Autonomic Nerves and Ganglia in Abdomen

The abdominal sympathetic nerves include the lumbar parts of the sympathetic trunks and their branches and contribute to the celiac, mesenteric, intermesenteric (abdominal aortic), hepatic, renal, adrenal, superior hypogastric, and other plexuses, including all subsidiary plexuses. Apart from the lumbar sympathetic trunks and branches, however, all the autonomic plexuses mentioned contain both sympathetic and parasympathetic elements.

The lumbar parts of the sympathetic trunks are directly continuous above with their thoracic counterparts behind the medial arcuate ligaments, whereas below, they pass over the pelvic brim and behind the common iliac vessels to become the sacral parts of the sympathetic trunks. The trunks lie in the retroperitoneal connective tissue on the anterolateral aspect of the lumbar vertebrae, along the medial margins of the psoas muscles; the right trunk is partly overlapped by the inferior vena cava and the cisterna chyli, and the left trunk is just lateral to the abdominal aorta. There are usually four lumbar ganglia on each side; the intervening cords may be single or split into two or even three strands. Each trunk supplies or receives communicating, visceral, vascular, muscular, osseous, and articular branches.

Only the upper two or, occasionally, three lumbar spinal nerves contribute white rami communicantes to the adjacent lumbar trunk ganglia, but every lumbar spinal nerve receives one or more gray communicating rami from adjacent trunk ganglia. White rami contain preganglionic and visceral afferent fibers, whereas gray rami contain vasomotor, sudomotor, and pilomotor fibers, which are distributed with the lumbar spinal nerves.

Three or four lumbar splanchnic nerves arise on each side and are seldom arranged symmetrically. The first lumbar splanchnic nerve arises from the first lumbar ganglion and ends in the renal, celiac, and/or intermesenteric plexuses, but some fibers may end directly in the duodenum, pancreas, and gastroesophageal junction. The second lumbar splanchnic nerve arises from the second lumbar ganglion and ends mainly in the intermesenteric plexus, although it may give direct contributions to the renal plexus, duodenum, and pancreas. The third lumbar splanchnic nerve usually originates from the third and fourth ganglia and ends in the upper part of the superior hypogastric plexus. The fourth lumbar splanchnic nerve, when present, arises from the fourth and/or the inconstant fifth lumbar ganglion and joins the lower part of the superior hypogastric plexus or the homolateral hypogastric nerve; it communicates with the ureteric and testicular plexuses.

Vascular fibers from the lumbar sympathetic trunks and their lumbar splanchnic branches pass to the abdominal aorta and the inferior vena cava, where they form the delicate intermesenteric and caval plexuses. All the aortic branches and vena caval tributaries are surrounded by subsidiary plexuses continuous with those around the parent vessels. Twigs from the right sympathetic trunk also supply the cisterna chyli and the commencement of the thoracic duct. Nerve fibers from the renal plexus, sometimes reinforced by fascicles from the second and third lumbar splanchnic nerves, usually join the plexus around the common or external iliac arteries.

Muscular, osseous and articular fibers supply the adjacent muscles, vertebrae, and joints in the lumbar region. They contain postganglionic (efferent) fibers, which are possibly vasomotor, and afferent fibers conveying impulses from meningeal, bony, and articular structures.

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