What triggers the autonomic actions that prevent the fall in arterial pressure? First, the carotid baroreceptor reflex is constantly adjusting the autonomic control of the cardiovascular system in response to any changes in the arterial pressure. However, physiologists do not, in fact, detect changes in arterial pressure as exercise begins. Thus, while the carotid baroreceptor reflex is important, it cannot by itself explain the response to exercise, since typically the pressure does not change as exercise begins.