The tongue is a digestive system organ located inside the mouth. The main function of the tongue is tasting. It also helps chewing and swallowing food, and speaking. The tongue is about 4 inches and full of taste buds. There are four kinds of tastes that respond to different flavors. The regions of taste sensations were stated by a German scientist in 1901.  
Structure and function
The tongue is composed of many kinds of muscles with the muscle tissues. Each of these muscles has a different role. In the tongue, there are extrinsic and intrinsic muscles. These muscles help the tongue move in many directions. Moreover, the muscles in the tongue play an important role in speech. 
Extrinsic muscles help to pull the tongue downwards, upwards, backwards, and forwards. During phonation, these muscles are soft and gooey. These are the four types of extrinsic muscle in the tongue.
- Genioglossus muscle helps to pull the tongue tip back.
- Hyoglossus muscle helps to retract the tongue and elevate the hyoid bone.
- Styloglossus muscle helps to pull the tongue upward and back.
- Palatoglossus musclehelps to pull the tongue back.  
- Superior longitudinal muscle helps the tip of the tongue move up and down.
- Inferior longitudinal muscle also helps the tip of the tongue move up and down.
- Transverse muscle helps the tongue lengthen.
- Verticalis muscle helps the tongue flattens.  
The upper side of the tongue is covered with papillae. Papillae are tiny bumps which contain taste buds. However, the papillae also can be found on the palate, the lips, and the pharynx. These are the four types of papillae. 
- Circumvallate papillae are the largest and surrounded by deep furrow, but have very few taste buds.
- Foliate papillae are located on the sides of the tongue. These papillae contain most of the taste buds.
- Filiform papillae have no taste buds at all. Each of these consist of connective tissue.
- Fungiform papillae are located on the entire top surface of the tongue. These papillae have some taste buds. 
There are about 10,000 taste buds on a human tongue. Taste buds are contained in most papillae except filiform papillae. However, the most sensitive taste buds are contained in the foliate papillae. In these taste buds, there are two types of cells.
- Gustatory cells are composed of an epithelial cell.
- Supporting cells form the bud shape. This bud has a taste pore with gustatory hairs. 
Taste zones in the tongue
In the tongue, there are thousands of taste buds that help to taste flavors. There are four sensations of taste. These four tastes are bitter, sour, salty, and sweet. These tastes are located in specific areas of the tongue, and each of them has a different function. Moreover, the taste can be affected by temperature.
The very back of the tongue contains the bitter sensation. This sensation responds to the foods and beverages that contain acrid flavors. 
The sides of the tongue contain the sour sensation. This sensation responds to the foods that contain sour tastes such as lemons, limes, and other citrus fruits. 
The salty sensation is located on the tip and the sides of the tongue. This sensation responds to the savory foods such as pretzels, chips, and other foods that contain a large amount of salt. 
The sweet sensation is located on the tip of the tongue. This sensation responds to the sugary foods such as cakes, cookies, chocolates, and ice-cream. 
There are many diseases that can be found in the tongue. These diseases can produce some symptoms such as sores, redness, and swelling. However, the symptoms of the tongue are commonly mild. The tongue diseases can be caused by yeast, viruses, or bacteria. 
- Geographic tongue or benign migratory glossitis is not a harmful and infectious disease. This disease brings red spots on the tongue. 
- Black Hairy tongue is usually caused by growth of papillae and bacteria. These bring a blackened appearance. 
- Burning mouth syndrome is not harmful and infectious. This disease brings burning sensations and loss of taste. However, women are more vulnerable to this disease than men. 
- HSV-1 is also known as herpes simplex virus 1. This disease can bring sores on the tongue and is hereditary. 
- Tongue cancer is cancer of the head and neck. It is also known as oral cavity cancer. This disease can bring difficulty of swallowing, mouth sores, numbness, and painful chewing. Smoking can cause tongue cancer. 
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