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Facial Nerve

 
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The facial nerve is the seventh (VII) of twelve paired cranial nerves
Cranial nerves

Cranial nerves are nerves that emerge directly from the brain stem in contrast to spinal nerves which emerge from segments of the spinal cord. Although thirteen cranial nerves in human anatomy fit this description, twelve are conventionally recognized....
. It emerges from the brainstem between the pons
Pons

The pons is a structure located on the brain stem. It is cranial to the medulla oblongata, caudal to the midbrain, and ventral to the cerebellum....
 and the medulla
Medulla oblongata

The medulla oblongata is the lower portion of the brainstem. It deals with Autonomic nervous system functions, such as breathing and blood pressure....
, and controls the muscles of facial expression, and taste
Taste

Sorry, no overview for this topic
 to the anterior two-thirds of the tongue
Tongue

The tongue is skeletal muscle on the floor of the mouth that manipulates food for chewing . It is the primary organ of taste. Much of the upper surface of the tongue is covered in papillae and taste buds....
. It also supplies preganglionic parasympathetic fibers to several head and neck ganglia.

motor part of the facial nerve arises from the facial nerve nucleus in the pons
Pons

The pons is a structure located on the brain stem. It is cranial to the medulla oblongata, caudal to the midbrain, and ventral to the cerebellum....
 while the sensory part of the facial nerve arises from the nervus intermedius
Nervus intermedius

The nervus intermedius, or intermediate nerve, is the part of the facial nerve located between the motor component of the facial nerve and the vestibulocochlear nerve ....
.

The motor part of the facial nerve enters the petrous temporal bone into the internal auditory meatus
Internal auditory meatus

The internal acoustic meatus is a canal in the temporal bone of the skull that carries nerves from inside the cranium towards the middle and inner ear compartments....
 (intimately close to the inner ear
Inner ear

The inner ear is the labyrinth , a system of passages comprising two main functional parts:* the organ of hearing, or cochlea* and the vestibular apparatus, the organ of balance that consists of three semicircular canals and the Vestibule of the ear....
) then runs a tortuous course (including two tight turns) through the facial canal
Facial canal

The facial canal is a canal running from the internal acoustic meatus to the stylomastoid foramen, with approximately 3cm total length is the longest osseous canal of a nerve in a man ....
, emerges from the stylomastoid foramen
Stylomastoid foramen

Between the styloid process and mastoid portion of the temporal bone processes of the temporal bone is the stylomastoid foramenIt is the termination of the facial canal, and transmits the facial nerve and stylomastoid artery....
 and passes through the parotid gland
Parotid gland

For the toad wart, see parotoid gland.The parotid gland is the largest of the salivary glands. It is found wrapped around the mandibular ramus, and it secretes saliva through Stensen's duct into the oral cavity, to facilitate mastication and swallowing....
, where it divides into five major branches.






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Encyclopedia


The facial nerve is the seventh (VII) of twelve paired cranial nerves
Cranial nerves

Cranial nerves are nerves that emerge directly from the brain stem in contrast to spinal nerves which emerge from segments of the spinal cord. Although thirteen cranial nerves in human anatomy fit this description, twelve are conventionally recognized....
. It emerges from the brainstem between the pons
Pons

The pons is a structure located on the brain stem. It is cranial to the medulla oblongata, caudal to the midbrain, and ventral to the cerebellum....
 and the medulla
Medulla oblongata

The medulla oblongata is the lower portion of the brainstem. It deals with Autonomic nervous system functions, such as breathing and blood pressure....
, and controls the muscles of facial expression, and taste
Taste

Sorry, no overview for this topic
 to the anterior two-thirds of the tongue
Tongue

The tongue is skeletal muscle on the floor of the mouth that manipulates food for chewing . It is the primary organ of taste. Much of the upper surface of the tongue is covered in papillae and taste buds....
. It also supplies preganglionic parasympathetic fibers to several head and neck ganglia.

