The lumbar splanchnic nerves are splanchnic nerves

Splanchnic nerves

The splanchnic nerves are paired nerves that contribute to the innervation of the viscera, carrying fibers of the autonomic nervous system as well as sensory fibers from the organs...

 that arise from the lumbar

Lumbar

In tetrapod anatomy, lumbar is an adjective that means of or pertaining to the abdominal segment of the torso, between the diaphragm and the sacrum ...

 part of the sympathetic trunk

Sympathetic trunk

The sympathetic trunks are a paired bundle of nerve fibers that run from the base of the skull to the coccyx.-Structure:...

 and travel to an adjacent plexus near the aorta

Aorta

The aorta is the largest artery in the body, originating from the left ventricle of the heart and extending down to the abdomen, where it branches off into two smaller arteries...

. They are originated from L1 and L2.

These nerves contain preganglionic sympathetic and visceral afferent fibers.

The site of synapse

Synapse

In the nervous system, a synapse is a structure that permits a neuron to pass an electrical or chemical signal to another cell...

 is found in the inferior mesenteric ganglion

Inferior mesenteric ganglion

The inferior mesenteric ganglion is a ganglion located near where the inferior mesenteric artery branches from the abdominal aorta....

 and the postsynaptic fibers innervate the smooth muscle

Smooth muscle

Smooth muscle is an involuntary non-striated muscle. It is divided into two sub-groups; the single-unit and multiunit smooth muscle. Within single-unit smooth muscle tissues, the autonomic nervous system innervates a single cell within a sheet or bundle and the action potential is propagated by...

 and glands of the pelvic viscera and hindgut

Hindgut

The hindgut is the posterior part of the alimentary canal. In mammals, it includes the distal third of the transverse colon and the splenic flexure, the descending colon, sigmoid colon and rectum.-Blood flow:...

.