Tongue

Lingua

Also known as: glossa

The tongue is a mobile mass of skeletal muscle covered by specialised mucosa. It moves food during chewing and swallowing, carries the taste buds and shapes speech sounds.

Show on body map Respiratory Tract

Overview

Vallate papillae8–12, in a V in front of the sulcus terminalis

Taste buds (total)≈2000–8000

Motor nerveCN XII (palatoglossus: CN X)

A V-shaped groove, the sulcus terminalis, divides the tongue into an anterior two-thirds (oral part) and a posterior one-third (pharyngeal part). The foramen caecum at the apex of the V is where the thyroid diverticulum began in the embryo. The split has an embryological basis. The anterior two-thirds develops from the first pharyngeal arch (lateral lingual swellings and tuberculum impar). The posterior third develops mainly from the third and fourth arches (copula and hypopharyngeal eminence). This explains the different sensory nerves of the two parts.

The muscles fall into two groups. Intrinsic muscles (superior and inferior longitudinal, transverse and vertical) lie entirely within the tongue and change its shape. Extrinsic muscles attach to bone and change its position: genioglossus protrudes it and depresses the centre, hyoglossus depresses it, styloglossus retracts and elevates it, and palatoglossus elevates the back. All are supplied by the hypoglossal nerve (XII) except palatoglossus, which is a palatal muscle supplied by the vagus through the pharyngeal plexus.

The dorsum carries four kinds of papillae. Filiform papillae are the most numerous, are keratinised, have no taste buds and give a rough surface for gripping food. Fungiform papillae are scattered over the tip and sides and carry taste buds. The 8–12 vallate (circumvallate) papillae sit in a row just in front of the sulcus terminalis; each is surrounded by a trench into which serous von Ebner glands open, and they hold many taste buds. Foliate papillae are folds on the posterior lateral margins. The posterior third has no papillae; its bumpy surface comes from the lymphoid nodules of the lingual tonsil.

Location: Floor of the oral cavity proper and the anterior wall of the oropharynx. It is anchored to the hyoid bone, mandible, styloid process and soft palate.

Parts & subdivisions

Anterior two-thirds (oral part)
Free tip, margins and dorsum in front of the sulcus terminalis. Carries the filiform, fungiform, foliate and vallate papillae.
Posterior one-third (pharyngeal part)
Behind the sulcus terminalis, facing the oropharynx. Carries the lingual tonsil and is joined to the epiglottis by glosso-epiglottic folds that bound the valleculae.
Intrinsic muscles
Superior and inferior longitudinal, transverse and vertical. They curl, flatten, narrow and elongate the tongue for speech and moving food.
Genioglossus
Fan-shaped extrinsic muscle from the superior mental spine of the mandible. It protrudes the tongue and keeps it from falling back to block the airway; tone is lost under anaesthesia and in obstructive sleep apnoea.
Hyoglossus, styloglossus, palatoglossus
Hyoglossus depresses and retracts, styloglossus retracts and elevates, and palatoglossus elevates the root and narrows the oropharyngeal isthmus.
Taste buds
Clusters of gustatory receptor cells in the fungiform, foliate and vallate papillae, also found on the soft palate and epiglottis.
Lingual frenulum
Midline mucosal fold joining the underside of the tongue to the floor of the mouth. The sublingual papillae and deep lingual veins lie beside it.

Anatomy

Innervation: Motor: hypoglossal nerve (XII) to all intrinsic and extrinsic muscles except palatoglossus (vagus via the pharyngeal plexus). Anterior two-thirds: general sensation via the lingual nerve (V3); taste via the chorda tympani (VII), which travels with the lingual nerve. Posterior one-third: both general sensation and taste via the glossopharyngeal nerve (IX). Root near the epiglottis: internal laryngeal branch of the vagus (X).
Arterial supply: Lingual artery (from the external carotid), with its deep lingual, dorsal lingual and sublingual branches. The tonsillar and ascending pharyngeal arteries supply the root.
Venous drainage: Dorsal and deep lingual veins to the lingual vein, then the internal jugular vein. The deep lingual veins can be seen under the tongue.
Lymphatic drainage: The tip drains to the submental nodes. The lateral anterior two-thirds drain to the submandibular nodes, and the central part drains bilaterally. The posterior third drains bilaterally to the deep cervical (jugulo-omohyoid and jugulodigastric) nodes.
Histology: Interlacing bundles of skeletal muscle running in three planes, separated by fat and minor salivary glands. Covered by stratified squamous epithelium, which is keratinised over the filiform papillae.
Development: The anterior two-thirds develops from the first-arch lateral lingual swellings and tuberculum impar. The posterior third develops from the copula and hypopharyngeal eminence (arches 3–4). The muscles come from occipital somites, which migrate forward with the hypoglossal nerve.

Function

Positions food between the teeth and forms it into a bolus.
Drives the voluntary oral phase of swallowing by pressing the bolus up against the palate and back into the oropharynx.
Taste (gustation) and general sensation, including texture and temperature.
Articulation of speech.
Secretes lingual lipase from von Ebner glands; this is important for fat digestion in neonates.

Clinical significance

Hypoglossal nerve palsy

With a lower motor neuron lesion the protruded tongue deviates towards the side of the lesion, because the healthy genioglossus pushes it across. Wasting and fasciculation on the affected side follow.

Carcinoma of the tongue

Usually squamous cell carcinoma of the lateral border. Lesions of the posterior third and midline drain to both sides of the neck, which worsens prognosis and makes bilateral nodal treatment necessary.

Ankyloglossia and glossitis

A short frenulum (tongue-tie) can affect breastfeeding and speech. A smooth, red, sore tongue (atrophic glossitis) points to iron, B12 or folate deficiency.

Mnemonics

Every "-glossus" is XII except one

Genioglossus, hyoglossus and styloglossus are all hypoglossal. Palatoglossus is a palatal muscle and, like the other palatal muscles except tensor veli palatini, is supplied by the vagus.

Test yourself

When a patient protrudes the tongue, it deviates to the left. Which nerve is most likely damaged?

Right hypoglossal nerve
Left hypoglossal nerve
Left lingual nerve
Right glossopharyngeal nerve

Answer: Left hypoglossal nerve

In a lower motor neuron hypoglossal lesion the protruded tongue deviates towards the weak side. The intact right genioglossus pushes the tongue across unopposed. The lingual and glossopharyngeal nerves are sensory to the tongue and do not move it.

Taste sensation from the anterior two-thirds of the tongue is carried by which nerve?

Lingual nerve (V3)
Glossopharyngeal nerve (IX)
Chorda tympani (VII)
Internal laryngeal nerve (X)

Answer: Chorda tympani (VII)

Taste from the anterior two-thirds travels in the chorda tympani, a branch of the facial nerve that runs with the lingual nerve. The lingual nerve itself carries only general sensation from that area. The glossopharyngeal nerve carries both taste and general sensation from the posterior third.