The The facial nervefacial nerve is the seventh (VII) of is the seventh (VII) of twelve paired twelve paired cranial nervescranial nerves. It emerges from . It emerges from

the brainstem between the the brainstem between the ponspons and the and the medullamedulla, and controls the muscles of facial , and controls the muscles of facial expression, and expression, and tastetaste to the anterior two- to the anterior two-

thirds of the thirds of the tonguetongue. It also has preganglionic . It also has preganglionic parasympatheticparasympathetic fibers to several head and fibers to several head and

neck neck gangliaganglia..

StructureStructure

1.The motor part of the facial nerve include 1.The motor part of the facial nerve include the the facial nerve nucleusfacial nerve nucleus in the in the ponspons

2.The sensory part of the facial nerve include 2.The sensory part of the facial nerve include the the nervusnervus intermediusintermedius..

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

the the geniculategeniculate ganglion ganglion for both taste and general for both taste and general afferent sensation. /nucleus tractus solitarii/afferent sensation. /nucleus tractus solitarii/

The cell bodies for muscular efferent nerves are The cell bodies for muscular efferent nerves are found in the found in the facial motor nucleusfacial motor nucleus The nucleus has a The nucleus has a dorsal and ventral region, with neurons in the dorsal dorsal and ventral region, with neurons in the dorsal region innervating muscles of the upper face and region innervating muscles of the upper face and neurons in the ventral region innervating muscles of neurons in the ventral region innervating muscles of the lower face.the lower face.

the cell bodies for the parasympathetic efferent the cell bodies for the parasympathetic efferent nerves are found in the nerves are found in the superior superior salivatorysalivatory nucleus nucleus

AnatomyAnatomy

The nucleus is situated in the caudal portion of The nucleus is situated in the caudal portion of the ventrolateral the ventrolateral pontinepontine tegmentumtegmentum. Its axons . Its axons take an unusual course, traveling dorsally and take an unusual course, traveling dorsally and looping around the looping around the abducensabducens nucleus nucleus, then , then traveling ventrally to exit the ventral pons traveling ventrally to exit the ventral pons medial to the medial to the spinalspinal trigeminal trigeminal nucleus nucleus. These . These axons form the motor component of the axons form the motor component of the facial nervefacial nerve, , parasympatheticparasympathetic and and sensorysensory components forming the components forming the nervusnervus intermediusintermedius

Parasympathetic fibersParasympathetic fibers

The The superior superior salivatorysalivatory nucleus nucleus contains the cell bodies of parasympathetic contains the cell bodies of parasympathetic axons within the nervus intermedius. These fibers reach the geniculate axons within the nervus intermedius. These fibers reach the geniculate ganglion but do not synapse. Some of these preganglionic parasympathetic ganglion but do not synapse. Some of these preganglionic parasympathetic fibers persist within the fibers persist within the greater greater petrosalpetrosal nerve nerve as they exit the geniculate as they exit the geniculate ganglion and subsequently synapse with neurons in the ganglion and subsequently synapse with neurons in the pterygopalatinepterygopalatine ganglion ganglion. These postganglionic neurons send . These postganglionic neurons send axonsaxons that provide that provide parasympathetic innervation to the parasympathetic innervation to the lacrimallacrimal gland gland..

The remaining preganglionic fibers continue as the mixed facial nerve The remaining preganglionic fibers continue as the mixed facial nerve proper as it extends through the facial canal. Before the nerve exits the proper as it extends through the facial canal. Before the nerve exits the skull via the skull via the stylomastoidstylomastoid foramen foramen and after the and after the nerve to the nerve to the stapediusstapedius muscle muscle has branched off, the facial nerve gives off the has branched off, the facial nerve gives off the chordachorda tympani nerve tympani nerve. This nerve exits the skull through the . This nerve exits the skull through the pterygotympanicpterygotympanic fissure fissure and merges with the and merges with the lingual nervelingual nerve, after which it synapses with , after which it synapses with neurons in the neurons in the submandibularsubmandibular ganglion ganglion. These postganglionic neurons . These postganglionic neurons provide parasympathetic innervation to the provide parasympathetic innervation to the submandibularsubmandibular and and sublingual glandssublingual glands

Sensory fibersSensory fibers

The sensory component of the nervus intermedius carries input The sensory component of the nervus intermedius carries input about sensation from the skin of the about sensation from the skin of the external auditory external auditory meatusmeatus, , from the from the mucous membranesmucous membranes of the of the nasopharynxnasopharynx and and nosenose, , and and tastetaste from the anterior two-thirds of the from the anterior two-thirds of the tonguetongue, floor of , floor of the mouth, and the the mouth, and the palatepalate. The sensory information from the . The sensory information from the mucous membranesmucous membranes of the nasopharynx and palate is carried of the nasopharynx and palate is carried along the greater petrosal nerve, while the chorda tympani along the greater petrosal nerve, while the chorda tympani nerve (and lingual nerve) carries taste input from the anterior nerve (and lingual nerve) carries taste input from the anterior two-thirds of the tonge, floor of mouth, and palate.two-thirds of the tonge, floor of mouth, and palate.

The geniculate ganglion contains the cell bodies of the sensory The geniculate ganglion contains the cell bodies of the sensory component of the nervus intermedius.component of the nervus intermedius.

