10 years old Ramu has increasing muscle weakness and raised CPK levels. The most likely defect is in plasma membrane of-
**Core Concept**
Muscle weakness and elevated creatine phosphokinase (CPK) levels in a child suggest a muscle disorder. The plasma membrane plays a crucial role in muscle function, and defects in its structure or function can lead to various neuromuscular disorders.
**Why the Correct Answer is Right**
The most likely defect in the plasma membrane of Ramu is in the **sarcolemma**, which is the plasma membrane of muscle fibers. Elevated CPK levels indicate muscle damage, and a defect in the sarcolemma can lead to muscle weakness due to impaired muscle contraction and relaxation. The sarcolemma is rich in receptors and ion channels that regulate muscle function, and defects in these proteins can lead to muscle disorders.
**Why Each Wrong Option is Incorrect**
* **Option A:** The endoplasmic reticulum (ER) is involved in protein synthesis and folding, but it is not directly related to muscle weakness or elevated CPK levels.
* **Option B:** The Golgi apparatus is involved in protein modification and transport, but it is not directly related to muscle function or plasma membrane defects.
* **Option C:** The mitochondria are involved in energy production in muscle cells, but a defect in the mitochondria would more likely lead to fatigue or energy metabolism disorders rather than muscle weakness and elevated CPK levels.
**Clinical Pearl / High-Yield Fact**
Duchenne muscular dystrophy (DMD) is a genetic disorder caused by a defect in the dystrophin gene, which codes for a protein that is essential for muscle function. DMD is characterized by progressive muscle weakness, elevated CPK levels, and a defect in the sarcolemma.
**Correct Answer:** C.