The recurrent laryngeal nerve (RLN) is a branch of the
vagus nerve
The vagus nerve, also known as the tenth cranial nerve, cranial nerve X, or simply CN X, is a cranial nerve that interfaces with the parasympathetic control of the heart, lungs, and digestive tract. It comprises two nerves—the left and right ...
(
cranial nerve
Cranial nerves are the nerves that emerge directly from the brain (including the brainstem), of which there are conventionally considered twelve pairs. Cranial nerves relay information between the brain and parts of the body, primarily to and ...
X) that supplies all the
intrinsic muscles of the
larynx
The larynx (), commonly called the voice box, is an organ in the top of the neck involved in breathing, producing sound and protecting the trachea against food aspiration. The opening of larynx into pharynx known as the laryngeal inlet is about ...
, with the exception of the
cricothyroid muscle
The cricothyroid muscle is the only tensor muscle of the larynx aiding with phonation. It is innervated by the superior laryngeal nerve. Its action tilts the thyroid forward to help tense the vocal cords.
Structure
The cricothyroid muscle orig ...
s. There are two recurrent laryngeal nerves, right and left. The right and left nerves are not symmetrical, with the left nerve looping under the aortic arch, and the right nerve looping under the
right subclavian artery
In human anatomy, the subclavian arteries are paired major arteries of the upper thorax, below the clavicle. They receive blood from the aortic arch. The left subclavian artery supplies blood to the left arm and the right subclavian artery supplie ...
then traveling upwards. They both travel alongside the trachea. Additionally, the nerves are among the few nerves that follow a ''recurrent'' course, moving in the opposite direction to the nerve they branch from, a fact from which they gain their name.
The recurrent laryngeal nerves supply sensation to the larynx below the vocal cords, give cardiac branches to the
deep cardiac plexus, and branch to the trachea, esophagus and the inferior constrictor muscles. The
posterior cricoarytenoid muscle
The posterior cricoarytenoid muscles are small, paired intrinsic muscles of the larynx that extend between cricoid cartilage to the arytenoid cartilages in the larynx.
Structure Origin and insertion
The posterior cricoarytenoid originates f ...
s, the only muscles that can open the vocal folds, are innervated by this nerve.
The recurrent laryngeal nerves are the nerves of the sixth
pharyngeal arch
The pharyngeal arches, also known as visceral arches'','' are structures seen in the embryonic development of vertebrates that are recognisable precursors for many structures. In fish, the arches are known as the branchial arches, or gill arch ...
. The existence of the recurrent laryngeal nerve was first documented by the physician
Galen
Aelius Galenus or Claudius Galenus ( el, Κλαύδιος Γαληνός; September 129 – c. AD 216), often Anglicized as Galen () or Galen of Pergamon, was a Greek physician, surgeon and philosopher in the Roman Empire. Considered to be one of ...
.
Structure
![Gray505](https://upload.wikimedia.org/wikipedia/commons/3/3c/Gray505.png)
The recurrent laryngeal nerves branch from the
vagus nerve
The vagus nerve, also known as the tenth cranial nerve, cranial nerve X, or simply CN X, is a cranial nerve that interfaces with the parasympathetic control of the heart, lungs, and digestive tract. It comprises two nerves—the left and right ...
, relative to which they get their names; the term "recurrent" from la, re- (back) and ''currere'' (to run), indicates they run in the opposite direction to the vagus nerves from which they branch. The vagus nerves run down into the thorax, and the recurrent laryngeal nerves run up to the larynx.
The vagus nerves, from which the recurrent laryngeal nerves branch, exit the skull at the
jugular foramen
A jugular foramen is one of the two (left and right) large foramina (openings) in the base of the skull, located behind the carotid canal. It is formed by the temporal bone and the occipital bone. It allows many structures to pass, including the i ...
and travel within the
carotid sheath
The carotid sheath is an anatomical term for the fibrous connective tissue that surrounds the vascular compartment of the neck. It is part of the deep cervical fascia of the neck, below the superficial cervical fascia meaning the subcutaneous adipo ...
alongside the
carotid arteries
In anatomy, the left and right common carotid arteries (carotids) (Entry "carotid"
in
aortic arch
The aortic arch, arch of the aorta, or transverse aortic arch () is the part of the aorta between the ascending and descending aorta. The arch travels backward, so that it ultimately runs to the left of the trachea.
