In order to understand the autonomic innervation of the pelvis, one must recall that the sympathetic outflow of the autonomic nervous system (ANS) originates in the lateral or intermediolateral column of gray matter within the thoracolumbar region of the spinal cord (T1 through L2). Some sympathetic fibers travel in the sympathetic chain into the pelvis, while other sympathetic fibers enter the pelvis from the superior hypogastric plexus, which passes over the common iliac arteries. Recall that the different regions of the sympathetic chain are named according to the portion of the vertebral column along which the chain lies. So, there is a cervical, thoracic, lumbar, and a sacral portion of the sympathetic chain. Therefore sympathetics ultimately reaching the pelvis have descended into the inferior hypogastric plexus from the lumbar region.
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