The tongue is a muscular organ that is present on the floor of the mouth. It is devoid of any bone and its main purpose is to assist in the process of mastication and it helps in the swallowing of the food. The tongue is the second organ after teeth that initiates the process of digestion. It is the organ required for perceiving a variety of tastes and also helps in the process of speech. The upper portion of the tongue comprises taste buds that are submerged within Lingual Papillae. The texture of the Tongue is typically rough because of the Lingual Papillae. These are small round structures present upon the upper surface of the tongue. This portion of the tongue is extremely sensitive due to the rich supply of nerves and blood vessels and is always kept moist by the saliva.
Structure of The Tongue
In Humans, the tongue is divided into two parts, the front part that is the oral part which is about two-thirds of the total length of the tongue responsible for the perception of taste, and the posterior part that is also called as the pharyngeal part which is the base of the tongue that lies close to the throat. This is nearly one-third of the total length of the tongue. The anterior portion of the tongue is the tip of the tongue and is narrow and thin followed by the thicker and broader part that lies behind. The posterior part of the tongue is connected to the Hyoid bone. The average length of the tongue is about 8-10 cm. The left and right portion of the Tongue is also divided by a fibrous tissue that lies vertically and ends into a groove and median sulcus on the surface.
The Tongue comprises of a group of intrinsic muscles which are 4 in number that helps in the altering of the shape of the tongue and are not attached to the bone and a group of extrinsic muscle that are 4 in number and are paired, these are attached to the bone and helps in the movement of the Tongue by changing the position of the Tongue. The tongue is further divided into anterior and posterior parts by a V-shaped groove known as the Terminal Sulcus. The Foramen Cecum is a blind foramen that lies at the tip of the terminal sulcus. This is formed during early embryonic development and is the leftover of the Thyroid Diverticulum.
Coming to the upper surface of the tongue which is called Dorsum of the tongue. The Dorsum of the tongue is divided into two halves by a median sulcus. The end of this division is marked by the foramen cecum. The nerves that supply the pharyngeal part and the oral part are Glossopharyngeal nerves and Lingual nerves respectively.
The lower surface of the tongue comprises of Frenulum. This is a fold of mucous membrane that lies in between the tongue at the lower surface that binds the tongue to the floor of the mouth. Both the sides of the frenulum consists of sublingual caruncles in which the saliva from the submandibular glands drain into. The submandibular glands make 70% of the saliva whereas the parotid gland and sublingual gland make 25% and 5% of saliva respectively.
The extrinsic muscles of the tongue are namely:
These muscles help the tongue move from side to side and to protrude and retract as well.
The intrinsic muscles are:
Superior longitudinal muscles
Inferior longitudinal muscles
These muscles help in shaping the tongue and help in swallowing of food and liquid, they also help in assisting the speech mechanism.
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Tastes Perceived By The Tongue
The tongue is said to identify 4 types of tastes that are: sweet, salty, bitter, and sour. The taste perception in the mouth depends upon the quantity and also on the level of identity of the stimuli. The intensity of the perception of taste depends upon the concentration of the stimulus. The body responds to different tastes and promotes more intake of the content that has enough concentration of carbohydrates and salts since the taste cells of the tongue respond more to these essential substances. Because of this reflex activity, the taste cells tend to identify substances that are bitter and are poisonous to the body even if they are ingested in low concentrations. As the sensitivity towards taste and hearing progresses with age, the need for the concentration of spices increases in adults when compared to children.
The arrangement of taste perception on different locations of the tongue was first proposed in the year 1901 by Dieter Hanig. According to his theory, the sweet taste is identified over the tip of the tongue, salt over the posterolateral edges, sour on the medial lateral edges, and finally bitter on the back of the tongue. This does not mean the other parts of the tongue cannot perceive the taste but it rather means these portions of the tongue are more sensitive to taste than the rest of the areas of the tongue. Different locations on the tongue hold different threshold levels for taste perception. Among all the tip of the tongue is considered to be most sensitive. Though the perception of the bitter-tasting compounds is more towards the back of the tongue practically.
The theory that states tongue is capable of perceiving only 4 main tastes that are sweet, salt, bitter, and sour is practically untrue since individuals also perceive a variety of other tastes than the above-stated ones which also includes pungent taste, astringent taste, metallic taste, and fatty taste which proves how sensitive the taste buds of the tongue are.
