Nucleus of solitary tract

The nucleus of tractus solitarius (NTS), located in the lateral medulla oblongata, processes sensory information from cranial nerves VII, IX, and X, integrating it to maintain cardiovascular and respiratory homeostasis. It comprises two regions: rostral and caudal.

The rostral part, or gustatory nucleus, processes taste signals from the anterior two-thirds of the tongue (CN VII), posterior third (CN IX), and epiglottis (CN X). Sensory axons of these nerves synapse in the NTS, and the signal is relayed to the thalamus (ventral posterior medial or VPM nucleus), ultimately reaching the primary sensory cortex.

The caudal part of the nucleus of tractus solitarius regulates blood pressure, heart rate, and respiratory functions by receiving inputs from baroreceptors and chemoreceptors through cranial nerves IX and X:

• Baroreceptors, located near the bifurcation of the common carotids, the carotid sinus, and the aortic arch, transmit data that influence systemic blood pressure and heart rate via baroreceptor reflexes. These reflexes provide short-term blood pressure regulation by inducing heart rate decreases and vasodilation in response to elevated blood pressure, as demonstrated during a carotid sinus massage intended to suppress ventricular tachycardia.

• Similarly, chemoreceptors in the carotid bodies (on the carotid sinus) sense blood pH and gas levels and send signals through the IX and X cranial nerves to the caudal part of the nucleus of tractus solitarius. The NTS integrates these signals and projects to the reticular formation, parasympathetic preganglionic neurons, hypothalamus, and thalamus, thus forming circuits that modulate sympathetic activity and ensure homeostatic adaptations to varying blood gas levels. Dysregulation of this central mechanism is observed in congenital central hypoventilation syndrome.