Motor fibersMotor fibers

The motor part of the facial nerve enters into The motor part of the facial nerve enters into the the internal auditory internal auditory meatusmeatus then runs a then runs a tortuous course (including two tight turns) tortuous course (including two tight turns) through the through the facial canalfacial canal, emerges from the , emerges from the stylomastoidstylomastoid foramen foramen and passes through the and passes through the parotid glandparotid gland, where it divides into five major , where it divides into five major branches. Though it passes through the parotid branches. Though it passes through the parotid gland, it does not innervate the gland. This gland, it does not innervate the gland. This action is the responsibility of cranial nerve IX, action is the responsibility of cranial nerve IX, the the glossopharyngealglossopharyngeal nerve nerve..

BranchesBranches

Inside the facial canalInside the facial canal Greater Greater petrosalpetrosal nerve nerve - provides parasympathetic - provides parasympathetic

innervation to lacrimal gland, as well as special taste innervation to lacrimal gland, as well as special taste sensory fibers to the palate via the sensory fibers to the palate via the nerve of nerve of pterygoidpterygoid canal canal..

Nerve to Nerve to stapediusstapedius - provides motor innervation for - provides motor innervation for stapediusstapedius muscle in middle ear muscle in middle ear

ChordaChorda tympani tympani - provides parasympathetic - provides parasympathetic innervation to submandibular and sublingual glands innervation to submandibular and sublingual glands and special sensory taste fibers for the anterior 2/3 of and special sensory taste fibers for the anterior 2/3 of the tongue.the tongue.

Outside skull Outside skull

Posterior auricular nervePosterior auricular nerve - controls movements - controls movements of some of the scalp muscles around the earof some of the scalp muscles around the ear

Five major facial branches (in parotid gland) - Five major facial branches (in parotid gland) - from top to bottom: from top to bottom: Temporal branch of the facial nerveTemporal branch of the facial nerve ZygomaticZygomatic branch of the facial nerve branch of the facial nerve BuccalBuccal branch of the facial nerve branch of the facial nerve Marginal Marginal mandibularmandibular branch of the facial nerve branch of the facial nerve Cervical branch of the facial nerveCervical branch of the facial nerve

FunctionFunction

EfferentEfferent Its main function is motor control of most of the Its main function is motor control of most of the

muscles of facial expressionmuscles of facial expression. It also innervates the posterior belly of the . It also innervates the posterior belly of the digastricdigastric muscle, the muscle, the stylohyoidstylohyoid muscle, and the muscle, and the stapediusstapedius muscle of the muscle of the middle middle earear. .

The facial also supplies The facial also supplies parasympatheticparasympathetic fibers to the fibers to the submandibularsubmandibular gland gland and and sublingual glandssublingual glands via via chordachorda tympani tympani and the and the submandibularsubmandibular ganglion ganglion. . Parasympathetic innervation serves to increase the flow of saliva from Parasympathetic innervation serves to increase the flow of saliva from these glands. It also supplies parasympathetic innervation to the nasal these glands. It also supplies parasympathetic innervation to the nasal mucosa and the mucosa and the lacrimallacrimal gland gland via the via the pterygopalatinepterygopalatine ganglion ganglion..

AfferentAfferent It is It is tastetaste sensations from the anterior two-thirds of the sensations from the anterior two-thirds of the tonguetongue. The facial . The facial

nerve also supplies a small amount of afferent innervation to the nerve also supplies a small amount of afferent innervation to the oropharynxoropharynx above the above the palatine tonsilpalatine tonsil. There is also a small amount of . There is also a small amount of cutaneous sensation carried by the cutaneous sensation carried by the nervusnervus intermediusintermedius from the skin in and from the skin in and around the around the auricleauricle

Testing the facial nerveTesting the facial nerve

Voluntary facial movements, such as wrinkling the brow, showing teeth, Voluntary facial movements, such as wrinkling the brow, showing teeth, frowning, closing the eyes tightly (lagophthalmos) , pursing the lips and frowning, closing the eyes tightly (lagophthalmos) , pursing the lips and puffing out the cheeks, all test the facial nerve. There should be no puffing out the cheeks, all test the facial nerve. There should be no noticeable asymmetry.noticeable asymmetry.

In an upper motor neuron lesion, called central seven, only the lower part In an upper motor neuron lesion, called central seven, only the lower part of the face on the opposite side will be affected, due to the bilateral control of the face on the opposite side will be affected, due to the bilateral control to the upper facial muscles.to the upper facial muscles.

Lower motor neuron lesions can result in Bell's palsy, manifested as both Lower motor neuron lesions can result in Bell's palsy, manifested as both upper and lower facial weakness on the same side of the lesion.upper and lower facial weakness on the same side of the lesion.

Taste can be tested on the anterior of the tongue. This can be tested with a Taste can be tested on the anterior of the tongue. This can be tested with a swab dipped in a flavoured solution, or with electronic stimulation (similar swab dipped in a flavoured solution, or with electronic stimulation (similar to putting your tongue on a battery).to putting your tongue on a battery).

Facial nerve can also be tested because it controls about 2/3 of the tongue. Facial nerve can also be tested because it controls about 2/3 of the tongue. Try making your finger moist, and dipping it in some sugar, or salt Try making your finger moist, and dipping it in some sugar, or salt (something sweet/salty) then touch your finger to the back of your tongue. (something sweet/salty) then touch your finger to the back of your tongue. See if you can taste it!See if you can taste it!