Development of Tongue During Embryonic Stage
The tongue starts developing during the fourth week of Embryonic Development. It begins developing as the median bud of the tongue from the first pharyngeal arch. The fifth week leads to the development of the lateral lingual swellings on both sides of the first pharyngeal arch. These swellings very soon swell and cover the median tongue bud. Then the anterior part of the tongue is formed which is the two-third of the total length of the tongue. This continues to develop in the further weeks of prenatal development. Median sulcus marks the line of the fusion.
Blood and Nerve Supply
Lingual artery and a branch of the external carotid artery supply blood to the tongue. Even the blood supply to the floor of the tongue is supplied by the Lingual artery. However, there is also a secondary blood supply to the tongue which is done by the ascending pharyngeal artery and the tonsillar branch of the facial artery.
The nerve supply is classified into special sensory fibers responsible for taste, general sensory fibers responsible for sensation in the tongue, and motor fibers supply.
The motor nerve supply to all the muscles of the tongue takes place by the efferent motor nerve fibers typically by the hypoglossal nerve except the palatoglossus and supplied by the vagus nerve.
The different parts of the tongue drain into different nodes. The tip of the tongue drains into the submental node. Posterior one-third of the tongue drains into jugulo-omohyoid nodes and the anterior two-thirds of the tongue drain into submandibular lymph nodes.
The presence of Tastants help in the understanding of the sense of taste. These are the chemical molecules that mix with the ingested food or saliva and activate the taste receptor cells. The taste receptor cells are present within the taste buds and the dorsal surface of the tongue has numerous taste buds. The different varieties of taste are detected and differentiated by the different taste receptor cells.
The tongue is one of the accessory organs of the digestive system. It assists in the process of mastication by getting the food between the teeth and the hard palate. It also helps in swallowing of the masticated food. The tongue also helps the process of speech. The muscles in the tongue are responsible for giving various shapes to the tongue that in turn facilitates the speech in an individual.
Some of the symptoms that appear on the tongue include:
Pain in the tongue
Swelling of the tongue
Burning sensation on the tongue
Loss of taste either partially or complete
Difficulty in the movement of the tongue
These symptoms either appear independently or in association with other diseases such as:
Thrush: The growth of yeast over the surface of the tongue and mouth. This generally happens in individuals who are exposed more to steroids.
Atrophic Glossitis: The rough surface of the tongue turns to become smooth. This usually happens with the deficiency of Vitamin B and also in cases of Anemia.
Ulcers: These are also called as Canker Sores. These are the ulcers that appear in the mouth and on the tongue. They don’t have any specific cause and are not contagious.
Oral Cancer: This is a non-healing ulcer that grows over the tongue or any part of the oral cavity. It grows steadily.
Stomatitis: Redness in the oral cavity with burning sensation with the intake of spicy food.
Lichen Planus: This is a kind of condition which is said to be a result of the immune system attacking the skin and altering the lining of the mouth.
1. What Are The Signs of An Unhealthy Tongue?
Ans: The tongue is capable of representing the health of an individual. A hairy tongue can signal a lack of proper hygiene or diabetes, a bright red tongue can reflect the deficiency of folic acid. A white tongue with slight inflammation can suggest the entrapment of bacteria, fungi, dirt, etc. This turns the tongue into white.
2. What Is The Length of The Normal Human Tongue?
Ans: The normal tongue of an adult man would measure about 8-9 cms, and a female tongue can measure somewhere about 7-8 cms.
3. What Are The Various Functions of The Tongue?
Ans: The tongue helps in salivating, chewing of food, pressing and grinding the food. The tongue along with teeth and cheek help in the total mastication process and keeps the food intact in the oral cavity. It also helps to form the food into a Bolus and further helps in the swallowing of the food.
4. What is Oral Cancer?
Ans: Oral cancer develops when there will be uncontrollable growth of cancer cells in the mouth. This is known as malignancy. Almost 90 percent of the oral cancers are the squamous cell carcinoma that forms flat squamous cells that line the mouth and the throat. The malignant cells can grow over the tongue, the lining of the cheek, the gums, bottom of the tongue, and also the roof of the mouth.