Structure
The aorta begins a ...
, and the right at the right
subclavian artery
In human anatomy, the subclavian arteries are paired major arteries of the upper thorax, below the clavicle. They receive blood from the aortic arch. The left subclavian artery supplies blood to the left arm and the right subclavian artery supplie ...
. The left RLN passes in front of the arch, and then wraps underneath and behind it. After branching, the nerves typically ascend in a groove at the junction of the
trachea
The trachea, also known as the windpipe, is a Cartilage, cartilaginous tube that connects the larynx to the bronchi of the lungs, allowing the passage of air, and so is present in almost all air-breathing animals with lungs. The trachea extends ...
and
esophagus
The esophagus (American English) or oesophagus (British English; both ), non-technically known also as the food pipe or gullet, is an organ in vertebrates through which food passes, aided by peristaltic contractions, from the pharynx to the ...
.
They then pass behind the posterior, middle part of the outer lobes of the
thyroid gland
The thyroid, or thyroid gland, is an endocrine gland in vertebrates. In humans it is in the neck and consists of two connected lobe (anatomy), lobes. The lower two thirds of the lobes are connected by a thin band of Connective tissue, tissue cal ...
and enter the
larynx
The larynx (), commonly called the voice box, is an organ in the top of the neck involved in breathing, producing sound and protecting the trachea against food aspiration. The opening of larynx into pharynx known as the laryngeal inlet is about ...
underneath the
inferior constrictor muscle
The inferior pharyngeal constrictor muscle is a skeletal muscle of the neck. It is the thickest of the three outer pharyngeal muscles. It arises from the sides of the cricoid cartilage and the thyroid cartilage. It is supplied by the vagus nerve ...
,
passing into the larynx just posterior to the cricothyroid joint. The terminal branch is called the ''inferior laryngeal nerve''.
Unlike the other nerves supplying the larynx, the right and left RLNs lack
bilateral symmetry
Symmetry in biology refers to the symmetry observed in organisms, including plants, animals, fungi, and bacteria. External symmetry can be easily seen by just looking at an organism. For example, take the face of a human being which has a pla ...
. The left RLN is longer than the right, because it crosses under the
arch of the aorta at the
ligamentum arteriosum
The ligamentum arteriosum (arterial ligament), also known as the Ligament of Botallo or Harvey's ligament, is a small ligament attaching the aorta to the pulmonary artery. It serves no function in adults but is the remnant of the ductus arteriosus ...
.
Nucleus
The
somatic motor fibers that innervate the
laryngeal muscles, and
pharyngeal muscles
The pharyngeal muscles are a group of muscles that form the pharynx, which is posterior to the oral cavity, determining the shape of its lumen, and affecting its sound properties as the primary resonating cavity.
The pharyngeal muscles (involunta ...
are located in the
nucleus ambiguus
The nucleus ambiguus ("ambiguous nucleus" in English) is a group of large motor neurons, situated deep in the medullary reticular formation named by Jacob Clarke. The nucleus ambiguus contains the cell bodies of neurons that innervate the muscle ...
and emerge from the
medulla
Medulla or Medullary may refer to:
Science
* Medulla oblongata, a part of the brain stem
* Renal medulla, a part of the kidney
* Adrenal medulla, a part of the adrenal gland
* Medulla of ovary, a stroma in the center of the ovary
* Medulla of t ...
in the
cranial root of the accessory nerve. Fibers cross over to and join the vagus nerve in the
jugular foramen
A jugular foramen is one of the two (left and right) large foramina (openings) in the base of the skull, located behind the carotid canal. It is formed by the temporal bone and the occipital bone. It allows many structures to pass, including the i ...
.
