[Campbell Biology P.1178] Myasthenia gravis is an autoimmune disease where the body produces ... | Practice Question

Myasthenia gravis is an autoimmune disease where the body produces antibodies against acetylcholine receptors on the muscle fiber's plasma membrane. Based on Figure 50.31 and the accompanying text, which of the following is the most direct consequence of myasthenia gravis on skeletal muscle contraction?

  • A: Inability of Ca2+ to bind to troponin, preventing exposure of myosin-binding sites.
  • B: Reduced ability of acetylcholine to bind to its receptors, impairing the generation of action potentials in the muscle fiber.
  • C: Excessive release of Ca2+ from the sarcoplasmic reticulum, leading to prolonged muscle contraction.
  • D: Impaired ATP production, leading to insufficient energy for cross-bridge cycling and Ca2+ reuptake.

Explanation

Myasthenia gravis is characterized by antibodies against acetylcholine receptors. According to Step 1 in Figure 50.31, acetylcholine binding to these receptors is crucial for triggering an action potential in the muscle fiber. If this binding is impaired, the subsequent steps of muscle contraction will not be initiated effectively, leading to muscle weakness.