microvilli on
FIGURE 16.5 • Diagram and photomicrograph of a taste bud. a. This diagram of a taste bud shows the neuroepithelial (sensory), supporting, and basal cells. One of the basal cells is shown in the process of dividing. Nerve fibers have synapses with the neuroepithelial cells. (Based on Warwick R, Williams PL, eds. Gray’s Anatomy, 35th ed. Edinburgh: Churchill Livingstone, 1973.) b. This high-magnification photomicrograph shows the organization of the cells within the taste bud. The sensory and supporting cells extend through the full length of the taste bud. The apical surface of these cells contains microvilli. The basal cells are located at the bottom of the taste bud. Note that the taste bud opens at the surface by means of a taste pore. 640.
their apical surface and possess tight junctions, but they do not synapse with the nerve cells. The turnover time of sup porting cells is also about 10 days. Basal cells are small cells located in the basal portion of the taste bud, near the basal lamina. They are the stem cells for the two other cell types.
In addition to those associated with the papillae, taste buds are also present on the glossopalatine arch, the soft palate, the posterior surface of the epiglottis, and the posterior wall of the pharynx down to the level of the cricoid cartilage.
Taste is a chemical sensation in which various chemicals elicit stimuli from neuroepithelial cells of taste buds.
Taste is characterized as a chemical sensation in which various tastants (taste-stimulating substances) contained in food or beverages interact with taste receptors located at the apical surface of the neuroepithelial cells. These cells react to five basic stimuli: sweet, salty, bitter, sour, and umami [Jap. delicious]. The molecular action of tastants can involve opening and passing through ion channels (i.e., salt and sour), closing ion channels (sour), or acting on a specific taste G protein–coupled receptors (i.e., bitter, sweet, and umami).
Stimulation of bitter, sweet, and umami receptors activates G protein–coupled taste receptors that belong to T1R and T2R chemosensory receptors families.
Bitter, sweet, and umami tastes are detected by a variety of receptor proteins encoded by the two taste receptor genes (T1R and T2R). Their products are all characterized as being G protein–coupled taste receptors.