PARASYMPATHETIC

Anatomy. Parasympathetic innervation of the urinary system is derived from cranial and sacral sources. Both sources send presynaptic fibers all the way to the target organ, where they synapse with intrinsic (intramural) postsynaptic neurons.

The cranial source, which innervates the kidneys and upper ureters, is the vagus nerve; it conveys presynaptic fibers through the celiac and aorticorenal ganglia to the intrinsic renal and upper ureteric plexuses.

The sacral source, which innervates the remainder of the ureters and bladder, begins in the S2-S4 spinal cord segments, which contains neurons that give rise to presynaptic parasympathetic fibers. These fibers enter the initial portions of spinal nerves S2-S4 and then exit via pelvic splanchnic nerves, which convey them to the intrinsic plexuses of the ureters and bladder. Of note, the upper ureter may receive branches of these parasympathetic fibers, even though its primary source of parasympathetic innervation is the vagus nerve.