Sensory fibers in the viscera originate from the cranial and spinal nerves with the cell bodies located in the posterior root ganglia. Their distal processes mostly course along with sympathetic but also parasympathetic nerves, reaching the viscera while their central processes pass via the dorsal (and occasionally the ventral) roots. The density of innervation of the viscera by spinal afferents is small compared with the density of afferent innervation in the skin and probably also in many deep somatic tissues. As Ness and Gebhart state, "Numerically, visceral afferents have been estimated to compose 5-15% of the neuronal cell bodies in the dorsal root ganglia at the spinal segments receiving maximal visceral afferent input. The relative number of spinal neurons that respond to visceral afferent input at these same spinal segments is, however, estimated to be 56-75%, supporting the assertion that visceral afferent terminals are widely distributed in the spinal cord." Therefore, a few visceral afferent fibers can activate many neurons in the spinal cord through extensive functional divergence.
Was this article helpful?