Tongue – Anatomy, Blood Nerve Supply, Functions

The tongue is the muscular organ found in the vertebrate mouth. It is attached via muscles to the hyoid bone, mandible?, styloid process, palate, and pharynx? and divided into two parts by the V-shaped sulcus terminalis. These two parts, an anterior two thirds, and a posterior one third are structurally and developmentally distinct. The foramen cecum? at the apex of the sulcus terminal indicates the site of the embryonic origin of the thyroglossal duct.[rx][rx][rx]

The following papillae cover the tongue and are used for taste perception:

• Vallarta papillae – are arranged in a V-shape anterior to the sulcus terminalis and studded with numerous taste buds. Innervation is by the glossopharyngeal nerve (CN IX).
• Fungiform papillae are mushroom-shaped papillae with erythematous domes, located on the lateral aspects and at the apex of the tongue.
• Filiform papillae are slim, cone-shaped projections organized in rows parallel to the sulcus terminalis.
• Foliate papillae are rarely found in humans (vestigial).

Another important part of the tongue is the lingual tonsil, a collection of nodular lymphatic tissue towards the posterior one-third of the dorsum of the tongue.

Structure and Function of Tongue

The functions of the tongue include taste, speech, and food manipulation in the oral cavity.

Taste Functions

Chemicals that interact with the taste buds in the tongue are referred to as “tastants.” Taste buds themselves are found within the various papillae of the tongue. Tastants interact with gustatory cell receptors in the taste buds, resulting in the transduction of a taste sensation. The five broad categories of taste receptors are

• (1) sweet,
• (2) salty,
• (3) sour,
• (4) bitter, and
• (5) umami.
• The lingual papillae are divided into the vallate (or circumvallate), fungiform, filiform, and foliate papillae. More than half of the taste buds are located on the vallate papillae at the junction of the oral and oropharyngeal tongue or tongue base.

Speech Functions

• Speech is produced in part by manipulation of the tongue in the mouth against the teeth and palate within the oral cavity. The intrinsic muscles of the tongue are involved primarily in shaping the tongue for speech.

Food Manipulation Functions

• The tongue moves food around the mouth within the oral cavity by pressing it against the hard palate and out to the sides to enable mastication. It enables the formation of the food bolus in the oral preparatory phase of swallowing.
• It also takes part in the oral phase of swallowing by elevating and sweeping posteriorly to propel the food bolus past the anterior tonsillar pillar, triggering the swallowing reflex.

Blood Supply and Lymphatics of Tongue

Blood supply to the tongue is predominantly from the lingual artery?, a branch of the external carotid artery between the superior thyroid? artery and the facial artery, which departs at the level of the greater horn of the hyoid bone within the carotid triangle. After branching from the external carotid artery, the lingual artery passes deep to the hyoglossus muscle and superficial to the middle pharyngeal constrictor muscle. It then gives rise to the following four arteries?:

• The suprahyoid artery – supplies the omohyoid, sternothyroid, and thyrohyoid muscles. They anastomose with the corresponding vessels from the opposite side.
• The dorsal lingual arteries – arise beneath the hyoglossus muscle and pass to the posterior part of the dorsum of the tongue. They supply the mucous membrane of this region as well as the glossopalatine arch, lingual tonsils, soft palate, and epiglottis?. They anastomose with their corresponding vessels on the opposite side.
• The sublingual artery – branches at the anterior border of the hyoglossus muscle before passing between the genioglossus muscle and mylohyoid muscle to the sublingual gland. It supplies the sublingual gland before giving branches to the mylohyoid muscle. One branch from the sublingual artery passes posterior to the alveolar process of the mandible and anastomoses with the corresponding artery from the other side. A second branch of the sublingual artery pierces the mylohyoid muscle and anastomoses with the submental branch of the facial artery.
• The deep lingual artery – which is the termination of the lingual artery, passes between the genioglossus muscle and inferior longitudinal muscle.

