- Baroreceptors are the primary sensory component of the feedback loop which coordinates short-term, second-to-minute regulation of the systemic arterial pressure. These are sensory neurons whose cell bodies are present in vascular walls and that are mechanically depolarized by increases in the pressure experienced by the vascular walls.
- Baroreceptors are present in clusters primarily within the walls of the aortic arch and in the "Carotid Sinus", located in the internal carotid artery immediately above its branching from the carotid. From there, the neurons send axonal processes to the vasomotor center in the brainstem. The vasomotor center receives information about the systemic arterial pressure from baroreceptor neurons and then makes a regulatory decision as described further on the vasomotor center page.
- Baroreceptors are "Mechanoreceptors", neurons whose membrane potential is modulated by local changes in tension. Changes in systemic arterial pressure change the tension within the vascular wall which in turn modulates the membrane potential of the baroreceptors and thus the frequency with which they fire action potentials. Baroreceptors respond to increases in systemic arterial pressure by increasing the frequency at which they fire action potentials. The vasomotor center in turn receives input from the baroreceptors and makes a regulatory decision as described on the vasomotor center page.
- Quantitative Relationship
- Experimental data have shown that the Baroreceptors are largely silent until systemic arterial pressures of roughly 60 mm Hg. Their firing rate then increases in a roughly sigmoidal fashion after the 60 mm Hg threshold and reaches a maximum at pressures of 180 mm Hg. The steepest portion of the sigmoidal function is centered around 100 mm Hg, which is roughly the normal mean value for the systemic arterial pressure (i.e. Mean Arterial Pressure). Consequently, the impulse frequency of baroreceptors is most sensitive to changes directly around the normal mean arterial pressure, likely not a mere coincidence but rather an evolutionarily derived feature of physiology.