What is the role of the sympathetic nervous system in the cardiovascular system?

The sympathetic nervous system plays a crucial role in preparing the body for "fight or flight" responses, particularly during periods of stress or acute physical activity. When activated, it releases catecholamines, such as adrenaline, which lead to physiological changes that support increased cardiac activity. This includes a rise in heart rate and enhanced contractility of the heart muscle, allowing for more efficient blood flow to vital organs and muscles during stressful situations. Such adaptations are necessary for optimal performance and survival in challenging circumstances.

In contrast, the other options reflect functions that do not align with the primary role of the sympathetic nervous system. The decrease in heart rate at rest is typically managed by the parasympathetic nervous system, while maintaining a constant cardiac output and lowering blood pressure during sleep also relates more significantly to the parasympathetic branch and overall homeostatic processes rather than the activation of the sympathetic nervous system.