Section V. THE SPECIAL SENSE OF TASTE (GUSTATION)
When a substance is put in the mouth, the substance is exposed to tiny receptors
in the taste buds. Each person has about 10,000 taste buds. Most of the taste buds
are on the surface of the tongue, but some are on the roof of the mouth and some are in
the throat. We seem to taste many substances, but actually there are only four primary
taste sensations: sour, salt, bitter, and sweet. Other tastes such as chocolate, pepper,
and coffee are combinations of these four tastes changed by olfactory sensations. If
you have a cold or an allergy, you may feel that you cannot taste your food. What is
happening is that your taste sensations are operating correctly, but your olfactory
(smell) sensations are not. Much of what we think of as taste is actually smell. The
odor from food passes upward into the nasopharynx and stimulates the olfactory
system. If the sense of smell is greatly impaired, the quality of taste can change
completely; fresh onions can taste sweet and limburger cheese taste very bland.
Receptors for the four primary tastes are located in different parts of the tongue. The
anterior tip of the tongue reacts to all four primary taste sensations, but it is more
responsive to sweet substances. Taste buds on the anterior edges of the tongue are
responsive to salty substances. Sour substance receptors are located on the lateral
margins of the tongue, and receptors for bitter substances are on the posterior
midportion of the tongue.
Figure 1-11. Organs of taste.