Learning Modules - Medical Gross Anatomy
Introduction to Autonomics, Part 1 - Page 5 of 8

    
The paravertebral ganglia consist of the right and left sympathetic chains or trunks. These ganglia are home to many postsynaptic sympathetic nerve cell bodies, and the site of many synapses between presynaptic sympathetic fibers and postsynaptic sympathetic neuron cell bodies. The sympathetic chains lie next to the vertebral column throughout its length, running across the necks of the ribs in the thorax and along the vertebral bodies in the abdomen. There is approximately one ganglion associated with each spinal cord segment, except in the cervical region and the sacral region. Adjacent ganglia of the sympathetic chain are connected to each other by interganglionic rami which contain sympathetic nerve fibers ascending or descending between ganglia.
 
The presynaptic sympathetic nerve fibers originate in the lateral horns of spinal cord segments T1-L2. From the lateral horns, all of these fibers must reach the sympathetic trunk. Presynaptic sympathetic fibers exit the spinal cord in the ventral roots (because they are motor fibers), pass through the spinal nerves and eventually enter the ventral primary rami of spinal cord segments T1-L2. Shortly after entering the ventral primary rami, the presynaptic sympathetic fibers exit the ventral primary rami via white rami communicantes which carry the presynaptic sympathetic fibers to the sympathetic trunk. The white rami communicantes are so named because they are collections of myelinated (therefore white-ish) axons communicating with the ventral primary rami. White rami communicantes are only found between spinal cord segments T1-L2 because there are no presynaptic sympathetic nerve fibers originating above or below those levels.

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