Taste and sensory inputfrom the pharynx and viscera

Key point

■ The solitary tract and its nucleus in the caudal brainstem receive visceral inputs from the tongue (taste - CNN VII, IX, X), the carotid sinus (CN IX), thoracic, and abdominal viscera (CN X).

The solitary tract and its nucleus are located in the pons and the medulla oblongata extending from the level of the facial nucleus to the obex; they are sited (dorso)lateral to the parasympathetic nucleus of X (see Figs. 4.13, A28, A29). Their appearance is indistinct on gross section. The solitary tract receives visceral afferents from the head to do with taste (via cranial nerves VII, IX, X), blood pressure from the carotid sinus (CN IX), and stretch or chemical changes in the thoracic and abdominal viscera (CN X) and projects them to the medially located, nucleus of the solitary tract. Cranial nerve VII conveys taste from the rostral two-thirds of the tongue, while the glossopharyngeal and vagus nerves convey taste from the caudal third and the base of the epiglottis. The rostral portion of the nucleus, which receives taste sensory input, is also known as the gustatory nucleus.

The nucleus functions as a relay station (interneurons and projection neurons) for sensory input, and is involved in reflexes associated with the auditory tube, pharynx, larynx, oesophagus, trachea, thoracic and abdominal viscera.