The trochlear nerve innervates:

(Superior oblique): Ref: 108-109-BDC-3NERVE SUPPLY OF EXTRAOCULAR MUSCLES ISO-4, LR-6, AO-31* Superior oblique - Trochlear nerve (SO-4)* Lateral rectus - Abducent nerve (LR - 6)* Superior, inferior and medial reacti, inferior - Oculomotor nerve (AO i.e. all others - 3)In fourth nerve paralysis: The patient complaints of double vision on looking straight downward, this is because the superior oblique is paralyzed and the eye turns medially as the inferior rectus pulls the eye downward (910- Snell 7th)The trochlear nerve is a motor nerve, the most slender of the cranial nerves leaves the posterior surface of the mid brain and immediately decussates with the nerve of the opposite side.