Thetongue is amuscularorgan in themouth of a typicaltetrapod. It manipulates food for chewing and swallowing as part of thedigestive process, and is the primary organ of taste. The tongue's upper surface (dorsum) is covered bytaste buds housed in numerouslingual papillae. It is sensitive and kept moist bysaliva and is richly supplied withnerves andblood vessels. The tongue also serves as a natural means of cleaning the teeth.[2] A major function of the tongue is to enable speech in humans andvocalization in other animals.
The human tongue is divided into two parts, anoral part at the front and apharyngeal part at the back. The left and right sides are also separated along most of its length by a vertical section offibrous tissue (thelingual septum) that results in a groove, the median sulcus, on the tongue's surface.
There are two groups of glossal muscles. The four intrinsic muscles alter the shape of the tongue and are not attached to bone. The four paired extrinsic muscles change the position of the tongue and are anchored to bone.
The underside of a human tongue, showing its rich blood supply.
The tongue is amuscular hydrostat that forms part of the floor of theoral cavity. The left and right sides of the tongue are separated by a vertical section of fibrous tissue known as thelingual septum. This division is along the length of the tongue save for the very back of the pharyngeal part and is visible as a groove called the median sulcus. The human tongue is divided intoanterior and posterior parts by the terminal sulcus, which is a "V"-shaped groove. The apex of the terminal sulcus is marked by a blind foramen, the foramen cecum, which is a remnant of the medianthyroid diverticulum in earlyembryonic development. The anteriororal part is the visible part situated at the front and makes up roughly two-thirds the length of the tongue. The posteriorpharyngeal part is the part closest to thethroat, roughly one-third of its length. These parts differ in terms of theirembryological development andnerve supply.
The average length of the human tongue from theoropharynx to the tip is 10 cm.[4] The average weight of the human tongue from adult males is 99g and for adult females 79g.[5]
Inphonetics andphonology, a distinction is made between thetip of the tongue and theblade (the portion just behind the tip). Sounds made with the tongue tip are said to beapical, while those made with the tongue blade are said to belaminal.
Foramen cecum and terminal sulcus labelled aboveFeatures of the tongue surface
The upper surface of the tongue, the dorsal surface, is called the dorsum, and is divided by a groove into symmetrical halves by themedian sulcus. Theforamen cecum marks the end of this division (at about 2.5 cm from the root of the tongue) and the beginning of theterminal sulcus. The foramen cecum is also the point of attachment of thethyroglossal duct and is formed during the descent of thethyroid diverticulum inembryonic development.
The terminal sulcus is a shallow groove that runs forward as a shallow groove in aV shape from the foramen cecum, forwards and outwards to the margins (borders) of the tongue. The terminal sulcus divides the tongue into a posteriorpharyngeal part and an anteriororal part. The pharyngeal part is supplied by theglossopharyngeal nerve and the oral part is supplied by thelingual nerve (a branch of the mandibular branch (V3) of thetrigeminal nerve) for somatosensory perception and by thechorda tympani (a branch of thefacial nerve) fortaste perception.
On the undersurface, the ventral surface, of the tongue is a fold of mucous membrane called thefrenulum that tethers the tongue at the midline to the floor of the mouth. On either side of the frenulum are small prominences calledsublingual caruncles that the major salivarysubmandibular glands drain into.
The eight muscles of the human tongue are classified as eitherintrinsic orextrinsic. The four intrinsic muscles act to change the shape of the tongue, and are not attached to any bone. The four extrinsic muscles act to change the position of the tongue, and are anchored to bone.
Lateral view of the tongue, with extrinsic muscles highlighted
The four extrinsic muscles originate from bone and extend to the tongue. They are thegenioglossus, thehyoglossus (often including thechondroglossus) thestyloglossus, and thepalatoglossus. Their main functions are altering the tongue's position allowing for protrusion, retraction, and side-to-side movement.[6]
The genioglossus arises from themandible and protrudes the tongue. It is also known as the tongue's "safety muscle" since it is the only muscle that propels the tongue forward.
The hyoglossus, arises from thehyoid bone and retracts and depresses the tongue. The chondroglossus is often included with this muscle.
The styloglossus arises from thestyloid process of thetemporal bone and draws the sides of the tongue up to create a trough for swallowing.
The palatoglossus arises from thepalatine aponeurosis, and depresses thesoft palate, moves thepalatoglossal fold towards the midline, and elevates the back of the tongue during swallowing.
