During a neurological examination of a patient with a brainstem lesion, the examiner strokes the cornea lightly. The patient blinks on the ipsilateral side but not on the contralateral side. Which structure is most likely damaged?

• A Ipsilateral CN V (ophthalmic division)
• B Contralateral facial motor nucleus
• C Ipsilateral facial motor nucleus ✓
• D Ipsilateral CN VII nerve fiber

Explanation

The corneal reflex afferent arc is the ophthalmic division of CN V; the efferent arc is CN VII to the orbicularis oculi. The consensual blink requires CN VII motor neurons bilaterally because each facial motor nucleus receives bilateral cortical input and crossed brainstem connections. Damage to the ipsilateral facial motor nucleus abolishes the ipsilateral blink but preserves the consensual blink (contralateral side normal), whereas CN V damage abolishes both blinks when that eye is touched.

Reference: BD Chaurasia's Human Anatomy, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.