(CN 4) Trochlear nerve

Nuclei - The nucleus of the fourth cranial nerve lies ventral to the periaqueductal gray matter immediately below the oculomotor nuclear complex at the level of the inferior colliculi.

Topography

Its radicular fibers run around the central gray matter and cross to the opposite side within the superior medullary velum.

The trochlear nerve then exits the dorsal surface of the brainstem, emerging from the midbrain tectum into the quadrigeminal cistern. Its further course takes it laterally around the cerebral peduncle toward the ventral surface of the brainstem, so that it reaches the orbit through the superior orbital fissure together with the oculomotor nerve. It then passes to the superior oblique muscle, which it innervates.