Fig. 1.

Illustrates the pelvic nerve dichotomy (A) and viscero-visceral convergence of colon and bladder afferent fibers on to spinal dorsal horn neuron (B). A: Although the primary sensory neurons are pseudounipolar cells, retrograde labeling of bladder and colon shows colabeling of dorsal root ganglion (DRG) soma in the lumbosacral spinal cord, suggesting that there are two axon collaterals innervating two pelvic structures. Therefore, sensitization of a spinal neuron by inflammation of one organ may influence the sensitivity of the noninflamed organ innervated by the axon collateral. B: Common convergence of two primary sensory afferents from two organs a spinal dorsal neuron is another neural pathway which can exhibit cross-organ sensitization. It has been documented that a small proportion of colorectal distension-sensitive neurons are also sensitive to urinary bladder distension and most of these neurons are in the deeper laminae of the spinal cord.