Oculomotor nerve

Nervus oculomotorius (N. III.), oculomotor nerve. Like most other cranial nerves (nervi craniales) it emerges from the brainstem.

Anatomy
Contains 2 types of efferent fibers: somatomotor


 * innervate the oculomotor muscles together with N. IV. (m. obliquus bulbi superior) and N. VI. (m. rectus lateralis)


 * They come from the motor nucleus ncl. nervi oculomotorii in the tegmentum

visceromotor parasympathetic


 * parasympathetic innervating ganglion ciliare and through it m. ciliaris (accommodation) and m. sphincter pupillae (miosis)
 * come from ncl. accessorius nervi oculomotorii in the mesencephalon tegmentum

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Progress
Extracerebral course of the nerve:


 * exit from the brain medially from the crura cerebri to the side of the fossa interpeduncularis


 * penetrates into the subarachnoid cistern – a sheath is formed around the nerve and the a. superior cerebelli and a. cerebri posterior run there


 * leaves the subarachnoid space between the attachment of the tentorium cerebelli and its free edge

Extradural course:


 * first under the inner sheet 'dura mater encephali' laterally from the processus clinoideus posterior and goes to the ceiling of the sinus cavernosus


 * before entering the orbit, sympathetic fibers from the sulcus caroticus internus join it and attach to the n. ophthalmicus


 * enters the orbit at the fissura orbitalis superior, but even before that it divides into 2 branches: ramus superior et inferior

Extracranial course:


 * ramus sup. : runs along the lateral edge of the optic nerve and heads forward, where it divides into smaller branches innervating the ``m. rectus superior bulbi and levator palpebrae superioris'''


 * ramus inf. : divides into 3 branches, they go under the n. opticus and innervate the m. rectus medialis, m. rectus inferior, m. obliquus inferior;

It emerges from the brainstem on the medial side of the peduncle in the sulcus nervi oculomotorii in the fossa interpeduncularis. It continues in the subarachnoid space, laterally from the ramus communicans posterior (Willis circle). It pierces the dura mater, laterally from the processus clinoideus posterior it enters the sinus cavernosus and continues in its lateral wall to the fissura orbitalis superior''. It enters the orbit through anulus tendineus communis (Zinni) and there it divides into ramus superior (weaker) and ramus inferior(stronger). These branches further lead to the oculomotor muscles.''

Near the ramus inferior lies the nervus opticus in the eye socket and about 1 cm behind the eyeball the parasympathetic ganglion ciliare, into which N. III. supplied by parasympathetic preganglionic fibers. Ganglion ciliare :


 * 1-2 mm
 * in the orbit in front of the fissura orbitalis superior
 * in the fatty tissue between n. opticus and m. rectus lateralis bulbi
 * also receives sympathetic fibers that just pass through it

Main Branches
a) motor


 * ramus superior - innervates m. levator palpebrae superioris and m. rectus superior;
 * b) motor and parasympathetic
 * ramus inferior - m. rectus medialis, m. rectus inferior, m. obliquus inferior ;
 * ramus ad ganglion ciliare (radix parasympathica ganglii ciliaris) continues from the ganglion ciliare as postganglionic fibers nn. ciliares breves for m. sphincter pupillae and m. ciliaris

Pupil innervation
Parasympathetic fibers n. III. they innervate the m. sphincter pupillae which causes miosis. Mydriasis (dilation) is made possible by the sympathetic.

Sympathetic pathways for innervation of the pupil originate in the hypothalamus, pass through the brainstem and terminate in the ciliospinal sympathetic center in the spinal cord segments C8–Th1. Here the preganglionic fibers exit to the cervical ganglia - 'ggl. stellatum and ggl. cervicale superius'. Postganglionic fibers accompany the a. carotis interna to the sinus cavernosus and join the n. ophthalmicus and innervate the m. dilatator pupillae and m. tarsalis.

Pupil photoreaction
Tr. opticus sends nerve fibers contralaterally and ipsilaterally to both Edinger-Westphal nuclei, each innervating its ipsilateral m. sphincter pupillae, so eye miosis occurs when one eye is illuminated illuminated (direct photoreaction) and unilluminated (indirect photoreaction).


 * If the N. II. is affected, the direct photoreaction of the affected eye and the indirect photoreaction of the healthy eye will be extinguished.
 * When the N. III. is affected, the direct reaction is extinguished in the affected eye, the indirect photoreaction is preserved in the healthy one.

Impairment of the oculomotor nerve
As a result of the lesion N. III. a set of symptoms arises:


 * ptosis - drooping of the upper eyelid,
 * strabismus divergens - divergent squinting (predominance of the unaffected muscles m. obliquus superior and m. rectus lateralis) and as a result diplopia double vision)
 * iridoplegia (ophthalmoplegia) - mydriatic pupil unresponsive to light,
 * disorders of close accommodation.

Impairment of sympathetic fibers - Horners syndrome

 * Horner syndrome = ptosis (mild), miosis, enophthalmos (rather apparent);
 * central lesion – disruption of the sympathetic between the hypothalamus and the spinal cord center;
 * peripheral lesion – disruption of the cervical sympathetic system;

Related Articles

 * Cranial Nerve Exits
 * Ocular muscles
 * Orbit
 * Disorders of selected cranial nerves/PGS