Sympathetic nerves of the cardiovascular system primarily act to

• A. Nerves that decrease heart rate.
• B. Nerves that regulate digestion.
• C. Nerves that increase heart rate and contractility; originate from the spinal cord and extend to the heart.
• D. Nerves that control respiration.

Answer: (C)

The main idea is that sympathetic innervation to the heart ramps up its performance during activity. These nerves originate in the spinal cord (thoracic levels) and travel through the sympathetic chain to reach the heart, where postganglionic fibers release norepinephrine. This neurotransmitter mainly acts on beta-1 adrenergic receptors in the SA and AV nodes and the myocardium, increasing the rate of depolarization, speeding conduction, and boosting contractile force. In simple terms, they raise heart rate and contractility (positive chronotropy and inotropy), which is why this option is the best match. The other functions—slowing the heart (parasympathetic), digestion, or respiration—are not the primary actions of cardiac sympathetic nerves.