Tongue

The tongue is a muscular organ in the mouth of most vertebrates that manipulates food for mastication, and is used in the act of swallowing. It is of importance in the digestive system and is the primary organ of taste in the gustatory system. The tongue's upper surface (dorsum) is covered by taste buds housed in numerous lingual papillae. It is sensitive and kept moist by saliva, and is richly supplied with nerves and blood vessels. The tongue also serves as a natural means of cleaning the teeth.[2] A major function of the tongue is the enabling of speech in humans and vocalization in other animals.

The human tongue is divided into two parts, an oral part at the front and a pharyngeal part at the back. The left and right sides are also separated along most of its length by a vertical section of fibrous tissue (the lingual septum) that results in a groove, the median sulcus on the tongue's surface.

There are two groups of muscles of the tongue. 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.

Tongue
زبان tongue
The human tongue
Details
Precursorpharyngeal arches, lateral lingual swelling, tuberculum impar[1]
Arterylingual, tonsillar branch, ascending pharyngeal
Veinlingual
NerveSensory: Anterior 2/3: lingual nerve & chorda tympani Posterior 1/3: Glossopharyngeal nerve (IX) Motor Innervation: - CN XII (Hypoglossal) except palatoglossus muscle supplied by cranial part of Vagus Nerve.
LymphDeep Cervical, Submandibular, Submental
Identifiers
Latinlingua
MeSHD014059
TAA05.1.04.001
FMA54640
Anatomical terminology

Etymology

The word tongue derives from the Old English tunge, which comes from Proto-Germanic *tungōn.[3] It has cognates in other Germanic languages — for example tonge in West Frisian, tong in Dutch and Afrikaans, Zunge in German, tunge in Danish and Norwegian, and tunga in Icelandic, Faroese and Swedish. The ue ending of the word seems to be a fourteenth-century attempt to show "proper pronunciation", but it is "neither etymological nor phonetic".[3] Some used the spelling tunge and tonge as late as the sixteenth century.

In humans

Structure

Facies inferior linguae
The underside of a human tongue, showing its rich blood supply.

The tongue is a muscular hydrostat that forms part of the floor of the oral cavity. The left and right sides of the tongue are separated by a vertical section of fibrous tissue known as the lingual 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 into anterior 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 median thyroid diverticulum in early embryonic development. The anterior oral part is the visible part situated at the front and makes up roughly two-thirds the length of the tongue. The posterior pharyngeal part is the part closest to the throat, roughly one-third of its length. These parts differ in terms of their embryological development and nerve supply.

The anterior tongue is, at its apex (or tip), thin and narrow, it is directed forward against the lingual surfaces of the lower incisor teeth. The posterior part is, at its root, directed backward, and connected with the hyoid bone by the hyoglossi and genioglossi muscles and the hyoglossal membrane, with the epiglottis by three glossoepiglottic folds of mucous membrane, with the soft palate by the glossopalatine arches, and with the pharynx by the superior pharyngeal constrictor muscle and the mucous membrane. It also forms the anterior wall of the oropharynx.

The average length of the human tongue from the oropharynx to the tip is 10 cm.[4] The average weight of the human tongue from adult males is 70g and for adult females 60g.

In phonetics and phonology, a distinction is made between the tip of the tongue and the blade (the portion just behind the tip). Sounds made with the tongue tip are said to be apical, while those made with the tongue blade are said to be laminal.

Upper surface of the tongue

Foramen caecum
Foramen cecum and terminal sulcus labelled above
Tongue
Features of the tongue surface

The upper surface of the tongue is called the dorsum, and is divided by a groove into symmetrical halves by the median sulcus. The foramen cecum marks the end of this division (at about 2.5 cm from the root of the tongue) and the beginning of the terminal sulcus. The foramen cecum is also the point of attachment of the thyroglossal duct and is formed during the descent of the thyroid diverticulum in embryonic development.

The terminal sulcus is a shallow groove that runs forward as a shallow groove in a V shape from the foramen cecum, forwards and outwards to the margins (borders) of the tongue. The terminal sulcus divides the tongue into a posterior pharyngeal part and an anterior oral part. The pharyngeal part is supplied by the glossopharyngeal nerve and the oral part is supplied by the lingual nerve (a branch of the mandibular branch (V3) of the trigeminal nerve) for somatosensory perception and by the chorda tympani (a branch of the facial nerve) for taste perception.

Both parts of the tongue develop from different pharyngeal arches.

Undersurface of the tongue

On the undersurface of the tongue is a fold of mucuous membrane called the frenulum that tethers the tongue at the midline to the floor of the mouth. On either side of the frenulum are small prominences called sublingual caruncles that the major salivary submandibular glands drain into.

