Cranial Nerves I-VI Quiz

See Movement of the Eyeball. Cranial Nerves III, IV and VI. Option D is correct because the abducens nerve (cranial nerve VI) has a single job: it supplies the lateral rectus. The lateral rectus sits on the outer side of the eyeball and pulls the eye outwards, away from the nose. That movement is called abduction, and the nerve takes its name from it. Because the abducens nerve supplies only this one muscle, damage to it leaves the eye unable to turn fully outwards. The affected eye may drift inwards at rest because the medial rectus, which turns the eye inwards, now pulls without opposition. The patient sees double (diplopia) in a horizontal line, and the double vision is most noticeable when they look towards the affected side. A lateral rectus problem therefore gives sideways double vision. The formula LR6 SO4 fixes the supplies in memory: lateral rectus is cranial nerve VI, superior oblique is cranial nerve IV, and every other eye muscle is cranial nerve III.

• Abducens nerve: Cranial nerve VI supplies only the lateral rectus.
• Action: The lateral rectus turns the eye outwards (abduction).
• Palsy: The eye cannot turn fully outwards, causing horizontal double vision.