Overview
The tongue is a voluntary muscular organ located in the floor of the oral cavity proper and attached via the frenulum. It functions as a digestive organ by facilitating movement of food during mastication and assisting swallowing, and also has important functions in speech and taste.
On the dorsal surface of the base of the tongue, there are 8 – 12 circumvallate papillae arranged in an inverted V-shape termed the sulcus terminalis, which divides the tongue into two parts: the anterior two-thirds (oral cavity) and posterior one-third (oropharynx).
Intrinsic Muscles
The intrinsic muscles of the tongue are a group of 4 muscular bands in the tongue which unlike extrinsic muscles, have no extraglossal attachments. They act to alter the shape of the tongue where as the extrinsic tongue muscles alter the position of the tongue.
Superior longitudinal
- Origin: Fibrous median septum and submucosal fibrous layer
- Inserts: Tongue margins and overlying mucous membrane
- Function: Curls the apex and lateral sides of the tongue upwards. Together with the inferior longitudinal muscle, shorts and retracts the tongue
- Innervation: Hypoglossal nerve
Inferior longitudinal
- Origin: Arises proximal to the root of the tongue
- Inserts: Tongue apex
- Function: Curls the apex and lateral sides of the tongue downwards. Together with the superior longitudinal muscle, shortens and retracts the tongue
- Innervation: Hypoglossal nerve
Transverse
- Origin: Originates from the fibrous median septum and submucosal fibrous layer and inserts distally to the lateral tongue margins. The fibres intersect with the vertical intrinsic muscle, lying between the superior and inferior longitudinal intrinsic muscle
- Function: Curls the apex and lateral sides of the tongue upwards. Together with the inferior longitudinal muscle, shorts and retracts the tongue
- Innervation: Hypoglossal nerve
Vertical
- Attachments: Arises proximal to the submucosal fibrous layer of the dorsum of th etongue and attaches distally to the inferior surface of the apex and lateral tongue margins. aThe fibres intersect with those of the transverse intrinsic muscle, lying between the superior and inferior longitudinal intrinsic muscles
- Function: Flattens and broadens the tongue
- Innervation: Hypoglossal nerve
Extrinsic Muscles
Genioglossus
- A fan-shaped muscle accounting for majority of the tongue body
- Attachments: Arises from the superior genial tubercle, located at the andibular symphysis inserts into the body of the hyoid bone and the entire length of the tongue mucosa
- Function: Inferior fibres protrude the tongue, middle fibres depress the tongue, and superior fibres draw the tip back and down
- Innervation: Motor innervation via the hypoglossal nerve (CNXII).
Hyoglossus
- Thin, flat quadrilaterally shaped muscle
- Attachments: Arises from the body and greater cornu of hyoid bone and inserts into the inferolateral aspect of the tongue, between styloglossus laterally and inferior longitudinal muscle medially
- Function: Depresses and retracts the tongue
- Blood supply: Lingual artery and submental branches of the facial artery
- Innervation: Motor innervation via the hypoglossal nerve (CNXII)
Styloglossus
- A triangular muscle, shortest and smallest of the three styloid muscles
- Attachments: Originates at the anterolateral surface of the styloid processes of the temporal bone and inserts into the posterolateral surface of the tongue, blending with the inferior longitudinal and hyoglossus muscles
- Function: Retracts and elevates the tongue
- Blood supply: Ascending pharyngeal artery
- Innervation: Motor innervation via the hypoglossal nerve (CNXII)
Palatoglossus
- A thin muscle which narrows in the middle and creates the palatoglossal arch in the lateral oropharyngeal wall, marking the lateral border of the oral cavity and oropharynx
- Attachments: Arises from the inferior surface of the palatine aponeurosis and inserts broadly across the posterolateral tongue, contributing to the palatoglossal arch
- Function: Elevates the posterior aspect of the tongue and draws the soft palate inferiorly
- Blood supply: Lingual artrey and collateral supply from the tonsillar artery (branch of the facial artery)
- Innervation: Motor innervation via the vagus nerve (CNX)
Innervation
Sensory supply
- General sensation (anterior two-thirds) – Lingual nerve (branch of the mandibular division of the trigeminal nerve)
- General sensation (posterior one-third) – Glossopharyngeal nerve and small branch of the internal larygneal nerve (branch of vagus nerve)
- Special sensation (taste) – chorda tympani (branch of facial nerve)
- Also carriers secretomotor fibres to the submandibular and sublingual glands
Motor supply
All of the intrinsic and extrinsic muscles are innervated by the hypoglossal nerve (CN XII), except palatoglossus, which has vagus nerve (CN X)
Vasculature
The lingual artery (branch of the external carotid) does most of the supply, but there is a branch from the facial artery, called the tonsillar artery, which can provide some collateral circulation. Drainage is by the lingual vein.
Lymphatic Drainage
- Anterior two-thirds – initially into the submental and submandibular nodes, which empty into the deep cervical lymph nodes
- Posterior one-third – directly into the deep cervical lymph nodes
Development
- The first branchial arch is supplied by the trigeminal nerve, the second by the facial, the third by the glossopharyngeal, and the fourth and sixth by the vagus
- Begins development in the fourth week of life, from the median tongue bud
- When the tongue is developing, it starts as a two longitudinal bulbous ridges, with contribution from the first four branchial arches. These ridges join, giving rise to the longitudinal line (median sulcus) down the centre of your tongue. The contribution from the second branchial arch is grown over by that of the third arch, but the nerve supply remains. Hence, why the majority of the tongue’s innervation is by the trigeminal nerve (CN V) and the glossopharyngeal nerve CN IX.
- The foramen cecum allows descent of the thyroid gland, via the thryoglossal duct