Taste sensation from posterior 1/3rd carried by:
**Core Concept**
The taste sensation from the posterior one-third of the tongue is mediated by the glossopharyngeal nerve, which is responsible for transmitting sensory information from this region to the brain. This is a crucial aspect of the cranial nerve's function, highlighting the complex interplay between taste, swallowing, and motor functions.
**Why the Correct Answer is Right**
The glossopharyngeal nerve (IX) carries taste fibers from the posterior one-third of the tongue, which is a vital component of the special visceral afferent (SVA) fibers that transmit taste information to the solitary nucleus in the brainstem. This nerve also plays a key role in swallowing, salivation, and vasomotor functions of the pharynx. The posterior one-third of the tongue is innervated by the lingual branch of the glossopharyngeal nerve, which carries these special sensory fibers.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the facial nerve (VII) primarily carries taste fibers from the anterior two-thirds of the tongue, not the posterior one-third.
**Option B:** This option is incorrect because the vagus nerve (X) is responsible for various visceral functions, including swallowing and salivation, but it does not carry taste fibers from the posterior one-third of the tongue.
**Option C:** This option is incorrect because the trigeminal nerve (V) primarily carries general sensory information from the face, including touch, temperature, and pain, but it does not carry taste fibers.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that the taste sensation from the posterior one-third of the tongue is mediated by the glossopharyngeal nerve, which can be tested clinically by assessing the patient's ability to taste sweet or sour substances in this region.
**Correct Answer: C. Glossopharyngeal nerve.