Corpus: Vagus nerve

The vagus nerve is the 10th cranial nerve and the main nerve of the parasympathetic nervous system, which regulates the activity of many internal organs. It carries general sensory, general visceral motor, special visceral motor, general visceral sensory, and special visceral sensory fibers.

The vagus nerve is considered one of the branchial arch nerves, developing from the nerves of the 4th to 6th branchial arches. It innervates all the muscles that develop from the muscle tissue of these arches.

The vagus nerve emerges laterally from the medulla oblongata and runs ventrally and caudally to the posterior section of the jugular foramen. Before or during its passage through the foramen, the superior sensory ganglion develops along its course. After passing through the foramen (extracranially), it forms the inferior visceral sensory ganglion. It then travels caudally in the carotid sheath and enters the thoracic cavity on the right side between the brachiocephalic vein and the subclavian artery, and on the left side between the brachiocephalic vein and the aortic arch.

In the posterior mediastinum, the right and left vagus nerves attach to the esophagus and form a fine nerve plexus, the esophageal plexus, where fibers from both sides intermingle. The plexus forms the anterior vagal trunk in front of the esophagus and the posterior vagal trunk behind the esophagus. The fibers of the anterior vagal trunk originate mainly from the left vagus nerve, while those of the posterior vagal trunk originate from the right vagus nerve. They pass through the esophageal hiatus of the diaphragm into the abdomen.

4.1. Head area

• Meningeal Branch (Ramus meningeus): This branch re-enters the cranial cavity through the jugular foramen and innervates the dura mater of the posterior cranial fossa with general sensory fibers.
• Auricular Branch (Ramus auricularis): Branching off within the superior ganglion, this nerve crosses under the internal jugular vein and runs into the mastoid canal. It reaches the skin surface through the tympanomastoid fissure, supplying part of the auricle, the external auditory canal, and part of the eardrum with general sensory fibers.

4.2. Cervical area

• Pharyngeal Branch (Ramus pharyngeus): This branch sends fibers to the pharyngeal plexus, providing motor supply to the pharyngeal muscles and sensory supply to the caudal pharyngeal region and taste receptors on the epiglottis.
• Superior Laryngeal Nerve: This nerve innervates the cricothyroid muscle and the mucous membrane above the glottis.
• Recurrent Laryngeal Nerve: This nerve supplies all laryngeal muscles except the cricothyroid muscle, as well as the mucoas of the larynx below the glottis. It also innervates the trachealis muscle. Its terminal branch, the inferior laryngeal nerve, anastomoses with the superior laryngeal nerve to form the Galen anastomosis.
• Cardiac Branches (Rami cardiaci): The superior and inferior cardiac branches contribute parasympathetic fibers to the cardiac plexus, which supplies the atrium and ventricles of the heart. They connect with postganglionic fibers in the cardiac ganglia.

4.3. Chest area

The parasympathetic and general visceral supply of the lungs, trachea, esophagus, and pericardium occurs via branches in the thoracic area (thoracic branches, tracheal branches, esophageal branches, pericardial branches).

4.4. Abdominal area

In the abdominal region, the vagus nerve innervates the stomach, kidneys, pancreas, liver, gall bladder, and intestines via the anterior and posterior vagal trunks up to the Cannon-Böhm point, providing parasympathetic and general visceral sensory fibers.

• General sensory fibers: The spinal nucleus of the trigeminal nerve, located in the medulla oblongata and spinal cord, represents the nucleus for the general sensory fibers of the vagus nerve.
• General visceral motor fibers: The nucleus for the general visceral motor fibers is located in the medulla oblongata and is known as the dorsal motor nucleus of the vagus nerve.
• Special visceral motor fibers: These fibers originate from the nucleus ambiguus in the medulla oblongata.
• General and special visceral sensory fibers: These fibers terminate in the solitary nucleus, also located in the medulla oblongata.

Motor failure of the vagus nerve is known as vagus palsy. It can be divided into central and peripheral paresis. In the case of peripheral lesions, the level of nerve damage determines the exact symptoms. Possible symptoms include paralysis of the soft palate, leading to phonation disorders, and hoarseness caused by paralysis of the recurrent laryngeal nerve.