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Adrian Nelson
Adrian Nelson

The Recurrent And Superior Laryngeal Nerves (20... ((FREE))



External branch of superior laryngeal nerve (EBSLN) is the smaller of the two branches of the superior laryngeal nerve. It descends to the region of the superior pole of the thyroid and travels medially along the inferior constrictor muscle. The EBSLN innervates the cricothyroid muscle, which is the only tensor of the vocal cords. The nerve enters the cricothyroid muscle laterally on its deep surface




The Recurrent and Superior Laryngeal Nerves (20...



The EBSLN also contributes innervations to the pharyngeal plexus. The pharyngeal plexus innervates the palate and pharynx and is formed by branches from the external laryngeal nerve, pharyngeal nerves, branches from the cranial nerve IX, and the sympathetic trunk.


In the neck, both nerves follow the same course and pass superiorly accompanied by the inferior thyroid artery. As it approaches the thyroid gland, the RLN may pass anterior or posterior to the inferior thyroid artery or between its branches. [6] The RLN on both sides pass deep to the lower border of the inferior constrictor muscle and enter the larynx posterior to the cricothyroid articulation.


The anastomosis of Galen (also called the ramus anastomoticus or Ansa of Galen) occurs within the framework of the larynx and is an anastomosis between the ipsilateral recurrent laryngeal nerve and the internal branch of the superior laryngeal nerve. Generally, the posterior branch of the RLN contributes to the anastomosis; however, the anterior branch can also contribute to the anastomosis. Traditionally, the anastomosis of Galen has been described to provide purely sensory and autonomic innervation. More recent studies have shown that the anastomosis may also contain motor fibers.


The innervation of the larynx is intricate, detailed, and represents some of the more complex relationships in the anatomy of the head and neck. The vagus nerve is the large nerve that supplies the many branches of nerves that innervate the larynx. The superior laryngeal nerve, its external and internal branches, and the recurrent laryngeal nerve all have very distinct roles in motor and sensory innervation of the larynx. Superiorly, sensory and motor innervation are separated by internal and external branches of the superior laryngeal nerves. Inferiorly, the sensory and motor innervation is provided by the recurrent laryngeal nerve.


The innervation of the larynx is similar to other areas of the body with both sensory and motor components. There is superior and inferior innervation, and these nerves' names reflect as much. The superior laryngeal nerve is a branch from the vagus nerve arising above the carotid bifurcation as it descends down the neck. The superior laryngeal nerve then divides into external and internal branches.[1] The external branch of the superior laryngeal nerve follows a course with the superior thyroid vessels and contains motor fibers that innervate the cricothyroid muscle.[2][3] While the internal branch of the superior laryngeal nerve pierces through the thyrohyoid membrane and carries sensory fibers that innervate the laryngeal mucosa superior to the vocal cords.[1][2]


The recurrent laryngeal branch of the vagus nerve originates from the 6th pharyngeal arch along with the intrinsic musculature of the larynx, except for the cricothyroid muscle. The superior laryngeal branch of the vagus nerve originates from the 4th pharyngeal arch along with the cricothyroid muscle. This developmental pattern elucidates why the cricothyroid muscle is the only muscle that receives innervation via the superior laryngeal nerve. The 4th and 6th pharyngeal arches contribute to the formation of the cartilages that are both vital to the structure and function of the larynx: thyroid, cricoid, arytenoid, cuneiform, and corniculate cartilages.


The external branch of the superior laryngeal nerve is immediately deep to the superior thyroid artery and descends on the larynx. The internal branch of the superior laryngeal pierces through the thyrohyoid membrane along with the superior laryngeal artery (a division of the superior thyroid artery). The course of the recurrent laryngeal nerves is interesting due to the lack of symmetry. On the left, the ipsilateral recurrent branches from the vagus nerve and is close to the aorta and wraps around it in an anterior to posterior fashion and ascends in the tracheoesophageal groove on its way to the larynx. On the right, the recurrent laryngeal nerve has a close relation to the right subclavian artery as it wraps around it in an anterior to posterior fashion and, like the left recurrent laryngeal nerve, ascends in the tracheoesophageal groove to the ipsilateral larynx.


