ONLINE ASSIGNMENT

TOPIC:

STRUCTURE ,FUNCTION AND DISEASES OF HUMAN

               TONGUE


             

             

INDEX

SL. NO	CONTENT	PAGE NUMBER
1	INTRODUCTION	4-5
2	STUCTURE OF TONGUE	6-7
3	FUNCTION OF EACH PART OF TONGUE	7-11
4	MUSCLES	11-13
5	FUNCTIONS OF TONGUE	14-15
6	TONGUE CONDITIONS	15-16
7	TONGUE TESTS	16
8	TONGUE TREATMENTS	16-17
9	CONCLUSION	17
10	REFERENCE	18

                                                   

INTRODUCTION

                           

                               Our bodies consist of a number of organs that carry out specific functions necessary for everyday living. The tongue is a muscular structure attached to the floor of the mouth. The tongue is the main sensory organ of the taste sense. The upper surface of a tongue is covered with taste buds which contain taste receptors. The human tongue has on average 3,000 - 10,000 taste buds. Tongue is a muscular structure that has the organs of taste reception. The organs for sense of taste are the taste buds. Tongue is located inside the mouth and is an important muscle. It does not have any bones. It is reddish-pink in color. 

                                The tongue also works as a natural way of cleaning teeth after eating. Humans also use the tongue for speech where it helps with changes in sound. On average, women have shorter tongues than men. Humans also use the tongue for speech where it helps with changes in sound. The tongue is anchored to the mouth by webs of tough tissue and mucosa. The average length of the human tongue from the back to the tip is 10 cm (4 in). There are five elements of taste perception: salty, sour, bitter, sweet, and umami (or savoury).

                       The tongue is a muscular structure that forms part of the floor of the oral cavity. The left and right sides of the tongue are separated by the lingual septum. The human tongue is divided into anterior and posterior parts. The anterior part is the visible part situated at the front and makes up roughly two-thirds the length of the tongue. The posterior part is the part closest to the throat, roughly one-third of its length. These parts differ in terms of their embryological development and nerve supply. The two parts of the tongue are divided by the terminal sulcus.

                      

                                    

                     

                 The anterior tongue is, at its apex, thin and narrow, it is directed forward against the lingual surfaces of the lower incisor teeth. The posterior part is, at its root, directed backward, and connected with the hyoid bone by the hyoglossi and genioglossi muscles and the hyoglossal membrane, with the epiglottis by three folds (glossoepiglottic) of mucous membrane, with the soft palate by the glossopalatine arches, and with the pharynx by the superior pharyngeal constrictor muscle and the mucous membrane. It also forms the anterior wall of the oropharynx. In phonetics and phonology, a distinction is made between the tip of the tongue and the blade (the portion just behind the tip). Sounds made with the tongue tip are said to be apical, while those made with the tongue blade are said to be laminal.

STRUCTURE OF TONGUE

              Papillae: Granular projection on the upper side of the tongue is known as papillae.  There are four types of papillae there,

·       Filiform (thread shaped): Without taste buds, they are presented as filaments and are most plentiful. These lingual papillae have mechanical functions but no gustatory functions.

·       Fungiform (mushroom shaped): Its cross section is similar to mushrooms’, and they are mainly distributed in the tip of the tongue.

·       Foliate (leaf shaped): They extend to the ditch and ridge in the root of the tongue.

·        Vallate (ringed shaped): Most people have only 3 to 14 such lingualpapillae, and they generally lie in the root of the tongue, arranging into a circle.

              Sulcus terminalis: Sulcus terminalis is not labeled, but it is visible at approximately the level of the circumvallate papillae.

Tonsils:  They are present at the back of the tongue. There are two types of tonsils,

v Lingual tonsils

v Palatine tonsils

Adenoids: Hypertrophy of the pharyngeal tonsil (adenoids) can obstruct the nasal airway, difficult mask ventilation, and difficult tracheal intubation.

        Frenulum linguae:  It is present on the under surface of the tongue.

       FUNCTION OF EACH PART OF THE TONGUE

Ø    Papillae: Papillae contains taste bud (chemo-receptors), which helps us identify between different tastes of food.  When we chew food, a portion of it dissolves in the saliva. This dissolved part of food comes in contact with the taste buds and generates nerve impulses. These nerve fibres are known as microvilli.  These nerve fibres carry messages to the taste center in the brain. Then brain perceives the taste.

·       Foliate, Vallate and Fungiform have taste buds which helps in identifying the taste

·         Filiform helps in holding the food ( to grip the food in place)

Tonsils:  Both the types of tonsils help in filtering germs.

Adenoids: They help in fighting infections.

        Frenulum linguae: It secures or holds the tongue in place inside the mouth.

•      Very small fibre-like or hair-like projections are present on the upper side of the tongue which connects with nerve fibres at the lower end of the tongue which lead to the brain.

                             There are about 3000 taste buds on the tongue of an adult person. There are four main tastes - sweet, salty, sour and bitter. These four main tastes are felt by different portion of the tongue. The tip of our tongue senses salt and sweet. The taste buds at the sides detect sour taste. The rear portion of the tongue detects bitter taste.

