Skeletal muscle cells have all of the following characteristics EXCEPT one. Which one?

Correct Answer: C

Rationale: Skeletal muscle cells feature neuromuscular junctions with acetylcholine, T-tubules for signal spread, and striations from sarcomere alignment, but aren't branched cardiac muscle is. Their long, cylindrical, multinucleate form suits voluntary movement, distinguishing them from branched, intercalated cardiac cells, key to their structural and functional identity in locomotion.

Correct Answer: C

Rationale: A muscle's origin is its fixed attachment, typically on a stationary bone (e.g., scapula for biceps), while the insertion moves (e.g., radius). This isn't a bone end or shaft line. The origin's stability enables leverage for movement, distinguishing it in muscle mechanics, critical for understanding contraction dynamics.

Correct Answer: A

Rationale: Intercostal muscles external, internal, innermost fill spaces between ribs, aiding breathing by elevating or depressing the ribcage. Costal cartilage connects ribs to the sternum, 'intercostal space' is the gap they occupy, and pleura lines the chest cavity. These striated, voluntary muscles distinguish the intercostal region's role in respiration, key to thoracic mechanics, contrasting with cartilage or membrane functions.

Correct Answer: D

Rationale: ATP fuels contraction via anaerobic glycolysis (glucose to pyruvate), aerobic respiration (mitochondrial oxidation), and creatine phosphate phosphorylating ADP. 'Anaerobic digestion of lactic acid' isn't a process lactic acid forms from pyruvate, not ATP. This distinguishes valid energy pathways, key to muscle metabolism understanding.

Correct Answer: D

Rationale: Contraction shortens sarcomeres myofibril segments via actin-myosin sliding, reducing Z-line distance. Fascicles (fibre bundles) shorten collectively, but actin and myosin molecules don't; filaments overlap. Sarcomeres' shortening distinguishes them as the contractile unit, summing to muscle movement.