Trochlear nerve
(B) Is the only cranial nerve to emerge from the dorsal aspect of the brainstem # TROCHLEAR NERVE emerges from the superior medullary velum near the frenulum veli just below the inferior colliculus.> Trochlear nerve is the only cranial nerve which emerges on the dorsal aspect of the brainstem.> When the trochlear nerve is damaged, diplopia occurs on looking downwards: vision is single so long as the eyes look above the horizontal plane.