Facial nerve

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Facial nerve
Cranial nerve VII.svg
The course of the facial nerve is shown here
Gray790.png
The nerves of the scalp, face, and side of neck.
Details
From Facial nerve nucleus, intermediate nerve
To Greater superficial petrosal nerve
InnervatesMotor: Muscles of facial expression, posterior belly of digastric, stylohyoid, stapedius
Special sensory: taste to anterior two-thirds of tongue
Parasympathetic: submandibular gland, sublingual gland, lacrimal glands
Identifiers
Latin nervus facialis
MeSH D005154
NeuroNames 551
TA98 A14.2.01.099
TA2 6284
FMA 50868
Anatomical terms of neuroanatomy

The facial nerve, also known as the seventh cranial nerve, cranial nerve VII, or simply CN VII, is a cranial nerve that emerges from the pons of the brainstem, controls the muscles of facial expression, and functions in the conveyance of taste sensations from the anterior two-thirds of the tongue. [1] [2] The nerve typically travels from the pons through the facial canal in the temporal bone and exits the skull at the stylomastoid foramen. [3] It arises from the brainstem from an area posterior to the cranial nerve VI (abducens nerve) and anterior to cranial nerve VIII (vestibulocochlear nerve).

Contents

The facial nerve also supplies preganglionic parasympathetic fibers to several head and neck ganglia.

The facial and intermediate nerves can be collectively referred to as the nervus intermediofacialis.[ citation needed ]

Structure

The path of the facial nerve can be divided into six segments:

  1. intracranial (cisternal) segment (from brainstem pons to internal auditory canal)
  2. meatal (canalicular) segment (within the internal auditory canal)
  3. labyrinthine segment (internal auditory canal to geniculate ganglion)
  4. tympanic (or horizontal) segment (from geniculate ganglion to pyramidal eminence)
  5. mastoid (or vertical) segment (from pyramidal eminence to stylomastoid foramen)
  6. extratemporal segment (from stylomastoid foramen to post parotid branches)

The motor part of the facial nerve arises from the facial nerve nucleus in the pons, while the sensory and parasympathetic parts of the facial nerve arise from the intermediate nerve.

From the brain stem, the motor and sensory parts of the facial nerve join 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 the shortest and narrowest segment of the facial nerve and ends where the facial nerve forms a bend known as the geniculum of the facial nerve (genu meaning knee), which contains the geniculate ganglion 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. Postsynaptic fibers of the greater petrosal nerve innervate the lacrimal gland.

In the tympanic segment, the facial nerve runs through the tympanic cavity, medial to the incus.

The pyramidal eminence is the second bend in the facial nerve, where the nerve runs downward as the mastoid segment, the longest segment of the facial nerve. In the temporal part of the facial canal, the nerve gives branch to the stapedius muscle 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 and submandibular glands.

Upon emerging from the stylomastoid foramen, the facial nerve gives rise to the posterior auricular branch. It then gives rise to the branch to the posterior belly of the digastric, and then the branch to the stylohyoid. The facial nerve then passes through the parotid gland, which it does not innervate, to form the parotid plexus. The nerve then bifurcates at the pes anserinus to become the upper and lower divisions of the facial nerve. [4] It then splits into five branches (temporal, zygomatic, buccal, marginal mandibular and cervical), innervating the muscles of facial expression. [5] [6]

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 palatine glands, the lacrimal gland, and the pharyngeal gland. It also provides parasympathetic innervation to the sphenoid sinus, frontal sinus, maxillary sinus, ethmoid sinus, and nasal cavity. This nerve also includes taste fibers for the palate via the lesser palatine nerve and greater palatine nerve.

