Final answer:
The sympathetic system constricts arterioles to increase blood pressure, while the parasympathetic system has no significant effect on systemic blood vessels. However, exceptions exist where sympathetic input can cause dilation of blood vessels in certain areas.
Step-by-step explanation:
In the cardiovascular system, the sympathetic and parasympathetic divisions of the autonomic nervous system have opposite effects on blood vessels called arterioles. The sympathetic system constricts the arterioles, increasing blood pressure, while the parasympathetic system has no significant input on systemic blood vessels. However, there are exceptions to this general rule, such as the blood vessels in skeletal muscle that are more likely to dilate under sympathetic control. Additionally, the parasympathetic system can cause dilation of blood vessels in the erectile tissue of reproductive organs.