Sympathetic trunk

At a glance

English

Sympathetic trunk

Latin (TA2)

Truncus sympathicus

System

Nerve

Region

Neck

Side

Paired, left and right

About the sympathetic trunk

Each sympathetic trunk, also called the sympathetic chain or gangliated cord, is a long cord of nerve fibres studded with ganglia. The two trunks lie one on each side of the vertebral column, beside the vertebral bodies, along its whole length. They are the main highway of the sympathetic division of the autonomic system.

In the neck the trunk lies behind the carotid sheath, on the prevertebral muscles, and carries superior, middle and inferior cervical ganglia. Its upper end follows the internal carotid artery into the carotid canal and continues as a plexus on that artery inside the skull. In the thorax it crosses the heads of the ribs behind the pleura. It passes behind the medial arcuate ligament into the abdomen, where it runs on the front of the lumbar vertebral bodies beside psoas, then descends over the sacrum medial to the anterior sacral foramina. Over the coccyx the two trunks join at a single ganglion impar.

The trunk links with every spinal nerve through rami communicantes. White rami, present only from T1 to L2, bring preganglionic fibres in from the spinal cord; grey rami return postganglionic fibres to all spinal nerves so that sympathetic supply reaches skin and vessels at every level. Because the outflow from the cord is confined to the thoracolumbar segments, the trunk is what allows fibres to climb to the cervical levels and descend to the lower lumbar and sacral levels before relaying. Several nerves also leave the trunk directly, among them cardiac branches and most of the splanchnic nerves to the abdominal ganglia.

Interrupting the cervical part of the trunk, for example by a tumour at the lung apex, causes Horner syndrome: a drooping upper lid, a small pupil and loss of sweating on that side of the face. Surgeons can divide the upper thoracic trunk to treat severe sweating of the hands.

Course and supply

Arises from

Begins at the base of the skull, its upper end continuing as the internal carotid plexus through the carotid canal.

Ends in

Ends anterior to the coccyx, where the right and left trunks meet at the ganglion impar.

Supplies

Lets preganglionic sympathetic fibres from T1 to L2 travel up and down to relay at other levels, returns postganglionic fibres to every spinal nerve, and gives rise to cardiac and splanchnic nerves.