The two primary cardiac responses to sympathetic discharge are which pair?

The two primary cardiac responses to sympathetic discharge are which pair?

• A. Decreased heart rate and decreased AV conduction
• B. Increased heart rate and increased AV conduction
• C. Increased heart rate and decreased AV conduction
• D. Decreased heart rate and increased AV conduction

Answer: (B)

Sympathetic activation makes the heart beat faster and pass impulse more quickly from atria to ventricles. Norepinephrine acting on beta-1 receptors in the SA node speeds the rate of spontaneous depolarization, increasing heart rate (positive chronotropy). It also acts on the AV node to enhance calcium-mediated conduction, shortening the AV nodal delay and increasing conduction velocity (positive dromotropy). Together, these changes raise cardiac output during demands like exercise or stress. The other patterns would either slow the heart or slow AV conduction, which is not how sympathetic discharge affects the heart.

Sympathetic activation makes the heart beat faster and pass impulse more quickly from atria to ventricles. Norepinephrine acting on beta-1 receptors in the SA node speeds the rate of spontaneous depolarization, increasing heart rate (positive chronotropy). It also acts on the AV node to enhance calcium-mediated conduction, shortening the AV nodal delay and increasing conduction velocity (positive dromotropy). Together, these changes raise cardiac output during demands like exercise or stress. The other patterns would either slow the heart or slow AV conduction, which is not how sympathetic discharge affects the heart.