oculomotor nerve

Oculomotor nerve

Dr / Hytham Nafady

Introduction Oculomotor nerve consists of two components with distinct functions:

Somatic motor(general somatic efferent)

Supplies 4 of the 6 extraocular muscles of the eye and the levator palpebrae superioris muscle of the upper eyelid.

Visceral motor(general visceral efferent)

Parasympathetic innervation of the constrictor pupillae and ciliary muscles.

From To

Uncrossed fibers

ipsilateral oculomotor nucleus

Medial rectus.

Inferior rectus.

Inferior oblique.

Crossed fibers

Contralateral oculomotor nucleus

Superior rectus.

Crossed and uncrossed fibers

Both oculomotor nuclei

Levator palpebrae superioris muscle.

Uncrossed para-sympathetic fibers

Ipsilateral Edinger Westphal nucleus

Constrictor pupliae muscle.

Ciliary muscle.

•Medial rectus

•Inferior rectus

•Levator palpebrae superioris

•Superior rectus

•Inferior oblique

Oculomotor nerve anatomy

Origin

Oculomotor nucleus:

• Tegmentum of midbrain at the level of superior colliculus.

• Ventral to the peri-aqueductal grey matter.

• It is column shaped nucleus & consists of complex subnuclei.

Edinger Westphal nucleus:

• The Edinger Westphal nucleus form the parasympathetic general visceral efferent (GVE) component of the nuclear complex.

• It is located medial to the rostral end of the oculomotor nucleus.

Central segment

The central segment courses ventrally

• From the midbrain tegmentum,

• through the red nucleus,

• to emerge from the medial aspect of the cerebral peduncle.

Cisternal segment

• Course ventrolaterally through the interpeduncular cistern between the PCA & SCA.

Cisternal segment of oculomotor nerve

Cn 3

Interpeduncular cistern

Cisternal segment of oculomotor nerve

BA Cn 3SCA

PCA

Cisternal segment of oculomotor nerve

Cisternal segment of oculomotor nerve

Cisternal segment

ICA

Cavernous segment

• The oculomotor nerve enters the cavernous sinus superior to the petro-clinoid ligament and inferior to the inter-clinoid ligament.

• The cavernous segment of the oculomotor nerve course through the lateral wall of the cavernous sinus superiorly.

• It is surrounded by CSF dural cuff (oculomotor cistern).

4 5 O

6

3

5 mx

Oculomotor cistern

Orbital segment

• The oculomotor nerve enters the orbit through the superior orbital fissure within the annular ring or Zinn.

• It divides into superior and inferior divisions.• The superior division supplies the contralateral

superior rectus & levator palpebrae superioris muscles bilaterally.

• The inferior divison supply the ipsilateral inferior & medial recti & inferior oblique muscles.

Superior orbital fissure & annular ring of Zinn

Cn 3 i

Cn 3 s

Cn 6

Cn 4

Oculomotor palsy

Oculomotor nerve palsy with pupillary sparing(medical 3rd Cn palsy)

• DM.

• Hypertension.

Oculomotor nerve palsy without pupillary sparing

• Nucleus.

• Central segment.

• Cisternal segment.

• Cavernous segment.

• Orbital segment.

Oculomotor nucleus

Cisternal segment

Cisternal segment

PCoA aneurysm

Lymphoma

Lymphoma

Cavernous segment

Cavernous sinus lesion with 3rd cranial nerve palsy

Schwannoma

3

Right carotid cavernous fistula with 3rd & 4th Cn palsy

Orbital segment

• Lesions of the orbital apex cause 3rd , 4th and 6th cranial nerve palsies

Tolosa hunt syndrome

Tolosa Hunt syndromeophthalmoplegia

3

3

3

4

6

Testing accomdation reflex