Cranial Nerve 3

Aka: Cranial Nerve 3, Cranial Nerve III, Oculomotor Nerve, CN 3, Oculomotor Nucleus, Edinger-Westphal Nucleus, Oculomotor Nerve Palsy, Oculomotor Nerve Paralysis, CN 3 Palsy, Cranial Nerve 3 Paralysis

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II. Anatomy

  1. neuroCn3oculomotorGrayBB775.gif Lewis (1918) Gray's Anatomy 20th ed (in public domain at Yahoo or BartleBy)
  2. EyePupillaryReactionNeuroPath.png
  3. EyePupillaryReaction.png

III. Physiology

  1. Parasympathetic fibers follow Cranial Nerve III
    1. Innervates the ciliary Ganglion which in turn supplies sphincter pupillae and ciliaris Muscles
    2. Parasympathetic impulses result in Pupil Constriction
    3. Uncal Herniation (Temporal LobeHerniation) compresses the third nerve
      1. Parasympathetic fibers are most susceptible to injury as they lie on the outside of CN III
      2. Parasympathetic fiber injury results in an ipsilateral pupil that is fixed/unresponsive and dilated
      3. With increasing pressure on Cranial Nerve III, complete oculomotor paralysis occurs
      4. Ultimately contralateral Cranial Nerve 3 involvement ensues
  2. Innervates five extrinsic eye Muscles
    1. Levator palpebrae superioris
    2. Medial rectus
    3. Superior rectus
    4. Inferior rectus
    5. Inferior oblique

IV. Course

  1. Images
    1. neuroCn3.png
  2. Nucleii
    1. Nucleii are located in the floor of Cerebral Aqueduct at the level of the Midbrain
    2. Oculomotor Nucleus
      1. Origin of the eye somatic motor fibers that innervate five extrinsic eye Muscles
      2. Subdivided into focus for each eye Muscle
    3. Edinger-Westphal Nucleus
      1. Origin of the visceral motor fibers that innervate pupillary sphincter and ciliary Muscles
      2. Slightly medial to the Oculomotor Nucleus
  3. Course
    1. As with all other Cranial Nerves (except CN 4), fibers remain ipsilateral (do not cross over)
      1. Exception: Superior Rectus Muscle is innervated by the contralateral Oculomotor Nucleus
    2. Nerve courses between Superior Cerebellar Artery and Posterior Cerebral Artery
    3. Forward and lateral to Posterior Clinoid process
    4. Cavernous Sinus lateral wall
    5. Enters orbit via superior orbital fissure

V. Exam

  1. Extraocular Movement
    1. See Extraocular Movement
    2. eye_eom.png
  2. CN III Palsy Findings
    1. eye_eom.png
    2. Eye Deviation inferolaterally (eye is "down and out")
    3. Eyelid Ptosis
  3. Unilateral Pupil Paralysis (Blown Pupil or fixed, non-reactive dilated pupil)
    1. See Unilateral Mydriasis
    2. Increased Intracranial Pressure
    3. Subarachnoid Hemorrhage
  4. Oculomotor Nerve Palsy with pupil involvement
    1. May be due to expanding Cerebral Aneurysm (esp. Posterior Communicating Artery)
  5. Oculomotor Nerve Palsy with pupil sparing
    1. Seen as complication with Diabetes Mellitus

VI. 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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