The sympathetic trunks pass under the medial arcuate ligaments of the diaphragm, on top of the psoas major muscles, to enter the abdomen. As they descend within the abdomen, they give off the lumbar splanchnic nerves anteriorly. Lumbar splanchnic nerves arise from ganglia at L1 to L4 level (the L5 ganglion is usually missing).
The thoracic and lumbar splanchnic nerves pass into preaortic ganglia, so named because they lie primarily on the abdominal aorta. There, these presynaptic fibers synapse, and postsynaptic fibers pass into perivascular plexuses, or autonomic plexuses associated with the arteries supplying abdominal viscera. |  |
