Facial nerve

The processes of cells that form the nucleus of the facial nerve first follow the dorsal direction, rounding the nucleus of the abducent nerve , then forming the face of the facial nerve, are directed ventrally and extend to the lower surface of the brain at the posterior edge of the bridge , higher and lateral than the olive of the medulla oblongata .

The facial nerve itself is a motor nerve, but after joining an intermediate nerve ( lat. N.intermedius ), represented by sensitive (taste and secretory) and motor fibers, it acquires a mixed character.

On the basis of the brain, the intermediate nerve ( lat. N.intermedius ) appears along with the facial. Subsequently, both nerves together with the vestibulo-cochlear nerve ( lat.n.vestibulocochlearis ) (VIII pair of cranial nerves ) enter through the internal auditory opening ( lat. Porus acusticus internus ) of the temporal bone pyramid into the internal auditory meatus ( lat. Meatus acusticus internus ). Here, the facial and intermediate nerves are connected and through the field of the facial nerve ( lat. Area n.facialis ), enter the channel of the facial nerve. At the bend of this canal, the facial nerve ring ( lat. Geniculum n.facialis ) is formed, and thickens due to the knot of the knee ( lat. Ganglion geniculi ). This node contains the first nuclei of the sensitive part of the intermediate nerve.

The facial nerve repeats all the bends of the same bone canal and, leaving the temporal bone through the styloid opening ( lat. Foramen stylomastoideum ), lies in the thickness of the parotid gland ( lat. Glandula parotis ), where it divides into its main branches.

Inside the temporal bone pyramid, a number of branches depart from the intermediate nerve:

1. The large stony nerve ( lat. N. petrosus major ), begins near the knee node and consists of parasympathetic fibers. He leaves the pyramid of the temporal bone through the crevice of the canal of a large stony nerve ( lat.hiatus canalis n.petrosi majoris ), lays in the groove of the same name and leaves the cranial cavity through a ragged hole ( lat. Foramen lacerum ). Subsequently, this nerve, passing through the pterygoid canal of the sphenoid bone ( lat.canalis pterygoideus ossis sphenoidalis ), enters the pterygo-anterior fossa ( lat. Fossa pterygopalatina ), reaching the pterygo-anterior node ( lat. Ganglion pterygopalatinum ). The preganglionic fibers of the large stony nerve switch on the cells of this node. Postnodal fibers are part of the zygomatic nerve, and then - as part of the connective branch with the lacrimal nerve and lacrimal nerve, reaching and innervating the lacrimal gland ( lat. Glandula lacrimalis ). Thus, a large stony nerve innervates the lacrimal gland.
2. The connecting branch with a tympanic plexus ( lat. Ramus communicans cum plexus tympanico ) departs from the knee node or from the large stony nerve and follows the small stony nerve ( lat. N.petrosus minor ).
3. The stirrup nerve ( lat. N.stapedius ) is a very thin branch that starts from the descending part of the facial nerve, approaches the stirrup muscle and innervates it.
4. The connecting branch with the vagus nerve ( Latin Ramus communicans cum nervo vago ) is a thin nerve that approaches the lower node of the vagus nerve .
5. The drum string ( lat. Chorda tympani ) is the terminal branch of the intermediate nerve. It departs from the trunk of the facial nerve slightly higher than the styloid opening, enters the tympanic cavity ( lat.cavum tympani ) from the side of the posterior wall, forming a small arc facing concave down, and lies between the handle of the malleus and the long leg of the anvil. Approaching the stony-drum gap ( lat. Fissura petrotympanica ), the drum string leaves the skull through it. In the future, it goes down and, passing between the medial and lateral pterygoid muscles of the lat. m.pterygoideus medialis et lateralis , at an acute angle enters the lingual nerve lat. n.lingualis . In its course, the drum string of branches does not return, only at the very beginning, after leaving the skull, it is connected by several branches to the ear node. A drum string consists of two types of fibers: parasympathetic prenodal, which are axons of the cells of the upper salivating nucleus ( lat.nucleus salivatorius superior ), and taste sensitivity fibers - dendrites of the cells of the knee of the facial nerve. The central processes ( axons ) of the knee node end in the nucleus of a single path ( lat. Nucleus tractus solitarii ). Some of the fibers of the tympanic string, which are part of the lingual nerve, are sent to the submandibular and hyoid nodes in the nodal branches, and the other part reaches the mucous membrane of the back of the tongue.

