[Plate 304, Autonomic Reflex Pathways: Schema]Autonomic Nerves
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Parasympathetic nerves
Preganglionic fibres
Provided by vagus nerve and sacral splanchnic nerves
Synapse with postganglionic fibres in the walls of the relevant organs
Vagus nerve (CN X)
Give rise to anterior and posterior vagal trunks in thorax
Trunks enter abdomen at the esophageal hiatus
Anterior trunk (mainly from the left vagus)
Enters anterior to the esophagus
Gives branches to the anterior surface of the stomach and to the liver
Posterior trunk (mainly from the right vagus)
Enters posterior to the esophagus
Gives branches to the posterior surface of the stomach and celiac plexus
Fibers pass inferiorly to root of superior mesenteric artery
Fibers contribute to perivascular plexuses
Accompanying celiac and superior mesenteric artery and their branches
Extend as far as the arterial supply (two thirds of the way along the transverse colon)
Pelvic splanchnic nerves
From spinal cord levels S2-S4
Emerge through pelvic sacral foramina
Ascend from pelvis running in sigmoid mesocolon and peritoneum of posterior abdominal wall
Supply distal one third of transverse colon, descending colon, sigmoid colon, and superior rectum
Postganglionic (postsynaptic) parasympathetic neurons found in enteric ganglia in wall of viscus
Sympathetic nerves
Right and left sympathetic trunks
Enter behind the medial arcuate ligament of the diaphragm
Descend along psoas major, with right trunk behind inferior vena cava (IVC)
Lie on anterolateral sides of lumbar vertebrae
Receive white rami communicantes from, and send gray rami communicantes to, ventral rami of L1-L3 spinal nerves