Sensory cell bodies are located in the
inferior jugular ganglion,
and the fibers terminate in the
solitary nucleus
In the human brainstem, the solitary nucleus, also called nucleus of the solitary tract, nucleus solitarius, and nucleus tractus solitarii, (SN or NTS) is a series of purely sensory
nuclei (clusters of nerve cell bodies) forming a vertical column ...
.
Parasympathetic fibers to segments of the trachea and esophagus in the neck originate in the
dorsal nucleus of the vagus nerve
The dorsal nucleus of vagus nerve (or posterior nucleus of vagus nerve or dorsal vagal nucleus or nucleus dorsalis nervi vagi or nucleus posterior nervi vagi) is a cranial nerve nucleus for the vagus nerve in the medulla that lies ventral to the fl ...
.
Development
During human and all
vertebrate
Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, ...
development, a series of
pharyngeal arch
The pharyngeal arches, also known as visceral arches'','' are structures seen in the embryonic development of vertebrates that are recognisable precursors for many structures. In fish, the arches are known as the branchial arches, or gill arch ...
pairs form in the developing
embryo
An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male spe ...
. These project forward from the back of the embryo towards the front of the face and neck. Each arch develops its own artery, nerve that controls a distinct muscle group, and skeletal tissue. The arches are numbered from 1 to 6, with 1 being the arch closest to the head of the embryo, and the fifth arch only existing transiently.
Arches 4 and 6 produce the laryngeal cartilages. The nerve of the sixth arch becomes the recurrent laryngeal nerve. The nerve of the fourth arch gives rise to the superior laryngeal nerve. The arteries of the fourth arch, which project between the nerves of the fourth and sixth arches, become the left-sided arch of the aorta and the right subclavian artery. The arteries of the sixth arch persist as the
ductus arteriosus
The ''ductus arteriosus'', also called the ''ductus Botalli'', named after the Italian physiologist Leonardo Botallo, is a blood vessel in the developing fetus connecting the trunk of the pulmonary artery to the proximal descending aorta. It a ...
on the left, and are obliterated on the right.
After birth, the ductus arteriosus regresses to form the
ligamentum arteriosum
The ligamentum arteriosum (arterial ligament), also known as the Ligament of Botallo or Harvey's ligament, is a small ligament attaching the aorta to the pulmonary artery. It serves no function in adults but is the remnant of the ductus arteriosus ...
. During growth, these arteries descend into their ultimate positions in the chest, creating the elongated recurrent paths.
Variation
In roughly 1 out of every 100–200 people, the right inferior laryngeal nerve is nonrecurrent, branching off the vagus nerve around the level of the
cricoid cartilage
The cricoid cartilage , or simply cricoid (from the Greek ''krikoeides'' meaning "ring-shaped") or cricoid ring, is the only complete ring of cartilage around the trachea. It forms the back part of the voice box and functions as an attachment si ...
. Typically, such a configuration is accompanied by variation in the arrangement of the major arteries in the chest; most commonly, the right subclavian artery arises from the left side of the aorta and crosses behind the esophagus. A left nonrecurrent inferior laryngeal nerve is even more uncommon,
requiring the aortic arch be on the right side, accompanied by an arterial variant which prevents the nerve from being drawn into the chest by the left subclavian.
In about four people out of five, there is a connecting branch between the ''inferior laryngeal nerve'', a branch of the RLN, and the
internal laryngeal nerve
The superior laryngeal nerve is a branch of the vagus nerve. It arises from the middle of the inferior ganglion of vagus nerve and in its course receives a branch from the superior cervical ganglion of the sympathetic nervous system.
The superi ...
, a branch of the
superior laryngeal nerve
The superior laryngeal nerve is a branch of the vagus nerve. It arises from the middle of the inferior ganglion of vagus nerve and in its course receives a branch from the superior cervical ganglion of the sympathetic nervous system.
The superi ...
. This is commonly called the ''anastomosis of Galen'' ( la, ansa galeni), even though
anastomosis
An anastomosis (, plural anastomoses) is a connection or opening between two things (especially cavities or passages) that are normally diverging or branching, such as between blood vessels, leaf#Veins, leaf veins, or streams. Such a connection m ...
usually refers to a
blood vessel
The blood vessels are the components of the circulatory system that transport blood throughout the human body. These vessels transport blood cells, nutrients, and oxygen to the tissues of the body. They also take waste and carbon dioxide away ...
