Visceral Pain

The sensory (afferent) innervation of the viscera is unique in that each organ is innervated by two spinal nerves arising from different vertebral levels, or a spinal and vagal nerve branch. Extensive central terminal arborization and convergence of visceral afferents onto second-order neurons make it difficult to localize the site of visceral pain. Chronic visceral pain and hypersensitivity typically involve persistent sensitization of visceral afferents by substances including inflammatory mediators released from immune-competent cells. Afferent sensitization drives central sensitization that further amplifies primary afferent input and which can also produce cross-organ sensitization due to the unique pattern of visceral innervation described above.