**Question:** Taste sensation from the posterior 1/3rd of tongue are carried by nerve:

A. Hypoglossal nerve (CN XII)
B. Facial nerve (CN VII)
C. Vagus nerve (CN X)
D. Glossopharyngeal nerve (CN IX)

**Correct Answer:**

**Core Concept:**
The taste sensation from the posterior 1/3rd of the tongue is mediated by specific cranial nerves that carry information to the brain for interpretation. Taste receptors are found on the taste papillae on the posterior third of the tongue. These taste receptors are stimulated by different tastes, which are then transmitted to the brain via specific cranial nerves.

**Why the Correct Answer is Right:**
The taste sensation from the posterior 1/3rd of the tongue is carried by the glossopharyngeal nerve (CN IX). This nerve is responsible for transmitting taste information from the posterior tongue, as well as information about saliva, pharynx, and the esophagus. The other options are incorrect because:

- Hypoglossal nerve (CN XII) controls tongue movement and doesn't carry taste information.
- Facial nerve (CN VII) is responsible for facial expressions, balance, and some taste sensation from the anterior two-thirds of the tongue.
- Vagus nerve (CN X) carries information about the pharynx, larynx, and some taste sensation from the posterior two-thirds of the tongue.

**Why Each Wrong Option is Incorrect:**

- Hypoglossal nerve (CN XII): Hypoglossal nerve controls tongue movement and doesn't carry taste information. Taste sensation is mainly carried by the glossopharyngeal nerve (CN IX) and the facial nerve (CN VII).
- Facial nerve (CN VII): While the facial nerve does carry some taste sensation from the anterior two-thirds of the tongue, it is not responsible for taste sensation from the posterior one-third of the tongue. Glossopharyngeal nerve (CN IX) carries taste sensation from the posterior two-thirds of the tongue, as well as information about saliva, pharynx, and the esophagus.
- Vagus nerve (CN X): The vagus nerve carries taste sensation from the posterior two-thirds of the tongue, but not specifically from the posterior one-third. Glossopharyngeal nerve (CN IX) is responsible for taste sensation from the posterior one-third of the tongue, along with information about saliva, pharynx, and the esophagus.

**Clinical Pearl:**
The glossopharyngeal nerve (CN IX) is essential for the proper functioning of the taste receptors in the posterior one-third of the tongue. This nerve is involved in transmitting taste information, saliva production, pharyngeal swallowing reflex, and the initiation of the gag reflex. The other cranial nerves also play important roles but are not responsible for taste sensation from the posterior one-third of the tongue.

**Explanation:**

The posterior one-third of the tongue is primarily responsible for detecting sour and bitter