Tongue

The tongue is a muscular organ located in the oral cavity, playing a critical role in speech, taste, chewing, and swallowing. It is composed of skeletal muscles covered by a mucous membrane, giving it both flexibility and strength for its various functions. The surface of the tongue is covered with small structures called papillae, which contain taste buds responsible for detecting flavors such as sweet, sour, salty, bitter, and umami.

The tongue is divided into two main parts—the anterior two-thirds, which is visible in the mouth, and the posterior one-third, which extends into the oropharynx. It is richly supplied with nerves, blood vessels, and lymphatics, ensuring sensitivity, mobility, and immune defense. The tongue also houses lingual glands that produce saliva, aiding in lubrication and digestion. Its unique combination of muscles and sensory receptors makes it essential for both oral and systemic health.

Location

The tongue is located within the oral cavity and partially extends into the oropharynx. It is anchored to the floor of the mouth by a thin fold of tissue called the lingual frenulum. Its base connects to the hyoid bone, mandible, and styloid process, providing structural support. The tip of the tongue lies freely at the front of the mouth, while the posterior portion extends downward into the throat, playing a role in swallowing and airway protection.

Anatomy

The tongue is a muscular organ located in the oral cavity and partially extending into the oropharynx. It is composed of skeletal muscles covered by a mucous membrane and is highly vascularized and innervated. The tongue is divided into two main parts:

• Anterior Two-Thirds (Oral Part) – Lies within the oral cavity and is primarily involved in taste and speech articulation.
• Posterior One-Third (Pharyngeal Part) – Located in the oropharynx, playing a role in swallowing and immune defense.

The tongue is connected to the mandible, hyoid bone, and styloid process, giving it structural stability while allowing mobility and flexibility for complex movements.

Parts of the Tongue

• Tip (Apex)
  • The most anterior portion of the tongue.
  • Highly sensitive and mobile, involved in speech and tasting.
• Body
  • Forms the anterior two-thirds of the tongue.
  • Covered with papillae, which contain taste buds and provide texture.
• Root (Base)
  • The posterior one-third of the tongue, extending into the oropharynx.
  • Contains lingual tonsils, which are part of the immune system.
• Dorsum
  • The upper surface of the tongue, divided into the oral and pharyngeal parts by the sulcus terminalis, a V-shaped groove.
  • Covered by papillae and lined with mucosa for taste and sensation.
• Inferior Surface
  • The underside of the tongue, smooth and highly vascularized.
  • Connected to the floor of the mouth by the lingual frenulum, which limits excessive movement.

Muscle Structure

The tongue consists of intrinsic and extrinsic muscles, which allow it to perform precise and versatile movements.

Intrinsic Muscles

• Located within the tongue and responsible for shape alterations.
• Superior Longitudinal Muscle – Shortens the tongue and curls it upward.
• Inferior Longitudinal Muscle – Shortens the tongue and curls it downward.
• Transverse Muscle – Narrows and elongates the tongue.
• Vertical Muscle – Flattens and broadens the tongue.

Extrinsic Muscles

• Originate outside the tongue and are responsible for its movement within the oral cavity.
• Genioglossus – Protrudes the tongue and depresses the center.
• Hyoglossus – Depresses and retracts the tongue.
• Styloglossus – Elevates and retracts the tongue.
• Palatoglossus – Elevates the back of the tongue and aids in swallowing.

Papillae on the Tongue

The dorsal surface of the tongue is covered with papillae, which give it a rough texture and house taste buds.

• Filiform Papillae
  • Small, cone-shaped structures distributed across the anterior part of the tongue.
  • Provide texture and grip but do not contain taste buds.
• Fungiform Papillae
  • Mushroom-shaped and scattered among the filiform papillae.
  • Contain taste buds and are most numerous near the tip of the tongue.
• Circumvallate Papillae
  • Large, dome-shaped papillae arranged in a V-shape near the sulcus terminalis.
  • Each contains multiple taste buds and is surrounded by a moat-like groove.
• Foliate Papillae
  • Located on the lateral sides of the tongue.
  • Contain taste buds and are more prominent in infants and children.

