Recurrent laryngeal nerve
Encyclopedia
The recurrent laryngeal nerve is a branch of the vagus nerve
(tenth cranial nerve) that supplies motor function and sensation to the larynx
(voice box). It travels within the endoneurium
. It is the nerve of the 6th Branchial Arch
.
before rising up between the trachea
and esophagus
to reach the neck.
The left laryngeal nerve, which is longer, branches from the vagus nerve
to loop under the arch of the aorta, posterior to the ligamentum arteriosum
before ascending. On the other hand, the right branch loops around the right subclavian artery. As the recurrent nerve hooks around the subclavian artery
or aorta
, it gives off several cardiac filaments to the deep part of the cardiac plexus
. As it ascends in the neck it gives off branches, more numerous on the left than on the right side, to the mucous membrane and muscular coat of the oesophagus; branches to the mucous membrane and muscular fibers of the trachea
; and some pharyngeal filaments to the superior pharyngeal constrictor muscle
.
The nerve splits into anterior and posterior rami before supplying muscles in the voice box – it supplies all laryngeal muscle
s except for the cricothyroid
, which is innervated by the external branch of the superior laryngeal nerve
.
The recurrent laryngeal nerve enters the pharynx, along with the inferior laryngeal artery
and inferior laryngeal vein
, below the inferior constrictor muscle to innervate the Intrinsic Muscles of the larynx responsible for controlling the movements of the vocal folds.
surgery, as it runs immediately posterior to this gland. If it is damaged during surgery, the patient will have a hoarse voice. Nerve damage can be assessed by laryngoscopy
, during which a stroboscopic
light confirms the absence of movement in the affected side of the vocal cords.
Similar problems may also be due to invasion of the nerve by a tumor
or after trauma
to the neck. A common scenario is paralysis of the left vocal cord due to malignant tumour in the mediastinum affecting the left branch of the recurrent laryngeal nerve. The left cord returns to midline where it stays.
is said to have first described the clinical syndrome of recurrent laryngeal nerve paralysis.
sounds upon inspiration.
It is treatable by specialists in equine medicine.
s) is cited as evidence of evolution
as opposed to intelligent design. The nerve's route would have been direct in the fish-like ancestors of modern tetrapods, traveling from the brain, past the heart, to the gills (as it does in modern fish). Over the course of evolution, as the neck extended and the heart became lower in the body, the laryngeal nerve was caught on the wrong side of the heart. Natural selection gradually lengthened the nerve by tiny increments to accommodate, resulting in the absurdly circuitous route now observed, which, if designed, could only be described as unintelligent.
Jerry Bergman, PhD, a Professor at the University of Toledo Medical School, would argue in support of Intelligent Design that the "redundancy” of the nerve's route allows for some preservation of function if one nerve is interrupted. He states studies have found that the route occupies a relatively safe position in a groove that renders it less prone to injury than a more direct route -- severing the nerve gives the inability to project ones voice at sufficient audible volume.
Bergman would argue that length is due to developmental constraints and the dynamics of development, evidenced by the slightly different routes of the nerve found when dissecting human cadavers.
Vagus nerve
The vagus nerve , also called pneumogastric nerve or cranial nerve X, is the tenth of twelve paired cranial nerves...
(tenth cranial nerve) that supplies motor function and sensation to the larynx
Larynx
The larynx , commonly called the voice box, is an organ in the neck of amphibians, reptiles and mammals involved in breathing, sound production, and protecting the trachea against food aspiration. It manipulates pitch and volume...
(voice box). It travels within the endoneurium
Endoneurium
The endoneurium, also referred to as an endoneurial channel, sheath or tube, is a layer of delicate connective tissue made up of endoneurial cells that encloses the myelin sheath of a spinal cord nerve fiber. These are bundled up into groups called nerve fascicles, which have a protective sheath...
. It is the nerve of the 6th Branchial Arch
Branchial arch
In the development of vertebrate animals, the pharyngeal arches are anlage for a multitude of structures. In humans, they develop during the fourth week in utero as a series of mesodermal outpouchings on the left and right sides of the developing pharynx...
.
