The sympathetic part of the autonomic division of the PNS leaves thoracolumbar regions of the spinal cord with the somatic components of spinal nerves T1 to L2 (Fig. 1.44). On each side, a paravertebral sympathetic trunk extends from the base of the skull to the inferior end of the vertebral column where the two trunks converge anteriorly to the coccyx at the ganglion impar. Each trunk is attached to the anterior rami of spinal nerves and becomes the route by which sympathetics are distributed to the periphery and all viscera.
Fig. 1.44: Sympathetic Part of the Autonomic Division of the Peripheral Nervous System. Adapted from Drake, Mitchell & Vogl. Gray’s Anatomy for Students, 5th Ed. 2024. © Elsevier.
Visceral motor preganglionic fibers leave the T1 to L2 part of the spinal cord in anterior roots. The fibers then enter the spinal nerves, pass through the anterior rami, and into the sympathetic trunks. One trunk is located on each side of the vertebral column (paravertebral) and positioned anterior to the anterior rami. Along the trunk is a series of segmentally arranged ganglia formed from collections of postganglionic neuronal cell bodies where the preganglionic neurons synapse with postganglionic neurons. Anterior rami of T1 to L2 are connected to the sympathetic trunk or to a ganglion by a white ramus communicans, which carries preganglionic sympathetic fibers and appears white because the fibers it contains are myelinated.
Preganglionic sympathetic fibers that enter a paravertebral ganglion or the sympathetic trunk through a white ramus communicans may take the following four pathways to target tissues.
