Which muscles help move the jaw during mastication?

Correct Answer: A

Rationale: Mastication (chewing) involves the masseter, temporalis, and medial/lateral pterygoid muscles, which elevate, retract, and laterally move the mandible. The masseter is the strongest, closing the jaw; temporalis assists in elevation and retraction; pterygoids enable grinding. Genioglossus and related tongue muscles move the tongue, not the jaw. Omohyoid and neck muscles affect the hyoid, not mastication. Rectus abdominis is an abdominal muscle, unrelated. The masseter-temporalis-pterygoid group is the correct answer, as it directly powers jaw movement during chewing, critical for breaking down food, unlike the other muscle groups focused on different functions.

Correct Answer: B

Rationale: The insertion is the tendon's attachment to a movable bone, drawn toward the origin during contraction, like the radius in the biceps brachii. The origin is the stationary end, belly is the muscle body, and aponeurosis is a tendon type. Insertion is the correct answer, as it identifies the dynamic attachment critical for movement, distinguishing it from the fixed origin in muscle mechanics.

Correct Answer: D

Rationale: Muscles are elastic tissue bundles with diverse roles movement, posture, heat production stretching and contracting to function. Skeletal muscles move bones, smooth muscles regulate organs, and cardiac muscles pump blood, showcasing versatility. Tendons, though fibrous, primarily transmit force, not perform varied tasks themselves. Ligaments stabilize joints, limiting motion, not acting broadly. Joints are bone junctions, not tissues. Muscles' elasticity and multifunctional nature contracting for strength, relaxing for flexibility define them, distinguishing their dynamic, active contributions from tendons' and ligaments' supportive, static roles or joints' structural purpose, making them the clear fit for this description.

Correct Answer: B

Rationale: During muscular contraction, the sliding filament theory explains sarcomere changes: actin filaments slide over myosin, shortening the sarcomere. The H-zone (myosin-only region) disappears as actin overlaps it. The I band (actin-only) shortens as Z lines approach each other. The A band (myosin length) remains constant, unaffected by sliding. The M line and Z lines get closer due to overall shortening. The A band widening doesn't occur, as its width is fixed by myosin filament length. The correct combination includes the H-zone vanishing, I band shortening, A band staying unchanged, and Z lines nearing the M line, reflecting the mechanics of contraction where filament overlap drives muscle shortening without altering myosin's span, a key principle in muscle physiology.

Correct Answer: C

Rationale: The A band, the dark region of a sarcomere, spans the thick myosin filaments, appearing dark under a microscope due to overlapping actin and myosin in most areas. It remains constant in length during contraction, reflecting myosin's extent. The H-zone, within the A band, is lighter, showing only myosin, narrowing as actin slides in. The Z-line anchors actin, defining sarcomere boundaries, not dark. The I band, light, contains only actin, shortening during contraction. The A band's darkness and myosin content distinguish it, central to sarcomere structure, unlike the lighter, shifting H-zone, structural Z-line, or actin-only I band, key to understanding muscle striation.