The splanchnic nerves are autonomic nerves that arise from the thoracic, sympathetic chain of ganglia. They are paired nerves that supply the thoracic organs (heart and lungs) as well as the abdominal viscera, carrying efferent fibers of the autonomic nervous system as well as sensory afferent fibers from the visceral organs. All carry sympathetic fibers except for the pelvic splanchnic nerves, which carry parasympathetic fibers. There are three paired, splanchnic nerves: the greater, lesser, and least, which are composed of pre-ganglionic sympathetic axon from ganglia 6 to 10 of the thoracic sympathetic trunk.
The term splanchnic nerves include the thoracic splanchnic nerves, the lumbar splanchnic nerves, sacral splanchnic nerves, and cardiopulmonary nerves. Thoracic splanchnic nerves are splanchnic nerves that arise from the sympathetic trunk in the thorax and travel inferiorly to provide sympathetic innervation to the abdomen. The nerves contain preganglionic sympathetic and visceral afferent fibers.