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 Figure 8-25).
Fibers of the two categories emerge together at the superficial origin from the ventral aspect of the midbrain, close to the midline and in series with other cranial nerves of predominantly somatic efferent composition and with the ventral roots of spinal nerves (Figure 8-19). In its intracranial course the oculomotor is related to the trochlear, abducent, and ophthalmic nerves and to the cavernous sinus, and it passes through the orbital fissure in their company. It divides within the orbit to supply the dorsal, medial, and ventral recti, the ventral oblique, and the levator muscle of the upper eyelid (some authors also include part of the retractor bulbi). The preganglionic parasympathetic fibers synapse within the small ciliary ganglion placed on one of the branches (Figure 8-45/9 and 8-70/7,6). From here, postganglionic fibers pass within the short ciliary nerves to supply the intraocular ciliary and constrictor pupillae muscles. Isolated injury or involvement in disease is not common; the effects can be deduced from consideration of the actions of the muscles it supplies (p. 345).
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