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The vagus nerve (cranial nerve
Structure and Function
The vagus nerve has its origin in the medulla oblongata and exits the skull via the jugular foramen. Tbelow are two ganglia on the vagus nerve (exceptional and inferior) as it exits the jugular foramen; the spinal accessory nerve (CN XI) joins the vagus nerve just distal to the inferior ganglion.<1><2>
The origin of cell bodies for the vagus nerve originates from the nucleus ambiguous; the dorsal motor nucleus of X, exceptional ganglion of X, and the inferior ganglion of X. The nerve fibers from the nucleus ambiguous are efferent, distinct visceral (ESV) fibers which assist to mediate swallowing and also phocountry. Fibers originating from the dorsal motor nucleus of X are efferent, general visceral (EGV) fibers which carry out the involuntary muscle control of organs it innervates (cardiac, pulmonary, esophageal) and also innervation to glands throughout the gastrointestinal tract. Superior ganglion of X gives afferent basic somatic innervation to the external ear and tympanic membrane. The inferior ganglion of X offers afferent general visceral fibers to the carotid and also aortic bodies; the efferent fibers of this nerve take a trip to the nucleus tractus solitarius; the inferior ganglion additionally provides taste sensation to the pharynx and also relays this information to the nucleus tractus solitarius.<2><1><3><4><5>
The vagus nerve continues by traveling inferiorly within the carotid sheath wright here it is situated posterior and also lateral to the inner and also prevalent carotid arteries, and medial to the internal jugular vein. The right vagus nerve travels anteriorly to the subclavian artery and also then posterior to the innominate artery; it provides its descent into the thoracic cavity by traveling to the appropriate of the trachea, and also posterior to the hilum on the right, moving medially to form the esophageal plexus with the left vagus nerve. The left vagus nerve travels anteriorly to the subclavian artery and also enters the thoracic cavity wedged in between the left common carotid and subclavian arteries; it then descends posteriorly to the phrenic nerve and also posterior to the left lung, then travels medially in the direction of to the esophagus creating the esophageal plexus with the best vagus nerve.<5><1><3><4>
Tbelow are four branches of the vagus nerve within the neck: pharyngeal branches, remarkable laryngeal nerve, represent laryngeal nerve, and the remarkable cardiac nerve.<6>
The pharyngeal nerve branches arise from the inferior ganglion of CN X containing both sensory and also motor fibers. These fibers develop the pharyngeal plexus–branches of this plexus innervate the pharyngeal and also palate muscles (except the tensor palatine muscle); the pharyngeal plexus additionally provides the innervation to the intercarotid plexus which mediates information from the carotid body.<3><6>
The premium laryngeal nerve travels in between the exterior and also inner carotid arteries; the nerve divides into interior and exterior branches near the level of the hyoid. The internal laryngeal nerve goes via the thyrohyoid membrane entering the larynx. The outside percentage travels distally via the premium thyroid vessels. The outside percent provides the cricothyroid muscle, whereas the inner branch gives the mucosa premium to the glottis.<6>
The appropriate represent laryngeal nerve’s fibers branch from the vagus nerve near the best subclavian artery, traveling superiorly to enter the larynx between the cricopharyngeus muscle and also the esophagus. The left reexisting laryngeal nerve then loops around the aortic arch distal to the ligamentum arteriosus and then enters the larynx. All of the laryngeal musculatures receives supply through the reexisting laryngeal nerve other than for the cricothyroid muscle (gave by the laryngeal nerve).<3><6>
While the vagus nerve is within the carotid sheath, it gives off the superior cardiac nerve and is connected with parasympathetic fibers and also travels to the heart.<7><4>
The vagus nerve gives off anterior and posterior bronchial branches in which the anterior branches are along the anterior lung creating the anterior pulmonary plexus, whereas the posterior branches form the posterior pulmonary plexus.<3><6>
Esophageal branches of the vagus nerve are anterior and also posterior and also create the esophageal plexus. The left vagus is anterior to the esophagus; the right vagus is posterior.<3><6>
Gastric branches supply the stomach; celiac branches (mainly acquired from the best vagus nerve) supply the pancreas, spleen, kidneys, adrenals, and also tiny intestine.<3><1><8><4>
The vagus nerve arises from the fourth branchial arch; this arch is likewise responsible for the breakthrough of the pharyngeal and also laryngeal muscles, the laryngeal cartileras, the aortic arch, and also subclavian artery.
