Which chronic autoimmune disease affects the neuromuscular junction and produces serious weakness of voluntary muscles?

Which chronic autoimmune disease affects the neuromuscular junction and produces serious weakness of voluntary muscles?

• A. Myasthenia gravis
• B. Alzheimer's disease
• C. Spinal muscular atrophy
• D. Guillain-Barré syndrome

Answer: (A)

This question hinges on understanding where the immune system goes wrong to cause weakness. In Myasthenia gravis, the immune system creates antibodies against acetylcholine receptors at the postsynaptic side of the neuromuscular junction. With fewer functional receptors, acetylcholine released from the nerve cannot reliably stimulate muscle fibers, so the end-plate potential fails to reach the threshold needed to trigger muscle contraction. The result is fatigable weakness of voluntary muscles that worsens with use and improves with rest. This pattern often starts with eye and facial muscles and can progress to other muscles. Alzheimer’s disease affects cognition and memory in the brain, not the neuromuscular junction. Spinal muscular atrophy is a genetic motor neuron disease leading to muscle weakness from motor neuron loss, not autoimmune attack at the junction. Guillain-Barré syndrome involves autoimmune damage to peripheral nerves (demyelination or axonal injury) and typically presents as an acute, ascending paralysis, not a chronic junction-specific weakness.

This question hinges on understanding where the immune system goes wrong to cause weakness. In Myasthenia gravis, the immune system creates antibodies against acetylcholine receptors at the postsynaptic side of the neuromuscular junction. With fewer functional receptors, acetylcholine released from the nerve cannot reliably stimulate muscle fibers, so the end-plate potential fails to reach the threshold needed to trigger muscle contraction. The result is fatigable weakness of voluntary muscles that worsens with use and improves with rest. This pattern often starts with eye and facial muscles and can progress to other muscles.

Alzheimer’s disease affects cognition and memory in the brain, not the neuromuscular junction. Spinal muscular atrophy is a genetic motor neuron disease leading to muscle weakness from motor neuron loss, not autoimmune attack at the junction. Guillain-Barré syndrome involves autoimmune damage to peripheral nerves (demyelination or axonal injury) and typically presents as an acute, ascending paralysis, not a chronic junction-specific weakness.