Susan Filsner, age 12, of St. Laurent, Que., Can., for her question:

How do the taste buds work?

Sugar is sweet and sea water is salty. Baby green apples are sour and often the medicines that do us the most good are bitter. These four major tastes are detected by the taste buds  and blended in various ways to add hundreds of different flavors to our foods. The little taste buds must be moist to gather their information and send it along through the nervous system to be interpreted by the brain.

The taste buds are small wads of sensitive cells called receptors. Naturally, they are located inside the mouth, where they can report on each bite of food before we swallow it. Actually the receptors do no more than react to certain chemicals in our foods. The rest is done by the nervous system with final analysis by the brain.

The nervous system uses electrochemical energy to flash messages through the body. To do this, the nerve cells and their long connecting threads must be moist at all times. The taste buds are at nerve endings and they, too, must be moist in order to relay their reactions to this or that food chemical. As a rule, this is no problem because the inside of the mouth is always damp with saliva.

Several groups of taste buds are located on the tongue, others in the cheeks and roof of the mouth. Some experts suspect that certain groups specialize in one of four basic flavors  sweet or sour, salty or bitter. However, many groups seem able to detect blended mixtures.

The tip of the tongue can report the taste of honey in a split second. Certainly the receptors in this group specialize in sweet flavors. Groups along the sides of the tongue report on salty flavors. Sour flavors are detected by groups farther back along the sides of the tongue. A V shape group toward the back of the tongue seems to specialize in bitter flavors.

However, the taste buds in the cheeks and in the roof of the mouth seem able to detect blended flavors. Maybe these groups include some of the four basic flavors. Or maybe some are sensitive enough to detect and blend several tastes into subtle flavors.    .

In any case, the moist taste buds relay their reactions along nerves to the brain. Toward the back of the brain, the various flavors are sorted out. These signals are sent to a taste interpretation center near the front of the brain.

Sensitive smelling cells in the nose add their information to the taste bud reports that go to the brain. There all this information is sorted, blended and interpreted to give us hundreds of different flavors.