Structure and Functions of the Human Tongue

Introduction

The tongue is a muscular organ present inside the oral cavity. It plays an important role in taste, chewing, swallowing and speech.

It helps us identify different tastes, move food inside the mouth, mix food with saliva and push it towards the throat during swallowing.

For example, when you eat a piece of fruit, the tongue helps move it between the teeth, mixes it with saliva and allows you to recognize its taste.

The tongue also contains specialized sensory structures called taste buds, which detect different taste sensations and send signals to the brain.

[IMG 1 — Horizontal anatomical illustration of the human tongue inside the oral cavity, showing the apex, body, root, dorsum, lingual frenulum and major surrounding structures.]

1. Structure and Parts of the Tongue

The tongue is a flexible, muscular organ covered by a moist mucous membrane. It is attached to the floor of the oral cavity and extends towards the oropharynx.

Anatomically, it is divided into three main parts:

A. Apex (Tip)

The apex is the pointed anterior end of the tongue.

It is highly mobile and helps in manipulating food, touching different parts of the mouth and producing certain speech sounds.

B. Body

The body forms the anterior two-thirds of the tongue.

It is the largest and most mobile portion. It contains numerous papillae, many of which are associated with taste sensation.

C. Root

The root forms the posterior one-third of the tongue.

It is attached to the floor of the oral cavity and extends towards the oropharynx. It is less mobile than the body and helps in swallowing.

Other Important Anatomical Features

Dorsum: The upper surface of the tongue is called the dorsum. It contains papillae and taste buds.

Ventral Surface: The lower surface of the tongue is relatively smooth and is connected to the floor of the mouth by a fold of tissue called the lingual frenulum.

Lingual Frenulum: It is a fold of mucous membrane that connects the underside of the tongue to the floor of the oral cavity. It helps stabilize the tongue while allowing movement.

[IMG 2 — Horizontal labelled superior and inferior views of the tongue showing apex, body, root, dorsum, ventral surface, terminal sulcus, lingual frenulum and posterior one-third.]

2. Muscles of the Tongue

The tongue contains skeletal muscles that allow it to change shape and move in different directions.

These muscles are divided into two groups: intrinsic and extrinsic muscles.

A. Intrinsic Muscles

Intrinsic muscles are located entirely within the tongue. They change its shape without moving its attachment points significantly.

Their actions include:

• Shortening or lengthening the tongue.

• Making the tongue narrow or broad.

• Flattening or curling the tongue.

These movements help in manipulating food and producing different speech sounds.

B. Extrinsic Muscles

Extrinsic muscles originate outside the tongue and attach to it. They mainly change the position of the tongue.

The major extrinsic muscles are:

1. Genioglossus

It helps protrude the tongue, meaning it moves the tongue forward. It also helps depress its central portion.

2. Hyoglossus

It helps depress and retract the tongue.

3. Styloglossus

It pulls the tongue upward and backward.

4. Palatoglossus

It elevates the posterior part of the tongue and helps narrow the opening between the oral cavity and oropharynx.

Clinical importance: The muscles of the tongue are essential for chewing, swallowing and speech. Damage to their nerve supply can affect tongue movement and may cause difficulty in speaking or swallowing.

[IMG 3 — Horizontal anatomical diagram showing intrinsic and extrinsic muscles of the tongue, including genioglossus, hyoglossus, styloglossus and palatoglossus.]

3. Papillae of the Tongue

Papillae are small projections present on the upper surface of the tongue. They give the tongue its characteristic rough texture.

They help in gripping and moving food. Some papillae also contain taste buds.

There are four major types of lingual papillae.

A. Filiform Papillae

Filiform papillae are the most numerous papillae on the tongue.

They are thin, thread-like projections that provide friction and help hold and manipulate food during chewing.

Important: Filiform papillae generally do not contain taste buds.

B. Fungiform Papillae

Fungiform papillae are mushroom-shaped structures found mainly near the tip and sides of the tongue.

They contain taste buds and help detect different taste sensations.

C. Circumvallate Papillae

Circumvallate papillae are large, circular papillae arranged in a V-shaped row near the posterior part of the body of the tongue.

They contain numerous taste buds along their sides and are associated with taste sensation.

D. Foliate Papillae

Foliate papillae are folds present along the posterolateral edges of the tongue.

They contain taste buds and contribute to taste perception. They are more prominent in children than in adults.

[IMG 4 — Horizontal comparison infographic showing the four types of tongue papillae: filiform, fungiform, circumvallate and foliate, with their shapes, locations and taste bud presence.]

4. Taste Buds and Their Structure

Taste buds are specialized sensory structures responsible for detecting taste.

