Myasthenia gravis is caused by dysfunction of –
**Core Concept**
Myasthenia gravis is an autoimmune disease characterized by **neuromuscular junction** dysfunction, leading to fluctuating muscle weakness. The underlying principle involves the **immune system** targeting specific components of the neuromuscular junction. This results in impaired **neurotransmission** from nerve to muscle.
**Why the Correct Answer is Right**
The correct answer involves the dysfunction of the **nicotinic acetylcholine receptor (nAChR)**, which is crucial for muscle contraction. In myasthenia gravis, **autoantibodies** against the nAChR are produced, leading to its destruction and reduced numbers on the muscle surface. This decreases the effectiveness of **acetylcholine** in initiating muscle contraction.
**Why Each Wrong Option is Incorrect**
**Option A:** Is incorrect because while other receptors may be involved in muscle function, they are not the primary target in myasthenia gravis.
**Option B:** Incorrect as it does not directly relate to the neuromuscular junction pathology seen in myasthenia gravis.
**Option D:** Also incorrect as it is not directly involved in the neurotransmission process affected in myasthenia gravis.
**Clinical Pearl / High-Yield Fact**
Myasthenia gravis is a classic example of an autoimmune disease affecting the neuromuscular junction, with symptoms worsening with activity and improving with rest. Remembering that **thymus abnormalities** are common in these patients can aid in diagnosis and treatment planning.
**Correct Answer:** D. Nicotinic acetylcholine receptor.