Mucous Membrane and Glands

The mucous membrane covers the tongue and is divided into keratinized epithelium (dorsal surface) and non-keratinized epithelium (ventral surface).

Salivary Glands associated with the tongue include:

• Lingual Glands – Produce serous and mucous secretions that aid in digestion.
• Von Ebner’s Glands – Located near the circumvallate papillae, secrete serous fluid to wash away food particles from the taste buds.

Blood Supply

The tongue receives its blood supply primarily from the lingual artery, a branch of the external carotid artery.

• Dorsal Lingual Arteries – Supply the root and posterior part.
• Deep Lingual Arteries – Supply the anterior part.
• Sublingual Arteries – Supply the underside and floor of the mouth.

Venous drainage occurs via the lingual vein, which empties into the internal jugular vein.

Nerve Supply

The tongue has a complex innervation system for motor and sensory functions.

Motor Innervation

• All intrinsic and extrinsic muscles (except palatoglossus) are innervated by the hypoglossal nerve (cranial nerve XII).
• Palatoglossus is supplied by the vagus nerve (cranial nerve X).

Sensory Innervation

• • Anterior Two-Thirds
    • General Sensation – Supplied by the lingual nerve (branch of the mandibular nerve, cranial nerve V3).
    • Taste Sensation – Carried by the chorda tympani (branch of the facial nerve, cranial nerve VII).
  • Posterior One-Third
    • Both general and taste sensation are supplied by the glossopharyngeal nerve (cranial nerve IX).
  • Base of the Tongue
    • Supplied by the vagus nerve (cranial nerve X) via its internal laryngeal branch.

Lymphatic Drainage

• Tip of the Tongue – Drains into the submental lymph nodes.
• Anterior Two-Thirds – Drains into the submandibular lymph nodes.
• Posterior One-Third – Drains into the deep cervical lymph nodes.

Histology

• Epithelium – The dorsal surface has keratinized stratified squamous epithelium for protection, while the ventral surface has non-keratinized epithelium for flexibility.
• Muscles – Consist of skeletal muscle fibers oriented in multiple directions, allowing precise movements.
• Taste Buds – Specialized clusters of cells found within papillae, containing gustatory receptors for detecting tastes.

Physical Features

• Color – Ranges from pink to reddish due to its rich vascular supply.
• Texture – Rough on the dorsal surface due to papillae and smooth on the ventral surface.
• Size – Length of approximately 10 cm in adults.

Function

Mastication (Chewing)

The tongue plays a crucial role in the mechanical digestion of food.

• It positions food between the teeth for efficient chewing.
• The muscles of the tongue manipulate food, mixing it with saliva to form a soft, cohesive bolus for swallowing.
• It assists in cleaning the oral cavity by pushing food particles away from the teeth.

Swallowing (Deglutition)

The tongue is essential in the process of swallowing by moving food from the oral cavity to the pharynx.

• Voluntary Stage – The tongue pushes the bolus toward the oropharynx.
• Involuntary Stage – It works with the soft palate and epiglottis to ensure the food moves safely into the esophagus, preventing aspiration into the airway.

Taste Sensation

The tongue is the primary organ for taste perception through taste buds located in the papillae on its surface.

Different areas of the tongue detect the five basic tastes:

• Sweet – Detected at the tip of the tongue.
• Salty – Recognized along the sides of the tip.
• Sour – Sensed along the sides of the tongue.
• Bitter – Perceived at the back of the tongue.
• Umami – Detected throughout the tongue.

Taste signals are transmitted to the brain via the facial nerve (cranial nerve VII) and glossopharyngeal nerve (cranial nerve IX).

Speech and Articulation

The tongue is vital for speech production by modifying airflow and vibrations created by the vocal cords.

