Myasthenia gravis:
A. Is caused by the destruction of gamma-aminobutyric acid (GABA) receptors on the postsynaptic membrane of muscles.
B. Results in the decreased release of ACh at the neuromuscular junction.
C. Is an autoimmune disease that destroys ACh receptors on the postsynaptic membrane of muscles, thus interferes with ACh binding for repetitive muscle contractions.
D. Is successfully treated with removal of the pituitary gland.
E. All of the above
ANS: C
Rationale: Myasthenia gravis is an autoimmune disease during which antibodies attack and destroy nicotinic receptors on muscle cells. Normal amounts of ACh are released into the cleft, but few receptors are available for binding, resulting in increasing weakness with repetitive muscle contractions.
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