anatomy of cranial nerve IV
Last reviewed 01/2018
The trochlear nerve begins at the trochlear nucleus. This is sited at the level of the inferior colliculus in the anterior part of the grey matter that surrounds the cerebral aqueduct of the midbrain. From here, the nerve passes posteriorly around the aqueduct to the opposite side where it emerges from the midbrain at the level of the superior medullary velum. The nerve then circumnavigates the side of the brainstem - it has the longest course of any cranial nerve - to enter the superior orbital fissure.
Within the orbital cavity trochlear nerve supplies the superior oblique muscle.
The trochlear nucleus receives cortical input, especially from the occipital cortex via the superior colliculus, and information from the third, sixth and eighth cranial nerves via the medial longitudinal fasciculus.