       Taste buds

                                   Taste buds are structures located on the surface of the tongue. They are embedded in the mucosa of the papillae of the tongue. The papillae are projections on the upper surface of the tongue.

               Each papillae may contain from few to a hundred taste buds and the surface of the tongue may have up to 10,000 taste buds.

 Structure of Taste Buds

                Each taste bud is a bulbous sac-like structure having a small pore-like opening on the surface of the tongue - Taste pore.

                

                                                

                     The bulbous portion of the taste bud consists of two types of cells

1.    Taste receptor cells or gustatory receptors

                  They are spindle-shaped cells that are neurosensory. They have hairs on their free ends and on the other end, they have nerve fibres. They number 5-15 in each taste bud.

2.    Supporting cells

          They are columnar cells, numbering about 40 found between the taste receptor cells, supporting them

              Sweet, Sour, Salty and Bitter Flavors

            Food has various flavors, and the perception of flavors is called the sense of taste. The human sense of taste includes being sweet, sour, bitter and salty. The flavor of food is commonly recognized by the sense of smell and sense of taste. The flavorus chemicals in food must dissolve in water first, or we can’t taste them out. If the mouth is very dry, no flavor is able to be tasted out.

                         

                                       

There are taste buds on the tongue, and these taste buds (there are about 10,000 taste buds in the human body) are classified in to four types, each one of which is made up of 50 to 150 receptor cells. The receptor cells have only a lifespan of one to tow weeks and will be replaced by new cells later. Receptors of the taste buds can make the best response to a give basic flavor. One receptor is able to sense a lot of flavors but only most sensitive to a certain flavor. Depending on different taste buds, the tongue also has areas especially sensitive to a certain sense of taste, e.g. the tip of the tongue is the sweet taste area, and the root of the tongue is sensitive to the bitter flavor. Each taste bud is made up of gustatory cells. Gustatory cells have taste hairs and the taste which gustatory cells sense is sent into the brain via the sensory nerve. After integrating the temperature, quality and various signals sensed by other receptors, the brain can judge which flavor it is.

1.   The origin of the bitter flavor is alkaloids and the position of perception is the root of the tongue.

2.   The origin of the salty flavor is the salt and the position of perception is the bilateral sides of the tongue and the tip of the tongue.

3.   The origin of the sour flavor is the acid and the position of perception is the bilateral sides of the tongue.

4.   The origin of the sweet flavor is the sugar and the position of perception is the tip of the tongue.

When the flavorus components in food contact the taste buds, this stimulus turns into a chemical signal and forms the sense of taste after processed by the brain. There are a lot of taste buds in one’s childhood but taste buds will change to some extent with age. Hence, the sense of taste is well-developed in one’s youth and any kind of food is very delicious. However, the number of the taste buds decreases with age such that the sense of taste becomes blunt and the diet amount also reduces.

Muscles

             The eight muscles of the human tongue are classified as either intrinsic or extrinsic. The four intrinsic muscles act to change the shape of the tongue, and are not attached to any bone. The four extrinsic muscles act to change the position of the tongue, and are anchored to bone.

                                                          

                                                       

                      

         

          Extrinsic

             The extrinsic muscles originate from bone and extend to the tongue. Their main functions are altering the tongue's position allowing for protrusion, retraction, and side-to-side movement.

1.    1. Genioglossus, which arises from the mandible and protrudes the tongue. It is also known as the "safety muscle" of the tongue since it is the only muscle having the forward action.

2. Hyoglossus, which arises from the hyoid bone and depresses the tongue

3.    3. Styloglossus, which arises from the styloid process of the temporal bone and elevates and retracts the tongue.

4.    4. Palatoglossus, which arises from the palatine aponeurosis, and depresses the soft palate, moves the palatoglossal fold towards the midline, and elevates the back of the tongue.

Intrinsic

Four paired intrinsic muscles of the tongue originate and insert within the tongue, running along its length. These muscles alter the shape of the tongue by: lengthening and shortening it, curling and uncurling its apex and edges, and flattening and rounding its surface. This provides shape, and helps facilitate speech, swallowing, and eating.

1.  The superior longitudinal muscle runs along the superior surface of the tongue under the mucous membrane, and elevates, assists in retraction of, or deviates the tip of the tongue. It originates near the epiglottis, the hyoid bone, from the median fibrous septum.

2.  The inferior longitudinal muscle lines the sides of the tongue, and is joined to the styloglossus muscle.

3.  The vertical muscle is located in the middle of the tongue, and joins the superior and inferior longitudinal muscles.

4.  The transverse muscle divides the tongue at the middle, and is attached to the mucous membranes that run along the sides.

Blood supply

                       The tongue receives its blood supply primarily from the lingual artery, a branch of the external carotid artery. The lingual veins, drain into the internal jugular vein. The floor of the mouth also receives its blood supply from the lingual artery. There is also a secondary blood supply to the tongue from the tonsillar branch of the facial artery and the ascending pharyngeal artery.

