Occulomotor (iii) Nerve

Occulomotor nerve [Ref: Harrison 17¹¹¹/e p 1727; 16/c, p 2388; ivww.emedicine.com/med/topic3468.html]

• Most unruptured intracranial aneurysms are completely asymptomatic. Symptoms are usually due to rupture and resultant subarachnoid hemorrhage. Occasionally neurological symptoms may arise due to mass effect of the aneurysm.
• Progressively enlarging unruptured aneurysm most commonly involves the occulomotor nerve. This usually occurs _.from an expanding aneurysm at junction of post communicating artery and internal carotid artery.
• Other neuropathies due to intracranial aneurysms are
• Cavernous sinus aneurysm can produce sixth nerve palsy.
• Supraclinoid carotid or anterior cerebral artery aneurysm can produce visual field defects.
• Posterior inferior cerebellar artery or anterior inferior cerebellar artery aneurysm may present as occipital & posterior cervical pain.
• An expanding middle cerebral artery aneurysm can produce pain in or behind the eye & in the low temple.
• Ophthalmic artery aneurysm can cause visual loss by compressing optic

nerve.

Lateral rectus muscle is supplied by abducens nerve. Extraocular muscles supplied by occulomotor nerve are superior, medial and inferior rectus and inferior oblique muscles. Trochlear nerve supplies superior oblique muscle.

• Medial rectus: Adduction
• Lateral rectus: Abduction
• Superior rectus: Elevation, intorsion, adduction
• Inferior rectus: Depression, extorsion, adduction
• Superior oblique: Intorsion, depression, abduction
• Inferior oblique: Extorsion, elevation, abduction

C i.e. Enters orbit through the inferior orbital fissure

A i.e., Miosis

A i.e. Abduction

• The midbrain is the narrow part of the brain that passes through the tentorial notch and connects the forebrain to the hindbrain. The midbrain comprises two lateral halves called the cerebral peduncles; each of these is divided into an anterior part, the crus cerebri, and a posterior part, the tegmentum, by a pigmented band of gray matter, the substantia nigra. 

Cross section of midbrain at the level of superior colliculus:

Grey matter

• Central grey matter contains nucleus of oculomotor nerve and the mesencephalic nucleus of the trigeminal nerve
• Pretectal nucleus
• Red nucleus
• Substantia nigra
• Superior colliculus

Nucleus of trochlear nerve is present in the midbrain at the level of inferior colliculus

Ans. C : Proptosis

Features of 3rd cranial nerve palsy:

• Downward and outward deviated eye
• Ptosis
• Dilated pupils
• Loss of pupillary/ light and accommodation reflexes.
• Absent medial and upward gaze.

Ans. is ‘c’ i.e., Lateral rectus

Lateral rectus is supplied of by sixth nerve (abducent) nerve and superior oblique is supplied by fourth (trochlear) nerve. All other extraocular muscles are supplied by occulmotor nerve.