Oculomotor nerve

1. Oculomotor Nerve
The third Nerve
Nuclei: Nerve originates from
two nuclei
1.Motor neurons in the oculomotor
(somatomotor)
2.Edinger-Westphal (visceral
motor) nuclei in the brainstem
Axons emerge out of nucleus , exit
the ventral surface of the
brainstem as the oculomotor nerve
passes 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

2. The superior
division supplies
levator palpebra
superioris and
superior rectus
muscles
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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

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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.