Are the majority (97%) of CN III fibers utilized for pupillary constriction or accommodation?

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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

Are the majority (97%) of CN III fibers utilized for pupillary constriction or accommodation?

Explanation:
The key idea is that the oculomotor nerve contains two main fiber types with different roles: somatic motor fibers to the extraocular muscles (and levator palpebrae) and parasympathetic fibers that innervate the sphincter pupillae and ciliary muscle to control pupil constriction and accommodation. The parasympathetic component, which drives pupil constriction and lens accommodation, is a relatively small portion of the total CN III fibers. The vast majority are dedicated to moving the eye itself. So neither pupil constriction nor accommodation uses the majority of CN III fibers.

The key idea is that the oculomotor nerve contains two main fiber types with different roles: somatic motor fibers to the extraocular muscles (and levator palpebrae) and parasympathetic fibers that innervate the sphincter pupillae and ciliary muscle to control pupil constriction and accommodation. The parasympathetic component, which drives pupil constriction and lens accommodation, is a relatively small portion of the total CN III fibers. The vast majority are dedicated to moving the eye itself. So neither pupil constriction nor accommodation uses the majority of CN III fibers.

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