Central (spinal) division
The central link of the sympathetic nervous system is located exclusively within the spinal cord. The main functional unit here is represented by sympathetic neurons, which form nuclei in the lateral horns (cornu laterale).
Topographically, this division has strict segmental alignment. The bulk of neurons lie in the spinal cord segments starting from the eighth cervical (C8) down to the twelfth thoracic (Th12). In some individuals, the lower limit of these nuclei may reach the second or third lumbar segment (L2–L3).
From a classification standpoint, these sympathetic neurons are defined as preganglionic. This means their nerve processes (axons) run to sympathetic ganglia. To leave the central nervous system, these axons run anteriorly and emerge together with motor fibers as part of the ventral roots of the spinal nerves.
Peripheral division
Once the fibers leave the spinal cord, they become part of the peripheral division of the sympathetic nervous system. This division is a complex system of pathways and switching stations providing innervation to internal organs.
The peripheral division includes the following anatomical structures:
- paired sympathetic trunks (trunci sympathici);
- sympathetic ganglia (ganglia sympathica), where impulse switching occurs;
- communicating branches ensuring communication with other nerves;
- visceral branches and plexuses heading directly to target organs.
Anatomy of the sympathetic trunks
The right and left sympathetic trunks (trunci sympathici) are the main highways of the peripheral division. They appear as two chains extending symmetrically along both sides of the vertebral column.
Their extent covers almost the entire body: the trunks begin high up at the very base of the skull and descend downwards, passing through the cervical, thoracic, lumbar, and sacral regions all the way to the coccyx.
An interesting anatomical feature is the termination of these trunks. At the lowest point, in the coccygeal region, the right and left sympathetic trunks approach each other and merge. Their fusion point is a special unpaired ganglion named ganglion impar.
Briefly: answers to topical questions
What topographical divisions is the sympathetic trunk divided into, and how many ganglia does each contain?
The sources explicitly mention the following topographical divisions of the sympathetic trunk and the number of ganglia for some of them:
- Cervical region — usually contains three ganglia: ganglion cervicale superius, ganglion cervicale medium, ganglion cervicothoracicum (stellatum).
- Thoracic region — contains 11–12 thoracic ganglia; another source indicates 10–12 pairs of thoracic ganglia.
- Lumbar region — mentioned as a division of the sympathetic trunk, but the number of its ganglia is not specified in the cited sources.
The right and left sympathetic trunks run along both sides of the vertebral column from the base of the skull to the coccyx and join in the region of the ganglion impar.
How do white communicating branches (rami communicantes albi) differ from grey ones (rami communicantes grisei)?
White and grey communicating branches differ in nerve fiber structure, origin, and direction.
| Characteristic | White communicating branches (rami communicantes albi) | Grey communicating branches (rami communicantes grisei) |
|---|---|---|
| Fiber type | Preganglionic myelinated | Postganglionic unmyelinated |
| Origin | From spinal nerves Th1–L2 | From all sympathetic trunk ganglia |
| Direction | To the sympathetic trunk ganglia | Return to the spinal nerves |
Which nerves arise from the cervical ganglia of the sympathetic trunk to the heart?
Cardiac nerves arise from the cervical ganglia of the sympathetic trunk to the heart. They carry postganglionic sympathetic fibers originating from the cervical and upper thoracic ganglia. These nerves head toward the organ and take direct part in forming the cardiac plexus (plexus cardiacus), providing sympathetic innervation of the heart together with parasympathetic fibers of the vagus nerve.
Into what two groups are the sympathetic ganglia of the peripheral division divided according to their location?
According to their location, the sympathetic ganglia of the peripheral division are divided into two main groups:
- Paravertebral ganglia — form the chain of the paired sympathetic trunk (truncus sympathicus) located on both sides of the spine.
- Prevertebral ganglia — located in the abdominal cavity and part of the sympathetic autonomic plexuses (e.g., the celiac plexus).
Intraorgan (intramural) ganglia are less characteristic of the sympathetic nervous system.
Which splanchnic nerves are formed from the branches of the thoracic sympathetic trunk?
Two main splanchnic nerves are formed from the branches of the thoracic sympathetic trunk:
- Greater splanchnic nerve (n. splanchnicus major) — arises from the V–IX thoracic ganglia.
- Lesser splanchnic nerve (n. splanchnicus minor) — is formed from the X–XI thoracic ganglia.
These nerves originate from the lower thoracic ganglia, pass through the hiatus of the crura of the diaphragm, and head toward the ganglia of the celiac plexus.
In the formation of which autonomic plexus of the abdominal cavity do the sympathetic splanchnic nerves participate?
Sympathetic splanchnic nerves participate in forming the celiac plexus (plexus celiacus), also called the solar plexus. It includes celiac ganglia, aorticorenal ganglia, and the superior mesenteric ganglion; the greater and lesser splanchnic nerves carrying preganglionic sympathetic fibers enter the plexus. Secondary plexuses accompanying vessels and innervating organs depart from the celiac plexus.
To remember the lower junction point of the trunks, use the association: 'Imperial ganglion' (ganglion impar) — one rules at the very bottom, uniting both sides.
Class and exam questions
In which spinal cord structures are the central sympathetic neurons located?
They are located in the lateral horns (cornu laterale) of the spinal cord, within segments C8 to Th12 (sometimes up to L2–L3).
How do preganglionic neuron axons leave the spinal cord?
Axons of preganglionic sympathetic neurons emerge from the spinal cord as part of the ventral roots of spinal nerves.
What is the ganglion impar?
This is an unpaired sympathetic ganglion located in the coccygeal region. The right and left sympathetic trunks connect within it.
What else to study on this topic
- Detailed study of the cytoarchitecture of the lateral horns of the spinal cord.
- Anatomical structure and topography of the sympathetic trunk ganglia.
- Classification of the communicating branches of the sympathetic trunk.
- Formation and course of visceral nerve plexuses.
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