The paired vagus nerve just vagus is also the tenth cranial nerve , N. X called. It is the largest nerve of the parasympathetic and is involved in regulating the activity of almost all internal organs . Its large area of distribution gave its name, the name derives from the Latin vagari ("wander around"), literally translated it means "the wandering nerve".
In addition to its vegetative function, it is involved in the motor control of the larynx , throat and the upper esophagus and transmits taste sensations from the base of the tongue as well as touch sensations from the throat, the larynx and part of the external auditory canal . The internal organs in the chest and abdomen are also reached by sensitive fibers (viscera afferents ), but these primarily serve to convey reflexes . The vagus thus contains the following fiber qualities: somatomotor (voluntary control), somatosensitive (consciously perceptible), sensory (taste), visceromotor and visceromotor (parasympathetic).
The nerve is connected to the IX. and XI. Cranial nerves ( glossopharyngeal nerve or accessory nerve ) also combined to form the " vagus group ".
Origin of the vagus
The perikarya (soma, nerve cell body) of the parasympathetic neurons within the vagus are located in the nucleus dorsalis nervi vagi (veterinary anatomy: nucleus parasympathicus nervi vagi ), a core area in the myelencephalon (medullary brain). The nerve cell bodies of the motor fibers are located in the nucleus motorius nervi vagi (also nucleus ambiguus ) in the medullary brain.
The sensory fibers project from the periphery to the nucleus spinalis nervi trigemini and probably also to the nucleus pontinus nervi trigemini , while the sensory fibers are directed to the nucleus tractus solitarii .
The nerve occurs in the area of the medulla oblongata in the sulcus retroolivaris on the side of the olive (together with the accessory nerve and glossopharyngeal nerve , lower group of three) on the surface of the brain and, like the other nerves of the vagus group, pulls out of the cranial capsule through the jugular foramen . Here it passes through two closely spaced ganglia :
- The superior ganglion (also jugular ganglion , in animals: proximal ganglion ): still within the cranial cavity or in the jugular foramen
- the ganglion inferius (also ganglion nodosum , in animals: ganglion distale ): outside the cranial cavity
The somata of the afferent fibers (a distinction between sensory and sensory is no longer made) of the vagus nerve are located in these two ganglia.
Course outside the skull
The vagus nerve runs along the neck together with the common carotid artery and the internal jugular vein in a shared connective tissue sheath , the carotid vagina , in the direction of the chest cavity. With a good ultrasound device, the nerve in the area of the carotid arteries can also be localized sonographically. In most other mammals it is about the entire neck with the sympathetic nervous system to the trunk vagosympathicus connected.
At the upper thoracic aperture, the right vagus nerve runs over the dextra subclavian artery, while the left vagus nerve runs over the aortic arch . In the chest cavity, the vagus runs through the upper mediastinum , later the posterior mediastinum.
This is where the right and left vagus of the esophagus ( esophagus ) are attached, whereby the fibers on both sides mix and form the plexus esophagus , but from this as the anterior vagus trunk (from the left vagus nerve, in animals: truncus vagalis ventralis ) and truncus vagalis posteriorly (from the right vagus nerve, in animals: truncus vagalis dorsalis ) together with the esophagus through the diaphragm via the hiatus esophagus into the abdomen.
Branches of the vagus nerve
The Ramus meningeus (Hirnhautast) moves through the jugular foramen back into the cranium and innervates the dura mater of the posterior fossa (posterior fossa). It also sensitively innervates the occipital sinus and transverse sinus .
The ramus auricularis (ear branch) runs through the canaliculus mastoideus and through the fissura tympanomastoidea. It sensitively supplies the skin on the inside of the auricle and the external auditory canal as well as part of the eardrum .
The branch is responsible for the fact that vegetative symptoms such as coughing or vomiting can occur when the external auditory canal is irritated (foreign bodies, rinsing with cold water) .
The rami pharyngei ( pharyngeal branches) run to the pharyngeal plexus . This is a network of nerves made up of vagus fibers, fibers from the glossopharyngeal nerve and sympathetic fibers from the superior cervical ganglion . The pharyngeal branches supply the pharyngeal muscles and those of the soft palate and are of great importance for the act of swallowing . They are therefore also responsible for the gag reflex and the swallow reflex .
The ramus oesophageus (esophageal branch) innervates the striated muscles of the esophagus by motor means .