Path
It is referred to as "recurrent" because the branches of the nerve innervate the laryngeal muscles in the neck through a rather circuitous route: it descends into the thoraxThorax
The thorax is a division of an animal's body that lies between the head and the abdomen.-In tetrapods:...
before rising up between the trachea
Vertebrate trachea
In tetrapod anatomy the trachea, or windpipe, is a tube that connects the pharynx or larynx to the lungs, allowing the passage of air. It is lined with pseudostratified ciliated columnar epithelium cells with goblet cells that produce mucus...
and esophagus
Esophagus
The esophagus is an organ in vertebrates which consists of a muscular tube through which food passes from the pharynx to the stomach. During swallowing, food passes from the mouth through the pharynx into the esophagus and travels via peristalsis to the stomach...
to reach the neck.
The left laryngeal nerve, which is longer, branches from the vagus nerve
Vagus nerve
The vagus nerve , also called pneumogastric nerve or cranial nerve X, is the tenth of twelve paired cranial nerves...
to loop under the arch of the aorta, posterior to the ligamentum arteriosum
Ligamentum arteriosum
The ligamentum arteriosum is a small ligament attached to the superior surface of the pulmonary trunk and the inferior surface of the aortic arch...
before ascending. On the other hand, the right branch loops around the right subclavian artery. As the recurrent nerve hooks around the subclavian artery
Subclavian artery
In human anatomy, the subclavian arteries are two major arteries of the upper thorax , below the clavicle . They receive blood from the top of the aorta...
or aorta
Aorta
The aorta is the largest artery in the body, originating from the left ventricle of the heart and extending down to the abdomen, where it branches off into two smaller arteries...
, it gives off several cardiac filaments to the deep part of the cardiac plexus
Cardiac plexus
The cardiac plexus is a plexus of nerves situated at the base of the heart that innervates the heart.-Structure:The cardiac plexus is divided into a superficial part, which lies in the concavity of the aortic arch, and a deep part, between the aortic arch and the trachea.The two parts are, however,...
. As it ascends in the neck it gives off branches, more numerous on the left than on the right side, to the mucous membrane and muscular coat of the oesophagus; branches to the mucous membrane and muscular fibers of the trachea
Vertebrate trachea
In tetrapod anatomy the trachea, or windpipe, is a tube that connects the pharynx or larynx to the lungs, allowing the passage of air. It is lined with pseudostratified ciliated columnar epithelium cells with goblet cells that produce mucus...
; and some pharyngeal filaments to the superior pharyngeal constrictor muscle
Superior pharyngeal constrictor muscle
The superior pharyngeal constrictor muscle is a quadrilateral muscle, thinner and paler than the inferior pharyngeal constrictor muscle and middle pharyngeal constrictor muscle.-Origin and insertion:The four parts of this muscle arise from:...
.
The nerve splits into anterior and posterior rami before supplying muscles in the voice box – it supplies all laryngeal muscle
Muscle
Muscle is a contractile tissue of animals and is derived from the mesodermal layer of embryonic germ cells. Muscle cells contain contractile filaments that move past each other and change the size of the cell. They are classified as skeletal, cardiac, or smooth muscles. Their function is to...
s except for the cricothyroid
Cricothyroid muscle
The cricothyroid muscle is the only tensor muscle of the larynx, aiding with phonation. It attaches to the anterolateral aspect of the cricoid and the inferior cornu and lower lamina of the thyroid cartilage, and its action tilts the thyroid forward to help tense the vocal cords...
, which is innervated by the external branch of the superior laryngeal nerve
Superior laryngeal nerve
The superior laryngeal nerve is a branch of the vagus nerve. It arises from the middle of the ganglion nodosum and in its course receives a branch from the superior cervical ganglion of the sympathetic....
.
The recurrent laryngeal nerve enters the pharynx, along with the inferior laryngeal artery
Inferior laryngeal artery
The inferior laryngeal artery ascends upon the trachea to the back part of the larynx under cover of the Constrictor pharyngis inferior, in company with the recurrent nerve, and supplies the muscles and mucous membrane of this part, anastomosing with the branch from the opposite side, and with the...
and inferior laryngeal vein
Inferior laryngeal vein
The inferior laryngeal vein is a vein which drains the larynx....
, below the inferior constrictor muscle to innervate the Intrinsic Muscles of the larynx responsible for controlling the movements of the vocal folds.