Nerves of Tongue

• The hypoglossal nerve (CN XII) provides motor innervation to all of the intrinsic and extrinsic muscles of the tongue except for the palatoglossus muscle, which is innervated by the vagus nerve (CN X). It runs superficial to the hyoglossus muscle. Lesions of the hypoglossal nerve cause deviation of the tongue to the ipsilateral (i.e., damaged) side.
• Taste to the anterior two-thirds of the tongue is achieved through innervation from the chorda tympani nerve, a branch of the facial nerve (CN VII). General sensation to the anterior two-thirds of the tongue is by innervation from the lingual nerve, a branch of the mandibular branch of the trigeminal nerve (CN V3). The lingual nerve is located deep and medial to the hyoglossus muscle and is associated with the submandibular ganglion?.
• On the other hand, taste to the posterior one-third of the tongue is accomplished through innervation from the glossopharyngeal nerve (CN IX), which also provides general sensation to the posterior one-third of the tongue.
• Taste perception also is performed by both the epiglottis and the epiglottic region of the tongue, which receives taste and general sensation from innervation by the internal laryngeal branch of the vagus nerve (CN X). Damage to the vagus nerve (CN X) causes contralateral deviation (i.e., away from the injured side) of the uvula.

Muscles of Tongue

The tongue’s intrinsic muscles include the following:

• The superior longitudinal lingual muscle, which shortens the tongue and curls it upward.
• The inferior longitudinal lingual muscle, which shortens the tongue and curls it downward.
• The transverse lingual muscle, which elongates and narrows the tongue.
• The vertical lingual muscle, which flattens the tongue.

The tongue’s extrinsic muscles include the following:

• The genioglossus muscle – which protrudes the tongue, and is innervated by the hypoglossal nerve (CN XII).
• The styloglossus muscle – which draws up the sides of the tongue to create a trough for swallowing following adequate mastication. The pair of styloglossus muscles works together on each side to retract the tongue. The styloglossus muscle is innervated by the hypoglossal nerve (CN XII).
• The hyoglossus muscle – which depresses and retracts the tongue and is innervated by the hypoglossal nerve (CN XII).
• The palatoglossus muscle – which elevates the posterior tongue, closes the oropharyngeal isthmus, aids in the initiation of swallowing, and prevents the spill of saliva from the vestibule into the oropharynx by maintaining the palatoglossal arch. It is the only extrinsic muscle of the tongue that is not innervated by the hypoglossal nerve; instead, it is innervated by the vagus nerve (CN X).

Physiologic Variants

• Ankyloglossia (“tongue-tie”) – occurs due to an abnormal length of the frenulum linguae which causes limited manipulation of the tongue during speech and results in a speech impediment. In the most common form of ankyloglossia, the frenulum extends to the tip of the tongue. Ankyloglossia can be corrected by surgically severing the lingual frenulum. [rx][rx]
• Fissured tongue (“scrotal tongue,” “plicated tongue”) – occurs when several small furrows present on the dorsal surface of the tongue. It can be an oral manifestation of psoriasis?. It is generally painless and benign?, and is often associated with other syndromes (e.g., Down syndrome?).[rx]
• Geographic tongue (“migratory glossitis”) – is a benign, asymptomatic? condition characterized by the presence of large red patches with a greyish-white border covering the dorsum of an otherwise normal tongue. It is caused by inflammation? of the mucous membrane of the tongue, which results in loss of lingual papillae. The lesions are known to migrate over time. The name arises from the map-like appearance of the tongue in this condition.[rx][rx]

Pathophysiology of Tongue

Developmental and structural abnormalities of the tongue are common features. The various morphological variations that may occur during the development of tongue are[rx]:

• Aglossia
• Microglossia
• Macroglossia
• Ankyloglossia
• Cleft tongue
• Pentafid tongue
• Fissured tongue
• Geographic tongue
• Hairy tongue
• Median rhomboid glossitis

Aglossia – Congenital? absence of the tongue is extremely rare. Usually, the tongue is absent in cases of gross underdevelopment or maldevelopment of the first visceral arches.

Macroglossia – It is an uncommon developmental condition and is also known as hypoglossia. Its defining feature is a rudimentary or an abnormally small tongue. It leads to limited muscular movement and is associated with syndromes such as Hanhart syndrome.