Superior laryngeal nerve
The superior laryngeal nerve (superior laryngeal nerve, referred to in animals as the cranial laryngeal nerve ) descends from the inferior ganglion and extends to the larynx . Its outer branch supplies the cricothyroid muscle , the inner one the sensitive mucous membrane of the larynx above the vocal folds . The superior laryngeal nerve carries the sensitive information that is responsible for the reflex closure of the larynx when it comes into contact with liquids and for the cough reflex .
The depressor nerve does not occur in humans. In animals, it arises at the front neck of the vagus and reunites with it shortly afterwards. At the entrance to the breast it separates from the vagus again and moves towards the aorta . It transmits information from receptors in the aortic wall that register blood pressure ( baroreceptors ) to the brain stem. In humans, these fibers run in the cardiac branches of the vagus nerve itself.
The nerve fibers, like those of the carotid sinus , regulate blood pressure.
The Rami cardiaci (heart branches) ensure the parasympathetic influence on the heart's activity . They form with sympathetic fibers of the first ganglia the cardiac plexus at the base of the heart. They mediate a decrease in the heart rate ( chronotropy , right vagus). The vagus has no influence on the contraction force of the heart ( inotropy ), since it only inhibits the transfer of excitation from the atrium to the ventricle (left vagus), but does not innervate the heart muscles. Only the sympathetic nervous system increases the muscle strength of the heart and thus has a positive inotropic effect (gr. Ís, inós = strength, muscle).
Recurrent laryngeal nerve
The recurrent laryngeal nerve (declining larynx nerve, vocal nerve) supplies all larynx muscles with the exception of the cricothyroid muscle as well as the esophagus and trachea.
Due to its special course and its important function, it is of great clinical importance (→ recurrent palsy ).
Smaller thoracic branches
The Rami tracheal (trachea branches) and Rami bronchales (bronchial) form at the root of the lung together with the sympathetic fibers of the sympathetic trunk of the pulmonary plexus (lung braid). Its sensitive fibers from the vagus are of great importance for the regulation of breathing and for the cough reflex . The parasympathetic fibers cause the bronchi to narrow .
Rami oesophagei (esophagus branches) supply the chest portion of the esophagus , Rami pericardiaci the pericardium .
The fibers that extend into the abdominal cavity via the anterior vagal trunk ( ventralis ) and posterior vagal trunk ( dorsalis ) parasympathetically supply the majority of the abdominal organs ( stomach , liver , kidneys and small intestine ) up to and including around two thirds of the large intestine , up to the so-called Cannon-Böhm point in the transverse colon . They also convey visceral sensitive information.
With the help of heart rate variability analysis it is possible to visualize the activity of the vagus. After recording the electrical cardiac activity ( EKG ) and analyzing its frequency, the part of the vagus appears as a curve maximum in the heart rate band (the actual heart rate is outside the illustration on the right). If the measurement is carried out in physical rest (approx. 60–80 beats / minute = 1.0–1.33 Hz), the activity of the vagus is in the frequency range between 0.15 and 0.4 Hz (blue curve), i.e. approximately in Rhythm from 3 to 7 heartbeats. If the heart rate increases, the activity of the vagus also shifts to a higher frequency range. With physical exertion (maximum physical exertion), the maximum is usually between 0.7 and 1.1 Hz (red curve).
- Vagotomy (cutting of the nerve)
- Vagotonia (increased activity of the nerve)
- Superior laryngeal neuralgia ( neuralgia of the upper laryngeal nerve)
- Vagus nerve stimulator (used in depression and epilepsy treatment)
- Jackson syndrome (cranial nerve syndrome) (lesions of the vagus nerve, accessory nerve, and hypoglossal nerve)
- Laryngeal whistling (paralysis of the caudal laryngeal nerve )
- Hoflund syndrome (damage to the terminal branches of the nerve with vagotonia in the chest area in ruminants )
- Martin Trepel: Neuroanatomy. Structure and function. 3rd, revised edition. Urban & Fischer, Munich a. a. 2004, ISBN 3-437-41297-3 .
- Franz-Viktor Salomon: nervous system, systema nervosum . In: Franz-Viktor Salomon, Hans Geyer, Uwe Gille (Ed.): Anatomy for veterinary medicine. Enke, Stuttgart 2005, ISBN 3-8304-1007-7 , pp. 464-577.