Myasthenia Gravis is best described by autoimmune antibodies directed against which site?

• A. Postsynaptic nicotinic acetylcholine receptors at the neuromuscular junction
• B. Myelin sheaths of peripheral nerves
• C. Presynaptic acetylcholine release
• D. Autonomic ganglia

Answer: (A)

The key idea is that myasthenia gravis is caused by autoantibodies that attack the postsynaptic nicotinic acetylcholine receptors at the neuromuscular junction. When these receptors are targeted, fewer functional receptors are available to respond to acetylcholine, so the end-plate potential often fails to reach the threshold needed to trigger a muscle contraction. This reduces motor unit transmission and leads to fatigable weakness that worsens with use and improves with rest or acetylcholinesterase inhibition. Some patients may have antibodies to other postsynaptic components like MuSK, but the classic description is antibodies against the postsynaptic nicotinic receptors themselves.

Antibodies against myelin sheaths would point to peripheral demyelinating neuropathies, antibodies affecting presynaptic acetylcholine release describe Lambert-Eaton syndrome, and antibodies to autonomic ganglia relate to autoimmune autonomic disorders—none of which capture the usual mechanism of myasthenia gravis.