Muscles

The eight muscles of the human tongue are classified as either intrinsic or extrinsic. 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.

Hyoglossus
Lateral view of the tongue, with extrinsic muscles highlighted

The four extrinsic muscles originate from bone and extend to the tongue. They are the genioglossus, the hyoglossus (often including the chondroglossus) the styloglossus, and the palatoglossus. Their main functions are altering the tongue's position allowing for protrusion, retraction, and side-to-side movement.[5]

The genioglossus arises from the mandible 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 the hyoid bone and retracts and depresses the tongue. The chondroglossus is often included with this muscle.

The styloglossus arises from the styloid process of the temporal bone and draws the sides of the tongue up to create a trough for swallowing.

The palatoglossus arises from the palatine aponeurosis, and depresses the soft palate, moves the palatoglossal fold towards the midline, and elevates the back of the tongue during swallowing.

Gray1020
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 the superior longitudinal muscle, the inferior longitudinal muscle, the vertical muscle, and the transverse muscle. These muscles alter the shape of the tongue by lengthening and shortening it, curling and uncurling its apex and edges as in tongue rolling, and flattening and rounding its surface. This provides shape and helps facilitate speech, swallowing, and eating.[5]

The superior longitudinal muscle runs along the upper surface of the tongue under the mucous membrane, and elevates, assists in retraction of, or deviates the tip of the tongue. It originates near the epiglottis, at the hyoid bone, from the median fibrous septum.

The inferior longitudinal muscle lines the sides of the tongue, and is joined to the styloglossus muscle.

The vertical muscle is located in the middle of the tongue, and joins the superior and inferior longitudinal muscles.

The transverse muscle divides the tongue at the middle, and is attached to the mucous membranes that run along the sides.

Blood supply

Gray559
Blood supply of the tongue

The tongue receives its blood supply primarily from the lingual artery, a branch of the external carotid artery. The lingual veins, drain into the internal jugular vein. The floor of the mouth also receives its blood supply from the lingual artery.[5] There is also a secondary blood supply to the root of tongue from the tonsillar branch of the facial artery and the ascending pharyngeal artery.

An area in the neck sometimes called the Pirogov triangle is formed by the intermediate tendon of the digastric muscle, the posterior border of the mylohyoid muscle, and the hypoglossal nerve.[6][7] The lingual artery is a good place to stop severe hemorrhage from the tongue.

Nerve supply

Innervation of the tongue consists of motor fibers, special sensory fibers for taste, and general sensory fibers for sensation.[5]

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).[8]

Lymphatic drainage

The tip of tongue drains to the submental nodes. The left and right halves of the anterior two-thirds of the tongue drains to submandibular lymph nodes, while the posterior one-third of the tongue drains to the jugulo-omohyoid nodes.

Microanatomy

Human tongue (251 09) Section
Section through the human tongue; stained H&E

The upper surface of the tongue is covered in masticatory mucosa a type of oral mucosa which is of keratinized stratified squamous epithelium. Embedded in this are numerous papillae that house the taste buds and their taste receptors.[9] The lingual papillae consist of filiform, fungiform, vallate and foliate papillae.[5] and only the filiform papillae are not associated with any taste buds.

The tongue can also 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.[10] 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.[11]

Development

Gray979
Floor of pharynx at about 26 days showing lateral swellings at first pharyngeal arch (mandibular arch).

The tongue begins to develop in the fourth week of embryonic development from a median swelling – the median tongue bud (tuberculum impar) of the first pharyngeal arch.[12]

In the fifth week a pair of lateral 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 through prenatal development. The line of their fusion is marked by the median sulcus.[12]

In the fourth week a swelling appears from the second pharyngeal arch, in the midline, called the copula. 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 the hypopharyngeal eminence, and this develops into the posterior part of the tongue (the other third). The hypopharyngeal eminence develops mainly by the growth of endoderm 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.[12] The terminal sulcus is shaped like a V with the tip of the V situated posteriorly. At the tip of the terminal sulcus is the foramen cecum, which is the point of attachment of the thyroglossal duct where the embryonic thyroid begins to descend.[5]

Function

Taste receptors are present on the human tongue in papillae

Tongue and taste buds
1402 The Tongue

Taste

Chemicals that stimulate taste receptor cells are known as tastants. Once a tastant is dissolved in saliva, it can make contact with the plasma membrane of the gustatory hairs, which are the sites of taste transduction.[13]

The tongue is equipped with many taste buds on its dorsal 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 of umami.[14] Umami receptor cells are the least understood and accordingly are the type most intensively under research.[15]

Mastication

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. The epithelium on the tongue’s upper, or dorsal surface is keratinised. Consequently, the tongue can grind against the hard palate without being itself damaged or irritated.[16]

Speech

The intrinsic muscles of the tongue enable the shaping of the tongue which facilitates speech.

