Which action is controlled by neurons in the abducens nucleus?

• A. Adduction of the eye
• B. Abduction of the eye
• C. Elevation of the eyelid
• D. Pupil constriction

Answer: (B)

Abduction of the eye is controlled by neurons in the abducens nucleus. This nucleus gives rise to the abducens nerve, which innervates the lateral rectus muscle. When the lateral rectus contracts, the eye moves laterally, away from the midline.

In contrast, adduction (moving the eye toward the midline) is controlled by the medial rectus via the oculomotor nerve, elevation of the eyelid is done by the levator palpebrae superioris via the oculomotor nerve, and pupil constriction is mediated by parasympathetic fibers from the Edinger-Westphal nucleus via the oculomotor nerve. The abducens nucleus is also involved in coordinating horizontal gaze with the opposite eye through connections in the pathway that ensures both eyes move together.