Nerves in the Abdomen
The abdomen holds a number of important organs, but its physiology includes an important network of nerves as well. The organs of the abdomen are under the control of the autonomic nervous system. The nerves come from the splanchnic nerves and the vagus nerve (also known as cranial nerve X).
Additional abdominal nerves lie along the abdominal wall. They include the thoracoabdominal nerves, subcostal nerves, iliohypogastric nerves, and the ilioinguinal nerves.
The sympathetic nerves
The sympathetic (fight-or-flight) nerves include the abdominopelvic splanchnic nerves, which carry presynaptic fibers to the abdomen and pelvis. The fibers originate from cell bodies of the intermediolateral cell column (lateral horn) of the 7th thoracic through 2nd lumbar spinal-cord segments. The presynaptic fibers pass through anterior roots, anterior rami, and white communicating branches of the spinal nerves on their way to the sympathetic trunks. These presynaptic neurons pass through the paravertebral ganglia without synapsing and become the abdominopelvic splanchnic nerves. They then enter the prevertebral ganglia and autonomic plexuses located primarily on the abdominal aorta and its branches. There they synapse on the cell bodies of postsynaptic neurons. Here are the two main types of abdominopelvic splanchnic nerves:
Lower thoracic splanchnic nerves: These three nerves (greater, lesser, and least) contain the most presynaptic sympathetic fibers. They pass through the diaphragm to send fibers to the celiac, aorticorenal, and superior mesenteric ganglia and plexuses.
Lumbar splanchnic nerves: These nerves start at the abdominal sympathetic trunk and produce three or four lumbar splanchnic nerves that join the intermesenteric, inferior mesenteric, and superior hypogastric plexuses.
The parasympathetic nerves
The parasympathetic nerves include anterior and posterior vagal trunks that are the continuations of the left and right vagus nerves that follow the esophagus into the abdomen. They carry presynaptic parasympathetic and visceral afferent fibers to the aortic and periarterial plexuses.
The pelvic splanchnic nerves come from the anterior rami of the 2nd through 4th sacral nerve segments. They carry presynaptic parasympathetic fibers to the pelvic plexus. Parasympathetic ganglia are found in the walls of the abdominal organs.
Abdominal autonomic plexuses
The abdominal autonomic plexuses are networks that contain both sympathetic and parasympathetic fibers. They surround the aorta and its major branches and serve the abdominal and pelvic organs:
Aortic plexus: Located around the abdominal aorta and forms periarterial plexuses on the branches of the aorta
Celiac plexus: Located around the root of the celiac trunk; has a parasympathetic root that contain fibers from the vagus nerves and the sympathetic roots are the greater and lesser splanchnic nerves
Hepatic plexus: Located around the hepatic artery and comes from the celiac plexus
Renal plexus: Surround the renal arteries; formed by fibers from the celiac plexus, aortic plexus, and the least splanchnic nerve
Superior mesenteric plexus: Surrounds the superior mesenteric artery; has three branches: the median branch comes from the celiac plexus, and the lateral branches come from the lesser and least splanchnic nerves
Inferior mesenteric plexus: Surrounds the inferior mesenteric artery; has a medial root from the intermesenteric plexus and lateral roots from the lumbar ganglia of the sympathetic trunks
Intermesenteric plexus: The part of the aortic plexus located between the superior and inferior mesenteric arteries; gives rise to the renal, testicular, ovarian, and uteric plexuses
Superior hypogastric plexus: Located anterior to the bifurcation of the aorta; a continuation of the intermesenteric and plexus
Right and left inferior hypogastric plexus: Located on the sides of the rectum, uterine cervix, and the urinary bladder; formed by hypogastric nerves that come from the superior hypogastric plexus and receives parasympathetic fibers from the pelvic spranchnic nerves