A baroreceptor is a collection of sensory nerve endings specialized to monitor changes in blood pressure. The main baroreceptors lie in the carotid sinuses and the aortic arch. Others are found in the walls of other large arteries and veins and some within the walls of the heart. Impulses from the receptors reach centers in the medulla oblongata, a part of the brain; from there autonomic activity is directed so that the heart rate and resistance of the peripheral blood vessels can be adjusted appropriately so that the necessary blood pressure is maintained.