Audrey O'Brien, age 14, of Carson City, Nev., for her question:
HOW DOES THE SENSE OF TASTE WORK?
Taste is an important sense. The taste of foods helps determine what and how much we eat. The sense of taste is sent from the mouth to the brain through taste buds which are located in the tongue.
Taste buds are actually grouped on the tongue into small mounds called papillae. The papillae on the front part of the tongue have their taste buds .connected to one nerve. The papillae on the edges of the tongue about halfway between front and back and those at the back of the tongue are connected to a second nerve.
When we take food into our mouth, the taste buds transmit information about the chemicals in the food to the nerves. The nerves may respond differently to the same chemicals in the food.
Small amounts of some chemicals are more easily tasted on the front of the tongue and others are more easily tasted on the back or sides of the tongue. The taste of still other chemicals changes little over the entire tongue.
The nerves from the papillae come together at the back part of the brain stem. Here, some taste signals carried by the nerves are separated according to the different chemicals they respond to.
The taste signals then travel to the front of the brain stem, the thalamus. From the thalamus, the signals move to the cerebral cortex of the brain. Here, the signals are interpreted and we become aware of taste.
The receptor cells that make up the taste buds are continually being replaced. The receptor cells develop from skin cells that surround the taste buds. The skin cells slowly move into the area of the taste buds. As the skin cells move, they turn into receptor cells. About half the receptor cells are replaced every 10 days.
Many people believe that there are four kinds of taste: salt, sour, sweet and bitter. But the receptor cells that make up our taste buds do not have structural or functional differences that correspond to these tastes.
The idea of the four categories of taste seems to be something that is learned. Taste categories may be only easily identified characteristic of taste. They tell us little about how the taste sense functions.
People may reject foods whose taste they dislike and so not have a proper diet.
Our sense of flavor is affected also by how things smell. When we have a cold and a stopped up nose, some foods may taste alike.
Food must be moist to be tasted. If the tongue and food are dry, there is no taste.
Generally we taste and smell food at the same time. Thus, we have come to think of the two senses as being related. But they are, in fact, separate. Only at some point in the brain are the separate senses combined.