,
and is one of several documented anastomoses between the two nerves.
As the recurrent nerve hooks around the
subclavian artery
In human anatomy, the subclavian arteries are paired major arteries of the upper thorax, below the clavicle. They receive blood from the aortic arch. The left subclavian artery supplies blood to the left arm and the right subclavian artery supplie ...
or
aorta
The aorta ( ) is the main and largest artery in the human body, originating from the left ventricle of the heart and extending down to the abdomen, where it splits into two smaller arteries (the common iliac arteries). The aorta distributes ...
, it gives off several branches. There is suspected variability in the configuration of these branches to the
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 ao ...
, trachea, esophagus and
inferior pharyngeal constrictor muscle
The inferior pharyngeal constrictor muscle is a skeletal muscle of the neck. It is the thickest of the three outer pharyngeal muscles. It arises from the sides of the cricoid cartilage and the thyroid cartilage. It is supplied by the vagus nerve ...
.
Function
The recurrent laryngeal nerves control all
intrinsic muscles of the larynx except for the
cricothyroid muscle
The cricothyroid muscle is the only tensor muscle of the larynx aiding with phonation. It is innervated by the superior laryngeal nerve. Its action tilts the thyroid forward to help tense the vocal cords.
Structure
The cricothyroid muscle orig ...
.
These muscles act to open, close, and adjust the tension of the vocal cords, and include the
posterior cricoarytenoid muscle
The posterior cricoarytenoid muscles are small, paired intrinsic muscles of the larynx that extend between cricoid cartilage to the arytenoid cartilages in the larynx.
Structure Origin and insertion
The posterior cricoarytenoid originates f ...
s, the only muscle to open the vocal cords.
The nerves supply muscles on the same side of the body, with the exception of the
interarytenoid muscle, which is innervated from both sides.
The nerves also carry sensory information from the mucous membranes of the larynx below the lower surface of the
vocal fold
The human voice consists of sound made by a human being
Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedality, bipedalism and exceptional cognitive skills due to a large and compl ...
,
as well as sensory, secretory and motor fibres to the cervical segments of the
esophagus
The esophagus (American English) or oesophagus (British English; both ), non-technically known also as the food pipe or gullet, is an organ in vertebrates through which food passes, aided by peristaltic contractions, from the pharynx to the ...
and the
trachea
The trachea, also known as the windpipe, is a Cartilage, cartilaginous tube that connects the larynx to the bronchi of the lungs, allowing the passage of air, and so is present in almost all air-breathing animals with lungs. The trachea extends ...
.
Clinical significance
Injury
![Rekurrens](https://upload.wikimedia.org/wikipedia/commons/e/e3/Rekurrens.png)
The recurrent laryngeal nerves may be injured as a result of trauma, during surgery, as a result of tumour spread, or due to other means.
Injury to the recurrent laryngeal nerves can result in a weakened voice (
hoarseness
A hoarse voice, also known as dysphonia or hoarseness, is when the voice involuntarily sounds breathy, raspy, or strained, or is softer in volume or lower in pitch. A hoarse voice, can be associated with a feeling of unease or scratchiness in the ...
) or loss of voice (
aphonia) and cause problems in the
respiratory tract
The respiratory tract is the subdivision of the respiratory system involved with the process of respiration in mammals. The respiratory tract is lined with respiratory epithelium as respiratory mucosa.
Air is breathed in through the nose to th ...
.
Injury to the nerve may paralyze the
posterior cricoarytenoid muscle
The posterior cricoarytenoid muscles are small, paired intrinsic muscles of the larynx that extend between cricoid cartilage to the arytenoid cartilages in the larynx.
Structure Origin and insertion
The posterior cricoarytenoid originates f ...
on the same side. This is the sole muscle responsible for opening the vocal cords, and paralysis may cause difficulty breathing (
dyspnea
Shortness of breath (SOB), also medically known as dyspnea (in AmE) or dyspnoea (in BrE), is an uncomfortable feeling of not being able to breathing, breathe well enough. The American Thoracic Society defines it as "a subjective experience of brea ...
