Model Answer
0 min readIntroduction
The tongue, a muscular hydrostat, is vital for speech, taste, and swallowing. Its complex structure is reflected in its rich innervation and vascular supply. The development of the tongue from branchial arches dictates its nerve supply, with contributions from multiple cranial nerves. Understanding the nerve supply is crucial not only for anatomical knowledge but also for diagnosing and managing conditions affecting taste, speech, and swallowing. This answer will detail the nerve supply of the tongue, correlating it with its development, and will also cover its blood supply, lymphatic drainage, and relevant applied anatomy.
Development of the Tongue
The tongue develops from the fusion of several branchial arches. Specifically:
- 1st Arch (Mandibular Arch): Contributes to the anterior two-thirds of the tongue.
- 2nd Arch (Hyoid Arch): Contributes to the posterior one-third of the tongue, including the root.
- 3rd Arch (Branchial Arch): Contributes to the base of the tongue and the epiglottis.
This embryological origin directly influences the nerve supply, as each arch is associated with a specific cranial nerve.
Nerve Supply of the Tongue
1. Motor Innervation
- Hypoglossal Nerve (CN XII): Innervates all intrinsic and extrinsic muscles of the tongue *except* the palatoglossus. This nerve is crucial for tongue movements like protrusion, retraction, elevation, and depression. Damage to CN XII results in ipsilateral tongue weakness and deviation towards the affected side during protrusion.
- Vagus Nerve (CN X): Innervates the palatoglossus muscle, which elevates the posterior tongue during swallowing.
- Glossopharyngeal Nerve (CN IX): Supplies the stylopharyngeus muscle, which elevates the pharynx and larynx during swallowing.
2. Sensory Innervation – Taste
- Chorda Tympani (branch of Facial Nerve - CN VII): Carries taste sensation from the anterior two-thirds of the tongue. It joins the lingual nerve.
- Glossopharyngeal Nerve (CN IX): Carries taste sensation from the posterior one-third of the tongue.
- Vagus Nerve (CN X): Carries taste sensation from the epiglottis and the root of the tongue.
3. General Sensory Innervation
- Lingual Nerve (branch of Trigeminal Nerve - CN V3): Provides general sensory innervation to the anterior two-thirds of the tongue. It also carries taste fibers from the chorda tympani.
- Glossopharyngeal Nerve (CN IX): Provides general sensory innervation to the posterior one-third of the tongue.
Table summarizing Nerve Supply:
| Nerve | Function | Area Innervated |
|---|---|---|
| Hypoglossal (CN XII) | Motor | All intrinsic & extrinsic tongue muscles (except palatoglossus) |
| Vagus (CN X) | Motor & Taste | Palatoglossus, Epiglottis, Root of Tongue |
| Glossopharyngeal (CN IX) | Motor, Taste & General Sensory | Posterior 1/3 of Tongue, Stylopharyngeus |
| Facial (CN VII) - Chorda Tympani | Taste | Anterior 2/3 of Tongue |
| Trigeminal (CN V3) - Lingual Nerve | General Sensory | Anterior 2/3 of Tongue |
Blood Supply of the Tongue
The tongue receives a rich blood supply primarily from the:
- Lingual Artery: A branch of the external carotid artery. It runs deep to the hyoglossus muscle and supplies the majority of the tongue.
- Dorsal Lingual Arteries: Branches of the lingual artery that supply the dorsal surface of the tongue.
- Deep Lingual Artery: Supplies the root of the tongue.
- Sublingual Artery: Supplies the sublingual gland and the floor of the mouth.
Lymphatic Drainage of the Tongue
Lymphatic drainage of the tongue follows its arterial supply:
- Anterior 2/3: Drains to the submandibular lymph nodes.
- Posterior 1/3: Drains to the deep cervical lymph nodes (jugulodigastric nodes).
- Tip of the tongue: Drains to the central neck lymph nodes.
Applied Anatomy
Glossopharyngeal Neuralgia: Intense, stabbing pain in the posterior tongue, pharynx, and ear, often triggered by swallowing.
Lingual Nerve Injury: Can occur during dental procedures or surgery in the floor of the mouth, leading to loss of taste and sensation in the anterior tongue.
Cancer of the Tongue: Frequently affects the lateral borders of the tongue, impacting nerve supply and causing pain, difficulty swallowing, and speech impairment. Early detection is crucial.
Conclusion
The nerve supply of the tongue is intricately linked to its developmental origins, with contributions from multiple cranial nerves. Understanding this relationship is vital for clinical diagnosis and management of conditions affecting tongue function. The rich blood supply and lymphatic drainage further contribute to the tongue’s complex anatomy and its susceptibility to various pathologies. A thorough knowledge of these aspects is essential for medical professionals dealing with head and neck disorders.
Answer Length
This is a comprehensive model answer for learning purposes and may exceed the word limit. In the exam, always adhere to the prescribed word count.