As discussed before, the external branch of the superior laryngeal nerve supplies the cricothyroid muscle. The function of the cricothyroid muscle is to tense the vocal cords, thereby increasing vocal pitch. The external laryngeal nerve also gives branches to the pharyngeal plexus and the superior portion of the inferior pharyngeal constrictor. The recurrent laryngeal nerve innervates the majority of the intrinsic laryngeal musculature, responsible for vocal production. These muscles include the major abductor of the vocal cords, the posterior cricoarytenoid muscle. Adductors innervated by the recurrent laryngeal nerve include the lateral cricoarytenoid muscles, arytenoid muscles (transverse and oblique), and the aryepiglottic muscle; these muscles contribute to the physiologic "cough." The lateral cricothyroid, thyroarytenoid (vocalis), and transverse and oblique arytenoid muscles. All these muscles are involved in vocal production. Other important muscles include the thyroarytenoid muscle in charge of relaxing the vocal folds and also approximate them, the vocalis muscle, which lies lateral to the vocal ligament and is in charge of shortening the vocal cords and finally the thyroepiglottic muscle which depresses the epiglottis and widens the laryngeal inlet.[5]


The laryngeal nerves have various anatomical variants. One crucial known variant is the lack of the recurrent laryngeal nerve being "recurrent" around the subclavian or aorta and instead arising from the vagal truck in the neck and traversing with the inferior thyroid artery to the larynx. It is imperative to be aware of this variation, especially when performing surgical interventions in the neck, particularly thyroid or parathyroid procedures.[4]


As mentioned, during thyroid and parathyroid procedures, surgical injury to these nerves is a feared complication. Intraoperative superior and recurrent nerve monitoring during head and neck procedures is common and is used frequently with thyroid and parathyroid procedures. Monitoring is primarily by the placement of a neural integrity monitoring (NIM) endotracheal tube. The nerve monitor is part of the endotracheal tube and is testable before the procedure begins to ensure proper placement.


The laryngeal nerves may suffer damage during surgical procedures, especially with thyroid and parathyroid surgeries. Injury to the recurrent laryngeal nerve during dissection produces vocal cord paralysis and results in reduced protection of the airway due to the lack of ability to medialize the vocal cords. With a unilateral injury, hoarseness would not be an unexpected finding. One rare but feared complication is a bilateral injury to the recurrent laryngeal nerves, which would result in a lack of ability to close the airway with the true vocal folds, significantly increasing the risk of aspiration. Additionally, the external branch of the superior laryngeal nerve, in charge of innervating the cricothyroid muscle, may be damaged during a cricothyrotomy or thyroidectomy and would lead to an inability to tense the vocal cords resulting in a decreased pitch of the voice.


The laryngeal ventricle is the fossa or sinus that lies between the vocal and vestibular folds on either side. The vocal folds are commonly referred to as the vocal cords and the vestibular folds as the false vocal cords. The laryngeal ventricle also demarcates the separation between the quadrangular membrane superiorly, and the cricovocal membrane found inferiorly. These two membranes together cover the entire interior portion of the larynx from the epiglottic and arytenoid cartilages superiorly to the cricoid cartilage inferiorly. These membranes are bilateral.


The laryngeal ventricle begins inferiorly to the free edge of the vestibular fold and continues laterally. The ventricle exists bilaterally, and secretes mucus over the superior surface of the vocal folds, forming a protective layer.


The recurrent laryngeal nerves then continue superiorly bilaterally and pass posterior to the lobe of the thyroid gland as they travel along the lateral surfaces of the trachea and esophagus in the tracheoesophageal groove. The nerves pass posterior to the cricothyroid joint as they enter the larynx at this level through fibers of the inferior constrictor muscles of the pharynx. At this point, the RLN becomes the inferior laryngeal nerve.


Extrinsic Muscles: These muscles are found in bilateral pairs and aid in the movement of the larynx at a gross level. Innervations of the extrinsic laryngeal muscles vary and include the following nerves: ansa cervicalis, trigeminal nerve, facial nerve, glossopharyngeal nerve, and hypoglossal nerve. The pharyngeal constrictors and palatopharyngeus receive innervation from the glossopharyngeal, vagus, and spinal accessory nerve via the pharyngeal plexus."


There also notes to be some physiologic variation to the laryngeal ventricle. In addition to extending laterally, the laryngeal ventricle may sometimes continue superiorly and anteriorly, forming a saccule beneath the fold.


Additionally, considering the thyroid glands relationship to the recurrent laryngeal nerve and the superior laryngeal nerve, surgical resection of the thyroid gland can result in injury to both nerves either directly or indirectly.


Background: Injury to the recurrent laryngeal nerve (RLN) is an unwelcome and not infrequent complication of operations on or near the upper thoracic or cervical esophagus. Because anatomic information useful to the surgeon is difficult to come by, the aim of this study was to reinvestigate and display the RLNs and superior laryngeal nerves in humans. 041b061a72


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