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

Correct Answer: B

Rationale: Sternocleidomastoid names origin (sternum, clavicle) and insertion (mastoid process), not just location, unlike biceps brachii (arm), rectus abdominus (abdomen), and flexor carpi radialis (wrist). Its attachment-based name distinguishes it from purely locational terms, aiding precise anatomical identification over regional descriptors.

Correct Answer: B

Rationale: Thick myofilaments in sarcomeres are composed of myosin, a motor protein with heads forming cross-bridges to actin during contraction. Actin forms thin myofilaments with tropomyosin and troponin, while acetylcholine is a neurotransmitter, not a filament component. Myosin's bundled structure, comprising about 300 molecules per filament, drives the sliding filament mechanism, distinguishing it as the thick filament's core protein, critical for muscle force generation and movement.

Correct Answer: A

Rationale: Gluteus maximus, medius, and minimus are named for size largest, middle, smallest among buttock muscles. Shape (e.g., trapezius), whimsy (e.g., sartorius), or fibre direction (e.g., rectus) aren't indicated. Size-based naming distinguishes them, reflecting relative mass critical for hip function and anatomical clarity.

Correct Answer: D

Rationale: For 10-15 seconds of vigorous activity, creatine phosphate rapidly phosphorylates ADP to ATP, sustaining high-intensity effort beyond stored ATP (seconds). Glycolysis (minutes) and aerobic respiration (long-term) are slower. This quick energy buffer distinguishes creatine phosphate's role, vital for short bursts like sprinting.