A muscle that has an action opposite that of the prime mover (agonist) and yields to the movement of the prime mover.

Correct Answer: C

Rationale: An antagonist is a muscle that opposes the action of the prime mover (agonist) and relaxes or yields to allow the intended movement to occur. For instance, when the biceps brachii (agonist) flexes the elbow, the triceps brachii (antagonist) extends it, working in opposition. This relationship ensures smooth, controlled motion and prevents overstretching. Compartment refers to a group of muscles, not an individual muscle's action. Anal triangle is a pelvic region, unrelated to muscle function in this context. Synergists assist the prime mover, not oppose it. The antagonist's role in opposing and yielding to the prime mover is a fundamental concept in muscle dynamics, making it the correct answer here, as it directly contrasts with the agonist's action while facilitating coordinated movement.

Correct Answer: B

Rationale: On the lateral abdomen, the muscle layers from superficial to deep are external oblique, internal oblique, and transversus abdominis. The external oblique runs diagonally downward and medially, the internal oblique courses upward and medially, and the transversus abdominis runs horizontally, deepest of the three, compressing the abdomen. Rectus abdominis is midline, not lateral, so it's excluded. Other options misorder the layers or include incorrect muscles. External oblique, internal oblique, transversus abdominis is the correct sequence, as it follows the anatomical layering of the lateral abdominal wall, critical for surgical or assessments.

Correct Answer: D

Rationale: The masseter forcefully closes the jaw during chewing and is superficial, lying over the mandible's ramus, easily palpable. Temporalis, also a jaw closer, is deeper under the scalp. Lateral pterygoid protrudes and depresses the jaw, not closing it forcefully, and is deep. Medial pterygoid closes the jaw but is deep to the masseter. Masseter's superficial position and power make it the correct answer, as it's the primary, visible jaw-closing muscle, vital for mastication.

Correct Answer: B

Rationale: Smooth muscle operates without conscious control, managing essential involuntary functions. It lines the digestive tract, facilitating peristalsis to move food, and surrounds blood vessels, aiding in blood flow regulation not pumping, which is the heart's role, but still vital for circulation. Voluntary movements, like running, rely on skeletal muscle, not smooth muscle, which lacks the striations for such tasks. Claiming it controls all involuntary movements overstates its scope, as cardiac muscle handles heartbeats independently. 'None of the above' dismisses its clear role. Smooth muscle's involuntary nature and presence in visceral organs and vascular walls make it key for digestion and circulation support, distinguishing it from skeletal muscle's voluntary domain and cardiac muscle's specialized pumping, aligning with its physiological purpose across multiple systems.

Correct Answer: D

Rationale: Exercise strengthens muscles by stressing fibers, prompting growth and repair. Resistance training or cardio increases muscle mass, endurance, and power through repeated contraction and recovery. Diet and food provide nutrients protein, carbs but without exercise, they don't build strength directly, only support it. Sleeping aids recovery, allowing muscle repair, but doesn't actively strengthen. Exercise's mechanical stress triggers hypertrophy, enhancing fiber size and efficiency, unlike diet's passive fuel role or sleep's restorative one. Regular activity, like lifting or running, directly fortifies muscles, making it the primary driver, supported but not replaced by nutrition and rest, critical for physical capability.