The solitary tract is a bundle of sensory fibers which runs longitudinally through the posterolateral region of the medulla, descending to the upper cervical segments of the spinal cord. It is composed of descending fibers of the vagus, glossopharyngeal, facial nerves, and primary sensory fibers. The solitary tract is surrounded by grey matter of the solitary nucleus, which is made up of nerve cell bodies. The solitary tract carries afferent information from stretch receptors and chemoreceptors in the walls of the cardiovascular, respiratory, and intestinal tracts. The information is integrated to a degree within the solitary nucleus, and then passed on either to other structures within the brainstem that control reflexive responses, or upwards to the forebrain for further processing.