The facial nerve, also known as the seventh cranial nerve, cranial nerve VII, or simply CN VII, is a

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 ...

that emerges from the

pons The pons (from Latin , "bridge") is part of the brainstem that in humans and other bipeds lies inferior to the midbrain, superior to the medulla oblongata and anterior to the cerebellum. The pons is also called the pons Varolii ("bridge of Va ...

of the

brainstem The brainstem (or brain stem) is the posterior stalk-like part of the brain that connects the cerebrum with the spinal cord. In the human brain the brainstem is composed of the midbrain, the pons, and the medulla oblongata. The midbrain is ...

, controls the

muscles of facial expression The facial muscles are a group of striated skeletal muscles supplied by the facial nerve (cranial nerve VII) that, among other things, control facial expression. These muscles are also called mimetic muscles. They are only found in mammals, a ...

, and functions in the conveyance of

taste The gustatory system or sense of taste is the sensory system that is partially responsible for the perception of taste (flavor). Taste is the perception produced or stimulated when a substance in the mouth reacts chemically with taste receptor ...

sensations from the anterior two-thirds of the

tongue The tongue is a muscular organ in the mouth of a typical tetrapod. It manipulates food for mastication and swallowing as part of the digestive process, and is the primary organ of taste. The tongue's upper surface (dorsum) is covered by taste ...

. The nerve typically travels from the pons through the facial canal in the

temporal bone The temporal bones are situated at the sides and base of the skull, and lateral to the temporal lobes of the cerebral cortex. The temporal bones are overlaid by the sides of the head known as the temples, and house the structures of the ears. ...

and exits the skull at the stylomastoid foramen. It arises from the brainstem from an area posterior to the cranial nerve VI (abducens nerve) and anterior to cranial nerve VIII (vestibulocochlear nerve). The facial nerve also supplies preganglionic

parasympathetic The parasympathetic nervous system (PSNS) is one of the three divisions of the autonomic nervous system, the others being the sympathetic nervous system and the enteric nervous system. The enteric nervous system is sometimes considered part of ...

fibers to several head and neck

ganglia A ganglion is a group of neuron cell bodies in the peripheral nervous system. In the somatic nervous system this includes dorsal root ganglia and trigeminal ganglia among a few others. In the autonomic nervous system there are both sympathe ...

. The facial and

intermediate nerve The intermediate nerve, nervus intermedius, nerve of Wrisberg or Glossopalatine nerve, is the part of the facial nerve (cranial nerve VII) located between the motor component of the facial nerve and the vestibulocochlear nerve (cranial nerve VIII ...

s can be collectively referred to as the nervus intermediofacialis.

Structure

The path of the facial nerve can be divided into six segments: # intracranial (cisternal) segment # meatal (canalicular) segment (within the internal auditory canal) # labyrinthine segment (internal auditory canal to geniculate ganglion) # tympanic segment (from

geniculate ganglion The geniculate ganglion (from Latin ''genu'', for "knee") is a collection of pseudounipolar sensory neurons of the facial nerve located in the facial canal of the head. It receives fibers from the facial nerve. It sends fibers that supply the ...

to pyramidal eminence) # mastoid segment (from pyramidal eminence to stylomastoid foramen) # extratemporal segment (from stylomastoid foramen to post parotid branches) The motor part of the facial nerve arises from the facial nerve nucleus in the

, while the sensory and parasympathetic parts of the facial nerve arise from the

. From the brain stem, the motor and sensory parts of the facial nerve join together and traverse the posterior cranial fossa before entering the petrous temporal bone via the internal auditory meatus. Upon exiting the internal auditory meatus, the nerve then runs a tortuous course through the facial canal, which is divided into the labyrinthine, tympanic, and mastoid segments. The labyrinthine segment is very short, and ends where the facial nerve forms a bend known as the geniculum of the facial nerve (''genu'' meaning knee), which contains the

for sensory nerve bodies. The first branch of the facial nerve, the greater petrosal nerve, arises here from the geniculate ganglion. The greater petrosal nerve runs through the pterygoid canal and synapses at the

pterygopalatine ganglion The pterygopalatine ganglion (aka Meckel's ganglion, nasal ganglion, or sphenopalatine ganglion) is a parasympathetic ganglion found in the pterygopalatine fossa. It is largely innervated by the greater petrosal nerve (a branch of the facial ner ...