Blood Supply and also Lymphatics
The middle meningeal artery offers the intracranial blood supply to the vagus nerve. The extracranial blood supply is from the widespread carotid artery, interior carotid artery, inferior thyroid artery, outside carotid artery, a posterior meningeal artery, interior thoracic arteries, bronchial arteries, and also esophageal arteries.<9><6>
The vagal mechanism is affiliated in regulating the contraction of lymphatic (containing actin) cells.
The vagus nerve has branches within the neck; these branches are the pharyngeal branches, superior laryngeal nerves, recurrent laryngeal nerves, and premium cardiac nerves. The structure and function of these nerves were described over.
The vagus nerve has numerous fibers that innervate the striated muscles of the larynx and pharynx; tbelow are 2 exceptions: the stylopharyngeus muscle (CNIX) and also the tensor veli palatini muscle (V3).<3>
The vagus nerve innervates one muscle of the tongue: palatoglossus muscle–its function is to elevate the posterior percentage of the tongue.<3>
The exterior branch of the remarkable laryngeal nerve provides the cricothyroid muscle.<3>
The pharyngeal branches of the vagus supply: levator veli palatini, salpingopharyngeus, palatopharyngeus, and also the uvula.<3>
Represent laryngeal nerves innervate the intrinsic muscles of the larynx, other than the cricothyroid muscle (the exterior branch of the exceptional laryngeal nerve).<3>
The recurrent laryngeal nerve has actually two branches before inserting right into the larynx; the branching is generally inferior to the cricoid cartilage; yet, tbelow are instances when tbelow are even more than two branches, and for this reason are dubbed esophageal branches.<10>
Tbelow are numerous variations of the non-reexisting vagus nerve.
Factor to consider for the branches of the recurrent laryngeal nerve is critical throughout surgical treatment of the thyroid gland. Since of the proximity of the thyroid gland and the branches of the recurrent laryngeal nerve, references are for maintaining all nerves in this area unless there is a compromise of the nerve itself by malignancy.<4><6><11>
The recurrent laryngeal nerve might be damaged during a cervical esophagectomy, in the time of the removal of a pharyngoesophageal diverticulum or a gastroesophageal anastomosis after percreating the trans-hiatal esophagectomy. In the diverticulum excision and also the anastomosis, the reexisting laryngeal nerve is lesioned from press applied by retractors in the operating room.<10><12><11>
Damage deserve to be done to the outside laryngeal nerve at the moment of ligation of the exceptional thyroid artery throughout a thyroidectomy.<4><11>
The vagus nerve is typically tested clinically in conjugation via the glossopharyngeal nerve because of their evident results that are oftentimes reliant upon one more. A patient is often asked to open their mouth and say ‘ah,’ this must reason elevation of the uvula. If there is a lesion, the uvula shifts amethod from the paralyzed side. Gag reflex must not be supplied as a clinical exam as tright here deserve to be a bilateral loss of the gag reflex in a healthy and balanced patient. If a patient is listed to have actually hoarseness in the time of the physical exam, this should present the have to test the vocal cords in the patient; if tbelow is hoarseness with a normal gag reflex and also palatal elevation, this indicates a lesion of the represent laryngeal nerve.<3>
Vagus nerve stimulation was produced as a means to reach a centrally situated neurological frameworks by minimally invasive indicates. In the standard vagus nerve stimulation approach, a device is implanted surgically under the skin in the chest, and electric wires affix to the left vagus nerve (left supplied more often than best, as the appropriate vagus nerve is even more likely to have branches to the heart). Vagus nerve stimulation is apshowed to treat epilepsy and also depression; however, via the wide circulation of the vagus nerve throughout the body, stimulation is being explored for various other purposes such as the therapy of obesity.<13><4>
Stimulation of the larynx provides reflexes consisting of cough, apnea, and also effects on the cardiovascular system such as bradycardia and also hypostress.
Central lesions of the vagus nerve can reason dysphagia, dysarthria and hoarseness; uvula deviation (in the direction of the oppowebsite side of the lesion); and also transient parasympathetic impacts.
Lateral medullary syndrome (posterior inferior cerebellar artery infarction) leads to the destruction of the glossopharyngeal and also vagus nerves, the nucleus ambiguous, the solitary nucleus, and also the spinocerebellar tracts.
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Mechanical alterations of the vagus nerve may be pertained to emotional troubles (depression and also anxiety) in patients with chronic obstructive airmethod disease and congestive heart faiattract. One of its dysfunctions might likewise be a resource of pain in the very same patient populace.<15><16><17>