It has been demonstrated in recent years that blood pressure is automatically regulated by alterations in the intra-arterial pressure. This automatic regulation is maintained by a system of pressoreceptor innervations localized in different areas of the vascular tree. The most important areas of such innervations are in the aorta and, especially, in the carotid sinus regions.
Because the carotid sinus regions have easily accessible nerve terminals and because they contain the most active pressoreceptors, these areas in man have been subjected to considerable investigation in recent years.
It was the illuminating experimental work of Hering1 which first demonstrated the presence of nerve connections between the carotid sinus regions and the medullary centers. He2 was also the first to demonstrate the occurrence of a drop in pressure on stimulation of the carotid sinus.
Hering found that in the adventitial coat of the pouched-out area of the internal carotid artery,