Parasympathetic Stimulation Increases Activity of the Enteric Nervous System. The
parasympathetic supply to the gut is divided into cranial and sacral divisions, which were discussed in
Chapter 60. Except for a few parasympathetic fibers to the mouth and pharyngeal regions of the
alimentary tract, the cranial parasympathetic nerve fibers are almost entirely in the vagus nerves. These fibers provide extensive innervations to the esophagus, stomach, and pancreas and somewhat
less to the intestines down through the first half of the large intestine.
The sacral parasympathetics originate in the second, third, and fourth sacral segments of the
spinal cord and pass through the pelvic nerves to the distal half of the large intestine and all the way to
the anus. The sigmoidal, rectal, and anal regions are considerably better supplied with parasympathetic
fibers than are the other intestinal areas.These fibers function especially to execute the defecation
reflexes, discussed in Chapter 63
