Which statement describes a muscular disorder listed?

• A. Myasthenia Gravis is unrelated to acetylcholine receptors
• B. Duchenne MD is caused by a lack of a protein to maintain the sarcolemma
• C. Muscular Dystrophy is caused by a viral infection
• D. Strain is defined as sudden joint dislocation

Answer: (B)

A key idea here is that Duchenne muscular dystrophy results from a missing structural protein that keeps the muscle fiber membrane (sarcolemma) intact during contraction. Dystrophin normally anchors the cytoskeleton inside the muscle cell to the surrounding extracellular matrix, stabilizing the sarcolemma as the muscle contracts. Without dystrophin, membranes tear easily, calcium enters the cells inappropriately, and fibers break down, leading to progressive weakness typical of Duchenne.

The other statements don’t fit because muscular disorders of this type aren’t described that way. Myasthenia gravis involves autoantibodies against acetylcholine receptors at the neuromuscular junction, so it is related to acetylcholine receptors, not unrelated. Muscular dystrophy is not caused by a viral infection; it’s genetic, due to mutations in dystrophin or other structural proteins. A strain is not a sudden joint dislocation; a strain is an injury to muscle or its tendon from overstretching or overuse, whereas dislocations involve the joint itself.