Sympathetic nervous system: Encyclopedia II - Sympathetic nervous system - Organization

Sympathetic nervous system - Organization

The sympathetic nerves emerge near the spinal cord, inside the vertebral column, travelling along the path of the nerve roots. After a few twists and turns, sympathetic nerves branch off and travel into major organs, glands, and other groupings of nerves (called ganglia). [1]

Its cells originate toward the middle of the spinal cord in the intermediolateral cell column (or lateral horn), beginning with cells in the first thoracic segment of the spinal cord and extending into the second or third lumbar segments. Because its cells begin in the thoracic and lumbar regions of the spinal cord, the SNS is said to have a thoracolumbar outflow. Axons of these nerves leave the spinal cord and form connections (synapses) with several major hubs (ganglia), which then distribute the nerves to various parts of the body.

These hubs include the superior cervical ganglion (which sends sympathetic nerve fibers to the head), the celiac and mesenteric ganglia (which send sympathetic fibers to the gut), and two chain ganglia, which run parallel to and on either side of the spinal cord and extend to the thorax and peripheral parts of the body.

In order to reach the target organs and glands, the axons must travel long distances in the body, and, to accomplish this, many axons link up with the axon of a second cell. The ends of the axons do not make direct contact, but rather link across a space, the synapse.

In the SNS and other components of the peripheral nervous system, these synapses are made at sites called ganglia. The cell that sends its fiber is called a preganglionic cell, while the cell whose fiber leaves the ganglion is called a postganglionic cell. As mentioned previously, the preganglionic cells of the SNS are located between the first thoracic segment and the second or third lumbar segments of the spinal cord. Postganglionic cells have their cell bodies in the ganglia and send their axons to target organs or glands.

Adapted from the Wikipedia article "Organization", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki