In Myasthenia Gravis, autoantibodies are directed toward which component at the NMJ?

• A. Dopamine receptor
• B. Acetylcholine receptor
• C. GABA receptor
• D. NMDA receptor

Answer: (B)

The main concept is that Myasthenia Gravis disrupts communication at the neuromuscular junction by attacking the postsynaptic receptors that respond to acetylcholine. Autoantibodies bind to acetylcholine receptors on the skeletal muscle side of the NMJ, blocking receptor activation, promoting internalization of receptors, and activating complement to damage the postsynaptic membrane. With fewer functional receptors, acetylcholine released from the nerve end cannot produce a sufficient end-plate potential to trigger a strong muscle contraction, leading to fatigable weakness that worsens with use. The other receptors listed (dopamine, GABA, NMDA) are located in the CNS and are not involved at the NMJ, so they aren’t targets in MG. (Some patients may have antibodies against MuSK, another component of the postsynaptic apparatus, but the classic, most common target in MG is the acetylcholine receptor.)