Where is the abducens nucleus located within the brainstem?

Where is the abducens nucleus located within the brainstem?

• A. Upper pons
• B. Lower pons
• C. Midbrain
• D. Medulla

Answer: (B)

The abducens nucleus sits in the pontine tegmentum of the brainstem, specifically in the caudal (lower) pons near the floor of the fourth ventricle. This dorsal location in the lower pons places its fibers to emerge as the abducens nerve and innervate the lateral rectus muscle to move the eye outward. You can also picture the facial colliculus on the dorsal floor of the fourth ventricle, where the facial nerve fibers loop around the abducens nucleus—another hint that the nucleus is in the lower pons. That’s why this is not in the midbrain (which houses nuclei for the oculomotor and trochlear nerves) and not in the medulla, and it’s not in the upper (rostral) pons. The correct region is the lower pons.

The abducens nucleus sits in the pontine tegmentum of the brainstem, specifically in the caudal (lower) pons near the floor of the fourth ventricle. This dorsal location in the lower pons places its fibers to emerge as the abducens nerve and innervate the lateral rectus muscle to move the eye outward. You can also picture the facial colliculus on the dorsal floor of the fourth ventricle, where the facial nerve fibers loop around the abducens nucleus—another hint that the nucleus is in the lower pons.

That’s why this is not in the midbrain (which houses nuclei for the oculomotor and trochlear nerves) and not in the medulla, and it’s not in the upper (rostral) pons. The correct region is the lower pons.