They are mainly present within the epithelium of fungiform, circumvallate and foliate papillae.

Each taste bud contains several types of cells:

1. Gustatory Receptor Cells

These are specialized sensory cells that detect chemicals from food dissolved in saliva. They help convert taste stimulation into signals that can be transmitted to the nervous system.

2. Supporting Cells

These cells provide structural and functional support to the taste receptor cells.

3. Basal Cells

Basal cells help replace old or damaged taste cells, allowing taste buds to maintain their function.

4. Taste Pore

The taste pore is a small opening through which dissolved substances come into contact with the microvilli of taste receptor cells.

When food substances dissolve in saliva, they interact with receptors or ion channels on taste receptor cells. This stimulates sensory pathways that carry information to the brain.

[IMG 5 — Horizontal labelled microscopic diagram of a taste bud showing taste pore, gustatory receptor cells, supporting cells, basal cells, microvilli and sensory nerve fibres.]

5. Five Basic Taste Sensations

The human tongue participates in detecting five basic taste sensations.

A. Sweet

Sweet taste is commonly associated with sugars and certain other substances.

For example, glucose, sucrose and honey produce a sweet sensation.

Sweet taste helps identify energy-rich food sources.

B. Salty

Salty taste is mainly associated with dissolved salts, particularly sodium-containing substances.

For example, common table salt (sodium chloride) produces a salty sensation.

C. Sour

Sour taste is mainly produced by acidic substances.

For example, lemon juice and vinegar produce a sour sensation because they contain acids.

D. Bitter

Bitter taste is produced by various chemical substances, including some naturally occurring plant compounds and certain medicines.

For example, quinine and some pharmaceutical preparations have a bitter taste.

Bitter taste can help detect potentially harmful substances, although not every bitter substance is toxic.

E. Umami

Umami is a savoury or meaty taste commonly associated with amino acids such as glutamate.

For example, tomatoes, mushrooms and foods containing monosodium glutamate (MSG) can produce an umami sensation.

Important: Taste is not limited to five specific regions of the tongue. Most regions containing taste buds can detect multiple basic taste sensations, although sensitivity may vary.

[IMG 6 — Horizontal educational infographic showing the five basic taste sensations: sweet, salty, sour, bitter and umami, with suitable food examples. Do not use the outdated tongue taste-zone map.]

6. Mechanism of Taste (Gustation)

Gustation is the process by which the body detects and identifies different taste sensations.

It involves taste receptor cells, sensory nerves and specific areas of the brain.

The mechanism occurs in the following steps:

Step 1: Dissolving of Food Substances

When food enters the mouth, saliva dissolves its chemical substances.

Step 2: Stimulation of Taste Receptors

The dissolved substances enter the taste pore and interact with receptors or ion channels on gustatory receptor cells.

Step 3: Generation of Signals

Stimulation of the taste receptor cells produces electrical signals that activate sensory nerve fibres.

Step 4: Transmission Through Cranial Nerves

Taste information travels through specific cranial nerves:

• Facial nerve (VII): Carries taste information from the anterior two-thirds of the tongue.

• Glossopharyngeal nerve (IX): Carries taste information from the posterior one-third of the tongue.

• Vagus nerve (X): Carries taste information from a small region near the epiglottis and lower pharynx.

Step 5: Processing in the Brain

The sensory information reaches the brainstem and is transmitted to the gustatory cortex, where taste sensations are interpreted.

This allows us to recognize whether food is sweet, salty, sour, bitter or umami.

[IMG 7 — Horizontal flow diagram showing the mechanism of taste: Food chemicals → Dissolving in saliva → Taste buds → Sensory cranial nerves VII, IX and X → Brainstem → Gustatory cortex → Recognition of taste.]

7. Nerve Supply of the Tongue

The tongue receives nerve supply for taste, general sensation and muscle movement.

It is important to understand that taste sensation and general sensation are not exactly the same.

• Taste sensation allows us to identify different tastes.

• General sensation allows us to feel touch, pain and temperature.

A. General Sensory Supply

General sensation includes touch, pain and temperature.

• Anterior two-thirds: Mainly supplied by the lingual nerve, a branch of the mandibular division of the trigeminal nerve (V3).

• Posterior one-third: Supplied by the glossopharyngeal nerve (IX).

• Small region near the epiglottis: Supplied by the vagus nerve (X).

B. Taste Sensory Supply

• Anterior two-thirds: Taste is carried by the chorda tympani branch of the facial nerve (VII).

• Posterior one-third: Taste is carried by the glossopharyngeal nerve (IX).

• Region near the epiglottis: Taste is carried by the vagus nerve (X).

C. Motor Supply

Most tongue muscles are supplied by the hypoglossal nerve (XII).