. Postsynaptic fibers of the greater petrosal nerve innervate the

lacrimal gland The lacrimal glands are paired exocrine glands, one for each eye, found in most terrestrial vertebrates and some marine mammals, that secrete the aqueous layer of the tear film. In humans, they are situated in the upper lateral region of each or ...

. In the tympanic segment, the facial nerve runs through the

tympanic cavity The tympanic cavity is a small cavity surrounding the bones of the middle ear. Within it sit the ossicles, three small bones that transmit vibrations used in the detection of sound. Structure On its lateral surface, it abuts the external auditor ...

, medial to the incus. The pyramidal eminence is the second bend in the facial nerve, where the nerve runs downward as the mastoid segment. In the temporal part of the facial canal, the nerve gives rise to the nerve to the

stapedius muscle The stapedius is the smallest skeletal muscle in the human body. At just over one millimeter in length, its purpose is to stabilize the smallest bone in the body, the stapes or strirrup bone of the middle ear. Structure The stapedius emerges from ...

and chorda tympani. The chorda tympani supplies taste fibers to the anterior two thirds of the tongue, and also synapses with the submandibular ganglion. Postsynaptic fibers from the submandibular ganglion supply the

sublingual Sublingual (abbreviated SL), from the Latin for "under the tongue", refers to the pharmacological route of administration by which substances diffuse into the blood through tissues under the tongue. The sublingual glands receive their primary ...

and submandibular glands. Upon emerging from the stylomastoid foramen, the facial nerve gives rise to the posterior auricular branch. The facial nerve then passes through the parotid gland, which it does not innervate, to form the

parotid plexus The parotid plexus or plexus parotideus is the branch point of the facial nerve (extratemporal) after it leaves the stylomastoid foramen. This division takes place within the parotid gland. Branches Commonly, it divides into the following branch ...

, which splits into five branches (temporal, zygomatic, buccal, marginal mandibular, and cervical) innervating the

Intracranial branches

The greater petrosal nerve arises at the superior salivatory nucleus of the pons and provides parasympathetic innervation to several glands, including the

nasal glands The nasal glands are the seromucous glands in the respiratory The respiratory system (also respiratory apparatus, ventilatory system) is a biological system consisting of specific organs and structures used for gas exchange in animals and pla ...

, the palatine glands, the

, and the pharyngeal gland. It also provides parasympathetic innervation to the sphenoid sinus, frontal sinus, maxillary sinus, ethmoid sinus, and

nasal cavity The nasal cavity is a large, air-filled space above and behind the nose in the middle of the face. The nasal septum divides the cavity into two cavities, also known as fossae. Each cavity is the continuation of one of the two nostrils. The nasal ...

. This nerve also includes taste fibers for the palate via the

lesser palatine nerve The lesser palatine nerves (posterior palatine nerve) are branches of the maxillary nerve (CN V2). They descends through the greater palatine canal alongside the greater palatine nerve, and emerge (separately) through the lesser palatine foramen t ...

and greater palatine nerve. The communicating branch to the otic ganglion arises at the

and joins the lesser petrosal nerve to reach the otic ganglion. The

nerve to stapedius The nerve to the stapedius is a branch of the facial nerve (CN VII) which innervates the stapedius muscle. It arises from the CN VII opposite the pyramidal eminence and passes through a small canal in this eminence to reach the stapedius muscle ...

provides motor innervation for the

in middle ear The chorda tympani provides parasympathetic innervation to the sublingual and submandibular glands, as well as special sensory taste fibers for the anterior two thirds of the tongue.

