INTERESTING QUESTION BY ONE OF ALFAISAL UNIVERSITY STUDENTS REGARDING TROCHLEAR NERVE One of my colleagues (Dr. Akram Jaffer- anatomist) from Sharjah university who is now in Toronto has this explanation; Dear Dr Khurshid, Thank you for posting me the interesting questions from your intelligent student. Kindly review my answer: There is no strict rule when it comes to the connections of cranial nerve nuclei and how an UMN or LMN would relate to them. Many of cranial nerve nuclei receive fibers form ipsi- and contra- lateral cortices. Perhaps, it is mainly the lower part of the facial motor nucleus that strictly receives upper neuron fibers from the contralateral cortex. The control of cranial nerve nuclei becomes more complicated when it is related to those innervating the extrocular muscles namely, CNIII, IV, and VI. The reason is that these nuclei and connected to each other via the medial longitudinal fasiculus that control the bilaterality of their function. If we assume that corticobulbar connections are as strict as a flowchart, then yes, LMN of trochlear nucleus would result in contralateral paralysis. I agree that there is no much emphasis on the crossing of the trochlear nerve within the midbrain, perhaps because it is not much clinically correlated. More emphasis is paid on the fact that it is the only cranial nerve that emerges from the back of the brain stem making it vulnerable to cerebellar tumors. Also, the trochlear nerve is tiny and has long intracranial course making it vulnerable to increased intracranial pressure. For a basic review of the midbrain please refer to my video on YouTube https://youtube/watch?v=1gQuznVG1F8&channel=akramjfr Dr.Akram A. Jaffar facebook/AnatomyEducation
Posted on: Fri, 15 Aug 2014 10:18:57 +0000