The Sacral Parasympathetic Innervation

Autonomic nerves distribute by a variety of methods. They are recognized as components of all spinal and some cranial nerves, but they also have a strong tendency to exhibit a hitch-hiker relationship to arteries and to other nerves. The perivascular plexuses of the head and neck, and of the thorax and abdomen, are especially typical of peripheral sympathetic distribution. In the parasympathetic division, preganglion& arising in the third, seventh, and ninth cranial nerves utilize the branches of the trigeminal nerve for passage to the structure innervated. The vagus nerve is a main parasympathetic route to structures of the neck and chest and its terminal fibers end in the abdomen by mingling in the celiac plexus with sympathetic postganglionic fibers. Intestinal autonomies are perivascular for both sympathetic and parasympathetic divisions. S t the brim of the pelvis the perivascular plexus of the aorta forms the hypogastric nerves which descend across the sacral promontory and distribute to the pelvic viscera without following their blood vessels, With these predominantly sympathetic nerves, parasympathetic fibers pass to the viscera of the pelvis and perineum, Anatomical description has recognized that the parasympathetic innervation of the descending and sigmoid portions of the large intestine is provided by components of the sacral parasympathetic roots from sacral nerves two, three, and four, which ascend from the pelvis to reach the colon. Implicit