Cranial Nerve Anatomy

Question 1

Cranial nerve III

Answer 1

Motor and autonomic.

Origin: nucleus lies in the periaqueductal gray at the level of the superior colliculus which runs through the tegmentum, red nucleus and substantia nigra to emerge from the medial aspect of the cerebral peduncle.

Cisternal portion: Passes in to the interpeduncular cistern passing anteriorly beneath the PCA and above the SCA.

Cavernous portion: Pierces dura to enter the lateral wall of the sinus (superior most nerve above CNIV).

Orbital portion: Enters the orbit via the SOF as two branches.

Superior division: Motor fibres to superior rectus, levator palpebrae superioris. Sympathetic fibres to LPS derived from the ICA.

Inferior division: Motor to the inferior rectus, medial rectus and inferior oblique. Parasympathetic fibres to the ciliary ganglion.

Question 2

Cranial nerve IV

Answer 2

Purely motor.

Origin: Nucleus within dorsal midbrain, ventral to the PAG. Passes posteriorly to exit the brainstem immediately below the inferior colliculus.

Cisternal portion: Passes around the cerebral peduncles in the ambient cistern and joins CNIII to pass between the PCA and SCA.

Cavernous portion: Pierces the dura to travel in the lateral wall of the cavernous sinus inferior to CNIII.

Orbital portion: Enters the orbit through the SOF however outside the tendinous ring superior to the superior ophthalmic vein. Supplies the superior oblique muscle.

Question 3

Cranial nerve VI

Answer 3

Purely motor.

Origin: Arises within the pons (beneath colliculus fascialis)

Cisternal portion: Emerges at the pontomedullary junction into the prepontine cistern. Courses anteriorly along the clivus within a fibrous sheath (Dorello’s canal).

Cavernous portion: Pierces the dura inferior to the posterior clinoid process to travel within the cavernous sinus inferolateral to the ICA.

Orbital portion: Enters the orbit through the SOF within the tendinous ring and supplies the lateral rectus.