<P> The baroreflex or baroreceptor reflex is one of the body's homeostatic mechanisms that helps to maintain blood pressure at nearly constant levels . The baroreflex provides a rapid negative feedback loop in which an elevated blood pressure reflexively causes the heart rate to decrease and also causes blood pressure to decrease . Decreased blood pressure decreases baroreflex activation and causes heart rate to increase and to restore blood pressure levels . The baroreflex can begin to act in less than the duration of a cardiac cycle (fractions of a second) and thus baroreflex adjustments are key factors in dealing with postural hypotension, the tendency for blood pressure to decrease on standing due to gravity . </P> <P> The system relies on specialized neurons, known as baroreceptors, in the aortic arch, carotid sinuses, and elsewhere to monitor changes in blood pressure and relay them to the Medulla . Baroreceptors are stretch receptors and respond to the pressure induced stretching of the blood vessel in which they are found . Baroreflex induced changes in blood pressure are mediated by both branches of the autonomic nervous system: the parasympathetic and sympathetic nerves . Baroreceptors are active even at normal blood pressures so that their activity informs the brain about both increases and decreases in blood pressure . </P>

How does the baroreceptor reflex control changes in blood pressure
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