Which bones are classified as facial bones?

Correct Answer: A

Rationale: Facial bones include maxilla (upper jaw) and mandible (lower jaw), shaping the face (14 total). Humerus/femur are limb, scapula/clavicle are pectoral girdle, occipital/parietal are cranial not facial. Maxilla/mandible's facial role, per skull, makes 'a' correct.

Correct Answer: C

Rationale: ATP stores energy in its phosphate bonds, releasing it controllably for cellular work (e.g., muscle contraction), a universal energy currency. It results from catabolism , but that's not why it's important storage is key. It doesn't release energy uncontrollably , that's inefficient. Not all only 'c' fits. ATP's energy storage role, per biochemistry, makes 'c' correct.

Correct Answer: D

Rationale: The lumbar region (lower back) is superior to the popliteal region (behind the knee), per anatomical regions lumbar above, popliteal lower on the leg. It's superior to gluteal , superior to umbilical , inferior to cervical . Superiority to popliteal, per body mapping, makes 'd' correct.

Correct Answer: A

Rationale: Thick myofilaments in sarcomeres are primarily myosin, a motor protein with a tail forming the filament backbone and heads projecting outward for actin binding. This structure, assembled from hundreds of myosin molecules, drives contraction via ATP-powered cross-bridge cycling. Thin filaments, conversely, comprise actin (a globular protein polymerized into strands), troponin (calcium-binding regulator), and tropomyosin (actin-covering modulator), not thick filaments. Combining myosin with troponin and tropomyosin lacks biochemical basis, as these regulate thin filaments. Actin alone forms thin filaments, not thick ones, and pairing myosin with actin misrepresents filament distinction. Myosin's unique tail-head configuration, detailed in structural biology, enables its role in force generation, distinct from thin filaments' regulatory proteins. Electron microscopy and X-ray diffraction reveal thick filaments as myosin aggregates, with heads engaging actin during contraction. This composition underpins muscle mechanics, ensuring thick filaments' contractile power, a fundamental concept in physiology distinguishing filament types.

Correct Answer: B

Rationale: A muscle's origin is its fixed attachment, typically the less movable bone, often more proximal (closer to the body's midline) in limb muscles. For example, the biceps brachii originates at the scapula (immovable relative to the arm) and inserts on the radius (movable). This anchors contraction, pulling the insertion toward the origin. 'Immovable' is relative bones shift slightly but the origin resists movement more, leveraging skeletal stability. Proximal positioning aligns with anatomical convention in limbs, though exceptions (e.g., abdominal muscles) exist. Aponeuroses, flat tendon sheets, may connect origins (e.g., rectus abdominis), but aren't universal. Movable origins contradict biomechanical principles: muscles shorten toward a stable point. Less proximal origins occur in rare cases, but the standard confirmed by dissection and kinesiology prioritizes the immovable, proximal end. This framework governs force direction, distinguishing origin from insertion in movement analysis.