https://stream.echo6.co/videos/watch/725a61c2-0cf6-4f66-86d3-67580eb70052 Official Ninja Nerd Website: https://ninjanerd.org Ninja Nerds! Join us in this lecture where Professor Zach Murphy will be discussing the trochlear nerve, cranial nerve IV, focusing on its unique anatomy, specialized function, and clinical relevance. We begin by describing its origin in the trochlear nucleus, located in the midbrain at the level of the inferior colliculus. This nerve is unique for two reasons—it is the only cranial nerve to emerge from the dorsal aspect of the brainstem, and it completely decussates before exiting, meaning each trochlear nerve innervates the contralateral superior oblique muscle. We follow its course as it emerges posteriorly, wraps around the brainstem, travels through the subarachnoid space, and enters the lateral wall of the cavernous sinus before passing through the superior orbital fissure into the orbit. Its single motor function is to innervate the superior oblique muscle, which primarily depresses the eye when it is adducted, and contributes to the globe's intorsion and slight abduction. This role is particularly important for coordinated vertical gaze and stabilizing vision during head movements. We then review the hallmark signs of a trochlear nerve palsy, which include vertical diplopia that worsens when looking down (e.g. going downstairs or reading) and compensatory head tilting away from the side of the lesion to minimize double vision. We explain why lesions affecting the nerve after it exits the brainstem cause ipsilateral symptoms, whereas lesions in the trochlear nucleus produce contralateral deficits due to the complete decussation of fibers. Enjoy the lecture and support us below! 🌐 Official Links Website: https://www.ninjanerd.org Podcast: https://podcast.ninjanerd.org Store: https://merch.ninjanerd.org 📱 Social Media https://www.tiktok.com/@ninjanerdlectures https://www.instagram.com/ninjanerdlectures https://www.facebook.com/ninjanerdlectures https://x.com/ninjanerdsci/ https://www.linkedin.com/company/ninja-nerd/ 💬 Join Our Community Discord: https://discord.gg/3srTG4dngW #ninjanerd #TrochlearNerve #CranialNerves Wed, 15 Apr 2026 09:54:59 GMT https://validator.w3.org/feed/docs/rss2.html PeerTube - https://stream.echo6.co https://stream.echo6.co/client/assets/images/icons/icon-512x512.png https://stream.echo6.co/videos/watch/725a61c2-0cf6-4f66-86d3-67580eb70052 All rights reserved, unless otherwise specified in the terms specified at https://stream.echo6.co/about and potential licenses granted by each content's rightholder.