What Is the Sympathetic Trunk?

The sympathetic trunk is a pair of structures alongside the spinal cord that makes up a key component of the sympathetic nervous system. It consists of chains of nerve cells linked together, with periodically spaced ganglia, clusters of sympathetic nerve cells used for information processing. Also known as the ganglionic cord or sympathetic chain, these structures run from the skull to the tailbone and carry a variety of signals to and from the viscera of the body. Damage to the nerves as a result of injury or disease can be problematic.

Some nerves that perform tasks inside the sympathetic nervous system arise directly from this structure. These include the splanchnic nerves, which carry signals to organs like the heart. Additionally, the sympathetic trunk connects with the spinal nerves with structures called rami communicantes. Some of these are covered in a myelin sheath, and are known as white rami communicantes, while others are unmyelinated, and classified as “grey” in a reference to the appearance of their exposed nerve cells.

Structurally, the two chains of the sympathetic trunk are symmetrical. They create a complex series of connections between the spinal nerves and the nerves of the sympathetic nervous systems. These allow for automation of critical functions, like contractions to aid digestion. Feedback is also provided through the nerves, to allow the brain to coordinate internal functions and address problems as they arise.

Simplified drawings of the spinal cord and neighboring structures may not include the sympathetic trunk and all its connections, for the purpose of clarity and readability. They will be added for drawings that specifically discuss this part of the anatomy. Schematics of the complex interconnections through the rami communicantes can also be provided. These illustrate the various ways signals can be sent through the sympathetic trunk and spinal cord to facilitate tasks from walking to processing bodily wastes.

As with other parts of the nervous system, the sympathetic trunk can be the site of tumors. These most commonly arise in the sympathetic ganglia, which contain large numbers of cells. If these begin to divide and replicate in error, they can create a growth, which may be malignant in nature. It will spread along the sympathetic trunk and neighboring structures and can create problems like paralysis and incontinence, depending on the location of the growth. In surgery, a doctor can carefully remove the tumor and attempt to retain as much function as possible.