Tongue

The tongue is a muscular organ found in the mouth that serves many different purposes. Perhaps the most important of the tongue's functions is the role it plays in the sense of taste. Composed of eight interwoven, striated muscles, the tongue is a flexible organ that can move in any direction. Further, the entire tongue is covered by a pinkish mucus membrane known as the mucosa. The top of the tongue, meanwhile, is covered by thousands of little bumps called papillae. In addition to giving the tongue's surface a rough texture, the papillae contain clusters of nerve-like cells called taste buds that connect to the nervous system and allow the brain to distinguish between different tastes during the consumption of food and drink. Along with this, the tongue also assists with functions such as chewing, swallowing, speaking, and oral cleansing. As a result, the tongue is one of the most versatile and useful parts of the body.

Background

During the early development of human fetuses, the tongue begins to form at just four weeks of gestation. In the average adult, the tongue is typically 3.3 inches (8.3 centimeters) long for men and 3.1 inches (7.8 centimeters) long for women. The visible part of the tongue is only one small part of the larger organ, however. The root of the tongue is anchored to the floor of the mouth. The freely moving portion of the tongue near the tip is connected on its underside to the floor of the mouth by a tissue called the lingual frenulum. From the tip, the tongue extends backward into the throat, where it is held in place by a series of special muscles that connect the tongue to the hyoid bone and the voice box. Muscles also connect the tongue with the base of the skull. Together, these and other muscles allow the tongue to extend and contract, advance and retract, raise up and down, move left and right, bend backward, fold into various shapes, and otherwise move between different positions. This level of mobility makes the tongue one of the body's most flexible and adaptable organs.

Much of the surface of the tongue is covered with small bumps called papillae. There are two main types of papillae: mechanical papillae and taste papillae. The mechanical papillae contribute to the sense of touch and help a person feel the texture of the food he or she consumes. The taste papillae, which are found mainly on the flat upper surface of the tongue, come in direct contact with particles that enter the mouth and allow the tongue to sense the taste of the foods and drinks that a person consumes. The taste papillae, or taste buds, can sense four basic tastes: sweet, sour, bitter, and salty. A fifth taste known as umami can also be derived from foods that contain a substance called glutamate, which is found in the flavor enhancer monosodium glutamate (MSG). In 2017, scientists in Binghamton, New York, also hypothesized the possible presence of a sixth type of taste receptor that is specifically triggered by water.

Overview

The tongue serves several different purposes. The most notable of these is of course the role it plays in taste. The tongue's taste buds contain special taste receptors where the chemical substances found in food and drink come in contact with and are identified by the sensory cells found within. The taste buds are also tied to one of the biggest misconceptions about the tongue. In 1901, German scientist David P. Hänig conducted an experiment to measure the threshold for taste perception around different parts of the tongue. To do this, he dripped salty, sweet, sour, and bitter substances around different parts of the tongue and measured how much of each substance it took for the corresponding taste sensation to be triggered. Through his work, Hänig found that certain areas of the tongue registered certain tastes more quickly than others did. When he subsequently published a paper on his findings, however, Hänig included a line graph of his measurements that was turned into a so-called taste map of the tongue in the 1940s. Unfortunately, this taste map was widely interpreted to mean that each taste was sensed only by specific parts of the tongue. In reality, all parts of the tongue that have taste buds are capable of sensing all tastes. The only difference between the parts in question, as Hänig wrote, is that some sense certain tastes more quickly than others do.

Aside from taste, the tongue also plays a number of other important roles relating to the process of eating. At the outset of this process, the tongue is used to help suck food or drink into the mouth. Once food enters the mouth, the tongue and the cheeks help move the food through the teeth so that it can be chewed and turned into bolus, which is a soft mass that can be swallowed. In addition, the tongue's movement also massages special glands on the floor of the mouth that release saliva, which also aids in the pre-digestion process. Once the food has been fully chewed, the tongue also helps move the bolus into the throat.

The tongue is also essential to a person's ability to speak. Together with the lips and teeth, the tongue allows people to turn sounds from the throat into comprehensible words. Certain letters cannot be properly pronounced without the tongue. Some of these include the consonants T and D and the rolling R used in languages like Spanish.

The tongue is susceptible to many different diseases and other medical conditions. One of the most common of these is thrush, a form of yeast infection that causes white patches to appear on the tongue's surface. Another is macroglossia, which is the condition of having an abnormally large tongue. Geographic tongue is a harmless condition in which colored spots migrate over the surface of the tongue. In some cases, the papillae can overgrow the tongue's surface, leading to a condition known as hair tongue. As with other parts of the mouth, the tongue can also be susceptible to oral cancer.

Bibliography

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Bradford, Alina. "The Tongue: Facts, Function, & Diseases." Live Science, 1 Oct. 2015, www.livescience.com/52362-tongue.html. Accessed 19 June 2017.

Calderone, Julia, and Ben Fogelson. "Fact or Fiction?: The Tongue Is the Strongest Muscle in the Body." Scientific American, 15 Aug. 2014, www.scientificamerican.com/article/fact-or-fiction-the-tongue-is-the-strongest-muscle-in-the-body/. Accessed 19 June 2017.

Hoffman, Matthew. "Picture of the Tongue." WebMD, www.webmd.com/oral-health/picture-of-the-tongue#1. Accessed 19 June 2017.

"How Does the Tongue Work?" PubMed Health, 23 Aug. 2016, www.ncbi.nlm.nih.gov/pubmedhealth/PMH0072591/. Accessed 19 June 2017.

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Munger, Steven D. "That Neat and Tidy Map of Tastes on the Tongue You Learned in School Is All Wrong." Conversation, 7 July 2015, theconversation.com/that-neat-and-tidy-map-of-tastes-on-the-tongue-you-learned-in-school-is-all-wrong-44217. Accessed 19 June 2017.

Underwood, Emily. "Scientists Discover a Sixth Sense on the Tongue – For Water." Science, 30 May 2017, www.sciencemag.org/news/2017/05/scientists-discover-sixth-sense-tongue-water. Accessed 19 June 2017.