Intimacy

The tongue plays a role in physical intimacy and sexuality. The tongue is part of the erogenous zone of the mouth and can be used in intimate contact, as in the French kiss and in oral sex.

Clinical significance

Disease

A congenital disorder of the tongue is that of ankyloglossia also known as tongue-tie. The tongue is tied to the floor of the mouth by a very short and thickened frenulum and this affects speech, eating, and swallowing.

The tongue is prone to several pathologies including glossitis and other inflammations such as geographic tongue, and median rhomboid glossitis; burning mouth syndrome, oral hairy leukoplakia, oral candidiasis (thrush), black hairy tongue and fissured tongue.

There are several types of oral cancer that mainly affect the tongue. Mostly these are squamous cell carcinomas.[17][18]

Food debris, desquamated epithelial cells and bacteria often form a visible tongue coating.[19] This coating has been identified as a major factor contributing to bad breath (halitosis),[19] which can be managed by using a tongue cleaner.[20]

Medication delivery

The sublingual region underneath the front of the tongue is an ideal location for the administration of certain medications into the body. The oral mucosa is very thin underneath the tongue, and is underlain by a plexus of veins. The sublingual route takes advantage of the highly vascular 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 efficacious route of administration (apart from Intravenous therapy) of nitroglycerin to a patient suffering chest pain from angina pectoris.

Other animals

Giraffe's tongue
Giraffe's tongue
Macroglossum stellatarum anatomy - MHNT
Extended proboscis of a long tongued Macroglossum moth

The tongue evolved with the amphibians from the same structures that form fins in fish. Most amphibians show a proper tongue after their metamorphosis. As a consequence most vertebrate animals - amphibians, reptiles, birds and mammals - have tongues. In mammals such as dogs and cats, the tongue is often used to clean the fur and body by licking. 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 a skin condition known as a lick 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.[21][22]

Some animals have tongues that are specially adapted for catching prey. For example, chameleons, frogs, and anteaters have prehensile tongues.

Other animals may have organs that are analogous to tongues, such as a butterfly's proboscis or a radula on a mollusc, but these are not homologous 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.[23] 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 most tetrapods.[24][25]

Society and culture

Figures of speech

The tongue can be used as a metonym for language. For example, the New Testament of the Bible, in the Book of Acts of the Apostles, Jesus' disciples on the Day of Pentecost received a type of spiritual gift: "there appeared unto them cloven tongues like as of fire, and it sat upon each of them. And they were all filled with the Holy Ghost, and began to speak with other tongues....", which amazed the crowd of Jewish people in Jerusalem, who were from various parts of the Roman Empire but could now understand what was being preached. The phrase mother tongue is used as a child's first language. Many languages[26] have the same word for "tongue" and "language".

A common temporary failure in word retrieval from memory is referred to as the tip-of-the-tongue phenomenon. The expression tongue in cheek refers to a statement that is not to be taken entirely seriously – something said or done with subtle ironic or sarcastic humour. A tongue twister is a phrase made specifically to be very difficult to pronounce. Aside from being a medical 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 a Freudian 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 of spiritual gift. Speaking in tongues is a common phrase used to describe glossolalia, which is to make smooth, language-resembling sounds that is no true spoken language itself. A deceptive person is said to have a forked tongue, and a smooth-talking person said to have a silver tongue.

Gestures

Sticking one's tongue out at someone is considered a childish gesture of rudeness and/or defiance in many countries; the act may also have sexual connotations, depending on the way in which it is done. However, in Tibet it is considered a greeting.[27] In 2009, a farmer from Fabriano, Italy was convicted and fined by the country'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.[28] Blowing a raspberry can also be meant as a gesture of derision.

Body art

Being a cultural custom for long time, tongue piercing and splitting has become quite common in western countries in recent decades. In one study, one-fifth of young adults were found to have at least one type of oral piercing, most commonly the tongue.[29]

As food

The tongues of some animals are consumed and sometimes considered delicacies. Hot tongue sandwiches are frequently found on menus in kosher delicatessens in America. Taco de lengua (lengua being Spanish for tongue) is a taco filled with beef 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, adding tomato sauce, onions and salt. Tongue can also be prepared as birria. Pig and beef tongue are consumed in Chinese cuisine. Duck tongues are sometimes employed in Szechuan dishes, while lamb's tongue is occasionally employed in Continental and contemporary American cooking. Fried cod "tongue" is a relatively common part of fish meals in Norway and Newfoundland. In Argentina and Uruguay cow tongue is cooked and served in vinegar (lengua a la vinagreta). In the Czech Republic and 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 jelled; beef tongues fetch a significantly higher price and are considered more of a delicacy. In Alaska, cow tongues are among the more common.

