THE OCULOMOTOR NERVE (CN III)

 

The Origin(s)

 
  • The GSE fibres from oculomotor nucleus near the midline of the midbrain, at the level of the superior colliculus.

  • GVE from Edinger-Westphal nucleus at the same level

The Course

  • Traverse substance of the midbrain and red nucleus

  • Exit the central nervous system in the interpeduncular fossa medial to crus cerebri.

  • Lies between the superior cerebellar and posterior cerebral arteries .

  • Pierces dura mater to enter the lateral wall of the cavernous venous sinus

  • Continues along the lateral and superior margin of the sinus

  • Enters the orbit through the superior orbital fissure.

  • Passes through the common tendinous ring, and splits into superior and inferior division.
Functional Components

• Parasympathetic (GVE) (already discussed)

• Somatic motor

• General somatic afferent from the neuromuscular spindles

Distribution

The oculomotor nerve supplies all the extra-ocular muscles except the superior oblique and lateral rectus These are the:

Superior division

  • Superior rectus
  • Levator palpebrae superioris

Inferior division

  • inferior rectus
  • inferior oblique
  • medial rectus.

 

Probable cause and sites of injury

•  Vascular lesions of the midbrain e.g. occlusion of the mesencephalic branch of the posterior cerebral artery (see Weber's syndrome).

•  Aneurysms of the arteries - posterior cerebral and superior cerebellar

•  Hypothalamic tumors in the interpeduncular fossa

•  Cavernous sinus thrombosis

•  Meningeal tumors

•  Orbital tumors

The effects of these possible injuries are best understood after the discussion of the other nerves that supply extra-ocular muscles.