During muscle contraction, what happens to the sarcomere length?

Correct Answer: A

Rationale: In muscle contraction, the sliding filament theory states that actin and myosin filaments slide past each other, shortening the sarcomere (the distance between Z-lines). This shortening contracts the muscle. It does not lengthen, stay unchanged, or vibrate, making 'It shortens' the correct answer.

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: Joints are classified by movement: immovable (e.g., skull sutures), slightly movable (e.g., vertebrae), and freely movable (synovial). Hinge joints (e.g., elbow) allow bending in one plane, and ball-and-socket joints (e.g., shoulder) permit multi-directional movement—both are correct per the document. Fixed joints don’t move, cartilage joints are slightly movable, and tendon joints aren’t a category, making 'hinge joints' a correct choice (noting ball-and-socket is also valid).

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.