Posterior Mediastinum - LO 6

6. What is the sympathetic trunk? Describe its function.

The sympathetic division of the autonomic nervous system consists of pre- and postganglionic fibers, which typically (but not always) synapse in ganglia of the sympathetic trunk. Preganglionic fibers travel from the interomediolateral (IML) cell columns (lateral horns), out via the ventral roots of spinal nerves to the ventral primary rami (VPR), and then leave the spinal nerves via white rami communicantes (at levels T1-L2) to the sympathetic trunk (IML columns → ventral roots → VPR → white rami communicantes).

The sympathetic trunk consist of paravertebral ganglia and their connections. Once in the trunk, preganglionic fibers may:

• • synapse,

  • leave the trunk as part of a splanchnic nerve (without synapsing), or

  • ascend or descend the sympathetic trunk (and then either synapse, or leave the trunk).

From the synapse, postganglionic fibers carry signals back to the VPR of the spinal nerve via gray rami communicantes. These fibers can then be distributed by the DPR and VPR. While white rami communicantes are restricted to the T1-L2 levels, the sympathetic trunks extend the entire length of the spinal cord, and gray rami communicantes conduct postganglionic fibers back to VPRs at every level of the cord. In the neck, there are typically 2-3 sympathetic ganglia, whereas in the thorax there are typically sympathetic ganglia at every spinal level (T1-T12).