Question #516
The trochlear nerve
The trochlear nerve, the fourth cranial nerve, is the only cranial nerve to arise from the dorsal surface of the brainstem. The nerve passes laterally around the brain stem, through the lateral wall of the cavernous sinus and then enters the orbit through the superior orbital fissure and supplies the superior oblique muscle. In addition to carrying motor fibres to this muscle, the trochlear nerve also carries proprioception fibres from the muscle.
The nerve does not pass through the tendinous ring of the orbit, nor does it carry any parasympathetic fibres.
The trochlear nerve is said to have the longest intracranial course of the cranial nerves. It is important to distinguish this from the abducent nerve which has the longest intracranial course in the subarachnoid space.