Facial nerve is a kind of nerveBone canalThe longest nerve in the brain is also the nerve most prone to paralysis[5]。
The facial nerve is a mixed nerve composed of motor fibersSensory fibreAnd parasympathetic fibers[2]。The motor fibers originate from the facial nerve nucleus at the ventrolateral end of the pons and innervate the facial muscles except the masticatory muscles and the levator palpebrae superioris muscles, as well as the ear muscles, occipital muscles, and platysma muscles.The taste fiber originates from the geniculate ganglion and controls the taste of the front 2/3 of the tongue.A few sensory fibers transmit the general sensation of the skin, lacrimal gland, salivary gland and part of the mucous membrane of the oral cavity in the auricle, external auditory canal and tympanic membrane.The parasympathetic fibers originate from the suprasalivary nucleus and control the secretion of sublingual and submandibular glands.
Chinese name
facial nerve
Foreign name
facial nerve[1]
Subordinate
The seventh pair of cranial nerves
Composition
Sensory, motor and parasympathetic nerve fibers
Features
Dominate facial expression muscles, etc
Facial nerve paralysis
It is divided into central type and peripheral type
It is the seventh pair of brain nerves, most of which are motor fibers, and a small part are parasympathetic and sensory fibers.After exiting the pons, the nerves walk together with the auditory nerves in the internal auditory canal. After exiting the internal auditory canal, they enter the facial nerve canal, and then exit the skull through the caulomastoid foramen. Then, they cross the styloid process, the posterior facial vein, and the external jugular vein forward between the posterior abdomen of the digastric muscles and the cartilage of the external auditory canal to enter the parotid isthmus. The distance from the caulomastoid foramen to the parotid gland is about 2cm.After entering the parotid gland, it is divided into the upper and lower main branches, and then into five branches, namely the temporal branch, zygomatic branch, buccal branch (also divided into the upper and lower buccal branches), mandibular marginal branch and cervical branch.When the facial nerve is paralyzed, the facial expression muscles it controls lose function, resulting in facial paralysis (see "facial nerve paralysis").The parasympathetic and sensory fibers of the facial nerve are responsible for the taste of the front 2/3 of the tongue and the secretion of the lacrimal and salivary glands.
Facial nerve canal:
It is the bony canal through which the facial nerve passes from the bottom of the internal auditory canal to the caulomastoid foramen when it exits the skull.This tube is adjacent to the inner ear and tympanum, so otitis media, mastoiditis or surgery is prone to cause nerve damage;Also because the facial nerve tube is narrow and thin, when cold, rheumatism, and mild edema seep out, the facial nerve will be damaged, and facial paralysis will occur.
(Reference materials of atlas "facial nerve":[1][3][5]）
The facial nerve is mainly motor nerveMixed nerveIt mainly controls the facial expression muscles and transmits the taste of the front 2/3 of the tongue as well as sublingual glandsSubmandibular glandAnd lacrimal gland secretion.Facial nucleusbe locatedPons, divided into upper and lower parts, the upper part is affected by both sidescerebral cortexSports areaAnd send out motor fibers to innervate the muscles in the upper half of the same side of the face, while the lower half of the nucleus is only innervated by the contralateral cerebral cortex, and send out motor fibers to innervate the muscles in the lower half of the same side of the face.
