Which of the muscles listed below is named according to its action?

Correct Answer: A

Rationale: Muscle names may reflect action, movement produced. Adductor longus indicates adduction drawing a limb toward the midline as its primary function, with longus denoting size. Temporalis refers to its temporal bone location, sternocleidomastoid to origin-insertion points, and peroneus longus to its fibular position and length. Only adductor directly names the action, a convention aiding functional understanding, distinguishing it from location- or attachment-based names, essential for predicting muscle roles in movement analysis.

Correct Answer: B

Rationale: Calcium's role is binding troponin, altering its shape to shift tropomyosin, exposing actin's binding sites for myosin. It doesn't propagate action potentials (acetylcholine does), bind myosin, or engage actin directly those involve ATP and cross-bridge mechanics. This troponin interaction regulates contraction, distinguishing it from nerve or energy roles, pivotal in the sliding filament process.

Correct Answer: C

Rationale: A sarcomere, a myofibril's repeating unit between Z-lines, contains overlapping actin and myosin myofilaments, contracting via their sliding. It's not the sarcolemma (membrane), sarcoplasm (cytoplasm), or just a filament bundle though filaments define it. Its sectional role distinguishes it, key to myofibril contraction and muscle function.

Correct Answer: B

Rationale: Wrist bending, or flexion/extension, involves specific muscles. The extensor carpi ulnaris extends the wrist, increasing the angle toward the forearm's dorsal side, effectively 'bending' it backward. Extensor digitorum extends fingers, flexor digitorum profundus flexes fingers, and abductor pollicis longus abducts the thumb none target wrist extension directly. Located along the ulna, extensor carpi ulnaris' action aligns with wrist movement, distinguishing it from finger or thumb movers, key for precise hand positioning in activities like lifting.

Correct Answer: A

Rationale: Skeletal muscle is striated (sarcomere-banded), voluntary (somatic control), multinucleate (syncytial), and named (e.g., biceps) unlike cardiac (striated, branched, involuntary, uninucleate) or smooth (non-striated, involuntary, uninucleate) muscle. This unique profile supports conscious movement, distinguishing it in structure and function, critical for anatomical classification.