All of the following structures are part of a muscle cell except one. Which one?

Correct Answer: A

Rationale: Muscle cell components have specialized roles. The sarcolemma is the plasma membrane, sarcoplasm the cytoplasm, and sarcoplasmic reticulum a calcium-storing organelle all integral to muscle function. Sarcoma, however, denotes a connective tissue cancer, not a cellular structure, unrelated to normal muscle anatomy. This distinction matters: muscle-specific terms prefix sarco for flesh, but sarcoma's pathological context excludes it from healthy cell anatomy, unlike the others, which enable contraction and signal transduction in skeletal muscle fibres.

Correct Answer: A

Rationale: Gluteus maximus denotes size maximus means largest relative to gluteus medius and minimus, all on the buttocks. Shape (e.g., trapezius), action (e.g., adductor), and origin-insertion (e.g., sternocleidomastoid) aren't specified. Its large mass aids hip extension, but size defines the name, distinguishing it in gluteal anatomy, reflecting naming conventions prioritizing relative scale.

Correct Answer: D

Rationale: Skeletal muscle's multinucleate nature a syncytium from fused myoblasts contrasts with uninucleate cardiac and smooth muscles. Striations occur in skeletal and cardiac, branching and intercalated discs are cardiac-specific. Multiple nuclei support skeletal muscle's size and repair, distinguishing it in structure and voluntary function, key to its histological identity.

Correct Answer: B

Rationale: Gluteus medius indicates size intermediate between maximus and minimus among gluteal muscles. Sternocleidomastoid names origin-insertion, flexor digitorum profundus action-depth, and trapezius shape. Medius' size-based naming distinguishes it, reflecting relative scale in gluteal anatomy, useful for comparative identification.

Correct Answer: B

Rationale: Thin myofilaments comprise actin (structure), tropomyosin (covers binding sites), and troponin (calcium receptor), regulating contraction. Thick myofilaments are myosin only, with heads forming cross-bridges not binding sites and lack tropomyosin/troponin. Myosin isn't in thin filaments. This composition distinguishes thin filaments' regulatory role, critical for controlled muscle action, contrasting with thick filaments' motor function.