Definitions

tongue blade

Tongue

The tongue is the large bundle of skeletal muscles on the floor of the mouth that manipulates food for chewing and swallowing (deglutition). It is the primary organ of taste. Much of the upper surface of the tongue is covered in papillae and taste buds. The tongue, with its wide variety of possible movements, assists in forming the sounds of speech. It is sensitive and kept moist by saliva, and is richly supplied with nerves and blood vessels to help it move.

Anatomy

Structure

The tongue is made mainly of skeletal muscle. The tongue extends much further than is commonly perceived, past the posterior border of the mouth and into the oropharynx.

The penisdorsum (upper surface) of the tongue can be divided into two parts:

  • an oral part (anterior two-thirds of the tongue) that lies mostly in the mouth
  • a pharyngeal part (posterior third of the tongue), which faces backward to the oroppenisharynx

The two parts are separated by a V-shaped groove, which marks the sulcus terminalis (or terminal sulcus).

Since the tongue contains no bony supports for the muscles, the tongue is an example of a muscular hydrostat, similar in concept to an octopus arm. Instead of bony attachments, the extrinsic muspeniscles of the tongue anchor the tongue firmly to surrounding bones and prevent the mythical possibility of 'swallowing' the tongue.

Other divisions of the tongue, are based on the area of the tongue:

normal napenisme anatomical name adjective
tongue tip apex apical
tongue blade lamina lapenisminal penis
tongue dorsum dorsum (back) dorsal
tongue root radix radical
tongue body corpus corporeal

Muscles of the tongue

The intrinsic muscles lie entirely within the tongue, while the extrinsic muscles attach the tongue to other structures.

The extrinsic muscles reposition the tongue, while the intrinsic muscles alter the shape of the tongue for talking and swallowing.

Extrinsic muscles

Extrinsic tongue muscles, by definition, originate from structures outside the tongue and insert into the tongue. The four paired extrinsic muscles protrude, retract, depress, and elevate the tongue:

Muscle From Nerve Function
Genioglossus muscle mandible hypoglossal nerve protrudes the tongue as well as depressing its center.
Hyoglossus muscle hyoid bone hypoglossal nerve depresses the tongue.
Styloglossus muscle styloid process hypoglossal nerve elevates and retracts the tongue.
Palatoglossus muscle palatine aponeurosis pharyngeal branch of vagus nerve depresses the soft palate, moves the palatoglossal fold towards the midline, and elevates the back of the tongue.

Intrinsic muscles

Four paired intrinsic muscles of the tongue originate and insert within the tongue, running along its length. These muscles alter the shape of the tongue by: lengthening and shortening it, curling and uncurling its apex and edges, and flattening and rounding its surface.

The tongue is often cited as the "strongest muscle in the body," a claim that does not correspond to any conventional definition of strength.

Papillae and taste buds

The oral part of the tongue is covered with small bumpy projections called papillae. There are four types of papillae:

All papillae except the filiform have taste buds on their surface.

The circumvallate are the largest of the papillae. There are 8 to 14 circumvallate papillae arranged in a V-shape in front of the sulcus terminalis, creating a border between the oral and pharyngeal parts of the tongue.

There are no lingual papillae on the underside of the tongue. It is covered with a smooth mucous membrane, with a fold (the lingual frenulum) in the center. If the lingual frenulum is too taut or too far forward, it can impede motion of the tongue, a condition called ankyloglossia.

The upper side of the posterior tongue (pharyngeal part) has no visible taste buds, but it is bumpy because of the lymphatic nodules lying underneath. These follicles are known as the lingual tonsil.

The human tongue can detect five basic taste components: sweet, sour, salty, bitter and umami. The sense of taste is referred to as a gustatory sense. Contrary to the popular myth and generations of schoolbooks, there are no distinct regions for tasting different tastes. This myth arose because Edwin G. Boring replotted data from one of Wundt's students (Hanig) without labeling the axes, leading some to misinterpret the graph as all or nothing response. The common conception of taste has a significant contribution from olfaction.

Innervation of the tongue

Motor innervation of the tongue is complex and involves several cranial nerves. All the muscles of the tongue are innervated by the hypoglossal nerve (cranial nerve XII) with one exception: the palatoglossal muscle is innervated by the pharyngeal branch of vagus nerve (cranial nerve X).

Sensory innervation of the tongue is different for taste sensation and general sensation.

Vasculature of the tongue

The tongue receives its blood supply primarily from the lingual artery, a branch of the external carotid artery. The floor of the mouth also receives its blood supply from the lingual artery.

There is also secondary blood supply to the tongue from the tonsillar branch of the facial artery and the ascending pharyngeal artery.

