Model Answer
0 min readIntroduction
The tongue is a muscular hydrostat, crucial for speech, taste, swallowing, and oral manipulation of food. Its development is a complex process involving the fusion of multiple branchial arches. Understanding its developmental origins is key to comprehending its anatomical structure and potential congenital anomalies. The tongue’s functionality relies heavily on its intricate nerve supply, which allows for both sensory perception and motor control. This answer will detail the embryological development, muscular components, and the comprehensive nerve supply of the tongue.
Development of the Tongue
The tongue develops from the first, second, and third branchial arches.
- First Branchial Arch: Contributes to the anterior two-thirds of the tongue, including the Tuberculum impar (median sulcus) and the hypobranchial eminence (lateral swellings).
- Second Branchial Arch: Forms the hyoid bone and contributes to the base of the tongue.
- Third Branchial Arch: Contributes to the posterior one-third of the tongue, including the root, and is associated with the glossopharyngeal nerve.
The sulcus terminalis, a V-shaped groove, divides the tongue into anterior two-thirds (oral part) and posterior one-third (pharyngeal part). The foramen cecum, located at the apex of the V, represents the site of the thyroglossal duct, which normally obliterates during development. Failure of obliteration can lead to thyroglossal duct cysts.
Muscular Components of the Tongue
The tongue is composed of intrinsic and extrinsic muscles.
- Intrinsic Muscles: These muscles are entirely contained within the tongue and alter its shape. They include:
- Superior Longitudinal: Shortens the tongue.
- Inferior Longitudinal: Lengthens the tongue.
- Transverse: Narrows and elongates the tongue.
- Verticalis: Flattens and broadens the tongue.
- Extrinsic Muscles: These muscles originate outside the tongue and move it. They include:
- Genioglossus: Protrudes the tongue and depresses the central part.
- Hyoglossus: Depresses and retracts the tongue.
- Styloglossus: Retracts and elevates the tongue.
- Palatoglossus: Elevates the posterior part of the tongue.
Nerve Supply of the Tongue
The nerve supply to the tongue is complex, involving multiple cranial nerves. The distribution varies depending on the region of the tongue.
| Region of Tongue | Motor Supply | Sensory Supply (Taste) | General Sensory Supply |
|---|---|---|---|
| Anterior 2/3 (Oral Part) | Hypoglossal Nerve (CN XII) | Chorda Tympani (branch of Facial Nerve - CN VII) | Lingual Nerve (branch of Trigeminal Nerve - CN V3) |
| Posterior 1/3 (Pharyngeal Part) | Hypoglossal Nerve (CN XII) | Glossopharyngeal Nerve (CN IX) | Glossopharyngeal Nerve (CN IX) |
| Root of Tongue | Hypoglossal Nerve (CN XII) | Glossopharyngeal Nerve (CN IX) | Vagus Nerve (CN X) |
Specific details:
- Hypoglossal Nerve (CN XII): Supplies all intrinsic muscles of the tongue and the extrinsic muscles (except palatoglossus).
- Chorda Tympani: Carries taste sensation from the anterior two-thirds of the tongue. It joins the Lingual Nerve.
- Lingual Nerve: Provides general sensory innervation to the anterior two-thirds of the tongue.
- Glossopharyngeal Nerve (CN IX): Supplies taste sensation and general sensation to the posterior one-third of the tongue.
- Vagus Nerve (CN X): Provides general sensory and motor innervation to the root of the tongue and pharynx.
Damage to the facial nerve can result in loss of taste on the anterior two-thirds of the tongue. Damage to the glossopharyngeal nerve can lead to difficulty swallowing and altered taste sensation in the posterior tongue. Hypoglossal nerve damage causes ipsilateral tongue deviation towards the paralyzed side during protrusion.
Conclusion
In conclusion, the tongue’s development from multiple branchial arches dictates its complex anatomy. Its functionality is dependent on the coordinated action of intrinsic and extrinsic muscles, all innervated by the hypoglossal nerve. The intricate sensory innervation, provided by the facial, glossopharyngeal, and vagus nerves, allows for taste perception and crucial reflexes. A thorough understanding of these components is essential for diagnosing and managing various tongue-related 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.