[Biology Class Notes] on Structure of Tongue Pdf for Exam

The tongue is a primary muscular organ in the oral cavity. It is covered with a moist, pink tissue called the mucosa. There are tiny bumps which are called papillae which give the tongue its rough texture. Several thousand taste buds are located on the surface of the papillae which are collections of nerve-like cells that connect to nerves running to the brain.

The tongue is anchored to the mouth by webs of tissue and mucosa and they tether holding down the front of the tongue which is known as the frenum. At the back of the mouth, the tongue is anchored to the hyoid bone. 

The tongue is the vital organ for the taste of food, chewing, swallowing and speech. In this topic, we will discuss the structure of the tongue and its functions.

Function and Structure – Tongue

The structure of the tongue is well designed, as it is a mass of muscle that is covered by a mucous membrane. The oropharynx and the oral cavity are occupied by the tongue. There are two parts of division- 

1. The presulcal part, also known as the anterior part.

2. The postural part, also known as the posterior part.

Tongue and its Parts

Most of the tongues are 10 cms in length and are divided into two definite parts –

1. The most mobile part of the tongue is called the apex or its tip. 

2. The tongue has a rough dorsal surface.

3. The tongue has lingual papillae and taste buds.

4. It has a smooth ventral surface on the floor attached to the oral cavity.

Anterior Two Thirds

The anterior part of the tongue includes the apex and body of the organ and it ends at the sulcus terminalis; this part extends laterally in an oblique direction from the foramen cecum towards the palatoglossal arch. The mucosa layer of the dorsal surface is made of 

• Circumvallate papillae.

• Filiform papillae.

• Fungiform papillae.

A longitudinal midline groove runs in an anteroposterior direction from the tip to the foramen cecum of the tongue.  It also represents the median lingual septum of the organ and the inserts in the hyoid bone.

The foliate papillae on the lateral surface of the tongue are arranged in a series of vertical folds. Coming to the ventral mucosa, it is smooth and continuous with the mucosa of the floor. The lingual veins are superficial and are observed on either side of the lingual frenulum. Lateral to the lingual veins are pleated folds of mucosa called plica fimbriata. They are angled anteromedially towards the apex of the tongue.

Posterior Third

The posterior third part of the organ is made up of the base of the organ. It is located behind the palatoglossal folds and functions as the anterior wall of the oropharynx. This part does not have any lingual papillae and the mucosa is populated by lymphatic tissue known as lingual tonsils. The mucosa is also continuous with the mucosa of the lateral palatine tonsils, the lateral pharyngeal walls, and the glossoepiglottic and epiglottis folds.

Structure of Taste Buds

The taste buds are sensory taste receptors located on the tongue, throat and palate, they help form the perception of taste. Taste buds or taste receptor cells detect chemicals dissolved in saliva from food and other objects and then send their sensory information through neurons to the gustatory center of the brain.

 

Taste receptor cells interact with incoming chemicals from food and other objects on the tongue in groups of 50–150. Each group forms a taste bud, which is grouped together with other taste buds into taste buds.

The taste buds are embedded in the epithelium of the tongue and they make contact with the outside environment through a taste pore. Microvilli-like structures extend from the outer ends of the taste buds through the taste pore, where the processes are covered by mucus that lines the oral cavity.

 

Intrinsic Muscles

There are four pairs of intrinsic muscles which allow the tongue to change shape.

1. The superior longitudinal muscles which run along with the organ just below the superior surface’s mucosa. It shortens the tongue and dorsiflexes its tip.

2. The inferior longitudinal muscles which shorten and provide ventroflexion to the tongue.

3. The transverse muscles run laterally across the tongue and connect the medial septum to the lateral aspect of the organ. They help in narrowing the tongue.

4. The vertical muscle connects the inferior and the superior and the inferior surfaces of the tongue. They help the tongue to flatten.

Extrinsic Muscles: 

There are many extrinsic muscles of the tongue originating outside the organ and inserting into it at various points. These muscles are

• Palatoglossus: In initiates the process of swallowing

• Styloglossus: Pulls the sides of the tongue up and pulls tongue back

• Hyoglossus: depresses the organ.

• Genioglossus: Extends and depresses the organ.

• Geniohyoid: Depresses mandible and elevates hyoid.

At their inner ends, the taste receptor cells synapse with afferent sensory neurons to conduct information to the brain. Each receptor cell synapses have several afferent sensory neurons and each afferent neuron branches to several taste papillae. Then each branch makes contact with many receptor cells.

The afferent sensory neurons occu
r in three different nerves, these are the facial nerve, the glossopharyngeal nerve, and the vagus nerve. Taste receptor cells or taste buds of vertebrates are continually renewed throughout the lifetime of the organism.

Glands:

There are three types of glands scattered throughout the tongue:

1. Mucous Glands

2. Serous Glands

3. Lymph Nodes

They make saliva which helps in chewing, swallowing and digestion of food.

Parts of the Tongue Taste

Five known tastes can be detected by taste buds or taste receptor cells. These are

• Sweet: The sweet taste is produced by carbohydrates such as sucrose and fructose, as well as artificial sweeteners such as aspartame and saccharin.

• Salty: The salty taste is formed by salts containing sodium ions, such as sodium chloride (table salt) and sodium bicarbonate (baking soda). Salts containing potassium, lithium, and other alkali metal ions also produce a mildly salty flavor.

• Sour: Sour taste is generated by acidic compounds, such as vinegar and citric acid (found in lemon)

• Bitter: Bitter taste is produced by a range of organic compounds and is considered an unpalatable flavor. 

• Umami: Umami, or savouriness, is the most recently discovered taste. It is found in foods that have a “meaty” taste due to the presence of the chemical glutamate. Meat, mushrooms, cheese, all contain glutamate.

Although all taste buds can sense all tastes, specific taste buds have a slightly higher sensitivity for certain tastes.

Tongue Function

The functions of the tongue include:

• Mastication: This mean’s chewing of food or any object. It helps in chewing food with the help of saliva.

• Deglutition: The tongue also helps in swallowing food.

• Taste: Taste buds on the tongue transmits taste signals to the brain and assists in sensing taste.

• Speech: Tongue plays a direct role in facilitating speech.

• Secretion: The organ also secretes mucous and serous fluid keeping the mouth moist.