Extracranial branches

Distal to stylomastoid foramen, the following nerves branch off the facial nerve: *

Posterior auricular nerve The posterior auricular nerve is a nerve of the head. It is a branch of the facial nerve (CN VII). It communicates with branches from the vagus nerve, the great auricular nerve, and the lesser occipital nerve. Its auricular branch supplies th ...

which controls movements of some of the scalp muscles around the ear * Branch to posterior belly of

digastric muscle The digastric muscle (also digastricus) (named ''digastric'' as it has two 'bellies') is a small muscle located under the jaw. The term "digastric muscle" refers to this specific muscle. However, other muscles that have two separate muscle bell ...

as well as the stylohyoid muscle * Five major facial branches (at

) – from superior to inferior: ** Temporal branch ** Zygomatic branch ** Buccal branch ** Marginal mandibular branch ** Cervical branch # At the tip of tragus where the nerve is 1 cm deep and inferior # At the posterior belly of digastric by tracing this backwards to the tympanic plate, the nerve can be found between these two structures # By locating the

posterior facial vein The retromandibular vein (temporomaxillary vein, posterior facial vein) is a major vein of the face. Anatomy Origin The retromandibular vein is formed by the union of the superficial temporal and maxillary veins. Course It descends in th ...

at the inferior aspect of the gland where the marginal branch would be seen crossing it. # Lateral semicircular canal # Foot of incus

Nucleus

The cell bodies for the facial nerve are grouped in anatomical areas called nuclei or

. The cell bodies for the afferent nerves are found in the

for taste sensation. The cell bodies for muscular efferent nerves are found in the

facial motor nucleus The facial motor nucleus is a collection of neurons in the brainstem that belong to the facial nerve (cranial nerve VII). These lower motor neurons innervate the muscles of facial expression and the stapedius. Structure The nucleus is situated ...

whereas the cell bodies for the parasympathetic efferent nerves are found in the superior salivatory nucleus.

Development

The facial nerve is developmentally derived from the second pharyngeal arch, or branchial arch. The second arch is called the hyoid arch because it contributes to the formation of the lesser horn and upper body of the

hyoid bone The hyoid bone (lingual bone or tongue-bone) () is a horseshoe-shaped bone situated in the anterior midline of the neck between the chin and the thyroid cartilage. At rest, it lies between the base of the mandible and the third cervical verteb ...

(the rest of the hyoid is formed by the third arch). The facial nerve supplies motor and sensory innervation to the muscles formed by the second pharyngeal arch, including the muscles of facial expression, the posterior belly of the digastric, stylohyoid, and stapedius. The motor division of the facial nerve is derived from the basal plate of the embryonic pons, while the sensory division originates from the cranial neural crest. Although the anterior two thirds of the tongue are derived from the first pharyngeal arch, which gives rise to the trigeminal nerve, not all innervation of the tongue is supplied by it. The lingual branch of the mandibular division (V3) of the

trigeminal nerve In neuroanatomy, the trigeminal nerve ( lit. ''triplet'' nerve), also known as the fifth cranial nerve, cranial nerve V, or simply CN V, is a cranial nerve responsible for sensation in the face and motor functions such as biting and che ...

supplies non-taste sensation (pressure, heat, texture) to the anterior part of the tongue via general somatic afferent fibers. Nerve fibers for taste are supplied by the chorda tympani branch of the facial nerve via special visceral afferent fibers.

Function

Facial expression

The main function of the facial nerve is motor control of all of the

. It also innervates the posterior belly of the digastric muscle, the stylohyoid muscle, and the

stapedius The stapedius is the smallest skeletal muscle in the human body. At just over one millimeter in length, its purpose is to stabilize the smallest bone in the body, the stapes or strirrup bone of the middle ear. Structure The stapedius emerges fr ...

muscle of the middle ear. All of these muscles are striated muscles of branchiomeric origin developing from the 2nd pharyngeal arch.