) during physical activity.
Injury to both the right and left nerve may result in more serious damage, such as
the inability to speak. Additional problems may emerge during healing, as nerve fibres that re-anastamose may result in ''vocal cord motion impairment'', uncoordinated movements of the vocal cord.
Surgery
The nerve receives close attention from surgeons because the nerve is at risk for injury during neck surgery, especially
thyroid
The thyroid, or thyroid gland, is an endocrine gland in vertebrates. In humans it is in the neck and consists of two connected lobes. The lower two thirds of the lobes are connected by a thin band of tissue called the thyroid isthmus. The thy ...
and
parathyroid
Parathyroid glands are small endocrine glands in the neck of humans and other tetrapods. Humans usually have four parathyroid glands, located on the back of the thyroid gland in variable locations. The parathyroid gland produces and secretes par ...
surgery; as well as esophagectomy.
Nerve damage can be assessed by
laryngoscopy
Laryngoscopy () is endoscopy of the larynx, a part of the throat. It is a medical procedure that is used to obtain a view, for example, of the vocal folds and the glottis. Laryngoscopy may be performed to facilitate tracheal intubation during ...
, during which a
stroboscopic light confirms the absence of movement in the affected side of the vocal cords. The right recurrent laryngeal nerve is more susceptible to damage during thyroid surgery because it is close to the bifurcation of the right inferior thyroid artery, variably passing in front of, behind, or between the branches.
Similarly, thermal injury can occur with the use of radio frequency ablation to remove thyroid nodules. The nerve is permanently damaged in 0.3–3% of thyroid surgeries, and transient paralysis occurs in 3–8% of surgeries; accordingly, recurrent laryngeal nerve damage is one of the leading causes of
medicolegal issues for surgeons.
Tumors
The RLN may be compressed by tumors. Studies have shown that 2–18% of
lung cancer
Lung cancer, also known as lung carcinoma (since about 98–99% of all lung cancers are carcinomas), is a malignant lung tumor characterized by uncontrolled cell growth in tissue (biology), tissues of the lung. Lung carcinomas derive from tran ...
patients develop hoarseness because of recurrent laryngeal nerve compression, usually left-sided.
This is associated with worse outcomes, and when found as a presenting symptom, often indicates inoperable tumors. The nerve may be severed intentionally during lung cancer surgery in order to fully remove a tumor.
The RLN may also be damaged by tumors in the neck, especially with malignant lymph nodes with extra-capsular extension of tumor beyond the capsule of the nodes, which may invade the area that carries the ascending nerve on the right or left.
Other disease
In
Ortner's syndrome or cardiovocal syndrome, a rare cause of left recurrent laryngeal nerve
palsy Palsy is a medical term which refers to various types of paralysisDan Agin, ''More Than Genes: What Science Can Tell Us About Toxic Chemicals, Development, and the Risk to Our Children;; (2009), p. 172. or paresis, often accompanied by weakness a ...
, expansion of structures within the
heart
The heart is a muscular organ in most animals. This organ pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste such as carbon dioxide t ...
or major blood vessels impinges upon the nerve, causing symptoms of unilateral nerve injury.
Other animals
Horses are subject to ''equine recurrent laryngeal neuropathy'', a
disease of the axons of the recurrent laryngeal nerves. The cause is not known, although a genetic predisposition is suspected. The length of the nerve is a factor since it is more common in larger horses, and the left side is affected almost exclusively. As the nerve cells die, there is a progressive paralysis of the larynx, causing the airway to collapse. The common presentation is a sound, ranging from a musical whistle to a harsh roar or heaving gasping noise (
stertorous), accompanied by worsening performance. The condition is incurable, but surgery can keep the airway open. Experiments with nerve grafts have been tried.
Although uncommon in dogs, bilateral recurrent laryngeal nerve disease may be the cause of wheezing (
stridor) when middle-aged dogs inhale.
