Final answer:
A decrease in arterial pressure causes cerebral vessels to b) dilate in order to maintain adequate blood flow to the brain, which is a protective autoregulatory mechanism.
Step-by-step explanation:
A decrease in arterial pressure typically causes cerebral vessels to b) dilate.
This is a compensatory mechanism that the body uses to maintain adequate blood flow (or perfusion) to the brain when blood pressure drops.
The dilation of blood vessels helps to ensure that enough oxygen and nutrients reach the brain despite the lower pressure.
It's an example of an autoregulatory mechanism that is crucial to protecting the brain from ischemic conditions.
In contrast, if blood pressure is too high, the cerebral vessels may constrict to protect the brain from the potential damage that high pressure could cause.