The communicating branch to the otic ganglion arises at the geniculate ganglion and joins the lesser petrosal nerve to reach the otic ganglion. [7]

The nerve to stapedius provides motor innervation for the stapedius muscle 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. [1]

Extracranial branches

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

Intra operatively the facial nerve is recognized at 3 constant landmarks:[ citation needed ]

  1. At the tip of tragus where the nerve is 1 cm deep and inferior [8]
  2. At the posterior belly of digastric by tracing this backwards to the tympanic plate, the nerve can be found between these two structures
  3. By locating the posterior facial vein at the inferior aspect of the gland where the marginal branch would be seen crossing it.
  4. Lateral semicircular canal
  5. Foot of incus

Nucleus

The cell bodies for the facial nerve are grouped in anatomical areas called nuclei or ganglia. The cell bodies for the afferent nerves are found in the geniculate ganglion for taste sensation. The cell bodies for muscular efferent nerves are found in the facial motor nucleus 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 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. [9]

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 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. [10]

Function

Facial expression

The main function of the facial nerve is motor control of all the muscles of facial expression. It also innervates the posterior belly of the digastric muscle, the stylohyoid muscle, and the stapedius muscle of the middle ear. These skeletal muscles are developed from the second pharyngeal arch.

Facial sensation

In addition, the facial nerve receives taste sensations from the anterior two-thirds of the tongue via the chorda tympani. Taste sensation is sent to the gustatory portion (superior part) of the solitary nucleus. General sensation from the anterior two-thirds of tongue are supplied by afferent fibers of the third division of the fifth cranial nerve (CN V-3). These sensory (CN V3) 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 geniculate ganglion, 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 solitary nucleus.

The facial nerve also supplies a small amount of afferent innervation to the oropharynx below the palatine tonsil. 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 parasympathetic fibers to the submandibular gland and sublingual glands 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 lacrimal gland via the pterygopalatine ganglion. 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.

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, which is usually manifested by facial paralysis. [11] Bell's palsy is one type of idiopathic 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. 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.[ citation needed ] Facial nerve decompression 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), [12] 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, 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 flavored solution, or with electronic stimulation (similar to putting your tongue on a battery).

Corneal reflex. 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

See also

Related Research Articles

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<span class="mw-page-title-main">Trigeminal nerve</span> Cranial nerve responsible for the faces senses and motor functions

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 chewing; it is the most complex of the cranial nerves. Its name (trigeminal, from Latin tri- 'three' and -geminus 'twin') derives from each of the two nerves (one on each side of the pons) having three major branches: the ophthalmic nerve (V1), the maxillary nerve (V2), and the mandibular nerve (V3). The ophthalmic and maxillary nerves are purely sensory, whereas the mandibular nerve supplies motor as well as sensory (or "cutaneous") functions. Adding to the complexity of this nerve is that autonomic nerve fibers as well as special sensory fibers (taste) are contained within it.

<span class="mw-page-title-main">Glossopharyngeal nerve</span> Cranial nerve IX, for the tongue and pharynx

The glossopharyngeal nerve, also known as the ninth cranial nerve, cranial nerve IX, or simply CN IX, is a cranial nerve that exits the brainstem from the sides of the upper medulla, just anterior to the vagus nerve. Being a mixed nerve (sensorimotor), it carries afferent sensory and efferent motor information. The motor division of the glossopharyngeal nerve is derived from the basal plate of the embryonic medulla oblongata, whereas the sensory division originates from the cranial neural crest.

<span class="mw-page-title-main">Mandibular nerve</span> Branch of the trigeminal nerve responsible for the lower face and jaw

In neuroanatomy, the mandibular nerve (V3) is the largest of the three divisions of the trigeminal nerve, the fifth cranial nerve (CN V). Unlike the other divisions of the trigeminal nerve (ophthalmic nerve, maxillary nerve) which contain only afferent fibers, the mandibular nerve contains both afferent and efferent fibers. These nerve fibers innervate structures of the lower jaw and face, such as the tongue, lower lip, and chin. The mandibular nerve also innervates the muscles of mastication.

<span class="mw-page-title-main">Submandibular gland</span> Human salivary gland

The paired submandibular glands are major salivary glands located beneath the floor of the mouth. In adult humans, they each weigh about 15 grams and contribute some 60–67% of unstimulated saliva secretion; on stimulation their contribution decreases in proportion as parotid gland secretion rises to 50%. The average length of the normal adult human submandibular salivary gland is approximately 27 mm, while the average width is approximately 14.3 mm.

<span class="mw-page-title-main">Otic ganglion</span> Parasympathetic ganglion of the head and neck

The otic ganglion is a small parasympathetic ganglion located immediately below the foramen ovale in the infratemporal fossa and on the medial surface of the mandibular nerve. It is functionally associated with the glossopharyngeal nerve and innervates the parotid gland for salivation.