Coming out through the styloid opening from the pyramid of the temporal bone, the facial nerve gives up a number of branches even before entering the thickness of the parotid gland:

1. The posterior ear nerve ( lat. N.auricularis posterior ), begins directly under the styloid opening, turns posteriorly and upward, goes behind the outer ear and is divided into two branches: the anterior ear branch ( lat. R.auricularis ), and the posterior - occipital ( lat . r.occipitalis ). The auricular branch innervates the posterior and anterior auricular muscles , the transverse and oblique muscles of the auricle , and the anti-tracheal muscle. The occipital branch innervates the occipital abdomen of the cranial muscle ( lat. M.epicranius ) and connects to the large auricular and small occipital nerves of the cervical plexus and to the ear branch of the vagus nerve.
2. The awl-sublingual branch ( lat. R.stylohyoideus ) can extend from the posterior ear nerve ( lat. N.auricularis posterior ). This is a thin nerve that goes down, enters the thickness of the same muscle, previously connected to the sympathetic plexus located around the external carotid artery
3. The double-abdominal branch ( lat. R. digastricus ) can depart both from the posterior ear nerve and from the facial trunk. It is located slightly lower than the stylohyal branch, descends along the posterior abdomen of the biceps muscle ( lat. M.digastricus ) and gives branches to it. It has a connecting branch with the glossopharyngeal nerve .
4. The lingual branch ( lat. R.lingualis ) is inconstant, is a thin nerve, enveloping the styloid process and passing under the palatine tonsil . Gives the connecting branch to the glossopharyngeal nerve and sometimes the branch to the styloid muscle ( lat. M.stylohyoideus ).

Having entered the thickness of the parotid gland, the facial nerve is divided into two main branches: a more powerful upper and a smaller lower one. Further, these branches are divided into branches of the second order, which diverge radially: up, forward and down to the muscles of the face. Between these branches in the thickness of the parotid gland, compounds are formed that make up the parotid plexus ( lat. Plexus parotideus ).

The following branches depart from the parotid plexus - the so-called large goose foot ( lat.pes anserinus major ):

1. Temporal branches ( lat. Rr.temporales ) - back, middle and front. They innervate the upper and front auricular muscles, the frontal abdomen of the cranial muscle , the circular muscle of the eye, the muscle that wrinkles the eyebrow.
2. Zygomatic branches ( lat. Rr.zygomatici ) - two, sometimes three, are directed forward and upward and approach the zygomatic muscles and the circular muscle of the eye.
3. The buccal branches ( lat. Rr.buccales ) are three or four fairly powerful nerves. They depart from the upper main branch of the facial nerve and send their branches to the following muscles: the large zygomatic, laughing muscle, buccal, raising and lowering the angle of the mouth, the circular muscle of the mouth and nasal. Occasionally, there are connecting branches between the symmetric nerve branches of the circular muscle of the eye and the circular muscle of the mouth.
4. The marginal branch of the lower jaw ( lat. R.marginalis mandibulae ), moving forward, runs along the edge of the lower jaw and innervates the muscles that lower the corner of the mouth and lower lip, the chin muscle.
5. The cervical branch ( lat. R.colli ) in the form of 2-3 nerves goes behind the corner of the lower jaw, approaches the subcutaneous muscle, innervates it and gives away a number of branches connecting to the upper (sensitive) branch of the cervical plexus.

The facial nerve is mainly motor, but in its trunk there are sensitive (gustatory) and parasympathetic (secretory) fibers, which are considered to be components of the intermediate nerve ( lat. N.intermedius ) (synonyms - Vrisberg nerve, Sapolini nerve, XIII cranial nerve )

Accordingly, fibers from several nuclei pass in the facial nerve. Its main (motor) part in the caudal divisions of the tire of the warolium bridge has one motor core, consisting of several cell groups, each of which provides the innervation of certain facial muscles. Those parts of the nucleus of the facial nerve that give rise to branches for the forehead and eyelids have bilateral cortical innervation. The forehead muscles provide an excellent example for the synergistic act of both areas; likewise, under normal conditions, the circular muscle of the eye contracts simultaneously on the right and left. On the contrary, the lower part of the nucleus of the facial nerve, which gives fibers to the mouth and cheeks, has cross cortical innervation; when eating, facial expressions, etc. muscles of the same name often function asymmetrically. It should also be noted that the nucleus of the hyoid nerve takes part in the innervation of the circular muscle of the mouth, a portion of which the lower branches of the facial nerve innervate. Therefore, paresis of the lips, observed next to the nuclear paralysis of the hyoid nerve does not prove damage to the facial nerve, if there are no other symptoms of paralysis.

The nuclei of the intermediate nerve are located mainly in the medulla oblongata and are common with the glossopharyngeal nerve ( lat. N.glossopharyngeus ). These are the upper parts of the nucleus of the single pathway ( lat. Nucleus tractus solitarii ) and the upper salivary nucleus ( lat. Nucleus salivatorius superior ). The intermediate nerve also includes an accumulation of parasympathetic cells located near the motor nucleus of n.facialis, which provide innervation of the lacrimal gland.

