Answer
$x_{y}$
If some stimulus caused the blood pressure ( controlled condition) in the cardiovascular system to fall, baroreceptors ( pressure receptors) in the blood vessel walls would start firing at a lower rate. Neural messages indicating this decrease in firing of the baroreceptors ( afferent messages) would be sent to the medulla oblongata of the brain (control center) via an afferent pathway. The medulla would respond by sending neural messages via the efferent pathway to sensors in relevant effectors-- the heart and blood vessels. The blood vessels would respond by constricting, and the pacemaker in the heart would increase its rate of firing, which would increase the heart rate. These responses of these effectors would serve to raise the blood pressure. Because the combined response of the effectors acts to negate or reverse the initial change in the controlled condition, this response is considered a negative feedback.
Work Step by Step
If some stimulus caused the blood pressure ( a controlled condition) to decrease, the heart rate would increase in an effort to raise the blood pressure back to values within the normal range (110-120/70-80 mm. Hg). This response of the heart and blood vessels would be an attempt to restore homeostasis through negative feedback control, achieved through afferent messages of change sent to the brain (control center) which in turn would send efferent messages to the heart to increase its rate of contraction.
