Which of the following muscles is NOT affected by Myasthenia Gravis?

• A. Orbicularis oculi
• B. Levator
• C. Muscle of Muller
• D. Extraocular muscles (EOMs)

Answer: (C)

Myasthenia gravis targets the neuromuscular junctions of skeletal (striated) muscles, causing fatigable weakness that most commonly affects muscles used for eye and eyelid movements. The muscles responsible for lifting the eyelid (levator palpebrae superioris), closing the eyelids (orbicularis oculi), and the extraocular muscles all have skeletal NMJs and nicotinic acetylcholine receptors, so they are typically weakened in MG. Muller muscle, however, is a smooth muscle in the eyelid controlled by the autonomic (sympathetic) system, not by the skeletal NMJ. Since MG specifically disrupts the skeletal NMJ, Muller muscle is not affected.