What is the primary function of sesamoid bones, such as the patella (kneecap)?

Correct Answer: C

Rationale: Sesamoid bones, like the patella, are embedded within tendons and primarily enhance muscle leverage. The patella improves the mechanical advantage of the quadriceps muscle, increasing force during knee extension. While they offer some protection, their key role is leverage, making 'Enhancing muscle leverage' the correct answer.

Correct Answer: B

Rationale: Troponin, a protein on actin filaments, binds calcium ions released from the sarcoplasmic reticulum. This binding shifts tropomyosin, exposing actin’s myosin-binding sites, enabling contraction. Tropomyosin prevents binding in a relaxed state, making 'Binding to calcium ions' the correct answer.

Correct Answer: C

Rationale: Myoglobin, a protein in muscle cells, binds and stores oxygen, releasing it for aerobic respiration during contraction when oxygen demand rises. ATP and creatine phosphate provide energy, while troponin regulates contraction, making 'Myoglobin' the correct answer.

Correct Answer: C

Rationale: The ribs, part of the thoracic cage in the axial skeleton, form a protective enclosure around vital organs. The 12 pairs of ribs, along with the sternum and thoracic vertebrae, shield the heart and lungs directly. The liver, located below the diaphragm, is partially protected by the lower ribs. Vertebrae protect the spinal cord, the skull protects the brain, and the femur is a leg bone, making 'ribs' the correct answer.

Correct Answer: B

Rationale: The skeleton protects soft organs (e.g., skull protects brain), supports the body (via structure), and stores minerals (calcium, phosphorus) and fat (yellow marrow). Vitamin D production occurs in the skin upon sunlight exposure, not the skeleton, though bones use vitamin D to absorb calcium. Thus, 'produces vitamin D' is NOT a skeletal function.