<prompt> Trochlear nerve all true exceptLongest intracranial courseArises from dorsum of brainstemSupplies ipsilateral superior oblique musclesEnter orbit though sup orbital fissure outside annulus of Zinn.  <response>: Trochlear nerve is thinnest nerve. It is the only nerve to emerge from dorsum of brain stem has longest intracranial course. It enters orbit through outer part of superior orbital fissure ie lateral to annulus of Zinn and supplies superior oblique muscle. Because its a crossed cranial nerve with decussation in mid brain, the trochlear nerve nucleus supplied contralateral superior oblique muscle. 