Facial sensation

In addition, the facial nerve receives

sensations from the anterior two-thirds of the

via the chorda tympani. Taste sensation is sent to the gustatory portion (superior part) of 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 ...

. General sensation from the anterior two-thirds of tongue are supplied by afferent fibers of the third division of the fifth cranial nerve (V-3). These sensory (V-3) and taste (VII) fibers travel together as the lingual nerve briefly before the chorda tympani leaves the lingual nerve to enter the tympanic cavity (middle ear) via the petrotympanic fissure. It joins the rest of the facial nerve via the canaliculus for chorda tympani. The facial nerve then forms the

, which contains the cell bodies of the taste fibers of chorda tympani and other taste and sensory pathways. From the geniculate ganglion, the taste fibers continue as the intermediate nerve which goes to the upper anterior quadrant of the fundus of the internal acoustic meatus along with the motor root of the facial nerve. The intermediate nerve reaches the posterior cranial fossa via the internal acoustic meatus before synapsing in the

. The facial nerve also supplies a small amount of afferent innervation to the

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

below the

palatine tonsil Palatine tonsils, commonly called the tonsils and occasionally called the faucial tonsils, are tonsils located on the left and right sides at the back of the throat, which can often be seen as flesh-colored, pinkish lumps. Tonsils only present a ...

. There is also a small amount of cutaneous sensation carried by the nervus intermedius from the skin in and around the auricle (outer ear).

Other

The facial nerve also supplies

fibers to the

submandibular gland The paired submandibular glands (historically known as submaxillary glands) are major salivary glands located beneath the floor of the mouth. They each weigh about 15 grams and contribute some 60–67% of unstimulated saliva secretion; on stimul ...

and

sublingual gland The paired sublingual glands are major salivary glands in the mouth. They are the smallest, most diffuse, and the only unencapsulated major salivary glands. They provide only 3-5% of the total salivary volume. There are also two other types of s ...

s via chorda tympani. Parasympathetic innervation serves to increase the flow of saliva from these glands. It also supplies parasympathetic innervation to the nasal mucosa and the

via the

. The parasympathetic fibers that travel in the facial nerve originate in the superior salivatory nucleus. The facial nerve also functions as the efferent limb of the

corneal reflex The corneal reflex, also known as the blink reflex or eyelid reflex, is an involuntary blinking of the eyelids elicited by stimulation of the cornea (such as by touching or by a foreign body), though it could result from any peripheral stimulus. ...

Functional components

The facial nerve carries axons of type GSA, general somatic afferent, to skin of the posterior ear. The facial nerve also carries axons of type GVE, general visceral efferent, which innervate the sublingual, submandibular, and lacrimal glands, also mucosa of nasal cavity. Axons of type SVE, special visceral efferent, innervate muscles of facial expression, stapedius, the posterior belly of digastric, and the stylohyoid. The axons of type SVA, special visceral afferent, provide taste to the anterior two-thirds of tongue via chorda tympani.

Clinical significance

Palsy

People may suffer from

acute facial nerve paralysis Facial nerve paralysis is a common problem that involves the paralysis of any structures innervated by the facial nerve. The pathway of the facial nerve is long and relatively convoluted, so there are a number of causes that may result in facia ...

, which is usually manifested by facial paralysis.

Bell's palsy Bell's palsy is a type of facial paralysis that results in a temporary inability to control the facial muscles on the affected side of the face. In most cases, the weakness is temporary and significantly improves over weeks. Symptoms can vary ...

is one type of

idiopathic An idiopathic disease is any disease with an unknown cause or mechanism of apparent spontaneous origin. From Greek ἴδιος ''idios'' "one's own" and πάθος ''pathos'' "suffering", ''idiopathy'' means approximately "a disease of its own kin ...

acute facial nerve paralysis, which is more accurately described as a multiple cranial nerve ganglionitis that involves the facial nerve, and most likely results from viral infection and also sometimes as a result of

Lyme disease Lyme disease, also known as Lyme borreliosis, is a vector-borne disease caused by the '' Borrelia'' bacterium, which is spread by ticks in the genus '' Ixodes''. The most common sign of infection is an expanding red rash, known as erythema ...

