By which term is a muscle that opposes or reverses a particular movement called?

Correct Answer: C

Rationale: Muscle roles define movement dynamics. An antagonist opposes or reverses an agonist's action, relaxing during the agonist's contraction e.g., triceps antagonize biceps in elbow flexion. Agonists drive the primary motion, synergists assist, and fixators stabilize. The antagonist's counteraction ensures controlled, reversible movements, a key biomechanical principle distinguishing it from supportive or driving roles, essential for coordinated skeletal motion.

Correct Answer: B

Rationale: Adductor longus names its action (adduction) and size (long), not location, unlike latissimus dorsi (back), rectus femoris (thigh), and biceps brachii (arm). Located on the thigh, its name prioritizes function, distinguishing it from location-centric terms, useful for understanding muscle roles beyond positional cues.

Correct Answer: D

Rationale: The flexor carpi ulnaris flexes the wrist, bending it toward the forearm's palmar side, mirroring the flexor carpi radialis' action, differing only in position (ulnar vs. radial). It doesn't flex the arm or fingers, nor extend like its extensor counterpart. This wrist-specific flexion distinguishes it, key to hand positioning movements.

Correct Answer: D

Rationale: Acetylcholine, released by somatic motor neurons, crosses the neuromuscular junction, binding sarcolemma receptors to depolarize the membrane, triggering an action potential. Inorganic phosphate and ADP relate to ATP cycling, calcium regulates contraction internally not membrane depolarization. Acetylcholine's neurotransmitter role initiates muscle activation, distinguishing it from intracellular or energy-related molecules, key to voluntary movement.

Correct Answer: C

Rationale: Cardiac muscle is striated but involuntary (autonomic), not voluntary unlike skeletal (striated, voluntary, syncytial) and smooth (visceral, involuntary, non-striated). This mischaracterization distinguishes cardiac's automatic heart function, critical for physiological accuracy, contrasting with skeletal's conscious control.