Corpus: Sympathetic trunk

The sympathetic trunk is a chain of 22-23 autonomic ganglia running from the base of the skull to the coccyx alongside the spinal column. These ganglia are connected by nerve fibres, forming a structure similar to a rope ladder. Due to their location, these ganglia are also called "paravertebral ganglia."

The peripheral efferent pathway of the autonomic nervous system involves two neurons. In the sympathetic nervous system, the cell bodies of the first efferent neuron are located in the lateral horns of the thoracic and upper lumbar spinal cord (C7-L2).

2.1. Preganglionic fibres

Preganglionic fibres emerge with motor fibres from the anterior root of the spinal cord and travel via the white communicating branch to a ganglion of the sympathetic trunk. Here, they synapse with a second neuron, whose fibres then travel to the target organs such as blood vessels, the heart, bronchi, salivary glands, and the eyes.

2.2. Postganglionic fibres

After the synapse in the ganglion, postganglionic fibres return to the spinal nerve via the grey communicanting branch and travel with the spinal nerve to the target organs.

For the gastrointestinal tract, urinary bladder, and reproductive organs, the motor fibres bypass the sympathetic trunk and travel via splanchnic nerves to prevertebral ganglia, such as the coeliac ganglion, where they synapse. Preganglionic fibres leaving the sympathetic trunk without synapsing are called splanchnic nerves.

3.1. Cervical region

The cervical part of the sympathetic trunk contains three cervical ganglia enclosed within the deep layer of the cervical fascia, dorsal to the carotid sheath:

• Superior cervical ganglion
• Middle cervical ganglion
• Stellate ganglion

Part of the sympathetic trunk runs behind the subclavian artery, while another part runs in front of it into the thoracic cavity. As it progresses, the sympathetic trunk forms a loop around the subclavian artery, known as the ansa subclavia. The lowest cervical ganglion, called the inferior cervical ganglion, is fused with the first thoracic ganglion to form the stellate ganglion.

3.2. Thoracic region

In the thorax, the thoracic ganglia lie near the heads of the ribs, covered by the parietal pleura, and crossed by intercostal vessels and nerves.

3.3. Lumbar region

The lumbar part contains four lumbar ganglia located medial to the psoas major muscle's origin.

3.4. Sacral region

The sacral ganglia lie medial to the sacral foramina of the sacrum. The sympathetic trunk terminates at the unpaired ganglion impar, located near the coccyx.

• Carotid plexuses (internal, external, and common): Sympathetic fibres run to head organs via these plexuses.

• Cervical cardiac nerves (superior, medial, and inferior): Carry fibres to the heart.
• Rami interganglionares: Connect individual ganglia of the sympathetic trunk, carrying preganglionic and sensory fibres.
• Rami communicantes: Connect the ganglia to spinal nerves, including the white communicating branch (preganglionic fibres) and the grey communicating branch (postganglionic fibres).
• Rami cardiaci thoracici: These postganglionic fibres originate from thoracic ganglia and run directly to the heart
• Greater splanchnic nerve: This nerve carries preganglionic sympathetic fibres from spinal segments T5 to T9 to the abdominal aortic plexus.
• Lesser splanchnic nerve: This nerve carries preganglionic fibres from spinal segments T10 and T11 to the abdominal aortic plexus.

• Unnamed branches to the thoracic aortic plexus: These branches originate from the plexus along the aorta and innervate the esophagus and lungs.

• Lumbar splanchnic nerves: These nerves carry fibres to the common iliac artery and surrounding areas.

• Sacral splanchnic nerves: These branches run to the pelvic organs, contributing to autonomic regulation in the pelvis.