Which of the following muscles is NOT named after its location in the body?

Correct Answer: A

Rationale: Deltoid reflects shape triangular, like the Greek delta not location, unlike extensor carpi ulnaris (wrist), rectus abdominus (abdomen), and biceps femoris (thigh's femur). Located on the shoulder, deltoid's name emphasizes form over position, distinguishing it from location-specific terms, useful for anatomical recognition beyond regional cues.

Correct Answer: C

Rationale: In skeletal muscle, cytoplasm is termed sarcoplasm, housing myofibrils and organelles, distinct from sarcolemma (membrane), sarcomere (contractile unit), and fasciculus (fibre bundle). The sarco prefix denotes muscle specificity, and sarcoplasm's role in supporting contraction distinguishes it, key to cellular anatomy and function.

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.