Even at resting levels of blood pressure, arterial baroreceptor discharge activates NTS neurons. Some of these NTS neurons are tonically activated by this resting blood pressure and thus activate excitatory fibers to the nucleus ambiguous and dorsal nucleus of vagus nerve to regulate the parasympathetic nervous system. These parasympathetic neurons send axons to the heart and parasympathetic activity slows cardiac pacemaking and thus heart rate. This parasympathetic activity is further increased during conditions of elevated blood pressure. Note that the parasympathetic nervous system is primarily directed toward the heart.