How do we perceive tastes and smells? How are taste and smell connected to communication?
Peggy and David seek out a connection between our senses of taste and smell.
Have you ever wondered why food loses its flavor when you have a cold? It's not your taste buds' fault. Blame your stuffed-up nose. Seventy to seventy-five percent of what we perceive as taste actually comes from our sense of smell. Taste buds allow us to perceive only bitter, salty, sweet, and sour flavors. It's the odor molecules from food that give us most of our taste sensation.
When you put food in your mouth, odor molecules from that food travel through the passage between your nose and mouth to olfactory receptor cells at the top of your nasal cavity, just beneath the brain and behind the bridge of the nose. If mucus in your nasal passages becomes too thick, air and odor molecules can't reach your olfactory receptor cells. Thus, your brain receives no signal identifying the odor, and everything you eat tastes much the same. You can feel the texture and temperature of the food, but no messengers can tell your brain, "This cool, milky substance is chocolate ice cream." The odor molecules remain trapped in your mouth. The pathway has been blocked off to those powerful perceivers of smell--the olfactory bulbs.
Of all our senses, smell is our most primal. Animals need the sense of smell to survive. Although a blind rat might survive, a rat without its sense of smell can't mate or find food. For humans, the sense of smell communicates many of the pleasures in life--the aroma of a pot roast in the oven, fresh-cut hay, a rose garden. Smells can also signal danger, fear, or dread.
Although our sense of smell is our most primal, it is also very complex. To identify the smell of a rose, the brain analyzes over 300 odor molecules. The average person can discriminate between 4,000 to 10,000 different odor molecules. Much is unknown about exactly how we detect and discriminate between various odors. But researchers have discovered that an odor can only be detected in liquid form. We breathe in airborne molecules that travel to and combine with receptors in nasal cells. The cilia, hairlike receptors that extend from cells inside the nose, are covered with a thin, clear mucus that dissolves odor molecules not already in vapor form. When the mucus becomes too thick, it can no longer dissolve the molecules.
Animals depend on odors secreted from their bodies to communicate. For humans, odors communicate a variety of messages, depending on the odor and the person receiving it. The aroma of a baking apple pie sends one message when someone is hungry and quite another when that person has just finished a six-course meal!
Additional sources of information
Test your classmates' senses of taste and smell to find out which sends the clearest message to the brain.
Recapture a "smell" memory. Put a number of different, fragrant items in separate paper bags--a pine bough, broken cinnamon sticks, mothballs, a cloth sprinkled with baby powder, lemons. Sniff each bag until one brings a strong memory to mind. Write about this memory.
Create a survey to identify the favorite smells and tastes of your friends. Conduct your survey and display the results on a graph. Which smells and tastes were most popular? Now place your results in a Venn diagram. Do you see any overlap between favorite smells and favorite tastes?
Can you tell the difference between an apple and a potato by using only the sense of taste? Cut an apple and a potato into the same size pieces. Close your eyes, plug your nose, and lick one of the pieces. Can you tell what it is? Next, unplug your nose and eat the piece. Can you identify it now?
Animals and insects use smells to send messages. Cats and dogs, for example, put their own personal smell stamp on objects to communicate the message "no trespassing." Ants lay down odor trails to mark the pathway to food. The monarch butterfly and ladybug produce odors that say, "I don't taste as good as I look." Research an animal by reading and thinking about how it uses smell to communicate.
Newton's Apple is a production of KTCA Twin Cities Public Television.
Made possible by a grant from 3M.
Educational materials developed with the National Science Teachers Association.