Once myosin binds to actin, heads change shape and slide the This is the sliding filament theory.

Correct Answer: D

Rationale: Myosin heads bind actin, change shape via ATP hydrolysis, and slide actin toward the sarcomere's center, the core of sliding filament theory, shortening the muscle. Actin doesn't slide myosin it's pulled. Troponin regulates, not slides, myosin or actin it shifts tropomyosin. Myosin sliding actin defines the power stroke, distinguishing it from regulatory or reversed actions, essential for contraction mechanics.

Correct Answer: B

Rationale: Semimembranosus and semitendinosus, with biceps femoris, form the hamstrings on the posterior thigh, aiding knee flexion and hip extension. The seminal vesicle is a reproductive organ, the forearm contains arm flexors/extensors, and back muscles (e.g., latissimus dorsi) differ in function and location. The thigh's dorsal placement aligns with hamstring anatomy, distinguishing it from unrelated regions, key for understanding lower limb movement.

Correct Answer: A

Rationale: Deltoid reflects shape triangular, like the Greek delta not location, unlike extensor carpi ulnaris (wrist), rectus abdominus (abdomen), and biceps femoris (thigh's femur). Located on the shoulder, deltoid's name emphasizes form over position, distinguishing it from location-specific terms, useful for anatomical recognition beyond regional cues.

Correct Answer: A

Rationale: The leg (knee-to-ankle) extends straightens via the quadriceps, on the thigh's front, contracting to pull the tibia. Hamstrings flex the knee, gluteals extend the hip, and calf muscles (soleus, gastrocnemius) plantarflex the foot, with tibialis anterior dorsiflexing. Quadriceps' specific leg-extension role distinguishes it, critical for standing or kicking motions.

Correct Answer: C

Rationale: In skeletal muscle, cytoplasm is termed sarcoplasm, housing myofibrils and organelles, distinct from sarcolemma (membrane), sarcomere (contractile unit), and fasciculus (fibre bundle). The sarco prefix denotes muscle specificity, and sarcoplasm's role in supporting contraction distinguishes it, key to cellular anatomy and function.