The major stimulus here is a person experiencing a fall in blood pressure (BP). The fall in blood pressure will be sensed by sensory organs that monitor the blood pressure which are the pressure receptors in the carotid and the aorta (the arteries will be less stretched). Therefore, there will be less neuronal impulses coming from the carotid and arterial baroreceptors to the medulla. The response of the medulla is to increase symphatetic stimulation and decrease parasymphatetic stimulation to the heart and blood vessels. The response will be to increase heart rate and contractility as well as vasoconstriction, and therefore rise in the blood pressure.
The consequent rise in the blood pressure will provide negative feedback by stimulating the baroreceptor response hence decreasing medullary efferents and then decreasing heart rate and contractility to normal.
