Final answer:
When blood pressure drops below homeostatic levels, the medulla's cardioacceleratory center is activated and vasoconstriction occurs, but vasodilation does not. Baroreceptors signal the need for these corrective actions.
Step-by-step explanation:
If blood pressure drops below homeostatic levels, several physiological responses occur to restore balance. One response that will not occur is the decrease in sympathetic stimulation that would lead to vasodilation. Instead, the medulla's cardioacceleratory center will be activated, and the vasomotor center of the medulla will trigger vasoconstriction. The baroreceptors, located in the carotid sinuses and aortic arch, will be stimulated due to reduced stretch on their walls, signaling a drop in blood pressure. The combination of these responses, including increased heart rate and vasoconstriction, works to raise blood pressure back to normal levels.