Identify the muscle that abducts the arm horizontally.

Correct Answer: B

Rationale: Deltoid abducts the arm horizontally, lifting it sideways from the body, due to its lateral fibers' orientation. Biceps brachii flexes the elbow. Trapezius elevates or adducts scapula. Triceps brachii extends the elbow. Deltoid's abduction role, centered at the shoulder, sets it apart, vital for arm positioning, distinct from elbow or scapular functions.

Correct Answer: B

Rationale: Sarcomere shortening, the basis of muscle contraction, occurs via the sliding filament mechanism. Myosin heads, protruding from thick filaments, bind to actin on thin filaments, forming cross-bridges. Using ATP-derived energy, these heads execute a power stroke, pulling actin toward the sarcomere's center specifically the A band's midpoint reducing the distance between Z lines and shortening the sarcomere. Acetylcholine initiates this by triggering an action potential, but it's not the direct shortening mechanism. Calcium release from the sarcoplasmic reticulum enables myosin-actin binding by shifting tropomyosin, a crucial step but not the act of shortening. ATP breakdown powers the process, yet the sarcoplasmic reticulum stores calcium, not hydrolyzes ATP for shortening. The myosin-actin interaction is the mechanical driver, making it the precise answer, central to muscle movement and the sliding filament theory.

Correct Answer: C

Rationale: The external occipital protuberance, a midline bump on the occipital bone, is termed the inion, a landmark for neck muscle attachment (e.g., trapezius). The nasion is the forehead-nose junction, a facial point. The acromion, on the scapula, is a shoulder feature, not cranial. The mental protuberance is the chin's prominence on the mandible. Inion's specific occipital location and role in muscle anchorage distinguish it, aligning with skull anatomy, unlike facial, shoulder, or mandibular misnomers.

Correct Answer: D

Rationale: Elite athletes in prolonged high-intensity exercise (>2.5 hours), like marathons, should consume 90 g of glucose plus fructose per hour. This mix leverages multiple transporters (SGLT1 for glucose, GLUT5 for fructose), maximizing absorption beyond glucose's 60 g/h limit, delivering ~1.5 g/min of energy. Solo 60 g glucose caps at 1 g/min, insufficient for sustained high intensity. Adding fructose to 60 g boosts uptake slightly, but 90 g optimizes fuel, reducing fatigue. Excess glucose alone (90 g) overloads SGLT1, risking GI distress. The dual-carb approach distinguishes it, critical for elite endurance performance.

Correct Answer: C

Rationale: The temporalis muscle spans the side of the head, originating from the temporal bone's fossa and inserting on the mandible, elevating it for chewing. The forehead hosts frontalis for brow movement. The neck has muscles like sternocleidomastoid for head turning. The chin area features mentalis for lip motion. Temporalis' lateral cranial position and masticatory role distinguish it, essential for jaw closure, unlike forehead, neck, or chin functions.