The Oculomotor Nerve (III)
The oculomotor nerve consists of somatic efferent fibers from the principal (motor) nucleus and visceral efferent fibers from the parasympathetic nucleus (of Edinger-Westphal), both of which are within the tegmentum of the midbrain (see Fig.
8.25/III and 18). Fibers of both nuclei emerge together as the oculomotor nerve from the ventral aspect of the midbrain, close to the midline (see Fig. 8.19). In its intracranial course, the oculomotor nerve travels close to the trochlear, abducent, and ophthalmic nerves and to the cavernous sinus and then passes through the orbital fissure alongside these structures. The nerve divides within the orbit to supply the dorsal, medial, and ventral recti, the ventral oblique, and the levator muscle of the upper eyelid (some writers also include part of the retractor bulbi). The preganglionic parasympathetic fibers synapse within the small ciliary ganglion placed on one of the branches (Figs. 8.45/9 and 8.71/1 and 6). From here, postganglionic fibers pass within the short ciliary nerves to supply the intraocular ciliary and constrictor pupillae muscles. Isolated injury of the oculomotor nerve and its involvement in disease are not common; the effects can be deduced from consideration of the actions of the muscles it supplies (p. 331).
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