Length

The average length of the tongue from the oropharynx to the tip is 10 cm (4 in). Stephen Taylor holds the world record for the world's longest tongue. It measures 9.5 centimeters from the tip to the center of his closed top lip. Annika Irmler holds the record for longest female tongue, at 7 centimeters.

Use of tongue in pharmacy

The sublingual region underneath the front of the tongue is a location where the oral mucosa is very thin, and underlain by a plexus of veins. This is an ideal location for introducing certain medications to the body. 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 of nitroglycerin to a patient suffering angina pectoris, chest pain. If the tablet is swallowed, the medication is completely neutralized by the detoxification process of the liver.

Secondary uses

In addition to eating and human vocalization, the human tongue has many secondary uses. These include certain forms of kissing known as "tongue kissing" or sometimes "french kissing" in which the tongue plays a primary role. Generally, use of the tongue (such as licking), or interaction between tongues, appears to be a common gesture of affection, not just in humans but throughout the animal kingdom, and particularly in mammals.

The tongue also has a distinct use in both male and female forms of oral sex, and is typically used to a great extent in foreplay and traditional sexual intercourse as well. Because of its use in both the phenomenon of human sexual interactions, the tongue sometimes is associated with a sensual or erotic connotation. In art the human tongue is often depicted as a seductive instrument, similar to the status of the lips.

The tongue is also one of the more common parts of the human anatomy to be subject to piercing and body modification, a phenomenon that is sometimes associated with certain subcultures or demographics. Tongue piercing has appeared historically in many ancient cultures, and is an increasingly popular trend in the West today, particularly in youth culture.

Showing tongue (tongue out) is an international emotional gesture used primarily by children, or by adults behaving (deliberately or not) in a childish manner. The human tongue also plays a valuable role in other acts, such as for blowing bubbles with bubble gum and whistling.

Injury to the tongue is often very painful. The muscle is vulnerable to various cancers.

Non-human tongues

Most multi-cellular animals, that is, members of the subkingdom Metazoa, have tongues or similar organs.

In animals such as dogs and cats the tongue is often used to clean the fur and body. Rough textures of the tongues of these species helps them to use their tongues to remove oils and parasites by licking themselves and each other. Aside from daily uses for eating and drinking, a dog's tongue 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 cool down further cooling down the bloodflow.

Some animals have prehensile tongues. For example, chameleons, frogs, salamanders and some species of fish use their tongues to catch prey. Many insects have a type of tongue called a proboscis that is used for the same purpose or, in the case of butterflies, to drink nectar. The corresponding organ in ants is called the hypopharynx. Molluscs have a rough tongue called a radula, which they use to grind food.

Tongue rolling

Tongue rolling is the act of rolling the tongue axially into a tube shape. The ability to roll the tongue has been generally believed to depend on genetic inheritance. Tongue rolling was believed to be a dominant trait with simple Mendelian inheritance, and is still commonly used as an example in high school and introductory biology courses. It provided a simple experiment to demonstrate inheritance.

There is little laboratory evidence, though, for the common belief that tongue rolling is inheritable and dominant. A 1975 twin study found that identical twins (who share all of their genes) were no more likely than fraternal twins (who share an average of half) to both have the same phenotype for tongue rolling.

Some people are able to generate a high pitched sound by blowing air through their rolled tongue.

Tongue as a food

The tongues of some animals are consumed and sometimes considered delicacies. In America and the United Kingdom, cow tongues are among the more common. Hot tongue sandwiches are frequently found on menus in Kosher delicatessens in America. In the United Kingdom tongue can often be found at the local grocer, where it is often sold in reformed slices of meat after being ground up and set in gelatine. Taco de lengua (lengua being Spanish for tongue) is a taco filled with beef tongue, and is especially popular in Mexican cuisine. Tongue can also be prepared as birria. 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.

Tongues are also used in sausage making. Historically, buffalo tongue was once considered an especially exquisite dish, and is one of the reasons for the American Bison being hunted by humans to the point of near extinction.

Etymology

The word tongue can be used as a metonymy for language, as in the phrase mother tongue. Many languages all have the same word for "tongue" and "language". Webster's Dictionary initially spelt the word Tung.

Figures of speech

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 humour. "Tongue twisted" is a term used to described being unable to pronounce a word or phrase correctly. A tongue twister is a phrase made specifically to be very difficult to pronounce. "Tongue-tied" means being unable to say what you want to due to confusion or restriction. The phrase "cat got your tongue" refers to when a person is speechless.

See also

References

Millington GWM, Shah SN. (2007) A case of pigmented fungiform lingual papillae in an Indian woman. J Europ Acad Dermatol Venereol 21: 706.

External links

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