Course

The motor part of the facial nerve arises from the facial nerve nucleus in the pons
Pons

The pons is a structure located on the brain stem. It is cranial to the medulla oblongata, caudal to the midbrain, and ventral to the cerebellum....
 while the sensory part of the facial nerve arises from the nervus intermedius
Nervus intermedius

The nervus intermedius, or intermediate nerve, is the part of the facial nerve located between the motor component of the facial nerve and the vestibulocochlear nerve ....
.

The motor part of the facial nerve enters the petrous temporal bone into the internal auditory meatus
Internal auditory meatus

The internal acoustic meatus is a canal in the temporal bone of the skull that carries nerves from inside the cranium towards the middle and inner ear compartments....
 (intimately close to the inner ear
Inner ear

The inner ear is the labyrinth , a system of passages comprising two main functional parts:* the organ of hearing, or cochlea* and the vestibular apparatus, the organ of balance that consists of three semicircular canals and the Vestibule of the ear....
) then runs a tortuous course (including two tight turns) through the facial canal
Facial canal

The facial canal is a canal running from the internal acoustic meatus to the stylomastoid foramen, with approximately 3cm total length is the longest osseous canal of a nerve in a man ....
, emerges from the stylomastoid foramen
Stylomastoid foramen

Between the styloid process and mastoid portion of the temporal bone processes of the temporal bone is the stylomastoid foramenIt is the termination of the facial canal, and transmits the facial nerve and stylomastoid artery....
 and passes through the parotid gland
Parotid gland

For the toad wart, see parotoid gland.The parotid gland is the largest of the salivary glands. It is found wrapped around the mandibular ramus, and it secretes saliva through Stensen's duct into the oral cavity, to facilitate mastication and swallowing....
, where it divides into five major branches. Though it passes through the parotid gland, it does not innervate the gland. This action is the responsibility of cranial nerve IX, the glossopharyngeal nerve
Glossopharyngeal nerve

The glossopharyngeal nerve is the ninth of twelve pairs of cranial nerves . It exits the brainstem out from the sides of the upper Medulla oblongata, just rostral to the vagus nerve....
.

Inside one of the tight turns in the facial canal, the facial nerve forms the geniculate ganglion
Geniculate ganglion

The geniculate ganglion is an L-shaped collection of fibers and sensory neurons of the facial nerve located in the facial canal of the head. It receives fibers from the motor, sensory, and parasympathetic nervous system components of the facial nerve and sends fibers that will innervate the lacrimal glands, submandibular glands, sublingual g...
.

No other nerve in the body travels such a long distance through a bony canal.

Branches


Inside the facial canal
  • Greater petrosal nerve - provides parasympathetic innervation to lacrimal gland, as well as special sensory taste fibers to the palate via the Vidian nerve.
  • Nerve to stapedius - provides motor innervation for stapedius
    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....
     muscle in middle ear
  • Chorda tympani
    Chorda tympani

    The chorda tympani is a nerve that branches from the facial nerve inside the facial canal, just before the facial nerve exits the skull via the stylomastoid foramen....
     - provides parasympathetic innervation to submandibular gland
    Submandibular gland

    The paired submandibular glands are salivary glands located beneath the floor of the mouth. In humans, they account for 70% of the salivary volume and weigh about 15 grams....
     and sublingual gland
    Sublingual gland

    The sublingual glands are salivary glands in the mouth.They lie anterior to the submandibular gland under the tongue, beneath the mucous membrane of the floor of the mouth....
     and special sensory taste fibers for the anterior 2/3 of the tongue.


Outside skull (distal to stylomastoid foramen
Stylomastoid foramen

Between the styloid process and mastoid portion of the temporal bone processes of the temporal bone is the stylomastoid foramenIt is the termination of the facial canal, and transmits the facial nerve and stylomastoid artery....
)
  • Posterior auricular nerve
    Posterior auricular nerve

    The posterior auricular nerve arises close to the stylomastoid foramen and runs upward in front of the mastoid process; here it is joined by a filament from the auricular branch of the vagus and communicates with the posterior branch of the great auricular as well as with the lesser occipital....
     - controls movements of some of the scalp muscles around the ear
  • Branch to Posterior belly of Digastric and Stylohyoid muscle
  • Five major facial branches (in parotid gland) - from top to bottom:
    • Temporal branch of the facial nerve
    • Zygomatic branch of the facial nerve
    • Buccal branch of the facial nerve
      Buccal branch of the facial nerve