The major exception is the palatoglossus muscle, which is supplied through the vagus nerve (X) via the pharyngeal plexus.

[IMG 8 — Horizontal colour-coded anatomical diagram showing the sensory, taste and motor nerve supply of the tongue, with cranial nerves V, VII, IX, X and XII labelled.]

8. Functions of the Tongue

The tongue performs several important functions in daily life.

A. Taste Sensation

Taste buds detect different chemical substances present in food and help identify sweet, salty, sour, bitter and umami sensations.

B. Mastication (Chewing)

The tongue moves food between the teeth during chewing. It helps position food properly so that it can be broken down effectively.

C. Formation of Bolus

During chewing, the tongue mixes food with saliva and helps form a soft, rounded mass called a bolus.

This makes food easier to swallow.

D. Swallowing (Deglutition)

The tongue pushes the prepared food bolus towards the pharynx, initiating the swallowing process.

It plays an important role in transferring food from the oral cavity towards the oesophagus.

E. Speech Production

The tongue helps produce many speech sounds by changing its position and making contact with different parts of the oral cavity.

For example, sounds such as 't', 'd', 'l' and 'n' require coordinated tongue movements.

F. Oral Cleaning

The tongue helps move food particles and saliva around the oral cavity, contributing to the natural cleaning process of the mouth.

9. Common Disorders of the Tongue

Some conditions can affect the structure, movement or normal functioning of the tongue.

A. Glossitis

Glossitis is inflammation of the tongue.

It may cause the tongue to become swollen, red, smooth or painful.

Possible causes include nutritional deficiencies, infections, allergic reactions and irritation.

B. Oral Thrush

Oral thrush is a fungal infection caused by Candida species, commonly Candida albicans.

It may produce white patches on the tongue and other areas of the oral cavity.

It is more likely to occur in individuals with reduced immunity or after certain antibiotic treatments.

C. Geographic Tongue

Geographic tongue is a generally harmless condition in which irregular, smooth red patches develop on the surface of the tongue.

The patches may change their location and appearance over time.

Some individuals experience sensitivity to spicy or acidic foods.

D. Ankyloglossia (Tongue-Tie)

Ankyloglossia is a condition in which the lingual frenulum is unusually short, tight or restrictive.

It can limit tongue movement and may interfere with feeding, speech or other oral activities in some individuals.

E. Loss or Alteration of Taste

Taste disturbances may occur due to infections, certain medicines, nutritional deficiencies, nerve damage or other health conditions.

A reduced ability to taste is called hypogeusia, while a complete loss of taste is called ageusia.

10. Clinical and Pharmaceutical Importance

Understanding the tongue is important in pharmacy because it plays a role in taste perception, oral drug administration and certain specialized drug delivery systems.

A. Sublingual Drug Administration

Sublingual administration means placing a medicine underneath the tongue, where it dissolves and is absorbed through the oral mucosa.

This route can allow certain medicines to enter the systemic circulation without first passing through the gastrointestinal tract and liver.

Example: Nitroglycerin sublingual tablets are used for rapid relief of angina in suitable patients.

B. Buccal Drug Administration

In buccal administration, a medicine is placed between the cheek and gum, where it is absorbed through the buccal mucosa.

It is different from sublingual administration, which uses the area beneath the tongue.

C. Taste Masking in Pharmaceutical Formulations

Some medicines have an unpleasant bitter taste.

Pharmaceutical scientists use taste-masking techniques to improve patient acceptability, particularly in oral liquids, chewable tablets and formulations intended for children.

Examples of techniques include:

• Sweetening and flavouring agents.

• Coating of drug particles.

• Microencapsulation.

• Use of suitable formulation approaches to reduce contact between the drug and taste receptors.

Clinical importance: Improving the taste of medicines can help patients, especially children, take prescribed medicines more easily.

Key Takeaways

• The tongue is a muscular organ involved in taste, chewing, swallowing and speech.

• It is divided into the apex, body and root.

• Intrinsic muscles change the shape of the tongue, while extrinsic muscles change its position.

• The four major types of papillae are filiform, fungiform, circumvallate and foliate.

• Taste buds contain specialized receptor cells that detect chemical substances dissolved in saliva.

• The five basic taste sensations are sweet, salty, sour, bitter and umami.

• Taste information is carried mainly through cranial nerves VII, IX and X.

• Most tongue muscles receive motor supply from the hypoglossal nerve (XII).

• The tongue is important in mastication, bolus formation, swallowing and speech.

• Sublingual drug administration and taste masking are important pharmaceutical applications.

Remember: The tongue is not just a taste organ. It is a muscular structure that coordinates sensory perception, food movement, swallowing and speech.