During sympathetic activation, heart rate and contractility increase.

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Multiple Choice

During sympathetic activation, heart rate and contractility increase.

Explanation:
Sympathetic activation increases heart rate and contractility because norepinephrine (and epinephrine) bind beta-1 receptors on the SA node and cardiac myocytes. This stimulates a Gs protein → adenylyl cyclase → increased cAMP → activation of PKA. In the SA node, PKA enhances pacemaker currents and calcium handling, raising the firing rate and speeding conduction (positive chronotropy). In ventricular muscle, PKA phosphorylation increases L-type calcium current and boosts calcium release from the sarcoplasmic reticulum, raising intracellular calcium during systole and strengthening each beat (positive inotropy). Phospholamban phosphorylation by PKA also speeds relaxation and improves calcium reuptake, supporting a stronger, quicker-ready cycle. The overall effect of sympathetic tone is a higher heart rate and greater contractile force.

Sympathetic activation increases heart rate and contractility because norepinephrine (and epinephrine) bind beta-1 receptors on the SA node and cardiac myocytes. This stimulates a Gs protein → adenylyl cyclase → increased cAMP → activation of PKA. In the SA node, PKA enhances pacemaker currents and calcium handling, raising the firing rate and speeding conduction (positive chronotropy). In ventricular muscle, PKA phosphorylation increases L-type calcium current and boosts calcium release from the sarcoplasmic reticulum, raising intracellular calcium during systole and strengthening each beat (positive inotropy). Phospholamban phosphorylation by PKA also speeds relaxation and improves calcium reuptake, supporting a stronger, quicker-ready cycle. The overall effect of sympathetic tone is a higher heart rate and greater contractile force.

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