The nucleus is located along the length of the medulla (with a small portion in the lower pons). The solitary tract runs in the middle of the nucleus, creating a speck of white matter (axons of the tract), surrounded by grey matter (the nucleus). This stands out on a stained section, which is where the name solitary comes from.
The solitary nucleus is divided into a rostral (towards the top) gustatory nucleus and caudal (towards the bottom) cardiorespiratory nucleus. The cardiorespiratory nucleus can be further divided into a cardiovascular center, which sits at the midline of the nucleus, and a respiratory center, which is located laterally.
Inputs to the solitary nucleus
As well as taste from nerves VII, IX and X, the solitary nucleus handles information from the carotid (from IX) and aortic bodies and baroreceptors (from X), which controls blood volume.
Information about the gut wall, as well as stretch of the lungs and dryness of mucous membranes, also synapses at the solitary nucleus.
Outputs from the solitary nucleus
From the solitary nucleus, most information goes to the hypothalamus and cingulate gyrus, as well as to other nuclei in the brainstem (such as visceral motor or respiratory centres). There is not much conscious awareness of visceral sensation (visceral pain is not part of this system), most results are reflexes or unconscious.