Coronal section of tongue, showing intrinsic muscles
Four paired intrinsic muscles of the tongue originate and insert within the tongue, running along its length. They are thesuperior longitudinal muscle, theinferior longitudinal muscle, thevertical muscle, and thetransverse muscle. These muscles alter the shape of the tongue by lengthening and shortening it, curling and uncurling its apex and edges as intongue rolling, and flattening and rounding its surface. This provides shape and helps facilitate speech, swallowing, and eating.[6]
The superior longitudinal muscle runs along the upper surface of the tongue under the mucous membrane, and functions to shorten and curl the tongue upward. It originates near theepiglottis, at thehyoid bone, from the median fibrous septum.
The inferior longitudinal muscle lines the sides of the tongue, and is joined to the styloglossus muscle. It functions to shorten and curl the tongue downward.
The vertical muscle is located in the middle of the tongue, and joins the superior and inferior longitudinal muscles. It functions to flatten the tongue.
The transverse muscle divides the tongue at the middle, and is attached to themucous membranes that run along the sides. It functions to lengthen and narrow the tongue.
Innervation of taste and sensation is different for the anterior and posterior part of the tongue because they are derived from different embryological structures (pharyngeal arch 1 and pharyngeal arches 3 and 4, respectively).[9]
Anterior two-thirds of tongue (anterior to thevallate papillae):
The tip of tongue drains to the submental nodes. The left and right halves of the anterior two-thirds of the tongue drains tosubmandibular lymph nodes, while the posterior one-third of the tongue drains to the jugulo-omohyoid nodes.
The tongue can divide itself in dorsal and ventral surface. The dorsal surface is a stratified squamous keratinized epithelium, which is characterized by numerous mucosal projections called papillae.[11] The lingual papillae covers the dorsal side of the tongue towards the front of the terminal groove. The ventral surface is stratified squamous non-keratinized epithelium which is smooth.[12]
In the fifth week a pair oflateral lingual swellings, one on the right side and one on the left, form on the first pharyngeal arch. These lingual swellings quickly expand and cover the median tongue bud. They form the anterior part of the tongue that makes up two-thirds of the length of the tongue, and continue to develop throughprenatal development. The line of their fusion is marked by themedian sulcus.[13]
In the fourth week, a swelling appears from the secondpharyngeal arch, in the midline, called thecopula. During the fifth and sixth weeks, the copula is overgrown by a swelling from the third and fourth arches (mainly from the third arch) called thehypopharyngeal eminence, and this develops into the posterior part of the tongue (the other third and the posterior most part of the tongue is developed from the fourth pharyngeal arch). The hypopharyngeal eminence develops mainly by the growth ofendoderm from the third pharyngeal arch. The boundary between the two parts of the tongue, the anterior from the first arch and the posterior from the third arch is marked by the terminal sulcus.[13] The terminal sulcus is shaped like aV with the tip of the V situated posteriorly. At the tip of the terminal sulcus is theforamen cecum, which is the point of attachment of thethyroglossal duct where the embryonicthyroid begins to descend.[6]
The tongue is equipped with manytaste buds on itsdorsal surface, and each taste bud is equipped with taste receptor cells that can sense particular classes of tastes. Distinct types of taste receptor cells respectively detect substances that are sweet, bitter, salty, sour, spicy, or taste ofumami.[15] Umami receptor cells are the least understood and accordingly are the type most intensively under research.[16] There is acommon misconception that different sections of the tongue are exclusively responsible for differentbasic tastes. Although widely taught in schools in the form of thetongue map, this is incorrect; all taste sensations come from all regions of the tongue, although certain parts are more sensitive to certain tastes.[17]
The tongue is an important accessory organ in the digestive system. The tongue is used for crushing food against the hard palate, during mastication and manipulation of food for softening prior to swallowing. Theepithelium on the tongue's upper, or dorsal surface iskeratinised. Consequently, the tongue can grind against the hard palate without being itself damaged or irritated.[18]
The tongue is one of the primary articulators in the production ofspeech, and this is facilitated by both the extrinsic muscles that move the tongue and the intrinsic muscles that change its shape. Specifically, differentvowels arearticulated by changing the tongue's height and retraction to alter theresonant properties of thevocal tract. These resonant properties amplify specificharmonic frequencies (formants) that are different for each vowel, while attenuating other harmonics. For example, [a] is produced with the tonguelowered and centered and [i] is produced with the tongueraised and fronted.Consonants are articulated by constricting airflow through the vocal tract, and many consonants feature a constriction between the tongue and some other part of the vocal tract. For example,alveolar consonants like [s] and [n] are articulated with the tongue against thealveolar ridge, whilevelar consonants like [k] and [g] are articulated with the tongue dorsum against the soft palate (velum). Tongue shape is also relevant to speech articulation, for example inretroflex consonants, where the tip of the tongue is curved backward.
