Lumbar splanchnic nerves

Lumbar splanchnic nerves are visceral branches of the sympathetic trunks in the lumbar vertebral region. They arise from the four lumbar ganglia, on either side, and extend ventrally and medially to terminate in the prevertebral plexus. Amongst the four lumbar splanchnic nerves, the 1st, 2nd and 4th lumbar splanchnic nerves arise from the 1st, 2nd and 4th lumbar sympathetic ganglia, respectively. Whereas, the 3rd lumbar splanchnic nerve arises from both the 3rd and 4th lumbar sympathetic ganglia.

Like most other splanchnic nerves, the lumbar splanchnic nerves contains pre-ganglionic sympathetic neurons, which arise from the lower lumbar lateral horns of spinal cord and traverse un-relayed through the sympathetic trunk. They synapse with cell bodies of post-ganglionic sympathetic neurons within the ganglia inside the prevertebral plexus. More specifically, the 1st lumbar splanchnic nerve ends up in the coeliac, inferior mesenteric and superior hypogastric plexuses. 2nd lumbar splanchnic nerve ends up in the inferior mesenteric plexus only. Whereas, the 3rd and 4th terminate inside the superior hypogastric plexus.

From here onwards, the post-ganglionic sympathetic neurons invest the branches of the inferior mesenteric and other arteries to reach out to the glands and smooth muscle in the hindgut and lower abdominal and pelvic viscera.