Which of the following nerve carries taste sensations from the posterior 1/3rd of tongue?
## **Core Concept**
The question tests knowledge of the innervation of the tongue, specifically regarding the carriage of taste sensations. Taste sensation from the tongue is primarily mediated by the facial nerve (cranial nerve VII) and the glossopharyngeal nerve (cranial nerve IX). The **facial nerve** carries taste from the anterior two-thirds of the tongue, while the **glossopharyngeal nerve** carries taste from the posterior one-third.
## **Why the Correct Answer is Right**
The glossopharyngeal nerve (cranial nerve IX) is responsible for carrying taste sensations from the posterior one-third of the tongue. This nerve provides the sensory innervation to the posterior third of the tongue, including the circumvallate and foliate papillae, which contain taste buds. The **chorda tympani**, a branch of the facial nerve, carries taste from the anterior two-thirds of the tongue, making option **C. Glossopharyngeal nerve** the correct answer.
## **Why Each Wrong Option is Incorrect**
- **Option A:** The **Trigeminal nerve (cranial nerve V)** provides general sensory innervation to the face, including the tongue for non-taste sensations like touch and temperature, but it does not carry taste sensations.
- **Option B:** The **Facial nerve (cranial nerve VII)**, through its branch the chorda tympani, carries taste sensations from the anterior two-thirds of the tongue, not the posterior one-third.
- **Option D:** The **Vagus nerve (cranial nerve X)** carries taste sensations from the epiglottis and the back of the throat but not from the tongue itself.
## **Clinical Pearl / High-Yield Fact**
A key clinical correlation is that the **glossopharyngeal nerve** also provides motor innervation to the stylopharyngeus muscle and is involved in the gag reflex. Damage to this nerve can result in difficulty swallowing (dysphagia) and altered taste sensation from the posterior tongue.
## **Correct Answer: C. Glossopharyngeal nerve**