11.52: Taste and Smell
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Why are your senses of taste and smell important?
Imagine you open a gallon of milk, and you suddenly smell a foul odor. Your sense of smell has informed you that the milk has spoiled. So you pour the spoiled milk down the kitchen sink. Your sense of smell has possibly kept you from getting sick!
Taste and Smell
The senses of taste and smell are more complicated than many people might think and have a surprisingly large impact on behavior, perception and overall health. Imagine your sense of smell disappearing as you age. Though this doesn't usually happen, it could provide clues about diseases of the nervous system. What about differences in taste? Do all foods taste the same to all people? Are there some foods you would never eat because you don't like the taste? Does this food taste good to other people? Genetic differences in taste could help predict what we eat, how well our metabolism works, and even whether or not we're overweight. These two senses actually work together to provide some of the basic sensations of everyday life.
Your sense of taste is controlled by sensory neurons, or nerve cells, on your tongue that sense the chemicals in food. The neurons are grouped in bundles within taste buds. Each taste bud actually has a pore that opens out to the surface of the tongue enabling molecules and ions taken into the mouth to reach the receptor cells inside. There are five different types of taste neurons on the tongue. Each type detects a different taste. The tastes are:
- Sweet, which is produced by the presence of sugars, such as the common table sugar sucrose, and a few other substances.
- Salty, which is produced primarily by the presence of sodium ions. Common salt is sodium chloride, NaCl. The use of salt can donate the sodium ion producing this taste.
- Sour, which is the taste that detects acidity. The most common food group that contains naturally sour foods is fruit, such as lemon, grape, orange, and sometimes melon. Children show a greater enjoyment of sour flavors than adults, and sour candy such as Lemon Drops, Shock Tarts and sour versions of Skittles and Starburst, is popular. Many of these candies contain citric acid.
- Bitter is an unpleasant, sharp, or disagreeable taste. Common bitter foods and beverages include coffee, unsweetened cocoa, beer (due to hops), olives, and citrus peel.
- Umami, which is a meaty or savory taste. This taste can be found in fish, shellfish, cured meats, mushrooms, cheese, tomatoes, grains, and beans.
A single taste bud contains 50–100 taste cells representing all 5 taste sensations. A stimulated taste receptor cell triggers action potentials in a nearby sensory neuron, which send messages to the brain about the taste. The brain then decides what tastes you are sensing.
Your sense of smell also involves sensory neurons that sense chemicals. The neurons are found in the nose, and they detect chemicals in the air. Unlike taste neurons, which can detect only five different tastes, the sensory neurons in the nose can detect thousands of different odors. Have you ever noticed that you lose your sense of taste when your nose is stuffed up? That’s because your sense of smell greatly affects your ability to taste food. As you eat, molecules of food chemicals enter your nose (actually your nasal cavity). You experience the taste and smell at the same time. Being able to smell as well as taste food greatly increases the number of different flavors you are able to sense. For example, you can use your sense of taste alone to learn that a food is sweet, but you have to also use your sense of smell to learn that the food tastes like strawberry cheesecake.
Specific scents are often associated with our memories of places and events. That's because scents are more novel or specific than shapes or other things you might see. So an odor similar to that of your grandmother's kitchen or pantry might be more quickly associated with your memories of that place than a similar sight, which might be more generalized.
- Sensory neurons on the tongue detect five types of tastes: sweet, salty, sour, bitter, and umami.
- Sensory neurons that sense chemicals in your nose allow you to detect smells.
Use the resources below to answer the questions that follow.
Explore More I
- The Olfactory Pathway at http://www.youtube.com/watch?v=pM7H0Wud_Y0 (0:30)
- What is the function of the olfactory cortex?
- What stimulates the olfactory sensors in the nose?
Explore More II
- Taste Centers at http://www.youtube.com/watch?v=RIXtM2u--H8 (1:12)
- What covers the surface of the tongue?
- What four types of sensors can be found on the tongue? Are these distributed evenly over the tongue?
- How does stimulation of the taste buds stimulate the salivary glands?
- What controls the sense of taste?
- What are the five tastes sensed by neurons on the tongue?
- Why is your sense of taste affected when you have a stuffy nose?