**Core Concept**
Myasthenia gravis is an autoimmune disease characterized by weakness and rapid fatigue of the muscles under voluntary control. This condition occurs due to the production of antibodies against the acetylcholine receptor (AChR) at the neuromuscular junction, leading to impaired neurotransmission and muscle dysfunction.

**Why the Correct Answer is Right**
The correct answer is associated with the pathophysiology of myasthenia gravis, where the autoantibodies bind to the nicotinic acetylcholine receptors on the muscle endplate, causing a reduction in the number of functional receptors. This results in decreased acetylcholine binding, reduced muscle contraction, and the characteristic symptoms of myasthenia gravis. The involvement of the AChR is crucial in the disease process, and the correct answer is directly related to this mechanism.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not directly relate to the pathophysiology of myasthenia gravis. While muscle weakness is a symptom, it is not the underlying cause of the disease.

**Option B:** This option is incorrect because it is more commonly associated with other conditions, such as Lambert-Eaton myasthenic syndrome, where antibodies target the voltage-gated calcium channels.

**Option C:** This option is incorrect because it is not directly related to the disease process of myasthenia gravis. While muscle atrophy can occur in advanced cases, it is not a primary feature of the disease.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that myasthenia gravis can be associated with thymic abnormalities, such as thymoma or thymic hyperplasia, and that patients with this condition often respond well to immunosuppressive therapy.

**Correct Answer: B. Thymoma**