Sympathetic chain is each of the pair of ganglionated longitudinal cords of the sympathetic nervous system, situated on either side of the vertebral column. The sympathetic trunk travels from the base of the skull to the coccyx, just lateral to the vertebral bodies.
The sympathetic trunk consists of bundled nerve fibers that run from the base of the skull to the coccyx. Along the length of the trunk are ganglia called sympathetic ganglia or paravertebral ganglia. The ganglia interact with the spinal nerves or their ventral rami by means of white and gray rami communicans.
- The whiter rami are afferent fibers to the ganglion and found only from T1 to L2 segments. These contain the preganglionic and afferent sensory fibers.
- The gray rami communicans are present in all segments. They are efferent fibers of the sympathetic ganglia. These contain the postganglionic fibers.
The superior end of the sympathetic chain is continued into the skull through the carotid canal, in the form of a plexus on internal carotid artery. The inferior end travels in front of the coccyx and converges with the trunk of other side to form a structure known as ganglion impar.
Parts of sympathetic chain:
The sympathetic chain is divided into the following parts, depending on the region of the body where the chain is present.
- Cervical part
- Thoracic part
- Abdominal Part
- Pelvic part
Cervical sympathetic chain:
The cervical part of the chain extends from the base of the skull to first rib, below which it becomes continuous with the thoracic part of the chain. In the neck, the cervical sympathetic chain lies embedded in the deep fascia between the carotid sheath and the prevertebral layer of deep fascia.
The cervical sympathetic chain possesses three ganglia, as described below:
Superior cervical ganglion:
It lies immediately below the skull and has the following branches.
- Internal carotid nerve: It accompanies the internal carotid artery into the carotid canal and forms a plexus around the artery.
- Gray rami communicans: They are given to anterior rami of upper four cervical spinal nerves.
- Arterial branches: These supply the common carotid and external carotid arteries and form plexus over them.
- Cranial nerve branches: Branches are given to IX (glossopharyngeal), X (vagus) and XII (hypoglossal) cranial nerves.
- Superior cardiac branch: This branch descends in the neck and takes part in the formation of cardiac plexus.
Middle cervical ganglion:
It lies at the level of carotid cartilage and has the following branches:
- Gray rami communicans: They are given to the anterior rami of 5th and 6th cervical spinal nerves.
- Thyroid branches: These supply the thyroid gland.
- Middle cardiac branch: It descends in the neck and takes part in the formation of cardiac plexus.
Inferior cervical ganglion:
In most people, this ganglion is fused with first thoracic ganglion and form the stellate ganglion. It is present between the first rib and transverse process of seventh cervical vertebra. It gives the following branches:
- Gray rami communicans: These are given to the anterior rami of seventh and eighth cervical spinal nerves.
- Arterial branches: These supply the subclavian and vertebral arteries.
- Inferior cardiac branch: It takes part in the formation of cardiac plexus.
Thoracic sympathetic chain:
The thoracic part of the sympathetic chain is continuous above with the cervical and below with the abdominal parts. The chain runs downward on heads of ribs and leaves the thorax on the side of the body of the 12th thoracic vertebra behind the medial arcuate ligament.
Thoracic sympathetic chain has 12 segmentally arranged ganglia. The first thoracic ganglion is often fused with inferior cervical ganglion to form stellate ganglion. Each ganglion has white and gray rami communicans passing to the corresponding spinal nerve. The first thoracic ganglion is often fused with inferior cervical ganglion to form stellate ganglion.
Thoracic sympathetic chain has the following branches:
- Rami communicans: As described above, the ganglia have white and gray rami communicans passing to the corresponding spinal nerve. The gray rami communicans are important because through these the postganglionic sympathetic fibers are distributed to various structures via the branches of spinal nerves.
- Postganglionic fibers: The first five ganglia give postganglionic fibers to heart, aorta, lungs and esophagus.
- Preganglionic fibers: Lower eight ganglia mainly give preganglionic fibers, which are grouped together to form the splanchnic nerves. The greater splanchnic nerve arises from ganglia 5 to 9. The lesser splanchnic nerve arises from ganglia 10 and 11. The lowest splanchnic nerve arises from ganglion 12. The splanchnic nerves supply the abdominal viscera, where they enter by piercing the crura of diaphragm.
Abdominal sympathetic chain:
The abdominal part is continuous above with the thoracic part and below with the pelvic part. It runs downward along the medial border of the psoas muscle on the bodies of lumbar vertebrae. This part of the chain possesses 4 or 5 segmentally arranged ganglia. The first and second are often fused together.
Abdominal sympathetic chain has the following branches:
- White rami communicans: These are found only in the first to ganglia, which they join with first two lumbar nerves respectively. These contain preganglionic and afferent sensory fibers.
- Gray rami communicans: These are present for all the ganglia and joint them with corresponding lumbar spinal nerves. These contain postganglionic fibers.