AEMCA Practice Exam

What causes myasthenia gravis?

1. A genetic mutation affecting muscle fibers

2. A defect in nerve impulses at the neuromuscular junction

3. A lack of vitamin D leading to muscle degeneration

4. Environmental toxins impacting nerve health

The correct answer is: A defect in nerve impulses at the neuromuscular junction

Myasthenia gravis is primarily caused by a defect in nerve impulses at the neuromuscular junction. This condition is an autoimmune disorder wherein the body's immune system produces antibodies that mistakenly attack acetylcholine receptors on the muscle cells. Acetylcholine is a neurotransmitter essential for muscle contraction, and when its receptors are blocked or destroyed, the communication between nerves and muscles is impaired. This leads to weakness in the voluntary muscles, particularly those that control eye and eyelid movement, facial expressions, and swallowing. Understanding this mechanism clarifies why options relating to genetic mutations, vitamin deficiencies, or environmental toxins are less relevant in explaining the primary cause of myasthenia gravis. While genetic factors can contribute to susceptibility, the direct problem lies in the disruption of neurotransmission rather than an inherent defect in muscle fibers, a vitamin deficiency, or toxin exposure.