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.[30]

Additional images

Tongue.agr

The human tongue

Spots on the tongue

Spots on the tongue

زبان

Exclusive Lines on the tongue

Okapitongue

An okapi cleaning its muzzle with its tongue

Mouth illustration-Otis Archives

Medical illustration of a human mouth by Duncan Kenneth Winter

See also

References

This article incorporates text in the public domain from page 1125 of the 20th edition of Gray's Anatomy (1918)

  1. ^ hednk-024—Embryo Images at University of North Carolina
  2. ^ Maton, Anthea; Hopkins, Jean; McLaughlin, Charles William; Johnson, Susan; Warner, Maryanna Quon; LaHart, David; Wright, Jill D. (1993). Human Biology and Health. Englewood Cliffs, New Jersey, USA: Prentice Hall. ISBN 0-13-981176-1.
  3. ^ a b "Tongue". Online Etymology Dictionary. Retrieved 17 September 2017.
  4. ^ Kerrod, Robin (1997). MacMillan's Encyclopedia of Science. 6. Macmillan Publishing Company, Inc. ISBN 0-02-864558-8.
  5. ^ a b c d e f g Drake, Richard L.; Vogl, Wayne; Mitchell, Adam W. M. (2005). Gray's anatomy for students. Philadelphia, Pennsylvania: Elsevier. pp. 989–995. ISBN 978-0-8089-2306-0.
  6. ^ "Pirogov's triangle". Whonamedit? - A dictionary of medical eponyms. Ole Daniel Enersen.
  7. ^ Jamrozik, T.; Wender, W. (January 1952). "Topographic anatomy of lingual arterial anastomoses; Pirogov-Belclard's triangle". Folia Morphologica. 3 (1): 51–62. PMID 13010300.
  8. ^ Dudek, Dr Ronald W. (2014). Board Review Series: Embryology (Sixth ed.). LWW. ISBN 978-1451190380.
  9. ^ Bernays, Elizabeth; Chapman, Reginald. "taste bud | anatomy". Encyclopædia Britannica.
  10. ^ Fiore, Mariano; Eroschenko, Victor (2000). Di Fiore's atlas of histology with functional correlations (PDF). Lippincott Williams & Wilkins. p. 238.
  11. ^ Hib, José (2001). Histología de Di Fiore: texto y atlas. Buenos Aires: El Ateneo. p. 189. ISBN 950-02-0386-3.
  12. ^ a b c Larsen, William J. (2001). Human embryology (Third ed.). Philadelphia, Pennsylvania: Churchill Livingstone. pp. 372–374. ISBN 0-443-06583-7.
  13. ^ Tortora, Gerard J.; Derrickson, Bryan H. (2008). "17". Principles of Anatomy and Physiology (12th ed.). Wiley. p. 602. ISBN 978-0470084717.
  14. ^ Silverhorn, Dee Unglaub (2009). "10". Human Physiology: An integrated approach (5th ed.). Benjamin Cummings. p. 352. ISBN 978-0321559807.
  15. ^ Schacter, Daniel L.; Gilbert, Daniel Todd; Wegner, Daniel M. (2009). "Sensation and Perception". Psychology (2nd ed.). New York: Worth. p. 166.
  16. ^ Atkinson, Martin E. (2013). Anatomy for Dental Students (4th ed.). Oxford University Press. ISBN 978-0199234462. the tongue is also responsible for the shaping of the bolus as food passes from the mouth to the rest of the alimentary canal
  17. ^ "Oral Cancer Facts". The Oral Cancer Foundation. 28 August 2017. Retrieved 17 September 2017.
  18. ^ Lam, L.; Logan, R. M.; Luke, C. (March 2006). "Epidemiological analysis of tongue cancer in South Australia for the 24-year period, 1977-2001". Aust Dent J. 51 (1): 16–22. doi:10.1111/j.1834-7819.2006.tb00395.x. PMID 16669472.
  19. ^ a b Newman, Michael G.; Takei, Henry; Klokkevold, Perry R.; Carranza, Fermin A. (2012). Carranza's Clinical Periodontology (11th ed.). St. Louis, Missouri: Elsevier/Saunders. pp. 84–96. ISBN 978-1-4377-0416-7.
  20. ^ Outhouse, TL; Al-Alawi, R; Fedorowicz, Z; Keenan, JV (April 19, 2006). "Tongue scraping for treating halitosis". The Cochrane Database of Systematic Reviews (2): CD005519. doi:10.1002/14651858.CD005519.pub2. PMID 16625641. (Retracted, see doi:10.1002/14651858.cd005519.pub3. If this is an intentional citation to a retracted paper, please replace {{Retracted}} with {{Retracted|intentional=yes}}.)
  21. ^ "A Dog's Tongue". DrDog.com. Dr. Dog Animal Health Care Division of BioChemics. 2014.
  22. ^ Krönert, H.; Pleschka, K. (January 1976). "Lingual blood flow and its hypothalamic control in the dog during panting". Pflügers Archiv: European Journal of Physiology. 367 (1): 25–31. doi:10.1007/BF00583652. ISSN 0031-6768.
  23. ^ 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. ISBN 0-412-61390-5.
  24. ^ Romer, Alfred Sherwood; Parsons, Thomas S. (1977). The Vertebrate Body. Philadelphia, Philadelphia: Holt-Saunders International. pp. 298–299. ISBN 0-03-910284-X.
  25. ^ Kingsley, John Sterling (1912). Comparative anatomy of vertebrates. P. Blackiston's Son & Co. pp. 217–220. ISBN 1-112-23645-7.
  26. ^ Afrikaans tong; Danish tunge; Albanian gjuha; Armenian lezu (լեզու); Greek glóssa (γλώσσα); Irish teanga; Manx çhengey; Latin and Italian lingua; Catalan llengua; French langue; Portuguese língua; Spanish lengua; Romanian limba; Bulgarian ezik (език); Polish język; Russian yazyk (язык); Czech and Slovak jazyk; Slovene, Bosnian, Croatian, and Serbian jezik; Kurdish ziman (زمان); Persian and Urdu zabān (زبان); Arabic lisān (لسان); Aramaic liššānā (ܠܫܢܐ/לשנא); Hebrew lāšon (לָשׁוֹן); Maltese ilsien; Estonian keel; Finnish kieli; Hungarian nyelv; Azerbaijani and Turkish dil; Kazakh and Khakas til (тіл)
  27. ^ Bhuchung K Tsering (27 December 2007). "Tibetan culture in the 21st century". Retrieved 13 February 2012.
  28. ^ United Press International (19 December 2009). "Sticking out your tongue ruled illegal". Rome, Italy. Retrieved 17 September 2017.
  29. ^ 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. PMID 16262620.
  30. ^ Hawes, Charles Boardman (1924). Whaling. Doubleday.