      The Buccal Branches of the facial nerve , of larger size than the rest of the branches, pass horizontally forward to be distributed below the orbit and around the mouth....
    • Marginal mandibular branch of the facial nerve
    • Cervical branch of the facial nerve
      Cervical branch of the facial nerve

      The cervical branch of the facial nerve runs forward beneath the Platysma, and forms a series of arches across the side of the neck over the suprahyoid region....


A traditional mnemonic device for the five major branches of the facial nerve is, "The Zebra Bit My Cookie."

Embryology

The facial nerve is developmentally derived from the hyoid arch
Hyoid arch

The hyoid arch assists in forming the side and front of the neck....
 (second pharyngeal branchial arch
Branchial arch

In the embryogenesis of vertebrate, the pharyngeal arches are anlage for a multitude of structures. They develop during the fourth and fifth week in utero as a series of germ layer#Mesoderm outpouchings on the left and right sides of the developing pharynx....
).

Function


Efferent

Its main function is motor control of most of the muscles of facial expression
Facial muscles

The facial muscles are a group of striated muscles innervated by the facial nerve that, among other things, control facial expression. These muscles are also called mimetic muscles....
. It also innervates the posterior belly of the digastric muscle, the stylohyoid muscle, and the stapedius
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....
 muscle of the middle ear
Ear

The ear is the sense organ that detects sounds. The vertebrate ear shows a common biology from fish to humans, with variations in structure according to order and species....
. All of these muscles are striated muscles of branchiomeric
Special visceral efferent

Special visceral efferent refers to efferent nerves which supply muscles which derived from the branchial arches.Some sources prefer the term "branchiomotor", or "branchial efferent"....
 origin developing from the 2nd pharyngeal arch.

The facial also supplies parasympathetic
Parasympathetic nervous system

The parasympathetic nervous system is a division of the autonomic nervous system , along with the sympathetic nervous system and enteric nervous system ....
 fibers to the submandibular gland
Submandibular gland

The paired submandibular glands are salivary glands located beneath the floor of the mouth. In humans, they account for 70% of the salivary volume and weigh about 15 grams....
 and sublingual gland
Sublingual gland

The sublingual glands are salivary glands in the mouth.They lie anterior to the submandibular gland under the tongue, beneath the mucous membrane of the floor of the mouth....
s via chorda tympani
Chorda tympani

The chorda tympani is a nerve that branches from the facial nerve inside the facial canal, just before the facial nerve exits the skull via the stylomastoid foramen....
. 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
Lacrimal gland

The lacrimal glands are paired almond-shaped glands, one for each eye, that secrete the aqueous layer of the tears film. They are situated in the upper, outer portion of each Orbit ....
 via the pterygopalatine ganglion
Pterygopalatine ganglion

The pterygopalatine ganglion is a parasympathetic ganglion found in the pterygopalatine fossa. It is one of four parasympathetic ganglia of the head and neck....
.

The facial nerve also functions as the efferent limb of the corneal reflex
Corneal reflex

The corneal reflex, also known as the blink reflex, is an involuntary blinking of the eyelids elicited by stimulation of the cornea, or bright light, though could result from any peripheral stimulus....
.

Afferent

In addition, it receives taste
Taste

Sorry, no overview for this topic
 sensations from the anterior two-thirds of the tongue
Tongue

The tongue is skeletal muscle on the floor of the mouth that manipulates food for chewing . It is the primary organ of taste. Much of the upper surface of the tongue is covered in papillae and taste buds....
 and sends them to the nucleus of solitary tract. The facial nerve also supplies a small amount of afferent innervation to the oropharynx
Oropharynx

The Oropharynx reaches from the Uvula to the level of the hyoid bone.It opens anteriorly, through the isthmus faucium, into the mouth, while in its lateral wall, between the two palatine arches, is the palatine tonsil....
 above the palatine tonsil. There is also a small amount of cutaneous sensation carried by the nervus intermedius
Nervus intermedius

The nervus intermedius, or intermediate nerve, is the part of the facial nerve located between the motor component of the facial nerve and the vestibulocochlear nerve ....
 from the skin in and around the auricle
Auricle

Auricle has the following meanings:* the external portion of the ear, the pinna * a small conical pouch that projects from each atrium of the heart...
 (earlobe).

