Cranial Nerve 12

Aka: Cranial Nerve 12, Cranial Nerve XII, Hypoglossal Nerve, CN 12, Hypoglossal Nucleus

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II. Anatomy

  1. Hypoglossal Nucleus
    1. Originates in Hypoglossal Nucleus, in the Medulla
    2. Exits anterior to the Inferior Olivary Nucleus
      1. All other medulla Cranial Nerves (CN 7, CN 8, CN 9, CN 10) exit posterior to the Inferior Olivary Nucleus
  2. Images
    1. neuroHypoglossalCN12.png
    2. neuroCn12HypoglossalGrayBB795.gifLewis (1918) Gray's Anatomy 20th ed (in public domain at Yahoo or BartleBy)
  3. Course
    1. As with all other Cranial Nerves (except CN 4), fibers remain ipsilateral (do not cross over)
    2. Passes through hypoglossal canal beside foramen magnum
    3. Courses downward with neurovascular structures
      1. Internal Carotid Artery
      2. Jugular Vein
      3. Vagus Nerve (CN 10)
    4. Curves forward behind Mandible to lingual root

III. Physiology

  1. Motor Nerve to the Tongue

IV. Exam

  1. Patient protrudes Tongue in midline
    1. Unilateral paralysis causes deviation to weak side
    2. Observe for Tremor, atrophy, Fasciculations
  2. Test lingual speech, by having patient say:
    1. "Round the rugged rock the ragged rascal ran"
    2. "Third riding artillery brigade"

V. References

  1. Gilman (1989) Manter and Gatz Essentials of Neuroanatomy and Neurophysiology, Davis, p. 87-113
  2. Goldberg (2014) Clinical Neuroanatomy, p. 24-39
  3. Netter (1997) Atlas Human Anatomy, ICON Learning, p. 110-129

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