                         An area in the neck sometimes called Pirogov's triangle is formed by the intermediate tendon of the digastric muscle, the posterior border of the mylohyoid muscle, and the hypoglossal nerve. The lingual artery is a good place to stop severe hemorrage from the tongue.

FUNCTIONS OF TONGUE

  Taste:

                 Chemicals that stimulate taste receptor cells are known as tastants. Once a tastant is dissolved in saliva, it can make contact with the plasma membrane of the gustatory hairs, which are the sites of taste transduction.

The tongue is equipped with many taste buds on its dorsal surface, and each taste bud is equipped with taste receptor cells that can sense particular classes of tastes. Distinct types of taste receptor cells respectively detect substances that are sweet, bitter, salty, sour, spicy, or taste of umami. Umami receptors cells are the least understood and accordingly are the type most intensively under research.

    Mastication:

                   The tongue is also used for crushing food against the hard palate, during mastication. The epithelium on the tongue’s upper or dorsal surface is keratinised. Consequently, the tongue can grind against the hard palate without being itself damaged or irritate

    Swallowing and Chewing:

                                  The tongue helps the teeth and other parts of the mouth with chewing food and passing it down the throat as the first part of the swallowing process.

   Speech: The movements of the tongue are crucial for articulation.

   Cleaning: The movements of the tongue dislodge food particles stuck between the teeth, gum and cheek so that it can be spat out or swallowed.

  Forming of the bolus

  TONGUE CONDITIONS

• Thrush (candidiasis): Candida albicans (a yeast) grows over the surface of the mouth and tongue. Thrush can occur in almost anyone, but it occurs more often in people taking steroids or with suppressed immune systems, the very young, and the elderly.
• Oral cancer: A growth or ulcer appears on the tongue and grows steadily. Oral cancer is more common in people who smoke and/or drink alcohol heavily.
• Macroglossia (big tongue): This can be broken down into various categories based on the cause. These include congenital, inflammatory, traumatic, cancerous, and metabolic causes. Thyroid disease, lymphangiomas, and congenital abnormalities are among some of the causes of an enlarged tongue.
• Geographic tongue: Ridges and colored spots migrate over the surface of the tongue, periodically changing its appearance. Geographic tongue is a harmless condition.
• Burning mouth/burning tongue syndrome: A  relatively common problem. The tongue feels burned or scalded, or strange tastes or sensations develop. Apparently harmless, burning mouth syndrome may be caused by a mild nerve problem.
• Atrophic glossitis (bald tongue): The tongue loses its bumpy texture, becoming smooth. Sometimes this is due to anemia or a B vitamin deficiency.
• Canker sores (aphthous ulcers): Small, painful ulcers appear periodically on the tongue or mouth. A relatively common condition, the cause of canker sores is unknown; they are unrelated to the cold sores caused by herpes viruses. Canker sores are not contagious.
• Oral leukoplakia: White patches appear on the tongue that can’t be scraped off. Leukoplakia may be benign, or it can progress to oral cancer.
• Hairy tongue: Papillae can overgrow the surface of the tongue, giving it a white or black appearance. Scraping off the papillae corrects this harmless condition.
• Herpes stomatitis: The herpes virus can uncommonly cause cold sores on the tongue. Herpes virus cold sores are usually on the lip.
• Lichen planus: A harmless condition that can affect the skin or the mouth. The cause is unknown; however, it is believed to be caused by the immune system attacking the skin and lining of the mouth.

TONGUE TESTS

• Biopsy: A small sample of tissue is taken from a suspicious-looking area on the tongue. This is most often done to check for oral cancer.
• Flavor discrimination test: Four solutions of different amounts of sweetener are used to evaluate taste and smell.

TONGUE TREATMENTS

• Steroid gel: Applying a prescription steroid gel like Lidex hastens the resolution of canker sores.
• Silver nitrate: Doctors can apply this chemical to a canker sore, speeding healing and relieving pain.
• Viscous lidocaine: Applied to the tongue, lidocaine gel provides immediate, though temporary, pain relief.
• Antifungal medicines: Antifungal drugs can eliminate Candida albicans, the thrush-causing fungus. Swish-and-spit mouthwash and pills are both effective.
• Tongue scraping: Simply scraping the tongue can usually remove the overgrown papillae causing black or white hairy tongue.
• B vitamins: A B vitamin supplement can correct a vitamin deficiency, if present.
• Tongue surgery: Surgery may be required to remove oral cancer or leukoplakia.

CONCLUSION

                          

                                                     The tongue is a muscular structure that forms part of the floor of the oral cavity. The left and right sides of the tongue are separated by the lingual septum. The human tongue is divided into anterior and posterior parts. The anterior part is the visible part situated at the front and makes up roughly two-thirds the length of the tongue. The posterior part is the part closest to the throat, roughly one-third of its length. These parts differ in terms of their embryological development and nerve supply. 

        REFERENCE

1.    Principles of Anatomy and Physiology - Tortora. - 12th edition, chapter 17, p.602.

2.    Human Physiology: An integrated approach - Silverhorn -   5th edition, chapter 10, p.352.

3.  "Anatomy for dental students -       Atkinson, 4th edition.