Abducens Nerve (CN VI)

Summary

The abducens nerve, also known as cranial nerve 6 or the 6th cranial nerve, is a motor nerve that controls movement of the eye. Specifically, the nerve is responsible for innervating the lateral rectus muscles that allow for eye abduction, or movement of the eyes outwards to each side away from the midline. As a muscle that controls eye movement, the abducens nerve also plays a role in the vestibulo-ocular reflex, helping to stabilize vision in response to head movement. Anatomically, the abducens nerve originates from a nucleus in the pons and then travels out of the skull through the superior orbital fissure in order to reach the lateral rectus muscles controlling the eye.

Key Points

• Abducens Nerve (Cranial Nerve VI)
  • Nerve Type
    • Motor
  • Function
    • Eye abduction (lateral movement)
      • Innervates lateral rectus to control lateral eye movement
      • Test function via six cardinal positions of gaze test (tracking H-shape)
      • Damage to CN VI leads to unopposed CN III and inward deviation of eye, manifesting with horizontal diplopia
  • Nerve Entry/Exit
    • Exits brainstem at pons
      • Fibers originate from abducens nucleus in the pons
      • Exit occurs at the lower pons near the pontomedullary junction, medial to facial nerve
  • Cranial foramen
    • Superior orbital fissure
  • Reflexes
    • Vestibulo-ocular reflex (efferent motor)
      • Responsible for adjusting and stabilizing vision in response to vestibular balance
      • Damage leads to vertigo and nausea
  • Other Information
    • Often first cranial nerve compressed with increased ICP due to long intracranial course and location of exit, causing nerve palsy