Location of Cell Bodies

The cell bodies for the facial nerve are grouped in anatomical areas called nuclei
Nucleus (neuroanatomy)

In neuroanatomy, a nucleus is a brain structure consisting of a relatively compact cluster of neurons. It is one of the two most common forms of nerve cell organization, the other being layered structures such as the cerebral cortex or cerebellum....
 or ganglia
Ganglion

In anatomy, a ganglion is a biological tissue.Cells found in a ganglion are called ganglion cells, though this term is also sometimes used to refer specifically to Retinal ganglion cells....
. The cell bodies for the afferent nerves are found in the geniculate ganglion
Geniculate ganglion

The geniculate ganglion is an L-shaped collection of fibers and sensory neurons of the facial nerve located in the facial canal of the head. It receives fibers from the motor, sensory, and parasympathetic nervous system components of the facial nerve and sends fibers that will innervate the lacrimal glands, submandibular glands, sublingual g...
 for both taste and general afferent sensation. The cell bodies for muscular efferent nerves are found in the facial motor nucleus
Facial motor nucleus

The facial motor nucleus is a collection of neurons in the brainstem that belong to the facial nerve . These lower motor neurons innervate the muscles of facial expression and the stapedius....
 whereas the cell bodies for the parasympathetic efferent nerves are found in the superior salivatory nucleus.

Pathology

People may suffer from acute facial nerve paralysis
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, and so there are a number of causes that may result in facial nerve paralysis....
, which is usually manifested by facial paralysis. Bell's palsy
Bell's palsy

Bell's palsy is a paralysis of cranial nerve VII resulting in inability to control facial muscles on the affected side. Several conditions can cause a facial paralysis, e.g., brain tumor, stroke, and Lyme disease....
 is one type of idiopathic
Idiopathic

Idiopathic is an adjective used primarily in medicine meaning arising spontaneously or from an obscure or unknown cause. From Greek ?d???, idios + p????, pathos , it means approximately "a disease of its own kind."...
 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

Lyme disease, or borreliosis, is an emerging infectious disease caused by at least three species of bacteria belonging to the genus Borrelia....
. Iatrogenic Bell's Palsy may also be as a result of an incorrectly placed dental local-anesthetic (Infra-Aveola Nerve Block). Although giving the appearance of a hemi-plegic stroke, effects dissipate with the drug.

Testing the facial nerve

Voluntary facial movements, such as wrinkling the brow, showing teeth, frowning, closing the eyes tightly (lagophthalmos
Lagophthalmos

Lagophthalmos is defined as the inability to close the eyelids completely. Blinking covers the eye with a thin layer of tear fluid, thereby promoting a moist environment necessary for the cells of the exterior part of the eye....
) , pursing the lips and puffing out the cheeks, all test the facial nerve. There should be no noticeable asymmetry.

In an UMN
Upper motor neuron

Upper motor neurons are motor neurons that originate in the Motor cortex of the cerebral cortex or the brain stem and carry motor information down to the final common pathway, that is, any motor neurons that are not directly responsible for stimulating the target muscle....
 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
Lower motor neuron

Lower motor neurons are the motor neurons connecting the brainstem and spinal cord to muscle fibers, bringing the action potential from the upper motor neurons out to the muscles....
 lesions can result in a CNVII palsy (Bell's palsy
Bell's palsy

Bell's palsy is a paralysis of cranial nerve VII resulting in inability to control facial muscles on the affected side. Several conditions can cause a facial paralysis, e.g., brain tumor, stroke, and Lyme disease....
 is the term used to describe 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 2/3 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).

Additional images


External links