In the sliding filament theory of muscle contraction, what causes the myosin heads to detach from the actin filaments?

Correct Answer: B

Rationale: In the sliding filament theory, ATP binds to myosin heads, causing them to detach from actin after a power stroke. This allows the cycle to repeat. Calcium initiates binding, acetylcholine triggers the process indirectly, and sodium is unrelated, making 'ATP' the correct answer.

Correct Answer: A

Rationale: Flat bones, such as the scapula and cranial bones, are thin, broad, and plate-like, offering protection (e.g., skull) and muscle attachment surfaces. Irregular bones are complex, long bones are cylindrical, and short bones are cube-like, making 'flat' the correct answer.

Correct Answer: A

Rationale: An articulation is the point where two bones meet, forming a joint (e.g., knee). The diaphysis and epiphysis are parts of long bones, and the endosteum lines the marrow cavity, making 'articulation' the correct term.

Correct Answer: D

Rationale: Osteoclasts, which break down bone, derive from monocytes (white blood cells) in the bone marrow. Osteoprogenitor cells are stem cells, osteoblasts form bone, and osteocytes maintain it, making 'osteoclasts' the correct answer.

Correct Answer: A

Rationale: Bone fracture repair occurs in four stages: 1) hematoma (blood clot) forms at the break, 2) fibrocartilage callus bridges the gap, 3) bony callus replaces it with spongy bone, 4) remodeling shapes it into compact bone. 'hematoma, fibrocartilage callus, bony callus, remodeling' is correct.