Sympathetic Chain Ganglia

The sympathetic chain ganglia, also known as the paravertebral ganglia, are a series of interconnected nerve cell clusters located bilaterally along the vertebral column. They form part of the sympathetic nervous system and play a critical role in distributing sympathetic (fight-or-flight) output from the thoracolumbar spinal cord to the entire body. The chains run from the base of the skull to the coccyx and are involved in innervating smooth muscle, cardiac muscle, and glands throughout the thorax, abdomen, pelvis, and limbs.

Structure

The sympathetic chains consist of a vertical series of ganglia connected by longitudinal nerve fibers. Each ganglion contains postganglionic sympathetic neurons that relay signals from the spinal cord. The chains are located bilaterally to the vertebral bodies, anterior to the heads of the ribs in the thoracic region.

Number and Distribution

• Cervical region: 3 ganglia (superior, middle, inferior)
• Thoracic region: 11 or 12 ganglia
• Lumbar region: 4 or 5 ganglia
• Sacral region: 4 ganglia
• Coccygeal ganglion: 1 unpaired ganglion (ganglion impar)

Thoracic Sympathetic Chain

The thoracic portion of the sympathetic chain lies on the heads of the ribs and contains 11–12 ganglia. These ganglia receive input from spinal nerves T1 to T12 and contribute fibers to the thoracic viscera and abdominal plexuses.

Thoracic Ganglia Connections

• White rami communicantes: Carry preganglionic sympathetic fibers from spinal nerves into the chain (present only from T1–L2)
• Gray rami communicantes: Carry postganglionic sympathetic fibers back to spinal nerves (present at every level)

Pathways Through the Chain

Preganglionic sympathetic fibers entering the chain may:

• Synapse at the same level: Then exit via gray rami to spinal nerves
• Ascend or descend: To synapse in a higher or lower ganglion
• Pass through without synapsing: To form splanchnic nerves and synapse in prevertebral ganglia

Splanchnic Nerves Arising from Thoracic Ganglia

• Greater splanchnic nerve (T5–T9): Passes to the celiac ganglion
• Lesser splanchnic nerve (T10–T11): Passes to the aorticorenal ganglion
• Least (lowest) splanchnic nerve (T12): Passes to the renal plexus

Target Organs and Functions

Postganglionic sympathetic fibers from the thoracic chain ganglia innervate:

• Thoracic viscera: Heart, lungs, esophagus, via cardiac, pulmonary, and esophageal plexuses
• Blood vessels: Vasoconstriction of thoracic and abdominal vessels
• Sweat glands and arrector pili: In the thoracic and upper abdominal walls
• Abdominal viscera: Indirectly via splanchnic nerves and prevertebral ganglia

Histological Structure

Each sympathetic ganglion contains:

• Multipolar neuronal cell bodies: Of postganglionic sympathetic neurons
• Satellite glial cells: Supporting cells surrounding neuron bodies
• Connective tissue capsule: Enclosing the ganglion

Clinical Significance

• Sympathectomy: Surgical disruption of the chain for conditions like hyperhidrosis or vascular insufficiency
• Pancoast tumors: Can compress upper thoracic ganglia causing Horner’s syndrome (ptosis, miosis, anhidrosis)
• Referred pain: Thoracic ganglia contribute to visceral pain pathways, leading to somatic referral patterns (e.g., cardiac pain felt in the arm)

Topographic Summary

• Location: Bilateral to the vertebral column, anterior to the heads of ribs in thorax
• Number: Approximately 22–24 ganglia (3 cervical, 11–12 thoracic, 4–5 lumbar, 4 sacral, 1 coccygeal)
• Functions: Relay center for sympathetic innervation to thoracic and abdominal organs, vessels, skin
• Key branches: White and gray rami communicantes, splanchnic nerves