The vagus nerve is the tenth of twelve cranial nerves whose nuclei are located directly in the brain. The vagus nerve makes up most of the parasympathetic nervous system and is connected to almost all internal organs through multiple branches. In addition to its parasympathetic control function of the internal organs via its over visceromotor fibers, it also has motor and sensorimotor afferents.
What is the vagus nerve?
The vagus nerve – also known simply as the vagus – is the widely branched X. Cranial nerve that innervates almost all internal organs. The vagus nerve is also the largest nerve of the parasympathetic nervous system. Its name is derived from the Latin vagus, meaning wandering, unsteady. In its parasympathetic capacity to supplement and cancel increased autonomic activity by the sympathetic system, it has general and specific visceromotor and viscerosensory fibers, as well as somatosensory and -motor afferent and efferent fibers. In particular, in addition to its functions in the autonomic area, the vagus nerve is responsible for conscious motor movements in the pharynx and for some of the sensations of taste and touch in the pharynx. The vagus nerve is often associated in the literature with the IXth and XIth nerves. Hinrnerv (tongue pharyngeal nerve or leg nerve) to the vagus group. Through multiple branches, the vagus nerve reaches the lungs, heart, kidneys, liver, and digestive organs, and not only controls parasympathetic autonomic activities, but is also responsible for triggering certain reflexes.
Anatomy and structure
The nuclei of the parasympathetic neurons of the vagus nerve are located in a nuclear area of the medulla (myelencephalon), whereas the nuclei of the motor fibers are located in the nucleus motorius nervi vagi, a region also classified as part of the medulla. In the region of the medulla oblongate, the medulla oblongata, the nerve enters the brain surface and exits the skull through the large opening at the base of the skull (foramen jugulare) and passes through two closely spaced ganglia. The ganglia contain the cell bodies of the afferent nerve fibers of the vagus nerve ascending from the target organs. The further course of the nerve and also its branches is usually based on the courses of larger arteries or, for example, also the esophagus. Thus, the vagus runs in the neck together with the carotid artery and the great jugular vein in a common connective tissue sheath, the vagina carotica. It passes through the diaphragm together with the esophagus through the esophageal hiatus. From the first branch below the base of the skull arises the ramus meningeus, which passes back into the skull through the foramen jugulare to innervate the meninges (dura mater) of the posterior fossa somato-sensomatically.
Function and Tasks
The tasks and functions of the vagus nerve break down according to the affiliation of its efferent or afferent nerve fibers with the autonomic parasympathetic system or the somato-sensory or -motor system of conscious sensory and motor activity. In connection with the parasympathetic control of the innervated organs as a counterpart of the sympathetic control, there are also various protective reflexes that can be triggered by activities of the vagus. The most important protective reflex is the vagus reflex. It can be triggered by a blow to the larynx or upper abdomen, by the sight of blood, or by stress, fear, or severe pain. It causes the veins to dilate with a sudden drop in blood pressure and slowing of the heart rate, resulting in dizziness, pallor, and impaired consciousness or even fainting. In extreme cases, a so-called reflex death or vagus death can occur. In normal cases, the vagus, with regard to its parasympathetic functions, fulfills the task of returning the internal organs to their normal state after sympathetically increased activity and alertness, and of initiating the regeneration phase. This occurs mainly at night during the prolonged rest and sleep phase. The most important organs on which the vagus with its branches exerts a parasympathetic influence are the heart, liver, kidneys, spleen, stomach and most of the intestine, including the small intestine and about two-thirds of the colon.Outside the parasympathetic area, the vagus, with its motor afferent fibers, is responsible for conscious motor activity in the pharynx and for relaying somato-sensory, efferent, feedback from the same area.
Diseases
In principle, complaints can arise that are caused due to too weak nerve impulses of the vagus nerve or as a result of too much activity of the nerve. Functional impairment due to impaired conduction of the vagus in both afferent and efferent directions may have mechanical-physical causes or be due to disease of the nerve itself or other neurologic problems. Vagotonia or parasympathetic tonia is defined as excessive activity of the parasympathetic nervous system, or the vagus nerve, as the main representative of the parasympathetic system, in relation to the sympathetic nervous system. Symptoms include low blood pressure (hypotension), slow pulse, cold hands, cold feet, and narrow pupils. Differentiation of vagotonia as a normal condition of well athletically trained persons from pathological vagotonia is fluid and difficult to decide in individual cases. A well-known form of vagus disorder is laryngeus superior neuralgia. The laryngeus superior (upper laryngeal nerve) is a side branch of the vagus nerve that causes pain when swallowing, coughing, and speaking due to inflammation. Special medications are used for therapy, and if the effect is too weak, it is supplemented by neural therapy with a locally effective anesthetic. Vagus nerve stimulation (VNS), in which the vagus nerve is electrically stimulated at specific intervals, can be considered as a therapy for the treatment of epilepsy. A distinction is made between invasive and transcutaneous VNS. In invasive VNS, the stimulation device is connected to a branch of the vagus via an electrode in the chest area and sends automatic stimulation pulses. Transcutaneous VNS takes advantage of the fact that a sensitive side branch of the vagus supplies part of the auricle, where it lies just under the skin and can receive stimuli transcutaneously.
