Which one of the following is NOT a characteristic of skeletal muscle?

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: 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.

Correct Answer: C

Rationale: Contraction requires calcium binding to troponin, shifting tropomyosin to expose actin's binding sites, enabling myosin cross-bridges. Myofilaments slide, not shorten; ATP hydrolysis (not synthesis) energizes cross-bridges; acetylcholine moves from axon to sarcolemma, not reverse. Calcium's troponin interaction is essential, distinguishing it as the regulatory trigger, pivotal for the sliding filament process in muscle activation.

Correct Answer: D

Rationale: Myofibrils, within muscle fibres, are chains of sarcomeres Z-line-to-Z-line units containing myofilaments (actin, myosin). Myofilaments are filament strands, motor units are neuron-fibre groups, and myosin is a protein. Sarcomeres' serial linkage enables myofibril contraction, distinguishing them as the repeating structural unit, key to muscle shortening.

Correct Answer: D

Rationale: Tendons, fibrous muscle extensions, anchor to bone, transmitting force e.g., patellar tendon. Menisci cushion joints, ligaments link bones, and cartilage covers bone ends. Tendons' muscle-bone role distinguishes them, essential for movement mechanics, contrasting with joint-support structures.