Vagus nerves (nn. vagi)
The topography of the right and left vagus nerves in the thoracic cavity has significant anatomical differences that are important to consider in operative surgery.
The right vagus nerve enters the thoracic cavity, lying anterior to the right subclavian artery. It is at this level that the right recurrent laryngeal nerve (n. laryngeus recurrens) branches off. This branch characteristically loops around the subclavian artery inferiorly and passes posteriorly. The right trunk itself continues its downward path: it passes posterior to the right brachiocephalic and superior vena cava veins, and lies on the posterior surface of the root of the right lung. Reaching the level of the lower margin of the right main bronchus, the nerve shifts to the posterior surface of the esophagus. In this zone, it actively gives off branches that form the esophageal plexus and, together with the muscular tube of the esophagus, enters the abdominal cavity.
The left vagus nerve has a different entry route. It appears anterior to the origin of the left subclavian artery and passes posterior to the left brachiocephalic vein. The nerve descends along the left side of the aortic arch. Here, the left recurrent laryngeal nerve branches off, looping around the aortic arch inferiorly and posteriorly. Next, the left trunk enters the narrow slit between the aortic arch and the left pulmonary artery, emerging onto the posterior surface of the root of the left lung. At its lower margin, the nerve crosses to the anterior surface of the esophagus, after which it also heads into the abdominal cavity.
The main function of these nerves in the thorax is the formation of a robust esophageal nerve plexus (plexus oesophageus), which closely interacts with the sympathetic trunks and spinal nerves.
Sympathetic trunks (trunci sympathici)
The thoracic portion of the sympathetic trunks is a chain of 11–12 thoracic ganglia (ganglia thoracica). These ganglia are interconnected by thin interganglionic branches.
Localization and syntopy: The trunks lie within the leaflets of the prevertebral fascia, strictly on the surface of the rib heads. They are located anterior to the intercostal blood vessels. On the right, the trunk passes lateral to the azygos vein, and on the left, lateral to the hemiazygos vein.
Main branches of the thoracic region:
- Communicating branches — run to the intercostal nerves to provide sympathetic innervation to the thoracic wall.
- Splanchnic nerves (nn. splanchnici) — essential pathways heading to the abdominal organs.
- Greater splanchnic nerve (*n. splanchnicus major)* is formed by branches originating from the V–IX thoracic ganglia.
- Lesser splanchnic nerve (*n. splanchnicus minor)* originates from the X–XI thoracic ganglia.
Both nerves descend along the lateral surface of the thoracic vertebral bodies, pass through the cleft in the crura of the diaphragm, and reach the ganglia of the celiac (solar) plexus.
- Branches participating in the formation of extensive nerve plexuses within the thoracic cavity itself.
Nerve plexuses of the thoracic cavity
The nerve plexuses of the thoracic cavity are critical reflexogenic zones. They form in the adipose tissue of the mediastinum from branches of the sympathetic trunks, vagus nerves, and phrenic nerves.
Four key plexuses are distinguished:
- Superficial left cardiopulmonary plexus. It is localized on the anterior surface of the left part of the aortic arch, as well as on the anterior surface of the upper part of the root of the left lung. Its branches head toward the aortic arch itself, cardiac tissues, pericardium, and left lung.
- Deep right cardiopulmonary plexus. It lies on the anterior surface of the trachea, posterior to the aortic arch. Branches originating from the plexus of the root of the right lung innervate the aortic arch, pericardium, and right lung.
- Esophageal plexus. It is located directly on the muscular wall of the esophagus, spanning the area from the level of the tracheal bifurcation all the way down to the diaphragm. It gives off regulatory branches to the esophagus and lungs.
- Prevertebral plexus. It is located on the anterior surface of the vertebral column. Anatomically, it is best expressed at the level of the III–VI thoracic vertebrae. It is formed primarily by branches of the sympathetic trunks. The plexus surrounds organs adjacent to the spine (including the descending aorta, azygos and hemiazygos veins, and thoracic duct). It has close connections with the esophageal and cardiopulmonary plexuses.
Clinical significance: Damage to the prevertebral plexus during trauma or surgery not only disrupts the innervation of nearby organs but also reflexively affects the functions of other mediastinal plexuses.
Briefly: answers to topical questions
How do the phrenic nerves run in the thoracic cavity?
The phrenic nerves (n. phrenicus) run in the thoracic cavity between the pericardium and the mediastinal pleura, anterior to the roots of the lungs, accompanied by the pericardiacophrenic vessels (vasa pericardiacophrenica).
The topography of the nerves differs:
- Right phrenic nerve — crosses anterior to the right subclavian artery, runs along the right wall of the superior vena cava and along the right surface of the pericardium to the diaphragm.
- Left phrenic nerve — runs along the left surface of the aortic arch (1–2 cm anterior to the ligamentum arteriosum — lig. arteriosum), and then descends along the left surface of the pericardium.
What branches does the vagus nerve give off in the thoracic region, besides the recurrent laryngeal nerve?
In the thoracic region, the vagus nerve (n. vagus) gives off branches to the heart, bronchi, lungs, and esophagus.
- Thoracic cardiac branches — enter the cardiac plexus together with sympathetic fibers and innervate the heart.
- Bronchial branches (pulmonary nerves) — form the pulmonary plexus around the bronchi and penetrate the lungs.
- Esophageal branches — participate in the formation of the esophageal nerve plexus (plexus oesophageus), which is connected with the sympathetic trunks and spinal nerves.
Remembering the positions of the vagus nerves on the esophagus is easy using the rule of first letters: The right trunk lies Posterior (on the posterior surface), while the left lies anterior (to avoid confusion, you can associate the letter L with the "Facial/Anterior" side).
Class and exam questions
Where and how do the recurrent laryngeal nerves run?
The right recurrent laryngeal nerve branches off from the right vagus nerve and loops around the right subclavian artery inferiorly and posteriorly. The left branches off from the left vagus nerve and similarly (inferiorly and posteriorly) loops around the aortic arch.
From which sympathetic ganglia do the splanchnic nerves form?
The greater splanchnic nerve is formed by branches from the V to IX thoracic ganglia of the sympathetic trunk. The lesser splanchnic nerve is formed by branches from the X and XI thoracic ganglia.
Where is the prevertebral nerve plexus localized?
It is located on the anterior surface of the thoracic spine. This plexus is most pronounced at the level from the III to the VI thoracic vertebrae.
What else to study on this topic
- Topographical relationships of the vagus nerves with the roots of the lungs
- Formation and branches of the esophageal nerve plexus
- Syntopy of the sympathetic trunks with the azygos and hemiazygos veins
- Passage of the splanchnic nerves through the crura of the diaphragm
- Clinical significance of mediastinal reflexogenic zones
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