Which part of the autonomic nervous system is activated during tachycardia?

• A. Parasympathetic
• B. Somatic
• C. Sympathetic
• D. Central nervous system

Answer: (C)

During tachycardia, the sympathetic division of the autonomic nervous system is activated. Sympathetic nerves release norepinephrine onto beta-1 receptors in the heart, especially the SA and AV nodes, increasing the slope of phase 4 depolarization and speeding both heart rate and conduction. This sympathetic drive underlies the faster heartbeat seen in stress or exercise. In contrast, parasympathetic activation slows the heart via acetylcholine on M2 receptors, opposing tachycardia. The somatic nervous system governs voluntary muscles, and the central nervous system coordinates autonomic outflow, but the direct driver of tachycardia is the sympathetic division.