Regardless of the powerful role of metabolic control of coronary flow, neural influences can alter flow under certain circumstances. Sympathetic nerves to the heart and coronary vessels arise from the three sympathetic ganglia and the first four thoracic sympathetic ganglia, adrenergic fibers extensively innervate both the epicardial and the intramural arteries and veins.
Alpha-2 and beta-2 adrenergic receptors are found in the larger epicardial and intramural arteries, producing constriction and dilation, respectively. Relatively few parasympathetic (dilator) receptors are located in any of the coronary vessels; however, some direct coronary vasodilation that is mediated by the release of acetylcholine can be blocked by atropine. The coronary vessels do not have beta-1 adrenergic receptors, which appear to be limited to the myocardium. [SEE MISCONCEPTION