Muscles and Taste Sensation of the Tongue
The tongue is an organ of the oral cavity, which aids speech, swallowing, mastication, taste and oral clearing. This article will provide you with an overview of the extrinsic and intrinsic muscles that make up the tongue, definitions of the different papillae, an explanation of taste Sensation, together with an overview of the taste pathway. Also included are the most common pathological tongue disorders, their features and how to treat them.
The tongue is compiled of several extrinsic and extrinsic muscles. The extrinsic muscles are outside the tongue which aid in performing its correct function. These include the:
- Styloglossus muscle
- Hyoglossus muscle
- Genioglossus muscle
- Palatoglossus muscle
The Intrinsic muscles are those situated within the tongue:
- Superior longitudinal muscle
- Inferior longitudinal muscle
- Vertical muscle
- Transverse muscle
The tongue is covered with various forms of papillae:
- Filiform papillae: the most common type of papilla seen on the anterior region of the tongue; the only type that doesn’t contain taste buds
- Fungiform papillae: mushroom shaped papillae on the anterior portion of the tongue
- Foliate papillae: seen on the lateral margins of the tongue
- Circumvallate or vallate papillae: twelve to fourteen large, circular papillae seen in a upside-down ‘V’ shape on the posterior third of the tongue, just before the terminal sulcus
These papillae contain taste buds that register sweet, salty, bitter, sour and umami flavours.
A taste bud consists of a taste pore, through which the characteristic ions or anions of each flavor pass through in order to reach the sensory and sustentacular cells. Each taste bud is surrounded by stratified squamous epithelium and is basally secured by lamina propria.
- Taste bud stimulation
- Anterior third of tongue: Chorda Tympani (facial nerve - CN VII) signals both the otic and geniculate ganglia; Posterior third of the tongue: superior laryngeal nerve (vagus - CN X) and the glossopharyngeal nerve (CN IX) signal the Inferior node of the vagus ganglion and the petrosal ganglion respectively.
- Both pathways synapse on the nucleus of the solitary tract in the posterior inferior part of the medulla oblongata.
- The pontine taste area of the pons
- The amygdaloid body, the lateral hypothalamic body and the ventral posteromedial nucleus of the thalamus (VPM)
- The sensory cortex
Some of the most common tongue abnormalities include:
- Ankyloglossia (tongue-tie): when the lingual frenulum is too small and prevents a normal range of movement. Treated with a Frenectomy.
- Macroglossia: can be congential (as part of diseases such as Down syndrome, Hurler’s syndrome etc.) or acquired (acromegaly, amyloidosis, etc.) Treated by surgical reduction.
- Fissured Tongue: mostly non-pathological, but related to Down syndrome, Melkersson-Rosenthal syndrome and Sjogren’s syndrome. Can become infected with bacteria if the fissures are very deep. there is no treatment, just reassurance of the patient.
- Hairy Tongue: elongated filiform papillae can become discoloured by food consumption, smoking or colour producing bacteria. Treated by cessation of smoking, tongue scraping and sometimes antibiotics if bacteria are involved.
- Geographic tongue: migrating areas of papillary atrophy which appear, disappear and reappear with several weeks. The red atrophic areas have a white keratotic border. Treatment is not needed, just reassurance of the patient.
- Median rhomboid glossitis: similar to geographic tongue, except that it is a diamond-shaped, depapillated, non-migratory patch on the posterior third of the tongue. There is not treatment and generally no symptoms.
- Sore tongue (glossodynia): an anatomically healthy but painful or burning tongue that is mainly caused by iron-deficiency anemia, pernicious anemia, b-complex deficiencies, candidosis and lichen planus. Elimination of any underlying disease, the suspicion of one or any possible chemical stimulants usually treats the disorder.