External links

Beef tongue

Beef tongue (also known as neat's tongue or ox tongue) is a dish made of the tongue of a cow.

Beef tongue is very high in fat, contributing up to 72% of its caloric content. Some countries, including Canada and specifically the province of Alberta, export large quantities of beef tongue.

Chameleon

Chameleons or chamaeleons (family Chamaeleonidae) are a distinctive and highly specialized clade of Old World lizards with 202 species described as of June 2015. These species come in a range of colors, and many species have the ability to change color.

Chameleons are distinguished by their zygodactylous feet; their very extensive, highly modified, rapidly extrudable tongues; their swaying gait; and crests or horns on their brow and snout. Most species, the larger ones in particular, also have a prehensile tail. Chameleons' eyes are independently mobile, but in aiming at a prey item, they focus forward in coordination, affording the animal stereoscopic vision.

Chameleons are adapted for climbing and visual hunting. They live in warm habitats that range from rain forest to desert conditions, with various species occurring in Africa, Madagascar, southern Europe, and across southern Asia as far as Sri Lanka. They also have been introduced to Hawaii, California, and Florida, and often are kept as household pets.

First language

A first language, native language or mother/father/parent tongue (also known as arterial language or L1), is a language that a person has been exposed to from birth or within the critical period. In some countries, the term native language or mother tongue refers to the language of one's ethnic group rather than one's first language. Children brought up speaking more than one language can have more than one native language, and be bilingual or multilingual. By contrast, a second language is any language that one speaks other than one's first language.

French kiss

In English informal speech, a French kiss, also known as a deep kiss, is an amorous kiss in which the participants' tongues extend to touch each other's lips or tongue. A "kiss with the tongue" stimulates the partner's lips, tongue and mouth, which are sensitive to the touch and induce physiological sexual arousal. The oral zone is one of the principal erogenous zones of the body. The implication is of a slow, passionate kiss which is considered intimate, romantic, erotic or sexual. The sensation when two tongues touch, also known as "tongue touching", has been proven to stimulate endorphin release and reduce acute stress levels. French kissing is often described as ‘1st base’, and is used by many as an indicator of what stage a relationship has reached.

Geographic tongue

Geographic tongue, also known by several other terms, is an inflammatory condition of the mucous membrane of the tongue, usually on the dorsal surface. It is a common condition, affecting approximately 2–3% of the general population. It is characterized by areas of smooth, red depapillation (loss of lingual papillae) which migrate over time. The name comes from the map-like appearance of the tongue, with the patches resembling the islands of an archipelago. The cause is unknown, but the condition is entirely benign (importantly, it does not represent oral cancer), and there is no curative treatment. Uncommonly, geographic tongue may cause a burning sensation on the tongue, for which various treatments have been described with little formal evidence of efficacy.

