This is the 2007 version. Click here for the 2017 chapter 04 table of contents.

Gustation

Gustation is usually called the sense of taste, despite the fact that olfaction dominates our ability to taste foods and liquids. Taste cells are gathered together in taste buds on the tongue, and taste buds are hidden in bumps on the tongue called papillae.


There are many taste cells in each bud, and each bud is inside a pore between the papillae

Which sense dominates the taste of foods? What are taste cells, buds, and papillae?

Look closely at your tongue. You will see many small bumps. These are not taste buds; they are papillae (papilla is the singular). Taste buds are hidden in pores in the papillae. There are about 10,000 taste buds on the tongue, each with 10 to 20 taste cells that look like the sections of an orange. Taste cells are the actual receptors for taste. They are constantly rebuilt and replaced within the taste bud. Every seven days you get a new set of taste cells. If you burn your tongue on a hot drink, your gustatory ability will return in a week or less.

Why must a substance be dissolved in water, to be tasted?

Substances enter the taste buds through small pores on the papillae. For a substance to reach the receptors, it must dissolve in water so it can wash through the pores. In a classic chemistry class demonstration, a teacher calls a hapless student to the front of the room, dries off his or her tongue, and deposits a small mound of salt on it. The student can taste nothing. Only substances dissolved in water (or saliva, which is mostly water) can be tasted. Some substances such as glass and most metals do not dissolve in water at all, and they cannot be tasted.

What are the four classic taste qualities?

Taste cells are chemoreceptors. They respond to chemical substances. The four classical taste qualities are sour (e.g. vinegar), saline (e.g. salt water), sweet (e.g. sugar) and bitter (e.g. quinine). The tastes have different functions. "Sweetness, for example, means that a food has high caloric value, while bitterness tells us that it is a poison" (Barinaga, 2000).

What is the fifth basic taste, and what does it indicate to animals?

The Japanese researcher Kikunae Ikeda discovered a fifth basic taste. He calls it umami. This is the taste caused by a receptor for the transmitter glutamate (Mirsky, 2000). Umami is a taste characteristic of high-protein foods, and animals seek it out. Sensitivity to umami is enhanced by the food additive monosodium glutamate (MSG).


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