Your friend nods back and forth to you, making the yes motion. What muscle actions on the head at the neck are involved in this yes motion?

Correct Answer: C

Rationale: Nodding yes involves extension (head tilts back) and flexion (head tilts forward) at the neck, driven by muscles like the sternocleidomastoid and splenius. Rotation and circumduction involve turning or circling, not nodding. Lateral/medial rotation twists the head, not tilting it. Abduction/adduction don't apply to neck nodding. Extension and flexion are the correct actions, as they describe the up-and-down motion, fundamental to neck kinematics in this gesture.

Correct Answer: C

Rationale: Cellular respiration encompasses breaking down food (glucose) with oxygen to produce energy (ATP) in cells, mainly via aerobic means in mitochondria, releasing carbon dioxide and water. Anaerobic respiration skips oxygen, yielding less energy and lactic acid. Aerobic respiration is a subset, but cellular respiration covers all energy-making processes, fitting broadly. Oxygen is a reactant, not the process. This oxygen-dependent breakdown fuels most organisms, contrasting anaerobic's limited scope, and its cellular scope includes glycolysis and beyond, making it the precise term for energy formation across living systems.

Correct Answer: C

Rationale: In striated muscles (skeletal and cardiac), the sarcomere is the functional contractile unit, spanning from one Z line to the next. It contains actin and myosin filaments that slide during contraction, shortening the sarcomere to produce force, as per the sliding filament theory. The Z band anchors actin but isn't the unit itself. Cross bridges are myosin heads interacting with actin, a mechanism within the sarcomere, not the unit. A myofibril is a larger structure of many sarcomeres. The sarcomere's role as the basic repeating segment driving contraction makes it the best answer, central to understanding muscle mechanics and striation patterns.

Correct Answer: D

Rationale: When ADP and inorganic phosphate (P) release from myosin's head after ATP hydrolysis, the cross-bridge bends, pulling actin toward the sarcomere's center the power stroke. This single event encompasses bridge bending, filament pulling, and the stroke itself, driving contraction. Each aspect isn't separate; they're facets of one action. Bending alone omits the pull, pulling alone skips mechanics, and power-stroke alone undersells the full process. All occur simultaneously as myosin resets, distinguishing this step from prior ATP binding or later detachment, critical for the sliding filament cycle and muscle shortening.

Correct Answer: A

Rationale: Antagonists are muscles with opposing actions, like biceps flexing the elbow and triceps extending it, ensuring balanced movement and control. Agonists (prime movers) drive the main action, contracting together. Synergists assist agonists, stabilizing or refining motion. Prime movers overlap with agonists, not opposites. Antagonists' counteraction is unique, relaxing when agonists contract, distinct from cooperative or leading roles, essential for coordinated, reversible motion in the musculoskeletal system.