Glossitis

Glossitis can mean soreness of the tongue, or more usually inflammation with depapillation of the dorsal surface of the tongue (loss of the lingual papillae), leaving a smooth and erythematous (reddened) surface, (sometimes specifically termed atrophic glossitis). In a wider sense, glossitis can mean inflammation of the tongue generally. Glossitis is often caused by nutritional deficiencies and may be painless or cause discomfort. Glossitis usually responds well to treatment if the cause is identified and corrected. Tongue soreness caused by glossitis is differentiated from burning mouth syndrome, where there is no identifiable change in the appearance of the tongue, and there are no identifiable causes.

Human digestive system

The human digestive system consists of the gastrointestinal tract plus the accessory organs of digestion (the tongue, salivary glands, pancreas, liver, and gallbladder). Digestion involves the breakdown of food into smaller and smaller components, until they can be absorbed and assimilated into the body. The process of digestion has many stages. The first stage is the cephalic phase of digestion which begins with gastric secretions in response to the sight and smell of food. The next stage starts in the mouth.

Chewing, in which food is mixed with saliva, begins the mechanical process of digestion. This produces a bolus which can be swallowed down the esophagus to enter the stomach. Here it is mixed with gastric acid until it passes into the duodenum where it is mixed with a number of enzymes produced by the pancreas. Saliva also contains a catalytic enzyme called amylase which starts to act on food in the mouth. Another digestive enzyme called lingual lipase is secreted by some of the lingual papillae on the tongue and also from serous glands in the main salivary glands. Digestion is helped by the chewing of food carried out by the muscles of mastication, by the teeth, and also by the contractions of peristalsis, and segmentation. Gastric acid, and the production of mucus in the stomach, are essential for the continuation of digestion.

Peristalsis is the rhythmic contraction of muscles that begins in the esophagus and continues along the wall of the stomach and the rest of the gastrointestinal tract. This initially results in the production of chyme which when fully broken down in the small intestine is absorbed as chyle into the lymphatic system. Most of the digestion of food takes place in the small intestine. Water and some minerals are reabsorbed back into the blood in the colon of the large intestine. The waste products of digestion (feces) are defecated from the anus via the rectum.

Lillie Glacier

Lillie Glacier (70°45′S 163°55′E) is a large glacier in Antarctica, about 100 nautical miles (190 km) long and 10 nautical miles (19 km) wide. It lies between the Bowers Mountains on the west and the Concord Mountains and Anare Mountains on the east, flowing to Ob' Bay on the coast and forming the Lillie Glacier Tongue.

The glacier tongue (70°34′S 163°48′E), the prominent seaward extension of the glacier into Ob' Bay, was discovered by the British Antarctic Expedition, 1910–13, when the Terra Nova explored westward of Cape North in February 1911. It was named by the expedition for Dennis G. Lillie, a biologist on the Terra Nova. The name Lillie has since been extended to the entire glacier.

The lower half of the glacier was plotted by the Australian National Antarctic Research Expedition (Thala Dan) in 1962, which explored the area and utilized air photos taken by U.S. Navy Operation Highjump, 1946–47. The whole feature was mapped by the United States Geological Survey from surveys and U.S. Navy air photos, 1960–62.

Lingua franca

A lingua franca ( (listen); lit. Frankish tongue), also known as a bridge language, common language, trade language, auxiliary language, vehicular language, or link language is a language or dialect systematically used to make communication possible between groups of people who do not share a native language or dialect, particularly when it is a third language that is distinct from both of the speakers' native languages.Lingua francas have developed around the world throughout human history, sometimes for commercial reasons (so-called "trade languages" facilitated trade), but also for cultural, religious, diplomatic, and administrative convenience, and as a means of exchanging information between scientists and other scholars of different nationalities. The term is taken from the medieval Mediterranean Lingua Franca, a Romance-based pidgin language used (especially by traders and seamen) as a lingua franca in the Mediterranean Basin from the 11th to the 19th century. A world language – a language spoken internationally and by a large number of people – is a language that may function as a global lingua franca.

Mertz Glacier

Mertz Glacier (67°30′S 144°45′E) is a heavily crevassed glacier in George V Coast of East Antarctica. It is the source of a glacial prominence that historically has extended northward into the Southern Ocean, the Mertz Glacial Tongue. It is named in honor of the Swiss explorer Xavier Mertz.

