A cluster of neuron cell bodies in the medulla oblongata of the brain that controls the reflexes affecting heart function and blood vessel diameter. The neurons fall into four functional groups depending on whether they stimulate or inhibit the heart; or dilate or constrict blood vessels. The centre receives nerve inputs from the cerebral cortex, limbic system, and hypothalamus in the brain, and also information about blood pressure (from baroreceptors in the great arteries), blood composition (from chemoreceptors), and physical activity (from proprioceptors in muscles and joints). Output to the heart and blood vessels is via the sympathetic and parasympathetic divisions of the autonomic nervous system, which control the contractility of cardiac muscle and rate of heartbeat.