In
sauropod
Sauropoda (), whose members are known as sauropods (; from '' sauro-'' + '' -pod'', 'lizard-footed'), is a clade of saurischian ('lizard-hipped') dinosaurs. Sauropods had very long necks, long tails, small heads (relative to the rest of their bo ...
dinosaurs, the
vertebrate
Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, ...
s with the longest necks, the total length of the vagus nerve and recurrent laryngeal nerve would have been up to long in ''
Supersaurus'', but these would not be the longest neurons that ever existed: the neurons reaching the tip of the tail would have exceeded .
Evidence of evolution
The extreme detour of the recurrent laryngeal nerves, about in the case of
giraffe
The giraffe is a large African hoofed mammal belonging to the genus ''Giraffa''. It is the tallest living terrestrial animal and the largest ruminant on Earth. Traditionally, giraffes were thought to be one species, ''Giraffa camelopardalis ...
s, is cited as
evidence of evolution
Evidence of common descent of living organisms has been discovered by scientists researching in a variety of disciplines over many decades, demonstrating that all life on Earth comes from a single ancestor. This forms an important part of the e ...
, as opposed to
intelligent design
Intelligent design (ID) is a pseudoscientific argument for the existence of God, presented by its proponents as "an evidence-based scientific theory about life's origins". Numbers 2006, p. 373; " Dcaptured headlines for its bold attempt to ...
. The nerve's route would have been direct in the fish-like ancestors of modern
tetrapod
Tetrapods (; ) are four-limbed vertebrate animals constituting the superclass Tetrapoda (). It includes extant and extinct amphibians, sauropsids ( reptiles, including dinosaurs and therefore birds) and synapsids (pelycosaurs, extinct theraps ...
s, 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 circuitous route now observed.
History
Ancient Greek physician
Galen
Aelius Galenus or Claudius Galenus ( el, Κλαύδιος Γαληνός; September 129 – c. AD 216), often Anglicized as Galen () or Galen of Pergamon, was a Greek physician, surgeon and philosopher in the Roman Empire. Considered to be one of ...
demonstrated the nerve course and the clinical syndrome of
recurrent laryngeal nerve paralysis, noting that pigs with the nerve severed were unable to squeal. Galen named the nerve the ''recurrent nerve'', and described the same effect in two human infants who had undergone surgery for
goiter
A goitre, or goiter, is a swelling in the neck resulting from an enlarged thyroid gland. A goitre can be associated with a thyroid that is not functioning properly.
Worldwide, over 90% of goitre cases are caused by iodine deficiency. The term is ...
.
In 1838, five years before he would introduce the concept of
homology
Homology may refer to:
Sciences
Biology
*Homology (biology), any characteristic of biological organisms that is derived from a common ancestor
* Sequence homology, biological homology between DNA, RNA, or protein sequences
*Homologous chrom ...
to biology, anatomist
Richard Owen
Sir Richard Owen (20 July 1804 – 18 December 1892) was an English biologist, comparative anatomist and paleontologist. Owen is generally considered to have been an outstanding naturalist with a remarkable gift for interpreting fossils.
Owe ...
reported upon the dissection of three giraffes, including a description of the full course of the left recurrent laryngeal nerve.
Anatomists
Andreas Vesalius
Andreas Vesalius (Latinized from Andries van Wezel) () was a 16th-century anatomist, physician, and author of one of the most influential books on human anatomy, ''De Humani Corporis Fabrica Libri Septem'' (''On the fabric of the human body'' '' ...
and
Thomas Willis
Thomas Willis FRS (27 January 1621 – 11 November 1675) was an English doctor who played an important part in the history of anatomy, neurology and psychiatry, and was a founding member of the Royal Society.
Life
Willis was born on his pare ...
described the nerve in what is now regarded as an anatomically standard description, and doctor
Frank Lahey documented a way for its interoperative identification during thyroid operations.
Notes
References
External links
*
* ()
Dissection of a giraffe displaying the laryngeal nerveyouTube
{{Authority control
Vagus nerve
Human throat
Nerves of the head and neck