Skeletal muscle is responsible for

Correct Answer: C

Rationale: Skeletal muscle drives actions under conscious control, like typing or breathing (when deliberate), by contracting and pulling tendons attached to bones. This enables precise, intentional movements across the body. Involuntary processes like digestion depend on smooth muscle, which operates automatically in organ walls, while blood pumping is the cardiac muscle's domain in the heart. Suggesting skeletal muscle controls most involuntary movements misattributes its voluntary nature smooth and cardiac muscles handle those. 'None of the above' ignores its evident function. Skeletal muscle's voluntary role, tied to its striated structure and nervous system integration, sets it apart, supporting posture, locomotion, and deliberate actions, contrasting with the autonomic functions of other muscle types, making it indispensable for willed physical activity.

Correct Answer: A

Rationale: A ligament is a small, dense, white, fibrous band of elastic tissue connecting bones to stabilize joints, like the anterior cruciate ligament in the knee. Its collagen-rich structure provides strength and slight elasticity. A muscle junction (e.g., neuromuscular) involves nerve-muscle interaction, not fibrous tissue. Muscle filaments are actin/myosin within muscle cells, not bands. Muscle cartilage isn't a term cartilage is avascular, unlike fibrous tissue. Ligaments' role in joint support and their fibrous, elastic nature match the description perfectly, making them the correct choice, as they're distinct from muscle components or junctions in both structure and function.

Correct Answer: B

Rationale: In the sliding filament theory, calcium ions bind to troponin on thin filaments, causing a conformational shift that moves tropomyosin, exposing actin's myosin-binding sites. This enables cross-bridges to form, initiating contraction. Calcium doesn't bind myosin directly myosin's activation relies on ATP and site exposure. It also doesn't hydrolyze ATP ATP binds myosin for that. 'All of the above' overextends calcium's role. Its specific binding to troponin is pivotal, triggering the cascade for actin-myosin interaction, distinct from myosin's mechanics or ATP's energy role, central to contraction's molecular choreography.

Correct Answer: B

Rationale: Fast-twitch fibers fatigue quickly, relying on anaerobic glycolysis for rapid, powerful contractions, like sprinting, depleting ATP and accumulating lactic acid fast. Slow-twitch fibers, rich in mitochondria and myoglobin, use aerobic respiration for endurance, fatiguing slower, as in marathons. Equal fatigue ignores their metabolic differences. Non-fatiguing fibers don't exist both tire, but at different rates. Fast-twitch's high-energy, low-endurance profile contrasts slow-twitch's sustained capacity, distinguishing their roles in activity duration and fatigue onset.

Correct Answer: D

Rationale: Trapezius adducts the scapula, pulling it toward the spine, and extends the head backward when both sides contract. Buccinator compresses cheeks. Serratus anterior protracts scapula, not adducts. Sternocleidomastoid turns the head. Trapezius' dual role in scapular and neck movement sets it apart, key for posture and head positioning.