Download Anatomy of the Sympathetic (Thoracolumbar) Division

Anatomy of the Sympathetic
(Thoracolumbar) Division
The cell bodies of the preganglionic neurons in the sympathetic division
lie in the lateral horns of the spinal cord from the segments T1 through
L2. The axon of the preganglionic neuron typically exits at the same
level to synapse with the cell bodies and dendrites of the postsynaptic
sympathetic neurons. These postsynaptic neuronal cell bodies make up
the paravertebral ganglia that lie close to the spinal cord (aroundor by the vertebrae) or sympathetic chain ganglia (the ganglia form
a chain like structure on either side of the vertebral column). As
described below, the sympathetic chain has ganglia adjacent to the
thoracolumbar vertebrae, as well as adjacent to some cranial and sacral
vertebrae.
Adjacent paravertebral ganglia are connected via ascending and
descending preganglionic sympathetic fibers forming longitudinal cords
running parallel to the spinal cord. These connecting branches may be
referred to as interganglionic rami (ramus = branch). Together with
the ganglia, they form the sympathetic trunk on either side
(bilateral) of the vertebral column. Its cephalic end continues into the
skull through the carotid canal, while caudally it converges with its
counterpart anterior to the coccyx.
As mentioned in a previous comparison table (row 4), the ANS has a
sequential two-neuron efferent pathway, where each autonomic
ganglion contains the synapse between the preganglionic neuron (the
neuron that exits the CNS) and the postganglionic neuron (the neuron
that innervates the target organ).
The presynaptic sympathetic fibers entering the sympathetic
chain may:
1. synapse immediately on the postsynaptic neuron in the ganglion located at
the same level it entered;
2. ascend or descend down the sympathetic trunk before synapsing in a
ganglion located at a different level;
3. pass through the sympathetic chain ganglia without synapsing at all,
synapsing instead in a prevertebral ganglion (also known as the collateral
ganglion).
As you will see shortly, the internal organs of the abdomen and pelvis
are primarily supplied by the fibers of this third pathway, while,
generally, structures located in the head, neck, body wall, limbs and
thoracic cavity are innervated by one the first two pathways.