. Iatrogenic Bell's palsy may also be as a result of an incorrectly placed dental local-anesthetic ( inferior alveolar nerve block). Although giving the appearance of a hemiplegic stroke, effects dissipate with the drug. When the facial nerve is permanently damaged due to a birth defect, trauma, or other disorder, surgery including a cross facial nerve graft or masseteric facial nerve transfer may be performed to help regain facial movement.

Facial nerve decompression Facial nerve decompression is a type of nerve decompression (surgery), decompression surgery where abnormal compression on the facial nerve is relieved. Causes of facial nerve compression Pressure and compression of any cause on a peripheral n ...

surgery is also sometimes carried out in certain cases of facial nerve compression.

Examination

Voluntary facial movements, such as wrinkling the brow, showing teeth, frowning, closing the eyes tightly (inability to do so is called

lagophthalmos Lagophthalmos is the inability to close the eyelids completely. Cline D; Hofstetter HW; Griffin JR. ''Dictionary of Visual Science''. 4th ed. Butterworth-Heinemann, Boston 1997. Blinking covers the eye with a thin layer of tear fluid, thereby p ...

),Kliniska Färdigheter: Informationsutbytet Mellan Patient Och Läkare, LINDGREN, STEFAN, pursing the lips and puffing out the cheeks, all test the facial nerve. There should be no noticeable asymmetry. In an upper motor neuron lesion, called

central seven Central facial palsy (colloquially referred to as central seven) is a symptom or finding characterized by paralysis or paresis of the lower half of one side of the face. It usually results from damage to upper motor neurons of the facial nerve. ...

, only the lower part of the face on the contralateral side will be affected, due to the bilateral control to the upper facial muscles ( frontalis and orbicularis oculi). Lower motor neuron lesions can result in a CN VII palsy (Bell's palsy is the idiopathic form of facial nerve palsy), manifested as both upper and lower facial weakness on the same side of the lesion. Taste can be tested on the anterior two-thirds of the tongue. This can be tested with a swab dipped in a flavoured solution, or with electronic stimulation (similar to putting your tongue on a battery).

Corneal reflex The corneal reflex, also known as the blink reflex or eyelid reflex, is an involuntary blinking of the eyelids elicited by stimulation of the cornea (such as by touching or by a foreign body), though it could result from any peripheral stimulus. ...

. The afferent arc is mediated by the general sensory afferents of the trigeminal nerve. The efferent arc occurs via the facial nerve. The reflex involves consensual blinking of both eyes in response to stimulation of one eye. This is due to the facial nerves' innervation of the muscles of facial expression, namely orbicularis oculi, responsible for blinking. Thus, the corneal reflex effectively tests the proper functioning of both cranial nerves V and VII.

Additional images

File:Brain human normal inferior view with labels en.svg, Inferior view of the human brain, with the cranial nerves labelled. File:Gray781.png, Mandibular division of the trifacial nerve. File:Gray788.png, Plan of the facial and intermediate nerves and their communication with other nerves. File:Gray789.png, The course and connections of the facial nerve in the

. File:Gray792.png, Upper part of medulla spinalis and hind- and mid-brains; posterior aspect, exposed in situ. File:Gray1209.png, Left temporal bone showing surface markings for the tympanic antrum (red), transverse sinus (blue), and facial nerve (yellow). File:Head facial nerve branches.jpg, Head facial nerve branches File:Slide2umr.JPG, Facial nerve. Deep dissection.

References

External links

{{Authority control Cranial nerves Motor system Innervation of the face Autonomic nervous system Gustatory system Human mouth anatomy