Macroglossia – Macroglossia is an infrequently encountered condition characterized by tongue enlargement, seen in association with other congenital defects leading to syndromes such as down syndrome (trisomy 21), Beckwith-Wiedemann syndrome.

Ankyloglossia – It occurs due to failure in cellular degeneration leading to a longer anchorage between the tongue and floor of the mouth; this is commonly known as “tongue-tied” and demonstrates an abnormally short lingual frenulum. Ankyloglossia can range in severity from mild? to complete ankyloglossia in which the tongue gets fused to the floor of the mouth restricting its free movement.[rx] A short lingual frenulum leading to tongue-tie is also associated with several genetic? syndromes such as related Robinow syndrome, oral-facial-digital syndrome Type I, Opitz syndrome, and Van der Woude syndrome.

Cleft tongue – It is also known as bifid tongue and occurs when the lateral swellings fail to merge. It can be partial or complete. The former is a more common entity and is manifested as a deep groove on the dorsal surface of the tongue in the midline. It occurs when the mesenchymal proliferation interferes with the merging leading to failure of the obliteration of the groove. There are reports of bifid tongue in syndromic cases like Opitz G BBB syndrome, oral-facial-digital syndrome type I, Klippel–Feil anomaly, and Larsen syndrome.[rx]

Pentafid tongue – Disturbance in the mesodermal penetration and mesenchymal fusion during the development of tongue development is responsible for this malformation.

Fissured tongue – It is also known as scrotal tongue or lingua fissurata. It is congenital anomaly? manifested as grooves oriented anteroposteriorly on the dorsal aspect of the tongue with multiple branches extending towards the lateral aspect. The grooves range from 2 to 6 mm in depth. In a severe? form of the fissured tongue, when the grooves are extremely prominent and interconnected, the tongue may appear to be lobulated. It can also present in association with down syndrome or Melkerson-Rosenthal syndrome (a triad of the fissure, granulomatous cheilitis, and cranial nerve VII paralysis?).

Geographic tongue – Geographic tongue, also known as lingua geographica or benign migratory glossitis is an inflammatory disorder caused by loss of filiform papillae.

Hairy tongue – It is also known as a black hairy tongue and characteristically demonstrates the accumulation of excess keratin on the filiform papillae on the dorsal surface of the tongue leading to the formation of elongated strands resembling hair. This condition most commonly affects the midline just anterior to the circumvallate papillae, usually sparing the lateral and anterior borders.

Median rhomboid glossitis – It is a condition that presents in the midline of the dorsal surface of the tongue, just in front of the circumvallate papillae. It presents as a well-demarcated, symmetric, depopulated area. However, it also occasionally appears in the paramedical location.

Function of Tongue

The tongue participates in a variety of functions such as taste, speech, and food manipulation and cleaning of the oral cavity.

Taste Functions

The dorsal surface of the tongue is covered by a stratified squamous epithelium, with numerous papillae such as circumvallate papilla, fungiform papilla, filiform papilla, and foliate papilla. Taste buds which are intraepithelial chemosensory organs present within these papillae are responsible for taste perception. The circumvallate papilla carries the maximum number of taste buds. These taste buds via gustatory cell receptors interact with the chemicals present in the food and induce different taste sensations (sweet, salty, sour, and bitter).

Speech Functions

Various speech sounds require the interaction of the tongue with the teeth and different parts of the palate. The linguodental sounds such as “Th” require interaction between the tip of the tongue with the incisal surface of upper and lower incisors. The linguopalatal sounds may include the contact of the tongue with the anterior or the posterior part of the hard palate. When the tip of the tongue contacts with the anterior part of the hard palate, sounds such as “D, T, N, and, Z” is produced. When the tongue forms a valve and contacts the posterior part of the hard palate, it produces sounds like “ch” and “sh.” The velar sounds include a contact of the posterior part of the tongue with the soft palate. these sounds include “k” and “g .”

Food Manipulation Functions

The tongue aids in moving the food onto the occlusal surface of the teeth, mixing it with saliva as the food move away from the teeth, and in placing the food again on the teeth.[rx] Thus, it helps in the formation of food bolus during the oral phase of deglutition. It also helps in propelling the food bolus beyond the anterior tonsillar pillar, which triggers the swallowing reflex.

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