Oculomotor NerveThe third NerveNuclei: Nerve originates from two nuclei 1.Motor neurons in the oculomotor (somatomotor) 2.Edinger-Westphal (visceral motor) nuclei in the brainstemAxons emerge out of nucleus , exit the ventral surface of the brainstem as the oculomotor nervepasses through the dura mater, lateral wall of the cavernous sinus and then enters the superior orbital fissure to access the orbit.Somatomotor component of the nerve divides into a superior and inferior division

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• The inferior division supplies medial rectus, inferior rectus and inferior oblique muscles. • The visceromotor or parasympathetic component of the oculomotor nerve travels with inferior

division. In the orbit the inferior division sends branches that enter the ciliary ganglion where they form functional contacts (synapses) with the ganglion cells

The superior division supplies the levator palpebrae superioris and superior rectus muscles

• Disease of Oculomotor nerve• Paralysis of the oculomotor nerve, can arise due to direct trauma,

demyelinating diseases (e.g., multiple sclerosis), increased intracranial pressure, space-occupying lesion (e.g., brain cancer) or a spontaneous subarachnoid haemorrhage (e.g., berry aneurysm) and microvascular disease, e.g., diabetes.

Examination of oculomotor nerve• Eye muscles• Cranial nerves III, IV, and VI are usually tested together. The examiner

typically instructs the patient to hold his head still and follow only with the eyes a finger or penlight that circumscribes a large "H" in front of the patient.

Pupillary reflex• The oculomotor nerve also controls the constriction of the pupils and

thickening of the lens of the eye. This can be tested By moving a finger toward a person's face to induce accommodation, as well as his going cross-eyed, his pupils should constrict.

• Shining a light into one eye should result in equal constriction of the other eye. The neurons in the optic nerve decussate in the optic chiasm with some crossing to the contralateral optic nerve tract. This is the basis of the "swinging-flashlight test".

• Loss of accommodation and continued pupillary dilation can indicate the presence of a lesion on the oculumotor nerve.