The Mertz-Ninnis Valley (67°25′S 146°0′E) is an undersea valley named in association with the Mertz Glacier and the Ninnis Glacier.

Oral sex

Oral sex, sometimes referred to as oral intercourse, is sexual activity involving the stimulation of the genitalia of a person by another person using the mouth (including the lips, tongue or teeth) or throat. Cunnilingus is oral sex performed on female genitals, while fellatio is oral sex performed on a penis. Anilingus, another form of oral sex, is oral stimulation of a person's anus. Oral stimulation of other parts of the body (as in kissing and licking) is usually not considered oral sex.

Oral sex may be performed as foreplay to incite sexual arousal before other sexual activities (such as vaginal or anal intercourse), or as an erotic and physically intimate act in its own right. Like most forms of sexual activity, oral sex can pose a risk for contracting sexually transmitted infections (STIs/STDs). However, the transmission risk for oral sex, especially HIV transmission, is significantly lower than for vaginal or anal sex.Oral sex is often regarded as taboo, but most countries do not have laws which ban the practice. Commonly, people do not regard oral sex as affecting the virginity of either partner, though opinions on the matter vary. People may also have negative feelings or sexual inhibitions about giving or receiving oral sex, or may flatly refuse to engage in the practice.

Phonetics

Phonetics is a branch of linguistics that studies the sounds of human speech, or—in the case of sign languages—the equivalent aspects of sign. It is concerned with the physical properties of speech sounds or signs (phones): their physiological production, acoustic properties, auditory perception, and neurophysiological status.

Phonetics as a research discipline has three main branches:

Articulatory phonetics: the articulation of speech

Acoustic phonetics: the acoustics of speech

Auditory phonetics: the perception of speechPhonetic insight is used in a number of applied linguistic fields such as:

Forensic phonetics: the use of phonetics for legal purposes

Speech recognition: the analysis and transcription of recorded speech by a computer system

Speech synthesis: the production of human speech by a computer systemPhonology, on the other hand, is concerned with the abstract, grammatical characterization of systems of sounds or signs and how they pattern in and across languages. Phonology has been argued to relate to phonetics via the set of distinctive features, which map the abstract representations of speech units to articulatory gestures, acoustic signals or perceptual representations.

Postalveolar consonant

Postalveolar consonants (sometimes spelled post-alveolar) are consonants articulated with the tongue near or touching the back of the alveolar ridge, farther back in the mouth than the alveolar consonants, which are at the ridge itself but not as far back as the hard palate, the place of articulation for palatal consonants. Examples of postalveolar consonants are the English palato-alveolar consonants [ʃ] [tʃ] [ʒ] [dʒ], as in the words "ship", "'chill", "vision", and "jump", respectively.

There are a large number of types of postalveolar sounds, especially among the sibilants. The three primary types are palato-alveolar (such as [ʃ ʒ], weakly palatalized), alveolo-palatal (such as [ɕ ʑ], strongly palatalized), and retroflex (such as [ʂ ʐ], unpalatalized). The palato-alveolar and alveolo-palatal subtypes are commonly counted as "palatals" in phonology since they rarely contrast with true palatal consonants.

Retroflex consonant

A retroflex consonant is a coronal consonant where the tongue has a flat, concave, or even curled shape, and is articulated between the alveolar ridge and the hard palate. They are sometimes referred to as cerebral consonants, especially in Indology. Other terms occasionally encountered are apico-domal and cacuminal.

The Latin-derived word retroflex means "bent back"; some retroflex consonants are pronounced with the tongue fully curled back so that articulation involves the underside of the tongue tip (subapical). These sounds are sometimes described as "true" retroflex consonants. However, retroflexes are commonly taken to include other consonants having a similar place of articulation without such extreme curling of the tongue; these may be articulated with the tongue tip (apical) or the tongue blade (laminal).

Sibilant

In Phonetics, sibilants are fricative consonants of higher amplitude and pitch, made by directing a stream of air with the tongue towards the teeth. Examples of sibilants are the consonants at the beginning of the English words sip, zip, ship, and genre. The symbols in the International Phonetic Alphabet used to denote the sibilant sounds in these words are, respectively, [s] [z] [ʃ] [ʒ]. Sibilants have a characteristically intense sound, which accounts for their paralinguistic use in getting one's attention (e.g. calling someone using "psst!" or quieting someone using "shhhh!").

