Where are the acetylcholine receptors that MG targets located?

• A. Presynaptic terminal
• B. Postsynaptic motor endplate
• C. Within the myelin sheath
• D. In the cytoplasm of muscle fiber

Answer: (B)

The receptors MG targets are on the postsynaptic membrane of the neuromuscular junction, at the motor endplate. These are nicotinic acetylcholine receptors densely packed along the folds of the postsynaptic membrane. When acetylcholine released from the motor neuron binds to these receptors, it opens ion channels and triggers muscle depolarization. In myasthenia gravis, autoantibodies attack these receptors, reducing their number and impairing transmission, which leads to fatigable muscle weakness. The other locations—presynaptic terminals, the myelin sheath, or the cytoplasm of the muscle fiber—do not host the acetylcholine receptors involved in this disease.