Description
There are typically four sympathetic chain ganglia found at lumbar vertebral levels. They are known as lumbar paravertebral ganglia. The neurons in these ganglia are postganglionic sympathetic neurons that synapse with axons from preganglionic sympathetic neurons.
Preganglionic sympathetic axons emerge from the spinal cord at all thoracic nerve levels, in addition to the first and second lumbar nerve levels. At these levels, axons enter the sympathetic trunk via myelin rich axon tracts called the white rami communicans. Thus, only the first and second lumbar paravertebral ganglia are connected to the spinal nerves by a white rami communicans. The third and fourth lumbar paravertebral ganglia receive presynaptic sympathetic axons that have descended through the sympathetic trunk from higher levels. These tracts are the gray rami communicantes.
Postganglionic sympathetic axons leave the sympathetic trunk at all vertebral levels, via myelin poor tracts called the gray rami communicantes. Therefore, at each lumbar level, postsynaptic sympathetic fibers exit the lumbar paravertebral ganglia via a gray rami communicantes and travel to their targets throughout the body.
Neurons in the lumbar paravertebral ganglia will innervate blood vessels, sweat glands, and arrector pili muscles at segmental locations roughly corresponding to the dermatome of the equivalent spinal nerve.
In addition, axons passing through the first two lumbar paravertebral ganglia will give rise to lumbar splanchnic nerves. These nerves will synapse in the inferior mesenteric ganglia and target the hindgut and pelvic viscera.
