Sympathetic nerves run on the front surface of the spinal column and not in the spinal canal with the nerves that provide sensation and strength to your legs. The sympathetic nerves are part of the autonomic nervous system, which basically controls functions such as blood flow and temperature regulation to the arms and legs, sweating, heart rate, digestion, and blood pressure.
Sympathetic nerves are nerve fibers that originate in the spinal cord (from T1 to L2/L3 levels) and spread out to various organs. They prepare the body for stressful or emergency situations.
🔹 What Do They Do?
They activate physiological changes such as:
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Increased heart rate
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Dilated pupils
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Bronchodilation (airways open up)
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Inhibition of digestion
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Release of glucose from the liver
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Increased blood flow to muscles
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Sweating
Essentially, they gear the body up for action.
🔹 Pathway Overview:
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Preganglionic neurons start in the spinal cord.
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They travel to sympathetic ganglia (like the sympathetic chain).
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There, they synapse with postganglionic neurons.
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Postganglionic neurons extend to target organs (heart, lungs, pupils, etc.).
🔹 Neurotransmitters Involved:
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Acetylcholine (ACh) – used at the ganglia (preganglionic to postganglionic).
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Norepinephrine (NE) – main neurotransmitter released at the organ level by postganglionic neurons.
Sympathetic nerves arise from near the middle of the spinal cord in the intermediolateral nucleus of the lateral grey column, beginning at the first thoracic vertebra of the vertebral column and are thought to extend to the second or third lumbar vertebra. Because its cells begin in the thoracolumbar division – the thoracic and lumbar regions of the spinal cord – the sympathetic nervous system is said to have a thoracolumbar outflow. Axons of these nerves leave the spinal cord through the anterior root. They pass near the spinal (sensory) ganglion, where they enter the anterior rami of the spinal nerves.
However, unlike somatic innervation, they quickly separate out through white rami connectors (so called from the shiny white sheaths of myelin around each axon) that connect to either the paravertebral (which lie near the vertebral column) or prevertebral (which lie near the aortic bifurcation) ganglia extending alongside the spinal column.
To reach target organs and glands, the axons must travel long distances in the body, and, to accomplish this, many axons relay their message to a second cell through synaptic transmission. The ends of the axons link across a space, the synapse, to the dendrites of the second cell. The first cell (the presynaptic cell) sends a neurotransmitter across the synaptic cleft, where it activates the second cell (the postsynaptic cell). The message is then carried to the final destination.
Presynaptic nerves’ axons terminate in either the paravertebral ganglia or prevertebral ganglia. There are four different paths an axon can take before reaching its terminal. In all cases, the axon enters the paravertebral ganglion at the level of its originating spinal nerve. After this, it can then either synapse in this ganglion, ascend to a more superior or descend to a more inferior paravertebral ganglion and synapse there, or it can descend to a prevertebral ganglion and synapse there with the postsynaptic cell.[10]
The postsynaptic cell then goes on to innervate the targeted end effector (i.e. gland, smooth muscle, etc.). Because paravertebral and prevertebral ganglia are close to the spinal cord, presynaptic neurons are much shorter than their postsynaptic counterparts, which must extend throughout the body to reach their destinations.
A notable exception to the routes mentioned above is the sympathetic innervation of the suprarenal (adrenal) medulla. In this case, presynaptic neurons pass through paravertebral ganglia, on through prevertebral ganglia and then synapse directly with suprarenal tissue. This tissue consists of cells that have pseudo-neuron like qualities in that when activated by the presynaptic neuron, they will release their neurotransmitter (epinephrine) directly into the bloodstream.
In the sympathetic nervous system and other peripheral nervous system components, 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 sympathetic nervous system are located between the first thoracic segment and the 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.
The ganglia include not just the sympathetic trunks but also the cervical ganglia (superior, middle and inferior), which send sympathetic nerve fibers to the head and thorax organs, and the celiac and mesenteric ganglia, which send sympathetic fibers to the gut.
| Organ | Nerves[rx] | Spinal column origin[rx] |
|---|---|---|
| stomach |
|
T5, T6, T7, T8, T9, sometimes T10 |
| duodenum |
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T5, T6, T7, T8, T9, sometimes T10 |
| jejunum and ileum |
|
T5, T6, T7, T8, T9 |
| spleen |
|
T6, T7, T8 |
| gallbladder and liver |
|
T6, T7, T8, T9 |
| colon |
|
|
| pancreatic head |
|
T8, T9 |
| appendix |
|
T10 |
| bladder |
|
S2-S4 |
| kidneys and ureters |
|
T11, T12 |
What are the sympathetic nerves and why are sympathetic blocks helpful?
Nervous SystemThe autonomic nervous system is responsible for controlling bodily functions that you do not think about or have direct control over. However, there is a connection between the central nervous system (that you have control over) and the autonomic nervous system. Regulation of the connection can become altered, usually secondary to an injury. When regulation of the sympathetic nervous system is altered, various pain states can occur including complex regional pain syndrome, also known as Reflex Sympathetic Dystrophy(RSD).
What is a sympathetic block and why is it helpful?
A sympathetic nerve block involves injecting numbing medicine around the sympathetic nerves in the low back or neck. By doing this, the sympathetic nervous system in that area is temporarily ‘switched’ off in hopes of reducing or eliminating pain. If pain is substantially improved after the block, then a diagnosis of sympathetically mediated pain is established. The therapeutic effects of the anesthetic can occur, at times, longer than would be normally expected. The goal is to reset the sympathetic tone to a normal state of regulation. If the initial block is successful, then additional blocks may be repeated if the pain continues to sequentially diminish.
What will happen to me during the procedure?
An IV will be started for safety, and so relaxation medicine can be given if needed. After lying on an x-ray table, the skin over the area to be injected will be well cleansed. Next, the physician will numb a small area of skin with numbing medicine (anesthetic) which stings for a few seconds. The physician will use x-ray guidance to direct a needle to the sympathetic plexus of nerves. The physician will then inject contrast dye to confirm that the medicine only goes over the targeted sympathetic nerves. Once this occurs, numbing medicine (anesthetic) will then be slowly injected.
What should I do and expect after the procedure?
20-30 minutes after the procedure you will move the affected area to try to provoke your usual pain. You may or may not obtain improvement in the first few hours after the injection depending upon if the sympathetic nerves are carrying your pain signals. You may notice increased warmth in the affected extremity for 4-18 hours after the block. If the sympathetic nerves in the neck are injected (stellate ganglion), you will also notice a slight drooping of the eyelid and redness of the eye for several hours. This is normal, and will resolve over 4-18 hours. You should report your remaining pain (if any) and record the relief you experience during the next week on a “pain diaryâ we will provide. *Mail or fax the completed pain diary back one week after the injection so that your treating physician can be informed of your results and plan future tests and/or treatment if needed.
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You may notice a slight increase in your pain lasting for several days as the numbing medicine wears off. You might also experience mild pain at the injection site for several days. Ice will typically be more helpful than heat in the first 2-3 days after the injection. You may take your regular medicines after the procedure, but try to limit your pain medicines the first 4-6 hours after the procedure so that the diagnostic information obtained is accurate.
On the day of the injection, you should not drive and should avoid any strenuous activities. On the day after the procedure, you may return to your regular activities. If your pain is improved from this procedure, start your regular exercise/activities in moderation. Even if you are significantly improved, gradually increase your activities over 1-2 weeks to avoid recurrence of your pain.
