Which of the following is NOT innervated by the inferior division of CN III?

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Prepare for the NBEO Ocular Anatomy Posterior Segment and Cranial Nerves Test. Study with flashcards and multiple choice questions, each question has hints and explanations. Get ready for your exam!

Multiple Choice

Which of the following is NOT innervated by the inferior division of CN III?

Explanation:
The inferior division of CN III supplies three extraocular muscles — medial rectus, inferior rectus, and inferior oblique — as its motor targets. It also carries parasympathetic fibers that reach the ciliary ganglion to support pupil constriction and accommodation. But the iris sphincter isn’t driven by a direct motor branch of this division. Pupillary constriction uses parasympathetic fibers that travel with CN III to the ciliary ganglion and then via short ciliary nerves to the sphincter pupillae. Those parasympathetic fibers reach the sphincter through the ciliary ganglion pathway rather than as a distinct inferior-division motor branch. So the iris sphincter is not innervated by the inferior division.

The inferior division of CN III supplies three extraocular muscles — medial rectus, inferior rectus, and inferior oblique — as its motor targets. It also carries parasympathetic fibers that reach the ciliary ganglion to support pupil constriction and accommodation. But the iris sphincter isn’t driven by a direct motor branch of this division. Pupillary constriction uses parasympathetic fibers that travel with CN III to the ciliary ganglion and then via short ciliary nerves to the sphincter pupillae. Those parasympathetic fibers reach the sphincter through the ciliary ganglion pathway rather than as a distinct inferior-division motor branch. So the iris sphincter is not innervated by the inferior division.

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