Baroreceptors are present in the atria of the heart and vena cavae, but the most sensitive baroreceptors are in the carotid sinuses and aortic arch. While the carotid sinus baroreceptor axons travel within the glossopharyngeal nerve (CN IX), the aortic arch baroreceptor axons travel within the vagus nerve (CN X). Baroreceptor activity travels along these nerves directly into the central nervous system to excite (glutamatergic) neurons within the nucleus of the solitary tract (NTS) in the brainstem. Baroreceptor information flows from these NTS neurons to both parasympathetic and sympathetic neurons within the brainstem.