Presynaptic parasympathetic fibers originate in the Edinger-Westphal nucleus, the parasympathetic motor nucleus associated with the oculomotor nucleus in the brainstem. Axons from the Edinger-Westphal nucleus and the oculomotor nucleus run together in the brainstem and exit together as the oculomotor nerve (cranial nerve III). The oculomotor nerve passes through the lateral wall of the cavernous sinus and enters the orbit through the superior orbital fissure. It divides into branches that innervate the levator palpebrae superioris and four of the six extraocular muscles. Parasympathetic fibers initially run in the inferior division of the oculomotor nerve. They exit as one or two short “motor roots” that synapse in the ciliary ganglion.
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