Three sets of nerves reach the bladder itself, its sphincter apparatus and the posterior urethra. Two of these sets belong to the autonomic system, a pathway derived from the thoracicolumbar outflow of the autonomic system, and a pathway derived from its sacral outflow. The former is usually termed sympathetic; the latter, parasympathetic. The remaining set (pudic nerves) belongs to the somatic system, and arises from sacral segments of the spinal cord.
—The origins of the fibers forming the thoracicolumbar outflow are shown in figure 1. They are finally concentrated in the presacral nerve, or superior hypogastric plexus, which has a superficial position under the peritoneum in front of the last lumbar vertebra. More than half of the total number of fibers in the presacral nerve are medullated preganglionic fibers, which are chiefly the downward continuations of mesially directed branches from the lumbar sympathetic ganglions; the nonmedullated fibers appear