Taste Bud and Its Function

Figure 53-1 shows a taste bud, which has a diameter of about 1/30 millimeter and a length of about 1/16 millimeter. The taste bud is composed of about 50 modified epithelial cells, some of which are supporting cells called sustentacular cells and others of which are taste cells. The taste cells are continually being replaced by mitotic division of surrounding epithelial cells, so that some taste cells are young cells. Others are mature cells that lie toward the center of the bud; these soon break up and dissolve. The life span of each taste cell

Figure 53-1

Taste bud.

Figure 53-1

Taste bud.

is about 10 days in lower mammals but is unknown for humans.

The outer tips of the taste cells are arranged around a minute taste pore, shown in Figure 53-1. From the tip of each taste cell, several microvilli, or taste hairs, protrude outward into the taste pore to approach the cavity of the mouth. These microvilli provide the receptor surface for taste.

Interwoven around the bodies of the taste cells is a branching terminal network of taste nerve fibers that are stimulated by the taste receptor cells. Some of these fibers invaginate into folds of the taste cell membranes. Many vesicles form beneath the cell membrane near the fibers. It is believed that these vesicles contain a neurotransmitter substance that is released through the cell membrane to excite the nerve fiber endings in response to taste stimulation.

Location of the Taste Buds. The taste buds are found on three types of papillae of the tongue, as follows: (1) A large number of taste buds are on the walls of the troughs that surround the circumvallate papillae, which form a V line on the surface of the posterior tongue. (2) Moderate numbers of taste buds are on the fungiform papillae over the flat anterior surface of the tongue. (3) Moderate numbers are on the foliate papillae located in the folds along the lateral surfaces of the tongue. Additional taste buds are located on the palate, and a few are found on the tonsillar pillars, on the epiglottis, and even in the proximal esophagus. Adults have 3000 to 10,000 taste buds, and children have a few more. Beyond the age of 45 years, many taste buds degenerate, causing the taste sensation to become progressively less critical in old age.

Specificity of Taste Buds for a Primary Taste Stimulus. Micro-electrode studies from single taste buds show that each taste bud usually responds mostly to one of the five primary taste stimuli when the taste substance is in low concentration. But at high concentration, most buds can be excited by two or more of the primary taste stimuli, as well as by a few other taste stimuli that do not fit into the "primary" categories.

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Essentials of Human Physiology

Essentials of Human Physiology

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