CN 3: Oculomotor Nerve (Scheme, Pathway, Clinical Relevance) | Neuroanatomy

Content:
Introduction: 0:00
Optic Nerve Scheme: 01:00
Midbrain Anatomy: 03:46
Oculomotor nerve course: 06:20
Branches of the Oculomotor Nerve: 09:55
Parasympathetic fibers of Oculomotor Nerve: 12:15
Clinical Relevance 13:29
Oculomotor Nerve Palsy: 14:33
Recap: 17:03
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Oculomotor Pathway Scheme / Overview:
- Oculomotor nerve (nervus oculomotorius) allows movement of the eye muscles, constriction of the pupil and the position of the upper eyelid
- Starts with nucleus of oculomotor nerve and accessory oculomotor nucleus at the midbrain. They run together and exit through the oculomotor sulcus in the interpeduncular fossa. Then goes through the lateral wall of the cavernous sinus, goes through the superior orbital fissure and common tendinous ring, and then divides into superior branch and the inferior branch (somatomotor fibers). Parasympathetic fibers from the edinger-westphal nucleus run with the inferior branch and then goes to the ciliary ganglion as pre-ganglionic fibers. From here short cilliary nerves exit towards the ciliary muscle and sphincter pupillae.
Midbrain Anatomy:
- Posterior view: Cerebral peduncles (pedunculus cerebri) and tectal plate. Tectal plate consists of superior colliculi (colliculi superiores), Brachium of superior colliculus (brachium colliculi superioris), inferior colliculi (colliculi inferiores) and brachium of the inferior colliculus (brachium colliculi inferior)
- Anterior view: Cerebral peduncles and inferpeduncular fossa (fossa interpeduncularis), Oculomotor sulcus of the mesencephalon (sulcus nervi oculomotorii)
- Internal view: Aqueduct of midbrain, substantia nigra, superior colluculi, periaqueductal grey substance (sibstantia grisea centralis), reticular formation (formatio reticularis), red nucleus (nucleus ruber), nucleus of the oculomotor nerve (nucleus nervi oculomotorii), Edinger-Westphal nucleus/accessory nucleus of oculomotor nerve (nucleus accessorii nervi oculomotorii)
Course of the Oculomotor Nerve:
- Starts at the midbrain (level of superior colliculi)
- Somatic fibers from the nucleus of the oculomotor nerve
- Preganglionic parasympathetic fibers from the Edinger-Westphal nucleus/accessory nucleus of oculomotor nerve
- Leaves through the Oculomotor sulcus of the mesencephalon on the anterior surface
- It penetrates the dura mater and then pass through the lateral border of the cavernous sinus.
- Enters through the superior orbital fissure and common tendinous ring.
- Splits into superior branch and inferior branch
- Superior branch innervate the superior rectus and levator palpebrae superioris
- Inferior branch innervate the medial rectus, inferior rectus and inferior oblique
Extraocular muscles:
- Medial Rectus, Lateral Rectus, Inferior Rectus, Superior Rectus.
- Superior Oblique and Inferior Oblique
- Levator Palpebrae Superioris
Superior Branch:
- Superior rectus which elevates the eye
- Levator palpebrae superioris which elevated the eyelid
Inferior Branch
- Medial Rectus which is an adductor muscle
- Inferior Rectus which depresses the eye
- Inferior Oblique which originates medially and attaches to the inferolateral wall of the eye causing superior and lateral rotation
Autonomic innervation:
- Pre-ganglionic parasympathetic fibers from the edinger-westphal nucleus
- Runs with the inferior branch, and goes to the ciliary ganglion
- Ciliary ganglia give off post-ganglionic parasympathetic motor neurons as short ciliary nerves.
- Goes to pupillary sphincter causing pupillary constriction
- Goes to ciliary muscles for the accommodation reflex
Clinical Relevance:
- Stroke/bleeding of the midbrain can cause damage
- Increased pressure in cavernous sinus
- Posterior communicating artery aneurysms
- Meningitis
- Paranasal sinus infection
- Trauma
- Uncontrolled diabetes
- Chronic hypertension
Manifestation of oculomotor nerve damage
- Gaze stuck in downward out position
- Video illustrating left sided oculomotor nerve palsy
○ Neurological examination shows how the eye with oculmotor nerve palsy can't rotate medially.
○ This condition causes diplopia (double vision), Ptosis, dilated pupil
Sources:
- Singh, I. (2017). Human neuroanatomy (10th ed.).
Helwany M, Bordoni B. Neuroanatomy, Cranial Nerve 1 (Olfactory) [Updated 2022 Aug 8]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-
- Kozlowski, T. (2017). Memorix Anatomy: The Complete Study Guide. 2nd ed. Thieme Medical Publishers.
- Oculomotor nerve palsy illustration video: studmed.uio.no/elaring/fag/ne...

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