Final answer:
Myasthenia gravis is an autoimmune disorder characterized by the presence of anti-acetylcholine receptor antibodies, causing muscle weakness and fatigue.
Step-by-step explanation:
Myasthenia gravis is characterized by the presence of anti-acetylcholine receptor antibodies in the plasma. These autoantibodies are directed against acetylcholine receptors (AChRs) located at the synaptic cleft of neuromuscular junctions. This blockade hinders neuromuscular transmission, resulting in the typical symptoms of muscle weakness and fatigue in patients with myasthenia gravis. The antibodies reduce the effectiveness of neurotransmitter acetylcholine in stimulating muscle contractions, leading to progressive muscle weakness. Treatment may involve medications that enhance neuromuscular transmission or suppress the immune system's activity against the receptors.