Thick Filament is made up of

Correct Answer: D

Rationale: Thick filaments in sarcomeres are composed of myosin, with heads forming cross-bridges to pull actin during contraction, creating the A band's density. Troponin and tropomyosin, regulatory proteins, pair with actin in thin filaments, not thick. Actin forms thin filaments, overlapping myosin, not constituting thick ones. Myosin's exclusive role in thick filaments drives force generation, distinguishing it from thin filament components, fundamental to muscle contraction mechanics.

Correct Answer: B

Rationale: Within myofibrils, sarcomeres are the contractile units, shortening as actin and myosin slide past each other, powered by ATP. Sarcoplasm is cytoplasm, sarcolemma the membrane, and sarcoplasmic reticulum a calcium store not contractile. Sarcomeres' banded structure, from Z-line to Z-line, enables muscle contraction, their collective action summing to fibre shortening, distinguishing them as the functional core of myofibril mechanics in muscle physiology.

Correct Answer: B

Rationale: Skeletal muscle exhibits excitability (signal response), contractility (shortening), and extensibility (stretching), but is innervated by the somatic nervous system for voluntary control, not the autonomic system, which governs involuntary smooth and cardiac muscles. This voluntary innervation distinguishes skeletal muscle's conscious movement role e.g., lifting from autonomic-regulated visceral functions, key to its physiological classification.

Correct Answer: A

Rationale: A sarcomere, a myofibril segment between Z-lines (2 micrometres), is smaller than myofibrils (cell-length), muscle fibres (cells), and fasciculi (fibre bundles). Containing myofilaments, it's the basic contractile unit, distinguishing it as the smallest listed structure, foundational to muscle shortening and force generation.

Correct Answer: B

Rationale: Skeletal muscle, voluntary and striated, includes the diaphragm (breathing), vastus lateralis (thigh), and tongue (speech, swallowing). The pyloric sphincter, controlling stomach emptying, is smooth muscle involuntary, non-striated under autonomic control. This distinction reflects tissue type and function, key to digestive versus locomotive roles.