Acongenital disorder of the tongue is that ofankyloglossia also known astongue-tie. The tongue istied to the floor of the mouth by a very short and thickenedfrenulum and this affects speech, eating, and swallowing.
Thesublingual region underneath the front of the tongue is an ideal location for theadministration of certain medications into the body. Theoral mucosa is very thin underneath the tongue, and is underlain by a plexus of veins. The sublingual route takes advantage of the highlyvascular quality of the oral cavity, and allows for the speedy application of medication into the cardiovascular system, bypassing the gastrointestinal tract. This is the only convenient and efficaciousroute of administration (apart fromIntravenous therapy) ofnitroglycerin to a patient suffering chest pain fromangina pectoris.
Giraffe's tongueExtended proboscis of a long tonguedMacroglossummoth
The muscles of the tongue evolved inamphibians fromoccipitalsomites. Most amphibians show a proper tongue after theirmetamorphosis.[22] As a consequence, mosttetrapod animals—amphibians, reptiles, birds, and mammals—have tongues (thefrog family ofpipids lack tongue). In mammals such asdogs andcats, the tongue is often used to clean the fur and body bylicking. The tongues of these species have a very rough texture, which allows them to remove oils and parasites. Some dogs have a tendency to consistently lick a part of their foreleg, which can result in askin condition known as alick granuloma. A dog's tongue also acts as a heat regulator. As a dog increases its exercise the tongue will increase in size due to greater blood flow. The tongue hangs out of the dog's mouth and the moisture on the tongue will work to cool the bloodflow.[23][24]
Other animals may have organs that areanalogous to tongues, such as abutterfly'sproboscis or aradula on amollusc, but these are nothomologous with the tongues found in vertebrates and often have little resemblance in function. For example, butterflies do not lick with their proboscides; they suck through them, and the proboscis is not a single organ, but two jaws held together to form a tube.[25] Many species of fish have small folds at the base of their mouths that might informally be called tongues, but they lack a muscular structure like the true tongues found in mosttetrapods.[26][27]
The tongue can serve as ametonym forlanguage. For example, theNew Testament of the Bible, in the Book ofActs of the Apostles,Jesus' disciples on the Day ofPentecost received a type ofspiritual gift: "there appeared unto them cloven tongues like as of fire, and it sat upon each of them. And they were all filled with theHoly Ghost, and began to speak with other tongues ....", which amazed the crowd ofJewish people inJerusalem, who were from various parts of theRoman Empire but could now understand what was being preached. The phrasemother tongue is used as a child's first language. Many languages[28] have the same word for "tongue" and "language", as did theEnglish language before theMiddle Ages.
A common temporary failure in wordretrieval frommemory is referred to as thetip-of-the-tonguephenomenon. The expressiontongue in cheek refers to a statement that is not to be taken entirely seriously – something said or done with subtle ironic or sarcastic humour. Atongue twister is a phrase very difficult to pronounce. Aside from being amedical condition, "tongue-tied" means being unable to say what you want due to confusion or restriction. The phrase "cat got your tongue" refers to when a person is speechless. To "bite one's tongue" is a phrase which describes holding back an opinion to avoid causing offence. A "slip of the tongue" refers to an unintentional utterance, such as aFreudian slip. The "gift of tongues" refers to when one is uncommonly gifted to be able to speak in a foreign language, often as a type ofspiritual gift.Speaking in tongues is a common phrase used to describeglossolalia, which is to make smooth, language-resembling sounds that is no true spoken language itself. A deceptive person is said to have aforked tongue, and a smooth-talking person is said to have asilver tongue.
