Which of the following cranial nerve nucleus is located deep to facial colliculus?(AIIMS May 2015, November 2014)
**Core Concept**
The facial colliculus is a landmark on the floor of the fourth ventricle in the brainstem. It is formed by the facial nerve (cranial nerve VII) and the nucleus of the abducent nerve (cranial nerve VI) located deep to it. This anatomical relationship is crucial for understanding the cranial nerve nuclei and their positions within the brainstem.
**Why the Correct Answer is Right**
The abducent nerve nucleus is located in the pons, a part of the brainstem, and is situated deep to the facial colliculus. The facial colliculus is formed by the fibers of the facial nerve as they loop around the abducent nerve nucleus. This arrangement allows the facial nerve to decussate (cross over) to the opposite side of the brainstem, while the abducent nerve fibers continue straight ahead. This decussation is essential for the proper functioning of the facial nerve, which controls the muscles of facial expression, taste to the anterior two-thirds of the tongue, and other functions.
**Why Each Wrong Option is Incorrect**
**Option A:** is incorrect because it is the correct answer.
**Option B:** The glossopharyngeal nerve (cranial nerve IX) is located in the medulla oblongata, which is different from the location of the facial colliculus in the pons.
**Option C:** The facial nerve (cranial nerve VII) actually forms the facial colliculus, rather than being located deep to it.
**Option D:** The trigeminal nerve (cranial nerve V) is located in the pons, but it is not related to the facial colliculus.
**Clinical Pearl / High-Yield Fact**
The facial colliculus is a key landmark for identifying the location of the abducent nerve nucleus in the brainstem. Remember that the abducent nerve nucleus is situated deep to the facial colliculus, which is formed by the facial nerve fibers looping around it.
✓ Correct Answer: A. Abducent nerve