Tongue

The tongue is a muscular organ in the oral cavity that plays a vital role in speech, taste, mastication, and swallowing. Its complex structure, innervation, and vascular supply make it an important focus in both clinical and anatomical studies. Understanding its anatomy and physiology is essential for diagnosing tongue-related disorders.

Anatomy

Gross Anatomy

The tongue is divided into an anterior two-thirds (oral part) and a posterior one-third (pharyngeal part). The dorsal surface is characterized by papillae, while the ventral surface is smooth with visible veins. The tip, body, and root of the tongue are distinct regions with specific functional roles.

Muscles of the Tongue

The tongue contains both intrinsic and extrinsic muscles that coordinate its complex movements.

• Intrinsic Muscles: Superior longitudinal, inferior longitudinal, transverse, and vertical muscles, responsible for shaping the tongue and fine movements.
• Extrinsic Muscles: Genioglossus, hyoglossus, styloglossus, and palatoglossus, which position the tongue and facilitate gross movements during speech and swallowing.

Blood Supply

The arterial supply to the tongue is primarily from the lingual artery, a branch of the external carotid artery, with contributions from the sublingual artery. Venous drainage occurs through the lingual vein into the internal jugular vein.

Nerve Supply

The tongue receives both motor and sensory innervation:

• Motor Innervation: All intrinsic and extrinsic muscles except the palatoglossus are supplied by the hypoglossal nerve (cranial nerve XII). The palatoglossus is supplied by the vagus nerve (cranial nerve X).
• Sensory Innervation: Anterior two-thirds receive general sensation via the lingual nerve (branch of mandibular nerve) and taste via the chorda tympani (branch of facial nerve). The posterior one-third receives both general and taste sensation via the glossopharyngeal nerve (cranial nerve IX).

Lymphatic Drainage

Lymphatic vessels from the tongue drain primarily into the submental, submandibular, and deep cervical lymph nodes. The tip drains to submental nodes, lateral aspects to submandibular nodes, and the posterior tongue to deep cervical nodes.

Physiology

Motor Functions

The tongue is essential for speech articulation, allowing precise movements to produce consonant and vowel sounds. It also plays a critical role in mastication by positioning food between teeth and in swallowing by propelling the bolus posteriorly into the pharynx.

Sensory Functions

The tongue contains specialized receptors for taste and general sensation:

• Taste Sensation: Taste buds on the dorsal surface detect sweet, salty, sour, bitter, and umami flavors.
• General Sensation: Touch, pressure, pain, and temperature are sensed by mechanoreceptors and thermoreceptors throughout the tongue.

Other Functions

The tongue contributes to oral hygiene by mixing saliva and food, assisting in the mechanical cleaning of teeth. It also has a role in the immune response by harboring lymphoid tissue in the posterior portion, which contributes to local immunity.

Development and Embryology

Origin of Anterior 2/3 and Posterior 1/3

The anterior two-thirds of the tongue develop from the first pharyngeal arch, while the posterior one-third originates from the third and part of the fourth pharyngeal arches. The sulcus terminalis marks the boundary between these two regions in the adult tongue.

Tongue Musculature Development

Intrinsic and extrinsic tongue muscles arise from occipital somites, which migrate into the developing tongue. These muscles are responsible for the coordinated movements required for mastication, swallowing, and speech.

Innervation Development

The motor and sensory innervation of the tongue develops in parallel with the muscles and pharyngeal arches. Cranial nerves VII, IX, X, and XII establish connections with the respective regions of the tongue, allowing taste, sensation, and motor control to mature appropriately.

Common Disorders and Pathologies

Congenital Abnormalities

• Ankyloglossia: Shortened lingual frenulum restricting tongue mobility, potentially affecting speech and feeding.
• Macroglossia: Abnormally large tongue, which may be congenital or associated with conditions such as Down syndrome or hypothyroidism.
• Microglossia: Rare condition where the tongue is abnormally small, affecting oral function and speech.

Inflammatory Conditions

• Glossitis: General inflammation of the tongue, often painful and associated with nutritional deficiencies.
• Geographic Tongue: Benign condition with irregular, map-like patches on the dorsal tongue surface.
• Fissured Tongue: Presence of deep grooves on the dorsal surface, usually asymptomatic but may accumulate debris.

Infectious Causes

• Candidiasis: Fungal infection causing white plaques, often seen in immunocompromised patients.
• Viral Infections: Herpes simplex virus can cause painful ulcers on the tongue.

Neoplastic Conditions

• Benign tumors such as papillomas and granular cell tumors
• Malignant tumors including squamous cell carcinoma, particularly in the lateral tongue

Traumatic and Other Conditions

• Ulcers caused by mechanical trauma, burns, or irritants
• Lacerations and cuts from accidents or biting injuries

Clinical Examination

Inspection and Palpation Techniques

Examination of the tongue begins with visual inspection for color, texture, size, and the presence of lesions or ulcers. Palpation assesses consistency, tenderness, masses, and mobility. The tongue should be evaluated in both relaxed and protruded positions to detect asymmetry or restricted movement.

Assessment of Mobility, Symmetry, and Lesions

The examiner should observe tongue protrusion, lateral movements, and elevation to assess muscle function. Asymmetry or deviation may indicate cranial nerve involvement. Lesions, swelling, or induration should be noted and further investigated if necessary.

Neurological Examination

Evaluation of cranial nerves IX (glossopharyngeal), X (vagus), and XII (hypoglossal) is essential for assessing tongue function:

• Motor function of tongue protrusion and movement (hypoglossal nerve)
• Gag reflex and taste sensation (glossopharyngeal and vagus nerves)

Investigations

Laboratory Tests

Laboratory investigations may be indicated when infection or systemic disease is suspected:

• Complete blood count and inflammatory markers
• Cultures for bacterial or fungal infections
• Nutritional assessments, such as vitamin B12 or iron levels

Imaging Studies

Imaging is used to evaluate structural abnormalities or tumors:

• MRI or CT scans for mass lesions, deep tissue involvement, or vascular anomalies
• Ultrasound for superficial lesions and vascular assessment

Biopsy and Histopathology

When lesions are suspicious for malignancy or chronic pathology, a biopsy is performed. Histopathological examination helps confirm the diagnosis and guides management.

Management

Medical Treatment

Management of tongue disorders depends on the underlying cause. Medical treatment may include:

• Infections: Antifungal agents for candidiasis, antiviral therapy for herpes simplex, and antibiotics for bacterial infections.
• Inflammatory Conditions: Nutritional supplementation for deficiencies causing glossitis, topical anesthetics for symptomatic relief, and anti-inflammatory medications as needed.
• Pain Management: Analgesics or neuropathic pain medications for chronic or severe tongue pain.

Surgical Interventions

Surgery is indicated for structural, neoplastic, or congenital abnormalities affecting tongue function or health:

• Excision of benign or malignant tumors
• Frenuloplasty for ankyloglossia
• Reduction procedures for macroglossia causing airway or functional issues

Speech Therapy and Rehabilitation

Rehabilitation is essential when tongue mobility or function is compromised. Speech therapy helps restore articulation, swallowing, and oral motor control. Postoperative or post-injury exercises may improve recovery and functional outcomes.

References

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