Which part of the axial skeleton is responsible for protecting the spinal cord?

Correct Answer: C

Rationale: The axial skeleton includes the skull, vertebral column, and rib cage. The vertebral column, a series of vertebrae, forms a bony canal that encases and protects the spinal cord. The rib cage protects thoracic organs, the skull protects the brain, and the pelvic girdle is appendicular, making 'Vertebral column' the correct answer.

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: Carpals and tarsals are short bones, roughly equal in length and width, providing stability and flexibility in wrist and ankle joints. They are not irregularly shaped (like vertebrae) but are classified as short, making 'Short bone' the correct answer despite the question’s phrasing.

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).