fibrillar component
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Facial nerve is mixedCerebral nerve, containing 4 fiber components:
① The special visceral motor fibers originate from the facial nucleus in the pontine tegmentum and mainly control the movement of facial muscles;
② Generally, visceral motor fibers originate from the suprasalivary nucleus of the pons and belong to the preganglionic fibers of the parasympathetic nerve. The postganglionic fibers after the conversion of the relevant parasympathetic ganglia are distributed in the lacrimal glands, submandibular glands, sublingual glands, and mucous glands of the nose and palate to control the secretion of the above glands;
③ SpecialVisceral sensationFiber, namely taste fiber, whose cell body is located intemporal boneIn the petrous part, the knee ganglion at the bend of the facial nerve tube, the peripheral process is distributed in the anterior 2/3 mucosa of the tongueTaste budThe central process terminates in the nucleus of solitary tract in the brain stem;
④ The general somatosensory fibers transmit the somatosensory and expressive muscles of the ear skinProprioception。
The motor fibers originate from the motor nucleus at the ventrolateral part of the lower part of the pons, penetrate the brain stem at the caudal side of the pons, move outward and forward, enter the internal auditory canal above the auditory nerve, and then pass through theFacial canalThe caulomastoid foramen go out of the cranial cavity, and then pass through the parotid gland to separate a number of peripheral branches to the facial muscles.In the facial nerve segment, it also sends branches to the stapes muscle.Branches are sent out between the cervical mastoid foramen and the parotid gland to supply the occipital muscles, the posterior auricular muscles, the steohyoid muscles and the posterior abdomen of the digastric muscles.Facial nucleusThe upper part of is innervated by bilateral corticomedullary tracts, and the lower part is only innervated by contralateral corticomedullary tracts.[2]
The sensory fibers come from the geniculate ganglion in the facial nerve canal, and the peripheral branches and motor fibers go along to the posterolateral side. They leave the facial nerve canal near the caulomastoid foramen, called the chorda tympani nerve. They pass through the tympanic chamber forward, and the lingual nerve attached to the mandibular nerve controls the taste of the front 2/3 of the tongue.The central branch enters the nucleus of solitary tract of medulla oblongata.After the replacement of neurons, the fibers were sent to the thalamus via the contralateral medial thalamus, and then projected to the taste center at the lower edge of the central posterior gyrus and above the lateral fissure.[2]
The parasympathetic nerve fibers mainly originate from the superior salivary nucleus at the lower part of the pons, pass through the intermediate nerve, the geniculate ganglion, and the chordae tympani, and terminate in the submandibular ganglion, and innervate the submandibular glands, sublingual glands, and mucous glands in the mouth and tongue.The other part comes from the parasympathetic fibers of the nucleus at the bottom of the fourth ventricle, passing through the intermediate nerveGeniculate ganglionThe greater superficial petrosal nerve terminates in the sphenopalatine ganglion, and the postganglionic branch is innervated by the maxillary branch and the ophthalmic branch of the trigeminal nervelacrimal gland。[2]
anatomy
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The facial nerve is composed of two roots. One is the larger motor root, which originates from the ponscerebellumHorn area, ponsMedulla oblongataLateral sulcus outlet;One is the smaller mixed root, called the intermediate nerve, which exits the brain from the outside of the motor root and enters the brain from the outside of the motor rootinner earThe door is integrated into a trunk, which can be wornInternal auditory meatusBottom entry and middle earTympanumThe adjacent facial nerve canal runs horizontally first, then goes down vertically from the stem breast hole to the skull, and goes forward through the parotid gland to the face. There is an enlarged knee ganglion in the facial nerve canal.When the facial nerve passes through the facial nerve canal and finally through the parotid gland, it sends out many branches.[4]
Branches in the facial nerve canal:
① Chorda tympani: transmits taste impulse and controls submandibular gland andSublingual glandSecretion of;
② The greater petrosal nerve, also known as the greater superficial petrosal nerve, contains parasympathetic secretory fibers that govern the secretion of the glands of the lacrimal gland, palate and nasal mucosa;
③ Stapedius nerve: innervating the tympanic cavityStapes muscle。[4]
Extracranial branches: three small branches of the facial nerve are sent out immediately after the facial nerve exits the stem and mastoid foramen, which innervate the occipital muscles, the muscles around the ear, the posterior abdomen of the digastric muscles andStyloid hyoid muscle。The main trunk of the facial nerve goes forward to enter the parotid gland parenchyma, and branches inside the gland to form the parotid plexus, which branches to the front edge of the parotid gland, and is distributed on the faceEmotive muscle。
① Temporal branch: it innervates frontal muscle and orbicularis oculi muscle;
② Zygomatic branches: 3-4 branches, innervating orbicularis oculi and zygomaticus muscles;
③ Buccal branches: 3-4 branches, which govern the cheek muscles,Orbicularis oris muscleAnd other muscles around the mouth,
④ Marginal mandibular branch: distributed in the muscles of the lower lip,
⑤ Cervical branch: It controls the platysma.[4]
The total length of the facial nerve can be divided into 9 segments:
1. The superior segment of the motor nucleus starts from the facial nerve cortex center at the lower end of the central anterior gyrus of the frontal lobe and descends to the facial nerve motor nucleus at the lower part of the pons.
