Which is larger of the two leg bones and has a fibular notch?

Correct Answer: A

Rationale: The tibia, the larger leg bone, bears most of the body’s weight and has a fibular notch distally to articulate with the fibula, stabilizing the ankle.

Correct Answer: C

Rationale: The synovial membrane, lining synovial joint cavities, produces synovial fluid to lubricate and nourish the joint, reducing friction. Cartilage covers bone ends, ligaments connect bones, and periosteum covers bone surfaces—none produce this fluid.

Correct Answer: C

Rationale: Bones are classified into four main types based on shape: long, short, flat, and irregular. Long bones (e.g., femur) are longer than they are wide, short bones (e.g., carpals) are roughly equal in length and width, and flat bones (e.g., scapula) are thin and broad. Irregular bones, such as the vertebrae or certain skull bones, have complex shapes that do not fit neatly into the other categories due to their unique structure and function, making 'Irregular bone' the correct answer.

Correct Answer: A

Rationale: In muscle contraction, calcium ions play a key role in exposing binding sites on actin filaments. Troponin, a regulatory protein on the actin filament, binds to calcium ions when they are released from the sarcoplasmic reticulum. This binding causes tropomyosin to shift, uncovering myosin-binding sites on actin, allowing myosin heads to attach and initiate contraction. Thus, 'Troponin' is the correct answer.

Correct Answer: C

Rationale: Muscle contraction begins when calcium ions (Ca2+) are released from the sarcoplasmic reticulum into the muscle cell cytoplasm. Calcium binds to troponin, shifting tropomyosin to expose actin binding sites, allowing myosin to attach and contract the muscle. Sodium and potassium regulate nerve signals, not direct contraction, making 'Calcium (Ca2+)' the correct answer.