Clinical significance
The nerve is best known for its importance in thyroidThyroid
The thyroid gland or simply, the thyroid , in vertebrate anatomy, is one of the largest endocrine glands. The thyroid gland is found in the neck, below the thyroid cartilage...
surgery, as it runs immediately posterior to this gland. If it is damaged during surgery, the patient will have a hoarse voice. Nerve damage can be assessed by laryngoscopy
Laryngoscopy
Laryngoscopy is a medical procedure that is used to obtain a view of the vocal folds and the glottis. Laryngoscopy may be performed to facilitate tracheal intubation during general anesthesia or cardiopulmonary resuscitation or for procedures on the larynx or other parts of the upper...
, during which a stroboscopic
Stroboscope
A stroboscope, also known as a strobe, is an instrument used to make a cyclically moving object appear to be slow-moving, or stationary. The principle is used for the study of rotating, reciprocating, oscillating or vibrating objects...
light confirms the absence of movement in the affected side of the vocal cords.
Similar problems may also be due to invasion of the nerve by a tumor
Tumor
A tumor or tumour is commonly used as a synonym for a neoplasm that appears enlarged in size. Tumor is not synonymous with cancer...
or after trauma
Physical trauma
Trauma refers to "a body wound or shock produced by sudden physical injury, as from violence or accident." It can also be described as "a physical wound or injury, such as a fracture or blow." Major trauma can result in secondary complications such as circulatory shock, respiratory failure and death...
to the neck. A common scenario is paralysis of the left vocal cord due to malignant tumour in the mediastinum affecting the left branch of the recurrent laryngeal nerve. The left cord returns to midline where it stays.
- If the damage is unilateral, the patient may present with voice changes including hoarseness.
- Bilateral nerve damage can result in breathing difficulties and aphoniaAphoniaAphonia is the inability to speak. It is considered more severe than dysphonia. A primary cause of aphonia is bilateral disruption of the recurrent laryngeal nerve, which supplies nearly all the muscles in the larynx...
, the inability to speak. - The right recurrent laryngeal nerve is more susceptible to damage during thyroid surgery due to its relatively medial location.
History
GalenGalen
Aelius Galenus or Claudius Galenus , better known as Galen of Pergamon , was a prominent Roman physician, surgeon and philosopher...
is said to have first described the clinical syndrome of recurrent laryngeal nerve paralysis.
Veterinary medicine
In Veterinary medicine, 'roars' refers to a deficit in the left recurrent laryngeal nerve causing characteristic stertorousStertorous
Stertorous is a medical used word used to express respiration characterized by a heavy snoring or gasping sound, i.e hoarsely breathing. It occurs in common with mouth breathing due to chronic nasal obstruction. The patient is said to suffer from stertor....
sounds upon inspiration.
It is treatable by specialists in equine medicine.
Evidence of evolution
The extreme detour of this nerve (over fifteen feet in giraffeGiraffe
The giraffe is an African even-toed ungulate mammal, the tallest of all extant land-living animal species, and the largest ruminant...
s) is cited as evidence of evolution
Evidence of evolution
of living things has been discovered by scientists working in a variety of fields over many years. This evidence has demonstrated and verified the occurrence of evolution and provided a wealth of information on the natural processes by which the variety and diversity of life on Earth developed...
as opposed to intelligent design. The nerve's route would have been direct in the fish-like ancestors of modern tetrapods, traveling from the brain, past the heart, to the gills (as it does in modern fish). Over the course of evolution, as the neck extended and the heart became lower in the body, the laryngeal nerve was caught on the wrong side of the heart. Natural selection gradually lengthened the nerve by tiny increments to accommodate, resulting in the absurdly circuitous route now observed, which, if designed, could only be described as unintelligent.
Jerry Bergman, PhD, a Professor at the University of Toledo Medical School, would argue in support of Intelligent Design that the "redundancy” of the nerve's route allows for some preservation of function if one nerve is interrupted. He states studies have found that the route occupies a relatively safe position in a groove that renders it less prone to injury than a more direct route -- severing the nerve gives the inability to project ones voice at sufficient audible volume.
Bergman would argue that length is due to developmental constraints and the dynamics of development, evidenced by the slightly different routes of the nerve found when dissecting human cadavers.