Taste is one of the five senses (the others being smell, touch, vision, and hearing) through which all animals interpret the world around them. Specifically, taste is the sense for determining the flavor of food and other substances. One of the two chemical senses (the other being smell), taste is stimulated through the contact of certain chemicals in substances with clusters of taste bud cells found primarily on the tongue. However, taste is a complex sensing mechanism that is also influenced by the smell and texture of substances. An individual's unique sense of taste is partially inherited, but factors such as culture and familiarity can help determine why one person's favorite food made be hot and spicy while another just can't get enough chocolate.
The primary organ for tasting is the mouth. Clusters of cells called taste buds (because under the microscope they look similar to plant buds) cover the tongue and are also found to a lesser extent on the cheek, throat, and the roof of the mouth. First discovered in the 19th century by German scientists Georg Meissner and Rudolf Wagner, taste buds lie on the elevated or ridged surface of the tongue (called the papillae) and have hairlike extensions (microvilli) to increase the receptor surface of the cells. For most foods and substances, saliva breaks down the chemical components that travel through the pores in the papillae to reach the taste buds, which specialize primarily in processing one of the four major taste groups: sweet, sour, salty, and bitter.
Taste occurs when specific proteins in the food bind to receptors on the taste buds. These receptors, in turn, send messages to the brain's cerebral cortex, which interprets the flavor. The actual chemical processes involved for each major taste group vary. For example, salty and sour flavors occur when saliva breaks down sodium or acids, respectively. The chemical constituents of foods that give bitter and sweet tastes, however, are much harder to specify because many chemical components are involved.
Although certain taste buds seemed to have an affinity for one of the four major flavors, continued research into this intricate biological process has revealed a complex neural and chemical network that precludes simple black and white explanations. For example, each taste bud actually has receptors for sweet, sour, salty, and bitter sensations, indicating that taste buds are sensitive to a complex flavor spectrum just like vision is sensitive to a broad color spectrum grouped into the four major colors of red, orange, yellow, and green. Particular proteins of taste are also under study, like gustducin, which may set off the plethora of chemical reactions that causes something to taste bitter.
Taste buds for all four taste groups can be found throughout the mouth, but specific kinds of buds are clustered together in certain areas. Think about licking an ice cream cone; taste buds for sweetness are grouped on the tip of our tongue. The buds for sour tastes are on the sides of the tongue and salty on the front. Bitter taste buds on the back of the tongue can make people gag, a natural defense mechanism to help prevent poisoning.
People constantly regenerate new taste buds every 3-10 days to replace the ones worn out by scalding soup, frozen yogurt, and the like. Unfortunately, as people grow older, their taste buds lose their fine tuning because they are replaced at a slower rate. As a result, middle-aged and older people require more of a substance to produce the same sensations of sweetness or spiciness, for example, than would be needed by a child eating the same food.
Scientists have also discovered that genetic makeup partially accounts for individual tasting abilities and preferences for specific foods. According to researchers at Yale University, some people are genetically programmed to have more taste buds and, as a result, taste more flavors in a particular food. (The number of taste buds varies in different animal species. For example, cows have 25,000 taste buds, rabbits 17,000, and adult people approximately 10,000.) In general, a person's ability to taste can lie anywhere in a spectrum from poor to exceptional, with the ability to sense tastes increasing in proportion to the number of taste buds present. The difference in the number of taste buds can be extreme. Researchers have found anywhere from 11 to 1,100 taste buds per square inch in various young people tested. They have also found that women tend to have more taste buds than men and, as a result, are often better tasters. How well people taste greatly affects what they like. Studies at Yale, for example, revealed that children with fewer taste buds who are classified as poor tasters liked cheese more often than exceptional tasters, who experienced a more bitter sensation, probably because of increased sensitivity to the combination of calcium and the milk protein casein found in cheese.
Despite the important role that taste buds play in recognizing flavors, they do not work alone in providing the experience of taste. For example, the amount of naturally occurring salt in saliva varies; the result being that those with less saliva can better taste the saltiness of certain foods than others, who may end up adding salt to get a similar flavor. The smell and texture of foods are also important contributing factors to how people perceive a food to taste and whether or not they like it. Food in the mouth produces an odor that reaches the nose through the nasopharynx (the opening that links the mouth and the nose). Since smell is much more sensitive to odors than taste is to flavors, people often first experience the flavor of a food by its odor. A cold or flu is probably the most common example of how important smell is to taste. People with congestion often experience a diminished ability to taste. The taste buds, however, are working fine; it's the lack of smell that hinders the brain's ability to process flavor. The texture and temperature of food also influences how it tastes. For example, many people would not think of drinking cold coffee, while others will not eat pears because of a dislike for the fruit's gritty texture.
The predilection for certain foods and tastes is not determined merely by biology. Culture and familiarity with foods greatly influence taste preferences. The Japanese have long considered raw fish, or sushi, to be a savory delicacy. But only a decade or so ago, few Americans would have enjoyed such a repast. But as the number of Japanese restaurants with sushi bars grew, so did American's familiarity with this delicacy and, as a result, their taste for it.
The inability to taste is so intricately linked with smell that it is often difficult to tell whether the problem lies in tasting or smelling. An estimated two to four million people in the United States suffer from some sort of taste or smell disorder. The inability to taste or smell not only robs an individual of certain sensory pleasures, it can also be dangerous. Without smell or taste, for example, people cannot determine whether food is spoiled, making them vulnerable to food poisoning. Also, some psychiatrists believe that the lack of taste and smell can have a profoundly negative affect on a person's quality of life, leading to depression or other psychological problems.
There are a variety of causes for taste and smell disorders, from a biological breakdown to the effects of environmental toxins. In addition to cold or flu, common physical ailments that can assault the sense of taste and smell include allergies and various viral or bacterial infections that produce swollen mucous membranes. Fortunately, most of these problems are temporary and treatable. However, neurological disorders due to brain injury or diseases like Parkinson's or Alzheimer's can cause more permanent damage to the intricate neural network that processes the sense of taste and smell. Some drugs can also cause these disorders by inhibiting certain enzymes, affecting the body's metabolism, and interfering with the neural network and receptors needed to taste and smell. Exposure to environmental toxins like lead, mercury, insecticides, and solvents can also wreak havoc on the ability to smell and taste by causing damage to taste buds and sensory cells in the nose or brain.
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