Smell and Taste Sensory Process

Charles G. Morris , Albert A.Maisto

Smell

Although the sense of smell in humans is weaker than in most animals, it is still about 10,000 times as acure as that of taste. Like our other senses, smell undergoes adaptation, so that odors that seem strong at first gradually become less noticeable.

Most mammals, including humans, have a second sensory system devoted to the sense of smell-which some animals use for communications sexual, aggressive, or territorial signals. Receptors located in the roof of the nasal cavity detect chemicals called pheromones, which can have quite specific and powerful effects on behavior. For example, many animals, including dogs and wolves, use pheromones to mark their territory, identify sexually receptive mates, and recognize members of their group. Humans also have receptors for pheromones. Although the exact role that these receptors play in human behavior is not fully understood, recent research has shown that these receptors activate different areas of male and female brains when they are stimulated by the smell of testosterone and estrogen.

Taste

To understand taste, we must distinguish it from flavor-a complex interaction of taste and smell. Try holding your nose when you eat. You will notice that most of the food’s flavor will disappear, and you will experience only the basic taste qualities : sweet, sour, salty, and bitter. Most other tastes are derived from combinations of these.

The receptor cells for the sense of taste are housed in the taste buds, most of which are found on the tip, sides, and back of the tongue. The tip of the tongue is most sensitive to sweetness and saltiness; the back, to bitterness; and the sides, to sourness, although each are can distinguish all four qualities to some degree. Because the number of taste buds decreases with age, older people often lose interest in food-they simply cannot taste it as well as they used to.

The taste buds are embedded in the tongue’s papillae, bumps that you can see if you look at your tongue in the mirror. When we eat something, the chemical substances in the food dissolve in salive and go into the crevices between the papillae, where they come into contact with the taste receptors. The chemical interaction between food substances and the taste cells cause adjacent neurons to fire, sending a nerve impulse to the parietal lobe of the brain and to the limbic system.