During sympathetic activation, which effect on heart rate is most likely?

• A. Decreased heart rate
• B. Increased heart rate
• C. No change
• D. Heart rate variability

Answer: (B)

When the sympathetic system activates, the heart speeds up to prepare the body for action. This happens because norepinephrine (and circulating epinephrine) binds to beta-1 receptors on the heart, especially the SA node. That signaling raises levels of cAMP inside pacemaker cells, which increases the "funny" current and calcium entry. The SA node fires more quickly, so heart rate rises. The sympathetic influence also tends to enhance conduction through the AV node, but the main effect you feel is a faster heartbeat. The other possibilities describe either a slowing, no change, or a different metric (heart rate variability) that doesn’t directly capture the immediate rate increase produced by sympathetic activation. Hence, increased heart rate is the best answer.