Which of the following cranial nerves originates from dorsal aspect of the brain?

Ans. c (Trochlear). (Ref. BD Chaurasia, Human Anatomy-Vol III, 3rd ed., 90)TROCHLEAR NERVE (MH 05; AI09)# It is thinnest cranial nerve# It is the only cranial nerve, which emerges on the dorsal aspect of brain stem (from superior medullar velum near frenulum veli just below the inferior colliculus).# It supplies the contralateral superior oblique muscle of eyeball.# In fourth-nerve paralysis the patient complains of double vision on looking straight downward. This is because the superior oblique is paralyzed and eye turns medially as the inferior rectus pulls eye downward.# Hint:- LR6- SO4 (Lateral rectus is supplied by 6th cranial nerve & superior oblique by 4th cranial nerve)