The superior laryngeal nerve is a branch of the

vagus nerve The vagus nerve, also known as the tenth cranial nerve (CN X), plays a crucial role in the autonomic nervous system, which is responsible for regulating involuntary functions within the human body. This nerve carries both sensory and motor fibe ...

. It arises from the middle of the inferior ganglion of the vagus nerve and additionally receives a sympathetic branch from the

superior cervical ganglion The superior cervical ganglion (SCG) is the upper-most and largest of the cervical sympathetic ganglia of the sympathetic trunk. It probably formed by the union of four sympathetic ganglia of the cervical spinal nerves C1–C4. It is the only ...

. The superior laryngeal nerve produces two branches: the internal laryngeal nerve (its sensory branch) which supplies sensory fibers to the laryngeal mucosa, and the external laryngeal nerve (its motor branch) which innervates 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, thus increasing the pitch of the voice ...

Structure

Origin

The superior laryngeal nerve arises from the middle of the inferior ganglion of vagus nerve.

Course

The superior laryngeal nerve descends by the side of the

pharynx The pharynx (: pharynges) is the part of the throat behind the human mouth, mouth and nasal cavity, and above the esophagus and trachea (the tubes going down to the stomach and the lungs respectively). It is found in vertebrates and invertebrates ...

deep to the

internal carotid artery The internal carotid artery is an artery in the neck which supplies the anterior cerebral artery, anterior and middle cerebral artery, middle cerebral circulation. In human anatomy, the internal and external carotid artery, external carotid ari ...

before dividing into two branches —the external laryngeal nerve and the internal laryngeal nerve.

Branches

External laryngeal nerve

The external laryngeal nerve is the smaller, external branch. It descends on the

larynx The larynx (), commonly called the voice box, is an organ (anatomy), 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 ...

, beneath the

sternothyroid muscle The sternothyroid muscle (or sternothyroideus) is an infrahyoid muscle of the neck. It acts to depress the hyoid bone. Structure The two muscles are in contact with each other proximally (close to their origin), but diverge distally (towards t ...

, to supply the

. The external branch functions to stretch the vocal cords by activating the cricothyroid muscle, increasing pitch. The external laryngeal nerve gives branches to pharyngeal plexus and the superior portion of the

inferior pharyngeal constrictor 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 ner ...

, and communicates with the

superior cardiac nerve The superior cardiac nerve arises by two or more branches from the superior cervical ganglion, and occasionally receives a filament from the trunk between the first and second cervical ganglia. It runs down the neck behind the common carotid arter ...

behind the

common carotid artery In anatomy, the left and right common carotid arteries (carotids) () are artery, arteries that supply the head and neck with oxygenated blood; they divide in the neck to form the external carotid artery, external and internal carotid artery, inte ...

Internal laryngeal nerve

The internal laryngeal nerve is the internal branch. It descends to the

thyrohyoid membrane The thyrohyoid membrane (or hyothyroid membrane) is a broad, fibro-elastic sheet of the larynx. It connects the upper border of the thyroid cartilage to the hyoid bone. Structure The thyrohyoid membrane is attached below to the upper border of ...

, piercing it in company with the superior laryngeal artery, and is distributed to the

mucous membrane A mucous membrane or mucosa is a membrane that lines various cavities in the body of an organism and covers the surface of internal organs. It consists of one or more layers of epithelial cells overlying a layer of loose connective tissue. It ...

of the larynx. Of these sensory branches, some are distributed to the

epiglottis The epiglottis (: epiglottises or epiglottides) is a leaf-shaped flap in the throat that prevents food and water from entering the trachea and the lungs. It stays open during breathing, allowing air into the larynx. During swallowing, it closes ...

, the base of the

tongue The tongue is a Muscle, muscular organ (anatomy), organ in the mouth of a typical tetrapod. It manipulates food for chewing and swallowing as part of the digestive system, digestive process, and is the primary organ of taste. The tongue's upper s ...

, and the epiglottic glands; others pass posteriorly, in the

aryepiglottic fold The aryepiglottic folds are triangular folds of mucous membrane of the larynx. They enclose ligamentous and muscular fibres. They extend from the lateral borders of the epiglottis to the arytenoid cartilages, hence the name 'aryepiglottic'. The ...

, to supply the mucous membrane surrounding the entrance of the larynx, and the mucous lining of the larynx as far down as the vocal folds. A filament descends beneath the mucous membrane on the inner surface of the thyroid cartilage and joins the

recurrent laryngeal nerve The recurrent laryngeal nerve (RLN), also known as nervus recurrens, is a branch of the vagus nerve ( cranial nerve X) that supplies all the intrinsic muscles of the larynx, with the exception of the cricothyroid muscles. There are two recur ...

. Above the vocal folds the sensory innervation of the larynx is via the internal laryngeal nerve. Below the vocal folds it is by way of branches of the recurrent laryngeal nerve. The vocal fold itself receives dual innervation from both nerves.

Function

The superior laryngeal nerve innervates the

Clinical significance

A superior laryngeal nerve palsy changes the pitch of the voice and causes an inability to make explosive sounds due to paralysis of the cricothyroid muscle. If no recovery is evident three months after the palsy initially presents, the damage is most likely to be permanent. A bilateral palsy presents as a tiring and hoarse voice. It can be injured in surgery involving the removal of the

thyroid gland The thyroid, or thyroid gland, is an endocrine gland in vertebrates. In humans, it is a butterfly-shaped gland located in the neck below the Adam's apple. It consists of two connected lobes. The lower two thirds of the lobes are connected by ...

(

thyroidectomy A thyroidectomy is an operation that involves the surgery, surgical removal of all or part of the thyroid gland. In general surgery, endocrine or head and neck surgeons often perform a thyroidectomy when a patient has thyroid cancer or some other ...

). Understanding the most common anatomic variations of the distal portion of the external laryngeal nerve and its relation to the inferior constrictor muscle is critical and allows identifying and preserving the integrity of this nerve in most cases. The external branch is susceptible to damage during

cricothyrotomy A cricothyrotomy (also called cricothyroidotomy or laryngotomy) is a medical procedure where an opening is created through the cricothyroid membrane to establish a patent airway during emergency airway management. Cricothyrotomy is primarily per ...

, as it lies immediately deep to the

superior thyroid artery The superior thyroid artery arises from the external carotid artery just below the level of the greater cornu of the hyoid bone and ends in the thyroid gland. Structure From its origin under the anterior border of the sternocleidomastoid the super ...

. The ability to produce pitched sounds is then impaired along with easy voice fatigability, (usually mono-toned voice). Irritation of the internal laryngeal nerve results in uncontrolled coughing - usually as a result of food or water in the

laryngopharynx The pharynx (: pharynges) is the part of the throat behind the mouth and nasal cavity, and above the esophagus and trachea (the tubes going down to the stomach and the lungs respectively). It is found in vertebrates and invertebrates, though its ...

. The lesion of this branch (for example, during surgery) that seeks an anterior approach to the cervix, is associated with a loss of the laryngeal reflex of cough and an elevated risk of aspiration pneumonia.

Additional images

File:Gray1032.png, The position and relation of the esophagus in the cervical region and in the posterior mediastinum. Seen from behind.

References

External links

* () {{Authority control Vagus nerve Human throat