Which one of the following extraocular muscles is served by a contra lateral brainstem subnucleus?
**Core Concept:** Extraocular muscles are responsible for eye movements, and are controlled by the brainstem. They are innervated by specific subnuclei, which are part of the oculomotor nucleus (CN III). The contra lateral (opposite side) subnucleus provides motor innervation to these muscles.
**Why the Correct Answer is Right:** The correct answer (C) refers to the abducens nucleus (CN VI), which is part of the oculomotor nucleus and located on the contra lateral side to its function. The abducens nucleus controls the lateral rectus muscle, responsible for lateral (side-to-side) eye movements. The other options represent different subnuclei of the oculomotor nucleus, but they are located on the same side as their functions, making them incorrect choices.
**Why Each Wrong Option is Incorrect:**
A. The superior rectus muscle is innervated by the contralateral (same side) medial longitudinal fasciculus (MLF) branch of the oculomotor nerve (CN III), not the oculomotor nucleus.
B. The inferior rectus muscle is served by the contralateral (same side) medial longitudinal fasciculus (MLF) branch of the oculomotor nerve (CN III), not the contra lateral oculomotor nucleus.
D. The rectus inferior muscle is innervated by the contralateral (same side) medial longitudinal fasciculus (MLF) branch of the oculomotor nerve (CN III), not the contra lateral oculomotor nucleus.
**Clinical Pearl:** Understanding the anatomy and innervation of extraocular muscles is crucial for diagnosing and treating oculomotor palsies (paralysis) and misalignments. A lateral rectus palsy would cause lateral deviation of the eye, while an abducens palsy would cause difficulty in abducting the eye.
**Correct Answer:** C. Abducens nucleus (CN VI)