Different stimuli activate different sensory receptors. Chemical stimuli activate the chemoreceptors responsible for gustatory and olfactory perceptions. Because taste and smell are both reactions to the chemical makeup of solutions, the two senses are closely related. If you've ever had a cold during Thanksgiving dinner, you know that all of the subtlety of taste is lost without smell. In some species, however, the two chemical senses are practically one.
Invertebrates like worms do not have distinctions between gustatory and olfactory receptors. They instead differentiate between volatile and nonvolatile chemicals. In humans, the chemoreceptors that detect taste are called gustatory receptor cells. About 50 receptor cells, plus basal and supporting cells, make up one taste bud. Taste buds themselves are contained in goblet-shaped papillae -- the small bumps that dot your tongue.
Some papillae help create friction between the tongue and food. Every gustatory receptor cell has a spindly protrusion called a gustatory hair. This taste hair reaches the outside environment through an opening called a taste pore. Molecules mix with saliva, enter the taste pore and interact with the gustatory hairs. This stimulates the sensation of taste. Once a stimulus activates the gustatory impulse, receptor cells synapse with neurons and pass on electrical impulses to the gustatory area of the cerebral cortex.
The brain interprets the sensations as taste. In the next section, we'll learn about the primary tastes and how taste gives us clues about what we eat. When food scientists manipulate taste sensation, they use chemical compounds to block or stimulate taste receptor cells.
Senomyx states that its flavor enhancers and taste modulators will allow companies to "improve the nutritional profile" of packaged foods and beverages by cutting back on sugar, salt and MSG without compromising flavor [source: Senomyx ]. Until recently, scientists have accepted four basic tastes. You know them well -- sweet , salty , sour and bitter.
They are the building blocks of flavor and at the root of other tastes. Each primary taste triggers a particular gustatory receptor although receptors can, and frequently do, respond to multiple tastes.
The basic tastes went unchallenged for years, perhaps because of their familiarity -- name another taste that is as distinctive as one of the four. In the early s, however, a Japanese scientist sought to detect another taste -- that of the savory seaweed common in Japanese cooking.
Kikunae Ikeda eventually isolated glutamic acid as a distinct fifth taste -- one with its very own gustatory receptor.
Ikeda named this fifth taste umami , a Japanese word meaning delicious, savory taste. You can taste umami in meats and tomatoes. Researchers continued to study umami throughout the 20th century. An important breakthrough came in when scientists trying to mimic the controversial, flavor-enhancing substance MSG failed to replicate the taste with any combination of the basic four. But because Ikeda's study on taste was not translated into English until and because the taste of glutamic acid is subtle and less common in Western food , umami has only recently entered the taste canon.
Now that the gate is open, however, it's unlikely that scientists will ever be so secure in the limits of primary taste.
French researchers even identified a potential gustatory receptor for fat. Fat could actually be the sixth taste. The primary tastes gave early humans clues about what food was good to eat and what was harmful. Sweet foods usually had calories. Researchers are examining stem cells and how they transform into the neurons that mediate smell or taste, to better understand these senses.
They may find stem cell-based therapies to help restore taste or smell. You may notice the relationship between taste and smell when a cold stuffs up your nose and everything tastes bland. It seems like taste no longer works.
Taste and smell information appear to converge in several central brain regions. There are also neurons in the inferior frontal lobe that respond selectively to specific taste and smell combinations. Taste sense itself is rather crude, distinguishing only five basic taste qualities.
Our sense of smell adds great complexity to the flavors we perceive. Studies have found exposing people to matching combinations of familiar tastes and smells enhances their taste perceptions. Sugar tastes very sweet combined with the smell of strawberries and less sweet when paired with the smell of peanut butter or no odor.
Our chemical receptors, along with the brain networks that process taste and smell, give us access to the wonderful array of scents and flavors in our world. This article was adapted from the 8th edition of Brain Facts by Marissa Fessenden. Sandra Blumenrath Sandra H. Sandra lives in Silver Spring, Maryland, with her husband, daughter, and a tank full of fish.
A beginner's guide to the brain and nervous system. Viana, F. Chemosensory Properties of the Trigeminal System. ACS Chem Neurosci. Your Privacy Rights. To change or withdraw your consent choices for VerywellHealth.
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For example, vegetables in the Brussels sprouts family contain a substance called goitrin that is strongly bitter and disgusting to some people, but other people can barely taste it. Why is this? One reason is that different people have different numbers of taste buds [ 1 ]. Each taste bud cell adds a little bit to the strength of a taste, so people with more taste buds are more sensitive. This holds true for all tastes, not just bitter. Scientists even have names for people with different sensitivity levels.
What about your friends? Researchers around the world investigate the process of taste because taste affects what people eat, and what people eat affects their health [ 1 ]. There is even some taste research you can do in your own kitchen.
One theory you can investigate is that taste sensitivity is laid out like a map on your tongue. For many, many years, books have taught us that salty and sweet tastes are sensed at the tip of the tongue, while bitter is sensed at the back and sour at the sides Box 1 , figure.
The center of the tongue, which has few taste buds, is often left blank. However, taste researchers now believe that taste sensitivity does not follow a simple map. They say tastes can be perceived everywhere on the tongue. Try testing yourself using the experiment in the Do-it-Yourself Box 1. How well does taste sensitivity on your own tongue fit the map? Many books and magazines say taste sensitivity follows a map on your tongue: the front is for salty and sweet, the back is for bitter, and sour is at the sides figure.
Savory, which is a more recent discovery, is usually left out. This experiment will test the sensitivity of different regions of your tongue to sweet, sour, and salty tastes, so you can compare your own patterns with the map. Stir each glass well, rinsing the spoon between solutions. Dip a Q-Tip in the salt solution and dab it on the back of your tongue.
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