Neurophysiology of Cranial Nerves I-XII

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In virtual, every undergraduate and medical school human neuroanatomy course students struggle to remember the 12 cranial nerves in order and to grasp a general idea of their functions. Such nonsensical ditties as “On Old Olympus Towering Tops A Fin And German Viewed Some Hops” still rattle around in some of our hippocampi.1 The observation about these 12 paired neuroanatomic structures I find most intriguing, however, is that as the time for rattling off lists of nerves and broad functional designations fades into the past, the importance of these nerves to clinical neurophysiology remains as robust as ever, with new data and science informing clinical practice regularly being added to the literature.
This edition of JCN brings together an accomplished array of clinicians and neurophysiologists to update the reader on the state-of-the-art of the neurophysiology of each of the cranial nerves. Beginning with the olfactory and optic nerves, which most us consider as largely central structures and, therefore, in a slightly different class than their fellow cranial nerves, Parthasarathy Thirumala and his accomplished group from the University of Pittsburgh describe the almost unknown field on olfactory neurophysiology before turning to the firmer and better known ground of the optic nerve and visual evoked potentials. Dr. Thirumala also guides us through the methods of using extraocular muscle recordings intraoperatively for those with the wherewithal and courage to place needle electrodes so close to the globe to improve the safety of delicate neurosurgical procedures which may put cranial nerves III, IV, and VI at risk.
Iryna Muzyka at Mayo Clinic in Arizona deftly lays out the anatomy and physiology of the trigeminal and facial nerves that are perhaps the most familiar cranial nerves to many peripheral neurophysiologists in electromyography practice. Dr. Muzyka reminds us how facial nerve conduction studies and the trigeminal “blink” reflex as well as lesser known related techniques can help to pinpoint dysfunction in these important nerves both in the outpatient and intraoperative domains.
Because cranial nerve VIII is so critical to day-to-day human existence and our success negotiating the environment, and also for the reason that the neurophysiology of the vestibulocochlear, or as some would prefer separately, the vestibular and cochlear (formerly acoustic) nerves, is so complex, we have two experts in the field contributing detailed descriptions of the anatomy, physiology, and clinical utility of different techniques of studying cranial nerve VIII. Alan Legatt of Montefiore Medical Center in the Bronx, New York, lays out a masterful presentation of brainstem auditory evoked potentials and other techniques and their contribution to modern clinical neurophysiology. Jamie Bogle of Mayo Clinic in Arizona skillfully introduces many JCN readers for the first time to vestibular evoked myogenic potentials, a relatively new approach to documenting vestibular otolith organ function.
Moving on to the daunting task of the clinical neurophysiology of cranial nerves IX and X, Paulo Andre Teixeira Kimaid and his associates from Campinas, Brazil, accomplish the remarkable tasks of providing an update on the peripheral neurophysiology of voice and swallowing while at the same time considering these two cranial nerves together in terms of their autonomic functionality. Because autonomic neurophysiology is coming more and more to clinical practice in the twenty-first century, largely as the result of the field recognizing a whole new host of disorders and syndromes affecting autonomic circuitry, an understanding of reliable strategies to assess particularly vagal nerve function is paramount.
Amro Stino, on the faculty of the Ohio State University Medical Center in Columbus, Ohio, recently published a large series of patients with isolated hypoglossal mononeuropathy.
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