Which muscle naming criteria are used to name the quadriceps femoris?

Correct Answer: D

Rationale: Muscle names encode specific traits. Quadriceps femoris combines quadriceps, indicating four origins four distinct attachment points on the pelvis or femur with femoris, pinpointing its location on the thigh's femur bone. Action (e.g., extension) isn't specified, nor are insertion points (tibia via patella) or fibre direction (e.g., rectus). Location and origin count align with naming conventions, as seen in biceps or triceps, where number denotes origins and the second term locates it. This reflects skeletal muscle nomenclature's focus on anatomical anchors, distinguishing it from action-based or directional terms, crucial for identifying muscles in clinical and educational contexts.

Correct Answer: A

Rationale: Biceps brachii encodes two origins ( bi- ) two tendon heads on the scapula and location ( brachii ) on the arm's humerus. Action (flexion) isn't specified, nor is size (e.g., maximus) or shape (e.g., deltoid). This origin-location naming, common in muscles like triceps, aids anatomical mapping, distinguishing it from action- or shape-based names, reflecting skeletal muscle's attachment-based classification.

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: Myosin, a protein molecule (160 nm), forms thick myofilaments within sarcomeres, inside myofibrils, within muscle fibres (cells), grouped into fasciculi. As a molecular component, myosin is the smallest unit, distinguishing it from larger structural assemblies, foundational to contraction mechanics.

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.