In the alveolar hissing sibilants [s] and [z], the back of the tongue forms a narrow channel (is grooved) to focus the stream of air more intensely, resulting in a high pitch. With the hushing sibilants (occasionally termed shibilants), such as English [ʃ], [tʃ], [ʒ], and [dʒ], the tongue is flatter, and the resulting pitch lower.A broader category is stridents, which include more fricatives such as uvulars than sibilants. Because all sibilants are also stridents, the terms are sometimes used interchangeably. However, the terms do not mean the same thing. The English stridents are /f, v, s, z, ʃ, ʒ, tʃ, dʒ/. Sibilants are a higher pitched subset of the stridents. The English sibilants are /s, z, ʃ, ʒ, tʃ, dʒ/. On the other hand, /f/ and /v/ are stridents, but not sibilants, because they are lower in pitch.

"Stridency" refers to the perceptual intensity of the sound of a sibilant consonant, or obstacle fricatives or affricates, which refers to the critical role of the teeth in producing the sound as an obstacle to the airstream. Non-sibilant fricatives and affricates produce their characteristic sound directly with the tongue or lips etc. and the place of contact in the mouth, without secondary involvement of the teeth.

The characteristic intensity of sibilants means that small variations in tongue shape and position are perceivable, with the result that there are a large number of sibilant types that contrast in various languages.

Taste bud

Taste buds contain the taste receptor cells, which are also known as gustatory cells. The taste receptors are located around the small structures known as papillae found on the upper surface of the tongue, soft palate, upper esophagus, the cheek, and epiglottis. These structures are involved in detecting the five elements of taste perception: salty, sour, bitter, sweet and umami. A popular myth assigns these different tastes to different regions of the tongue; in reality these tastes can be detected by any area of the tongue. Via small openings in the tongue epithelium, called taste pores, parts of the food dissolved in saliva come into contact with the taste receptors. These are located on top of the taste receptor cells that constitute the taste buds. The taste receptor cells send information detected by clusters of various receptors and ion channels to the gustatory areas of the brain via the seventh, ninth and tenth cranial nerves.

On average, the human tongue has 2,000–8,000 taste buds.

Thwaites Glacier

Thwaites Glacier (75°30′S 106°45′W) is an unusually broad and fast Antarctic glacier flowing into Pine Island Bay, part of the Amundsen Sea, east of Mount Murphy, on the Walgreen Coast of Marie Byrd Land. Its surface speeds exceed 2 km/yr near its grounding line. Its fastest flowing grounded ice is centred between 50 and 100 km east of Mount Murphy. It was named by ACAN after Fredrik T. Thwaites, a glacial geologist, geomorphologist and professor emeritus at the University of Wisconsin–Madison. Thwaites Glacier is closely watched for its potential to raise sea levels.Along with Pine Island Glacier, Thwaites Glacier has been described as part of the "weak underbelly" of the West Antarctic Ice Sheet, due to its apparent vulnerability to significant retreat. This hypothesis is based on theoretical studies of the stability of marine ice sheets and observations of large changes on both of these glaciers. In recent years, the flow of both of these glaciers has accelerated, their surfaces have lowered, and the grounding lines have retreated.

Tongue-in-cheek

The idiom tongue-in-cheek refers to a humorous or sarcastic statement expressed in a mock serious manner.

Tongue and groove

Tongue and groove is a method of fitting similar objects together, edge to edge, used mainly with wood, in flooring, parquetry, panelling, and similar constructions. Tongue and groove joints allow two flat pieces to be joined strongly together to make a single flat surface. Before plywood became common, tongue and groove boards were also used for sheathing buildings and to construct concrete formwork.

A strong joint, the tongue and groove joint is widely used for re-entrant angles. The effect of wood shrinkage is concealed when the joint is beaded or otherwise moulded. In expensive cabinet work, glued dovetail and multiple tongue and groove are used.

Each piece has a slot (the groove) cut all along one edge, and a thin, deep ridge (the tongue) on the opposite edge. The tongue projects a little less than the depth of the groove. Two or more pieces thus fit together closely. The joint is not normally glued, as shrinkage would then pull the tongue off.

In another assembly method, the pieces are end-matched. This method eliminates the need for mitre joints, face nailing, and the use of joints on 16-inch (410 mm) or 24-inch (610 mm) centres of conventional framing.

For many uses, tongue and groove boards have been rendered obsolete by the introduction of plywood and later composite wood boards, but the method is still used in higher-quality boards. Plywood may also be tongued all round to fit it flush into a framed structure, and plywood for sub-floors used in platform framing is often supplied with tongue and groove edges.

When joining thicker materials, several tongue and groove joints may be used one above the other.

"Tongue and groove" is sometimes abbreviated as T&G (for example, on price tags and shelf tags).

Anatomy of the mouth
Lip
Cheek
Palate
Gums
Glands
Teeth
Tongue
Back of mouth
Anatomy of taste
Tongue
Path
Other
Basic tastes
Anatomy
Gustology
Other
See also

This page is based on a Wikipedia article written by authors (here).
Text is available under the CC BY-SA 3.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.