<span class="mw-page-title-main">Auriculotemporal nerve</span> Branch of the mandibular nerve

The auriculotemporal nerve is a sensory branch of the mandibular nerve (CN V3) that runs with the superficial temporal artery and vein, and provides sensory innervation to parts of the external ear, scalp, and temporomandibular joint. The nerve also conveys post-ganglionic parasympathetic fibres from the otic ganglion to the parotid gland.

<span class="mw-page-title-main">Chorda tympani</span> Nerve carrying taste sensations

Chorda tympani is a branch of the facial nerve that carries gustatory (taste) sensory innervation from the front of the tongue and parasympathetic (secretomotor) innervation to the submandibular and sublingual salivary glands.

<span class="mw-page-title-main">Greater petrosal nerve</span> Nerve in the skull

The greater petrosal nerve is a nerve of the head mainly containing pre-ganglionic parasympathetic fibres which ultimately synapse in the pterygopalatine ganglion. It branches from the facial nerve and is derived from the parasympathetic part of the nervus intermedius component of CN VII, with its cell bodies located in the superior salivary nucleus. In the connective tissue substance of the foramen lacerum, the greater petrosal nerve unites with the (sympathetic) deep petrosal nerve to form the nerve of the pterygoid canal which proceeds to the pterygopalatine ganglion.

<span class="mw-page-title-main">Pharyngeal arch</span> Embryonic precursor structures in vertebrates

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 arches.

<span class="mw-page-title-main">Lingual nerve</span> Human nerve relaying sense to the tongue

The lingual nerve carries sensory innervation from the anterior two-thirds of the tongue. It contains fibres from both the mandibular division of the trigeminal nerve (CN V3) and from the facial nerve (CN VII). The fibres from the trigeminal nerve are for touch, pain and temperature (general sensation), and the ones from the facial nerve are for taste (special sensation).

<span class="mw-page-title-main">Facial canal</span> Hole in the temporal bone of the skull carrying the facial nerve

The facial canal is a Z-shaped canal in the temporal bone of the skull. It extends between the internal acoustic meatus and stylomastoid foramen. It transmits the facial nerve.

<span class="mw-page-title-main">Submandibular ganglion</span>

The submandibular ganglion is part of the human autonomic nervous system. It is one of four parasympathetic ganglia of the head and neck..

<span class="mw-page-title-main">Parasympathetic ganglia</span> Autonomic ganglia of the parasympathetic nervous system

Parasympathetic ganglia are the autonomic ganglia of the parasympathetic nervous system. Most are small terminal ganglia or intramural ganglia, so named because they lie near or within (respectively) the organs they innervate. The exceptions are the four paired parasympathetic ganglia of the head and neck.

<span class="mw-page-title-main">Intermediate nerve</span> Portion of the facial nerve

The intermediate nerve, nervus intermedius, nerve of Wrisberg or glossopalatine nerve is the part of the facial nerve located between the motor component of the facial nerve and the vestibulocochlear nerve. It contains the sensory and parasympathetic fibers of the facial nerve. Upon reaching the facial canal, it joins with the motor root of the facial nerve at the geniculate ganglion. Alex Alfieri postulates that the intermediate nerve should be considered as a separate cranial nerve and not a part of the facial nerve.

<span class="mw-page-title-main">Salivatory nuclei</span>

The salivatory nuclei are pre-ganglionic parasympathetic neurons in the caudal pons representing the general visceral efferent (GVE) cranial nerve nuclei giving rise to axons which join the facial nerve and glossopharyngeal nerve to reach and innervate the salivary as well as lacrimal glands. The nuclei may also be involved in parasympathetic control of head vasculature.

<span class="mw-page-title-main">Outline of human anatomy</span> Overview of and topical guide to human anatomy

The following outline is provided as an overview of and topical guide to human anatomy:

<span class="mw-page-title-main">Outline of the human nervous system</span> Overview of and topical guide to the human nervous system

The following diagram is provided as an overview of and topical guide to the human nervous system:

References

PD-icon.svgThis article incorporates text in the public domain from page 901 of the 20th edition of Gray's Anatomy (1918)

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