The sinus nerve synapses in the brainstem. Arterial baroreceptors are sensitive to stretching of the walls of the vessels in which the nerve endings lie. Increased stretching augments the firing rate of the receptors and nerves, and recruits additional afferent nerves. Receptors within the aortic arch have a higher threshold pressure and are less sensitive than the carotid sinus receptors. Therefore, the carotid sinus receptors are normally the dominant arterial baroreceptor.
Receptors are sensitive to the rate of pressure change as well as to the steady or mean pressure.
Therefore, a combination of reduced mean pressure and pulse pressure reinforces the baroreceptor reflex. Figure 2 . Effects of arterial pressure on carotid sinus firing. Under normal physiological conditions, baroreceptor firing exerts a tonic inhibitory influence on sympathetic outflow from the medulla. Therefore, hypotension results in a disinhibition of the medullary centers.