Which protein, found in muscle fibers, slides along actin filaments during muscle contraction to generate force?

Correct Answer: A

Rationale: During muscle contraction, the sliding filament theory explains that myosin filaments slide along actin filaments to shorten the sarcomere and generate force. Myosin heads bind to actin, pulling it inward. Troponin and tropomyosin regulate this process, while collagen is structural, not contractile, making 'Myosin' the correct answer.

Correct Answer: C

Rationale: Acetylcholine (ACh) is released by the motor neuron at the neuromuscular junction, crossing the synaptic cleft to bind to muscle fiber receptors, triggering an action potential for contraction. It does not inhibit, relay sensory data, or degrade fibers, making 'Transmitting signals from the motor neuron to the muscle fiber' the correct answer.

Correct Answer: A

Rationale: Creatine phosphate stores high-energy phosphate bonds in muscle cells. During contraction, it transfers its phosphate to ADP, regenerating ATP to power myosin heads. Glycogen is a glucose store, myoglobin holds oxygen, and lactic acid is a byproduct, making 'Creatine phosphate' the correct answer.

Correct Answer: D

Rationale: The ribs, part of the axial skeleton’s thoracic cage, primarily protect thoracic organs like the heart and lungs by forming a bony enclosure. They don’t support lower limbs, protect the spinal cord (vertebral column’s role), or aid digestion, making 'Protecting the thoracic organs' correct.

Correct Answer: D

Rationale: The structure of a bone includes several layers: the periosteum (outer membrane), compact bone (dense outer layer), cancellous bone (spongy inner layer), and bone marrow (innermost part). Bone marrow, found in the medullary cavity of long bones and within cancellous bone, produces blood cells and stores fat, making it the innermost part and 'bone marrow' the correct answer.