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

A. Glossopharyngeal nerve (CN IX)
B. Vagus nerve (CN X)
C. Hypoglossal nerve (CN XII)
D. Trigeminal nerve (CN V)

**Core Concept:**

Taste is an essential sense for humans and other animals, allowing them to discern various flavors like sweet, sour, salty, bitter, and umami. Taste receptors for these flavors are located in specific regions of the tongue. In human anatomy, taste sensation is mediated by taste cells, which are located in the papillae on the tongue. These cells transmit their signals to the brain via cranial nerves.

**Why the Correct Answer is Right:**

The correct answer is the Glossopharyngeal nerve (CN IX), as it is responsible for transmitting taste information from the posterior one-third of the tongue. The posterior one-third of the tongue contains the largest concentration of taste buds, which are responsible for detecting the basic tastes. These taste buds send their signals to the brain via cranial nerves.

**Why Each Wrong Option is Incorrect:**

A. Vagus nerve (CN X): Although the posterior two-thirds of the tongue are responsible for swallowing and salivary secretion, they do not carry taste information. The vagus nerve is involved in other functions such as controlling the pharynx and regulating saliva production.

B. Vagus nerve (CN X): Similar to option A, the vagus nerve does not transmit taste information from the tongue. It is primarily involved in swallowing and regulating saliva production.

C. Hypoglossal nerve (CN XII): The hypoglossal nerve controls the tongue's movement and position, not taste sensation. It is responsible for moving the tongue downward, backward, and medially, allowing us to taste various foods.

D. Trigeminal nerve (CN V): The trigeminal nerve, specifically the ophthalmic, maxillary, and mandibular divisions, carry sensory information from the oral cavity, including the anterior two-thirds of the tongue. However, it does not specifically carry taste sensation information from the posterior one-third of the tongue.

**Clinical Pearls:**

1. The posterior one-third of the tongue houses the largest concentration of taste buds responsible for detecting basic tastes (sweet, sour, salty, bitter, and umami). These taste buds send their signals via the glossopharyngeal nerve (CN XII) to the nucleus of the solitary tract (NTS) in the brainstem.

2. Adequate functioning of the posterior two-thirds of the tongue is crucial for detecting sweet, sour, and bitter tastes. The anterior one-third of the tongue is responsible for detecting salty and umami tastes. The taste information from these regions is transmitted to the NTS via the trigeminal nerve (CN V).

3. The glossopharyngeal nerve (CN XII) and the vagus nerve (CN X)