Our tongues enable us to perform multiple key functions. We can taste a variety of foods with our tongues. This is made possible through the interaction of food with the taste buds or receptors located on the surface of the tongue. Apart from facilitating the taste sensation, our tongues are also involved in the act of chewing and swallowing food.
The tongue is also involved in moving the food around the mouth during the chewing process, and also helps in pushing the masticated food down the throat. In addition, it is useful in dislodging the food stuck between the cheeks, gums and teeth. Spitting is another function that is aided by the movements of the tongue.
Apart from manipulating food in mouth, our tongues also allow us to speak. Proper articulation of speech sounds depends on specific and precise movements of the tongue.
Anatomy of Tongue
The human tongue is a highly flexible and muscular organ. Its surface contains a variety of receptors, and is also covered by a thin mucous membrane. Even though we only see the tongue in our mouth, a part of it lies in the upper part of the throat (a region known as the oropharynx).
Surfaces of the tongue
The human tongue is a flat structure with two surfaces: the upper or superior surface, and the lower or inferior surface. The superior surface (top surface) of the tongue is further divided into the following two regions:
- Anterior surface: The anterior surface (front part) of the tongue is the part that is the most visible in the mouth. It is further divided into the apical part (apex or tip) and the body.
- Posterior surface: The posterior surface is made up of the root, which is hidden from view since it is placed in the oropharynx. The root of the tongue is located between the hyoid bone and the mandible.
The inferior surface of the tongue can also be subdivided into an apex and a body. This surface becomes visible when we lift the tongue to touch the roof of the mouth. A fold known as the frenulum can be seen to connect this inferior surface to the floor of the mouth. A vein, known as deep lingual vein, is also visible on the two sides of the frenulum.
The taste buds on the tongue are located inside the lingual papillae that are present on the anterior surface of the tongue. There are no taste buds or lingual papillae in the posterior part of the tongue.
Also read on strange taste in the mouth.
Muscles of the tongue
Despite its appearance, the tongue is not a single muscle. It is a combination of many different muscles that act in unison. The muscles in the tongue can be categorized into two groups:
- Intrinsic muscles: There are four intrinsic muscles in the tongue. These have their origins and terminations within the tongue. These intrinsic tongue muscles are named as: superior longitudinal muscle, inferior longitudinal muscle, transverse muscle and vertical muscle. The intrinsic muscles are involved in changing the shape of the tongue. For example, retraction of the tongue is made possible by the superior and inferior longitudinal muscles, which shorten the tongue and make it appear thick. Protrusion of tongue is made possible by the vertical and transverse muscles, which lengthen the tongue and make it appear narrow.
- Extrinsic muscles: The tongue also contains four extrinsic muscles, which are connected to some bones outside the tongue. These muscles are named as genioglossus, styloglossus, hyoglossus, and palatoglossus. These extrinsic muscles are mainly involved in mediating the movements of the tongue.
Nerves of the tongue
Except the palatoglossus, all the muscles of the tongue are innervated by the hypoglossal nerve (12th cranial nerve). The palatoglossus is innervated by the 10th cranial nerve. In addition to the motor nerves that drive the movements of the tongue, sensory nerves are also present to relay the sensations of taste, touch and temperature. The sensory nerves that innervate the tongue include branches of the 5th, 7th, and 9th cranial nerves. Branches of 7th and 9th cranial nerves are involved in the reception of taste, whereas branches of 5th and 9th cranial nerves are involved in reception of touch and temperature.
Blood and lymphatic drainage in the tongue
The lingual artery that branches from the external carotid artery supplies oxygenated blood to the tissues of the tongue. Deoxygenated blood is then carried away from the tongue through the dorsal and deep lingual veins.
Tissue lymph from different parts of the tongue is drained through a series of lymph nodes. These include the cervical lymph nodes (superior deep and inferior deep), submandibular lymph nodes, and the submental lymph nodes.
The following are some of the medical problems associated with the tongue:
Discoloration of the tongue
The human tongue has a pinkish or reddish color in normal conditions. This color is imparted by the rich blood supply in this organ. The reddish-pink color can change in both normal and abnormal conditions. For example, the tongue may get discolored or coated by eating certain foods. This is perfectly normal, and the coating can be removed by a tongue cleaner.
The tongue may also get a variety of colorations in some abnormal disease conditions. When abnormal, the tongue may appear white (as in leukoplakia, thrush, and lichen planus), intense red (as in glossitis, scarlet fever, vitamin deficiencies, Kawasaki syndrome, toxic shock syndrome, and geographic tongue), black (as in black hairy tongue), magenta (as in vitamin B2 deficiency), yellow (as in black hairy tongue and jaundice) and blue (as in cyanosis and suffocation).
Also read on tongue discoloration.
Loss of tasting ability
Taste disorders are technically known as dysugesia. The loss of tasting ability could either be partial (hypogeusia) or complete (ageusia). The reasons for the loss of tasting ability can usually be found in the mouth, the nerves or the brain. Examples of conditions that can lead to loss of tasting ability include gastroesophageal reflux disorder (GERD), mouth infections, oral cancer, inflammation of tongue (glossitis), dryness of mouth, burns or chemical damage to the tongue, stroke, transient ischemic attack, brain tumors, and head injuries. Taste sensations may also be affected due to sinusitis, hormonal changes, nutritional deficiencies, kidney failure, depression, and cirrhosis.
Paresthesia is a technical term that refers to abnormal sensations. Abnormal sensations typically felt on the tongue include tickling, numbness, burning, and pins-and-needles sensation. These are usually the result of certain medications, poisons, toxins, trauma, infections, and vitamin deficiencies.