Describe the role of the autonomic nervous system in cardiovascular responses to exercise.

• A. Sympathetic withdrawal reduces heart rate and contractility while parasympathetic activation increases heart rate; autonomic balance is not necessary.
• B. Parasympathetic activation increases heart rate and contractility.
• C. Sympathetic activation increases heart rate and contractility and reduces vasodilation in nonessential tissues; parasympathetic withdrawal further raises heart rate; autonomic balance maintains cardiac output and blood pressure.
• D. Autonomic nervous system is only involved in resting conditions.

Answer: (C)

The main idea is that the autonomic nervous system carefully tunes heart performance and blood flow to meet the demands of exercise. During activity, sympathetic activation boosts heart rate and contractility, which increases cardiac output to supply the working muscles. At the same time, sympathetic signals constrict many nonessential vessels to raise overall vascular resistance and help maintain blood pressure, effectively redirecting blood toward muscles that need it. The parasympathetic system steps back (withdrawal of vagal input), removing the normal brake on heart rate, allowing a bigger and quicker rise in heart rate as exercise intensity increases. All together, this autonomic balance drives the necessary boost in cardiac output and helps regulate blood pressure during exercise. It’s also worth noting that local metabolic factors in exercising muscles promote vasodilation there, a process that can override some sympathetic vasoconstriction to ensure ample blood flow where it’s needed most.