Journal Club April 2015: Learning Brainstem Anatomy: A Mnemonic Device

Article title: Learning Brainstem Anatomy: A Mnemonic Device

Author: James T. McDeavitt, MD, Kara C. King, PhD, Kathleen R. McDeavitt, BA

Journal/Source: Physical Medicine and Rehabilitation, 2014. Volume 6, pages 963-966

Discussion:

This article was a brief report in which a 3-part mnemonic device was presented. The mnemonics were created to help memorize the specific locations of the brainstem cranial nerve nuclei and long tracts. Utilizing the mnemonics in combination with a physical exam can be useful to localize brainstem pathology.

The first mnemonic presented is called the “Rule of 5.” Every cranial nerve nuclei that contains the Roman numeral V is located in the pons. Thus, cranial nerve III is cephalad in the midbrain, and nerves IX through XII are caudad in the medulla. Cranial nerve IV is an exception in two ways. First, cranial nerve IV’s nuclei is technically located between the midbrain and pons. Second, cranial nerve IV’s tracts crosses to the contralateral side. When it comes to innervating the head and face, the rest of the cranial nerves predominantly provide ipsilateral innervation.

The second mnemonic presented is called the “Rule of 12.” Any cranial nerve nuclei that is a factor of 12 is located medially. The rest are located laterally. The third and final mnemonic is called the “Rule of M/S.” The three tracts that run medially all begin with the letter “M”: 1) Motor Tract (corticospinal) 2) Medial Lemniscus 3)Medial Longitudinal Fasciculus. The three tracts that run laterally (to the side) all begin with the letter “S”: 1) Spinothalamic Tract 2) Sympathetic Tract 3) Spinocerebellar Tract.

Finally, the article goes on to describe the tracts. Those tracts which are assessed in a basic neurologic exam tend to cross to the contralateral side, whereas those tracts which are assessed in a more detailed neurologic exam tend to act ipsilaterally. Therefore, motor function (motor tract/corticospinal tract), pain sensation (spinothalamic tract), and vibratory/position sense (medial lemniscus) all act cross to act contralaterally on the head and neck. On the other hand, sympathetic function (sympathetic tract), ataxia (spinocerebellar tract), bilateral gaze coordination (medial long mostly runs ipsilateral.

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Discussion QuestionsAOCPMR-Journal-Club-April-2015-BrainstemMnemonic