Sticking one's tongue out at someone is considered a childish gesture ofrudeness or defiance in many countries; the act may also have sexual connotations, depending on the way in which it is done. However, inTibet it is considered a greeting.[29] In 2009, a farmer fromFabriano, Italy, was convicted and fined byItaly's highest court for sticking his tongue out at a neighbor with whom he had been arguing - proof of the affront had been captured with a cell-phone camera.[30]
Tongue piercing andsplitting have become more common in western countries in recent decades.[when?] One study found that one-fifth of young adults in Israel had at least one type of oral piercing, most commonly the tongue.[31]
The tongues of some animals are consumed and sometimes prized as delicacies. Hot-tongue sandwiches frequently appear on menus inkosherdelicatessens in America.Taco de lengua (lengua being Spanish for tongue) is a taco filled withbeef tongue, and is especially popular in Mexican cuisine. As part of Colombian gastronomy, Tongue in Sauce (Lengua en Salsa) is a dish prepared by frying the tongue and adding tomato sauce, onions and salt. Tongue can also be prepared asbirria. Pig and beef tongue are consumed in Chinese cuisine.Duck tongues are sometimes employed inSichuan dishes, whilelamb's tongue is occasionally employed in Continental and contemporary American cooking. Friedcod "tongue" is a relatively common part of fish meals inNorway and inNewfoundland. InArgentina andUruguay cow tongue is cooked and served in vinegar (lengua a la vinagreta). In the Czech Republic and in Poland, a pork tongue is considered a delicacy, and there are many ways of preparing it. In Eastern Slavic countries, pork and beef tongues are commonly consumed, boiled and garnished with horseradish or jellied; beef tongues fetch a significantly higher price and are considered more of a delicacy. In Alaska, cow tongues are among the more common. Both cow and moose tongues are popular toppings on open-top-sandwiches in Norway, the latter usually amongst hunters.
Tongues of seals and whales have been eaten, sometimes in large quantities, by sealers and whalers, and in various times and places have been sold for food on shore.[33][page needed]
^abcdefgDrake, Richard L.; Vogl, Wayne; Mitchell, Adam W. M. (2005).Gray's anatomy for students. Philadelphia, Pennsylvania: Elsevier. pp. 989–995.ISBN978-0-8089-2306-0.
^"Pirogov's triangle".Whonamedit? - A dictionary of medical eponyms. Ole Daniel Enersen.
^Jamrozik, T.; Wender, W. (January 1952). "Topographic anatomy of lingual arterial anastomoses; Pirogov-Belclard's triangle".Folia Morphologica.3 (1):51–62.PMID13010300.
^Dudek, Dr Ronald W. (2014).Board Review Series: Embryology (Sixth ed.). LWW.ISBN978-1451190380.
^Tortora, Gerard J.; Derrickson, Bryan H. (2008). "17".Principles of Anatomy and Physiology (12th ed.). Wiley. p. 602.ISBN978-0470084717.
^Silverhorn, Dee Unglaub (2009). "10".Human Physiology: An integrated approach (5th ed.). Benjamin Cummings. p. 352.ISBN978-0321559807.
^Schacter, Daniel L.; Gilbert, Daniel Todd; Wegner, Daniel M. (2009). "Sensation and Perception".Psychology (2nd ed.). New York: Worth. p. 166.ISBN9780716752158.
^Atkinson, Martin E. (2013).Anatomy for Dental Students (4th ed.). Oxford University Press.ISBN978-0199234462.the tongue is also responsible for the shaping of the bolus as food passes from the mouth to the rest of the alimentary canal
^"Oral Cancer Facts". The Oral Cancer Foundation. 28 August 2017. Archived fromthe original on 22 June 2013. Retrieved17 September 2017.
^Richards, O. W.; Davies, R. G. (1977).Imms' General Textbook of Entomology: Volume 1: Structure, Physiology and Development, Volume 2: Classification and Biology. Berlin: Springer.ISBN0-412-61390-5.
^Romer, Alfred Sherwood; Parsons, Thomas S. (1977).The Vertebrate Body. Philadelphia, Philadelphia: Holt-Saunders International. pp. 298–299.ISBN0-03-910284-X.
^Liran, Levin; Yehuda, Zadik; Tal, Becker (December 2005). "Oral and dental complications of intra-oral piercing".Dent Traumatol.21 (6):341–3.doi:10.1111/j.1600-9657.2005.00395.x.PMID16262620.
^Teilhet-Fisk, Jehanne, ed. (1973) [1973].Dimensions of Polynesia: Fine Arts Gallery of San Diego, October 7-November 25, 1973. Fine Arts Gallery of San Diego. p. 115. Retrieved15 April 2024.The mouth forms of Polynesia are expressive and contain a great deal of variation, from the snarling lips of Hawaiian sculture to the tight-lipped, pursed mouths of the Easter Island statues. [...] The presence or absence of a tongue is helpful in considering the meaning of the mouth forms. The mouth forms showing protrusion of the tongue occur in the Marginal Islands (New Zealand, Hawaii, and the Marquesas), Central Polynesia (Tahiti and the Cook Islands) and the Australs.
^Hawes, Charles Boardman (1924).Whaling. Doubleday.
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