2. Motor nucleus segment The facial nerve root of the motor nucleus segment leaves the facial nerve nucleus in the pons, bypasses the abducent nerve nucleus and penetrates to the lower edge of the pons.
3. Cerebellopontine segment The facial nerve of cerebellopontine segment leaves the pons, crosses the cerebellopontine angle, and reaches the inner ear gate together with the auditory nerve.Although this segment is not long, it can be forced to expand to 5cm without facial paralysis.
4. Internal auditory canal segment The facial nerve of the internal auditory canal segment enters the internal auditory canal from the internal auditory gate and reaches the bottom of the internal auditory canal together with the auditory nerve.
5. Labyrinthine segment The facial nerve enters the facial nerve canal from the anterior upper part of the bottom of the internal auditory canal, and reaches the genicu1ate ganglion outward between the vestibule and the cochlea.This section is the shortest, 2.25mm~3mm long.
6. The tympanic segment, also known as the horizontal segment, starts from the knee ganglion backward and slightly downward, passes through the bone canal of the inner wall of the tympanum, reaches above the vestibular window, below the external semicircular canal, and reaches the plane of the pyramidal eminence of the posterior wall of the tympanum.The bone canal here is the thinnest and vulnerable to lesion erosion or surgical injury.This segment can also be divided into tympanic segment (from the knee ganglion to the lower part of the lateral semicircular canal)
7. The pyramidal segment extends from the lower part of the lateral semicircular canal to the plane of the pyramidal eminence. Traditionally, the pyramidal segment is usually divided into the drum segment.
8. Mastoid segment (mastoid segment) is also called vertical segment, which extends from the height of the cone of the posterior wall of the tympanic chamber down to the caulomastoid foramen.This section is deep, and it is more than 2cm away from the mastoid surface in most adults.The total length of the facial nerve in the temporal bone is about 30 mm;The length from the knee ganglion to the pyramidal eminence is about 11 mm, and the length from the pyramidal eminence to the caulomastoid foramen is about 16 mm.
9. After the facial nerve of the external segment of the temporal bone exits the caulomastoid foramen, it sends out small branches such as the posterior auricular nerve, the digastric muscle branch, and the styloid hyoid muscle branch.The terminal branch of the facial nerve runs outward and forward from the outside of the styloid process into the parotid gland.The main trunk is divided into upper branch and lower branch in the parotid gland, and they are divided into 5 branches after arcing around the parotid headland;The fibers between the branches coincide with each other and are finally distributed in the facial expression muscles.[4]
Inspection method
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Facial muscle examination should first observe whether the forehead lines on both sides have disappeared, whether the eye fissure has widened, and whether the nasolabial groove has become shallow. Then ask the patient to wrinkle the forehead, frown, close the eyes, expose the teeth, bulge the cheeks, whistle and other movements, and observe whether the movements on both sides are symmetrical, and whether the corners of the mouth droop or tilt to one side.When checking the taste, ask the patient to stretch out his tongue and apply a cotton swab dipped with substances with different taste on 2/3 of the tongue surface on one side, and conduct a comparative inspection on both sides.
1. Central type: supranuclear tissue (including cortex, cortical brainstem fibersInternal capsule, pons, etc.), with paralysis of the lower facial muscles on the opposite side of the focus.From top to bottom, the nasolabial groove becomes shallower, the mouth angle drops when the teeth are exposed (or the mouth angle deviates to the focus side, that is, the opposite side of paralyzed facial muscles), and the whistling and cheek bulge are not allowed.It is mainly found in cerebrovascular diseasesbrain tumorAnd encephalitis.
2. Surrounding type:Facial nucleusOr when the facial nerve is damaged, all lesions appear on the same sideFacial paralysis, from top to bottom, they can't frown, close their eyesCorneal reflexDisappeared, the nasolabial groove became shallow, the teeth could not be exposed, the cheeks could not bulge, whistling, and the corners of the mouth were drooping (or the corners of the mouth were tilted to the opposite side of the focus, that is, the opposite side of the paralyzed facial muscles).It is commonly seen in cold, ear or meningeal infectionNeurofibromaIt causes peripheral facial paralysis.In addition, 2/3 of the front tongue may appearGustatory disturbance。
