Which nerves innervate the extraocular muscles and what movements do they control?

Which nerves innervate the extraocular muscles and what movements do they control?

• A. CN II and CN III control eye movements.
• B. CN III, IV, and VI control all eye movements in combination.
• C. CN III innervates most rectus muscles and inferior oblique; CN IV innervates the superior oblique; CN VI innervates the lateral rectus.
• D. CN V controls extraocular muscles.

Answer: (C)

Movement of the eye is controlled by three cranial nerves: the oculomotor, trochlear, and abducens nerves. The optic nerve is sensory for vision and does not move the eye, and the trigeminal nerve does not innervate extraocular muscles, so any statement claiming those nerves control eye movements isn’t correct. The oculomotor nerve supplies most of the eye muscles—medial rectus, superior rectus, inferior rectus, and the inferior oblique—so it handles many vertical and horizontal movements: adduction (toward the midline) with the medial rectus, elevation with the superior rectus, and depression with the inferior rectus. The inferior oblique contributes elevation and abduction (and extorsion) of the eye. It also carries parasympathetic fibers to constrict the pupil and adjust the lens, and it lifts the eyelid via the levator palpebrae superioris. The trochlear nerve innervates the superior oblique, which primarily depresses the eye when the eye is adducted and also intorts it. The abducens nerve innervates the lateral rectus, which abducts the eye (moves it outward away from the midline). So the correct mapping is: oculomotor nerve to most rectus muscles and inferior oblique with vertical and inward movements plus eyelid and pupil/lens control; trochlear nerve to the superior oblique for downward movement and intorsion; abducens nerve to the lateral rectus for outward movement.

Movement of the eye is controlled by three cranial nerves: the oculomotor, trochlear, and abducens nerves. The optic nerve is sensory for vision and does not move the eye, and the trigeminal nerve does not innervate extraocular muscles, so any statement claiming those nerves control eye movements isn’t correct.

The oculomotor nerve supplies most of the eye muscles—medial rectus, superior rectus, inferior rectus, and the inferior oblique—so it handles many vertical and horizontal movements: adduction (toward the midline) with the medial rectus, elevation with the superior rectus, and depression with the inferior rectus. The inferior oblique contributes elevation and abduction (and extorsion) of the eye. It also carries parasympathetic fibers to constrict the pupil and adjust the lens, and it lifts the eyelid via the levator palpebrae superioris.

The trochlear nerve innervates the superior oblique, which primarily depresses the eye when the eye is adducted and also intorts it.

The abducens nerve innervates the lateral rectus, which abducts the eye (moves it outward away from the midline).

So the correct mapping is: oculomotor nerve to most rectus muscles and inferior oblique with vertical and inward movements plus eyelid and pupil/lens control; trochlear nerve to the superior oblique for downward movement and intorsion; abducens nerve to the lateral rectus for outward movement.