Greater Thoracic Splanchnic Nerve

The greater thoracic splanchnic nerve is the largest of the thoracic splanchnic nerves and serves as a major conduit for sympathetic fibers traveling to abdominal viscera. It arises from the thoracic sympathetic chain ganglia and carries preganglionic sympathetic fibers that pass through the diaphragm to synapse in the celiac ganglion. It plays a vital role in the autonomic innervation of the foregut organs.

Origin

The greater thoracic splanchnic nerve arises from the 5th to 9th thoracic sympathetic ganglia, though there can be minor variations between individuals. The fibers originate from the lateral horn of the spinal cord segments T5 to T9.

Course

After emerging from the sympathetic chain, the greater splanchnic nerve descends obliquely and medially across the vertebral bodies. It passes through the crus of the diaphragm (usually the right crus) to enter the abdominal cavity. Once in the abdomen, it terminates by synapsing in the celiac ganglion, located around the origin of the celiac trunk from the abdominal aorta.

Preganglionic sympathetic fibers: From spinal cord levels T5–T9
Visceral afferent fibers: Carry sensory information (especially pain) from abdominal viscera back to the spinal cord

Termination

The greater thoracic splanchnic nerve terminates in the celiac ganglion, where its preganglionic fibers synapse with postganglionic neurons. These postganglionic fibers then distribute via the celiac plexus to supply the foregut organs.

Innervation Targets (via Celiac Plexus)

Stomach
Liver and gallbladder
Spleen
Pancreas
Duodenum (proximal to major papilla)
Adrenal glands (direct innervation in some fibers)

Topographic Relationships

Posterior: Vertebral column
Anterior: Parietal pleura (costovertebral area), thoracic aorta
Inferior: Diaphragmatic crus
Lateral: Sympathetic trunk

Histological Structure

The greater splanchnic nerve is composed of bundles of myelinated and unmyelinated fibers:

Preganglionic fibers: Myelinated axons from the lateral horn of the thoracic spinal cord
Afferent fibers: Unmyelinated or lightly myelinated fibers conveying visceral sensation
Surrounding connective tissue: Protects and supports the nerve bundle

Clinical Significance

Referred pain: Foregut pathology (e.g., gastric ulcers) may produce referred pain to the T5–T9 dermatomes (epigastric and lower thoracic regions)
Splanchnic nerve blocks: Used in pain management (e.g., chronic pancreatitis, upper abdominal cancers)
Sympathectomy: Rarely, sectioning the splanchnic nerve may be considered in intractable pain syndromes

Topographic Summary

Origin: T5–T9 thoracic sympathetic ganglia
Course: Descends medially through thorax, passes through diaphragm
Termination: Synapses in celiac ganglion
Function: Sympathetic innervation of foregut viscera