Which muscles extend the leg?

Correct Answer: A

Rationale: The leg (knee-to-ankle) extends straightens via the quadriceps, on the thigh's front, contracting to pull the tibia. Hamstrings flex the knee, gluteals extend the hip, and calf muscles (soleus, gastrocnemius) plantarflex the foot, with tibialis anterior dorsiflexing. Quadriceps' specific leg-extension role distinguishes it, critical for standing or kicking motions.

Correct Answer: A

Rationale: Calcium ions bind troponin, altering its shape to displace tropomyosin, exposing actin's binding sites for myosin. They don't detach cross-bridges (ATP does), propagate action potentials (acetylcholine initiates), or join ADP in respiration. This regulatory role distinguishes calcium as contraction's trigger, essential for sarcomere shortening, contrasting with energy or nerve functions.

Correct Answer: A

Rationale: Calcium binds troponin, shifting tropomyosin to expose actin's binding sites, enabling myosin attachment. It doesn't bind actin, detach from ATP (not involved), or release myosin (ATP does). This regulatory action distinguishes calcium's role, pivotal for initiating contraction, contrasting with energy or detachment processes.

Correct Answer: D

Rationale: Transversus abdominus indicates location (abdomen) and fibre direction (transverse, horizontal) compressing the abdomen. Size, origins, or action (e.g., flexion) aren't named. This location-direction naming distinguishes it, key to understanding abdominal wall structure and function.