• It interacts with the teeth, lips, and palate to produce specific sounds and phonemes.
• Helps in the pronunciation of consonants like T, D, L, and S, and vowel sounds by changing its shape and position.

Oral Cleaning and Hygiene

The tongue helps maintain oral hygiene by:

• Moving food particles to areas where they can be swallowed or removed.
• Assisting in saliva production, which cleanses the mouth and neutralizes acids.
• Scraping bacteria and debris off the teeth and gums, reducing plaque formation.

Taste and Texture Analysis

The tongue detects both taste and texture, contributing to the overall flavor perception of food.

• Papillae contain mechanoreceptors that sense texture and pressure, enabling differentiation between smooth, rough, or gritty foods.
• Helps identify foods that may be unsafe to consume, such as those that are spoiled or contaminated.

Immune Defense

The tongue contributes to the immune system through the presence of lingual tonsils located at its base.

• The lingual tonsils contain lymphoid tissue that traps pathogens and stimulates the production of immune cells.
• Protects the respiratory and digestive tracts from infections by serving as a first line of defense.

Temperature and Pain Sensation

The tongue contains thermoreceptors and nociceptors that allow it to:

• Detect temperature changes, distinguishing between hot and cold foods or liquids.
• Sense pain caused by injuries, burns, or irritants such as spices and acids.

Moistening and Lubrication

The salivary glands associated with the tongue help:

• Moisten food for easier swallowing.
• Dissolve substances for taste perception.
• Lubricate oral surfaces, reducing friction during speech and chewing.

Assists in Breathing

The tongue helps regulate airflow during breathing by:

• Maintaining an open airway during rest.
• Preventing airway obstruction by moving during sleep or speech.
• Adjusting positions to control airflow for snoring prevention and breathing efficiency.

Aesthetic and Facial Expression

The tongue aids in facial expressions and gestures, playing a role in non-verbal communication such as:

• Sticking out to express displeasure or playfulness.
• Enhancing facial symmetry by maintaining proper muscle tone and movement.

Developmental Function

In infants, the tongue assists with:

• Sucking and Latching – Ensures proper feeding during breastfeeding.
• Swallowing Reflex – Develops as an early motor skill.
• Speech Development – Helps in learning to form sounds and words.

Sensory Feedback

The tongue provides sensory feedback about the size, shape, and texture of objects in the mouth.

• Identifies foreign objects or bone fragments in food.
• Assists in exploring new textures, especially in infancy and childhood.

Secretion of Enzymes

The tongue aids in digestion through lingual glands that produce enzymes such as:

• Lingual Lipase – Begins the breakdown of lipids (fats) in food.
• Salivary Secretions – Help lubricate food and initiate starch digestion with enzymes like amylase.

Maintenance of Taste Balance

The tongue works to maintain a balance of flavors by analyzing multiple taste sensations simultaneously.

• Helps enhance appetite by stimulating taste receptors.
• Guides food preferences based on nutritional needs and dietary habits.

Clinical Significance

The tongue plays a critical role in speech, taste, swallowing, and oral health, making it a focus in diagnosing and managing various medical conditions. Tongue disorders can indicate both local issues and systemic diseases.

Glossitis, or inflammation of the tongue, can result from nutritional deficiencies (e.g., vitamin B12, iron), infections, or allergic reactions, leading to swelling, redness, and pain. Geographic tongue, a benign condition, presents as patchy areas with a map-like appearance, while fissured tongue appears with deep grooves and may be associated with genetic syndromes.

Oral cancer, particularly squamous cell carcinoma, often affects the lateral borders of the tongue, requiring early detection through biopsies and imaging. Tongue-tie (ankyloglossia) is a congenital condition where the lingual frenulum is unusually short, restricting movement and affecting speech and feeding.

Examinations of the tongue can also reveal systemic conditions, such as dehydration, anemia, and fungal infections (oral thrush). Regular oral hygiene, hydration, and nutritional balance are essential for maintaining tongue health.