**Question:** The posterior 1/3 of the tongue is supplied by nerve -

A. lingual nerve
B. hypoglossal nerve
C. glossopharyngeal nerve
D. vagus nerve

**Correct Answer:** D. vagus nerve

**Core Concept:** In the human body, peripheral nerves are responsible for supplying sensory, motor, and autonomic functions to the various organs and tissues. In this question, we are discussing the anatomy of the tongue and its nerves.

**Why the Correct Answer is Right:** The posterior 1/3 of the tongue, also known as the posterior one-third, is supplied by the vagus nerve (CN X) which is a cranial nerve. The vagus nerve plays a crucial role in the sensory, motor, and autonomic functions of the posterior 1/3 of the tongue. It carries sensory information from the posterior two-thirds of the tongue, and provides motor innervation to the muscles of mastication and swallowing.

**Why Each Wrong Option is Incorrect:**

A. Lingual nerve (CN V) supplies the anterior two-thirds of the tongue and is not responsible for the posterior one-third.

B. Hypoglossal nerve (CN XII) supplies the muscles of the tongue, but it does not supply the posterior one-third of the tongue.

C. Glossopharyngeal nerve (CN IX) supplies the posterior two-thirds of the pharynx but is not responsible for the posterior one-third of the tongue.

**Clinical Pearl:** The correct identification of the nerves supplying different regions of the tongue is crucial for understanding the anatomy, function, and potential surgical complications during tongue procedures.

**Explanation:**

* The posterior one-third of the tongue is crucial for swallowing and gag reflex, which helps in maintaining oral hygiene and preventing aspiration and choking.
* Understanding the anatomy of the tongue and its nerves can help in the diagnosis and management of tongue disorders, such as pain, numbness, or dysfunction, which may occur due to nerve injuries or diseases.

**Why Each Wrong Option is Incorrect:**

A. Lingual nerve (CN V) supplies the anterior two-thirds of the tongue, not the posterior one-third.
B. Hypoglossal nerve (CN XII) supplies the muscles of the tongue but not the posterior one-third of the tongue.
C. Glossopharyngeal nerve (CN IX) supplies the posterior two-thirds of the pharynx but not the tongue.

**Why These Nerves Supply Different Regions of the Tongue:**

* The tongue is a complex organ with different regions, each having distinct functions and innervation.
* The lingual nerve (CN V) supplies the anterior two-thirds of the tongue, specifically the anterior two-thirds that contain taste buds, and muscles involved in tongue movements.
* The hypoglossal nerve (CN XII) supplies the muscles of the tongue responsible for its movement, specifically the intrinsic muscles of the tongue.
* The glossopharyngeal nerve (