Kernels n.facialis and n.intermedius

1. Nucleus motorius n.facialis - the course of the fibers of the nucleus of the facial nerve in the thickness of the bridge is very complicated: the axons that exit from the cells of the nucleus first go dorsally and medially, reaching almost to the bottom of the fourth ventricle. The protrusion at the bottom of the rhomboid fossa formed by these fibers is called the facial tubercle. In the loop formed by these fibers is the core of the abduction nerve. Further, the fibers of the facial nerve pass through the thickness of the bridge and at its border with the oblong bridge exit the substance of the brain. This area is called the cerebellopontine angle. The motor core of the facial nerve is an integral part of several reflex arches. Corneal reflex - sensory impulses from the mucous membrane of the eye are conducted along the orbital nerve to the base of the sensory nucleus. Here they switch to the nucleus of the facial nerve on the same side. The efferent part of the reflex arc is represented by the peripheral neuron of the facial nerve. Visual impulses reach the nucleus of the facial nerve, passing from the upper mounds of the roof of the midbrain along the tecto-bulbar path, causing the eyelids to close when the eyes are bright enough - a blinking reflex , or a squinting reflex. Auditory impulses reach the nucleus of n.facialis through the dorsal nucleus of the trapezius. Depending on the intensity of the noise, this reflex arc provides either relaxation or tension of the stirrup muscle.
2. Nucleus salivatorius superior - this nucleus is located caudal and medial to the nucleus of the facial nerve, namely, on the border between the pons and the medulla oblongata, near the bottom of the fourth ventricle. The superior salivary nucleus receives impulses from the olfactory system through the posterior longitudinal bundle. Appetite-stimulating odors cause a salivary reflex. Lacrimation is caused by central stimuli from the hypothalamus (emotion) coming through the reticular formation and by impulses from the spinal node of the trigeminal nerve ( conjunctival irritation)
3. Nucleus tractus solitarii is a relay point for taste fibers. From here, taste impulses go to the contralateral visual tubercle (the exact path is unknown) and end in the most medial part of the posterior-medial ventral nucleus. From the thalamus, axons of other neurons go to the base of the opercular part of the postcentral gyrus near the islet.
4. The accumulation of parasympathetic cells near the motor nucleus of the facial nerve - most likely the axons of these cells are directed to the stapedius muscle m.stapedius

The branches of the intermediate nerve perform the following functions:

1. N.petrosus major contains secretory fibers that innervate the lacrimal gland and mucous glands of the nasal and oral cavities
2. N.stapedius innervates the muscle of the same name, which closes the fenestra ovalis of the tympanum with the base of the stapes
3. Chorda tympani - the drum string innervates the anterior 2/3 of the tongue (taste fibers - the bodies of the first neurons are in the ganglion geniculi). The second part of the fibers that enter the drum string goes to the submandibular and sublingual nodes, and from them to the submandibular and sublingual glands.

Peripheral Facial Paralysis

The defeat of the motor portion of the facial nerve leads to peripheral paralysis of the innervated muscles - the so-called peripheral paralysis n.facialis. In this case, the asymmetry of the face develops, noticeable at rest and sharply amplified with mimic movements. Half of the face on the affected side is motionless. The skin of the forehead when trying to wrinkle it in folds on this side is not going to, the patient’s eyes cannot be closed. When you try to close your eyes, the eyeball on the side of the lesion is wrapped up ( Bell symptom ) and a strip of sclera (cleft eye, lagophthalmos ) becomes visible through the gaping eye slit. In the case of moderate paresis of the circular muscle of the eye, the patient usually has the ability to cover both eyes, but cannot cover the eye on the affected side, leaving the eye on the healthy side open (eyelid dyskinesia, or Reviyo symptom). It should be noted that during sleep the eye closes better (relaxation of the muscle that lifts the upper eyelid). When the cheeks are inflated, the air exits through the paralyzed corner of the mouth, the cheek on the same side “flies” (a symptom of sail ). The nasolabial fold on the side of muscle paralysis is smoothed, the angle of the mouth is lowered. Passive raising of the corners of the patient’s mouth by the fingers leads to the fact that the angle of the mouth on the side of the facial nerve lesion rises higher due to a decreased muscle tone (Roussecki’s symptom). When you try to bite the teeth on the side of the paralyzed circular muscle of the mouth, they remain covered with lips. In this regard, the asymmetry of the oral gap is roughly expressed, the oral gap is somewhat reminiscent of a tennis racket, turned by the handle towards the lesion (symptom of a racket). A patient with facial paralysis caused by damage to the facial nerve experiences difficulty eating, food constantly falls over the cheek and has to be removed from there with the tongue. Sometimes biting of the mucous membrane of the cheek on the side of paralysis is observed. Liquid food and saliva may leak from the corner of the mouth on the affected side. The patient feels a certain awkwardness during a conversation. It is difficult for him to whistle, to blow out a candle.

Due to paresis of the circular muscle of the eye (paretic lower eyelid), the tear does not fall completely into the lacrimal canal and flows out - an impression of increased lacrimation appears.

With neuropathy of the facial nerve in the late period, contracture may appear with a pull of the face to the healthy side.

After peripheral paralysis of n.facialis, partial or incorrect regeneration of damaged fibers, especially vegetative ones, is possible. Preserved fibers can send new axons to damaged parts of the nerve. Such pathological reinnervation is able to explain the occurrence of contractures or synkinesia in the facial muscles of the face. Crocodile tears syndrome or Bogorad syndrome (paradoxical taste-tear reflex) is associated with imperfect reinnervation. Предполагают, что секреторные волокна для слюноотделительных желёз прорастают в шванновские оболочки дегенерированных поврежденных волокон, первоначально снабжавших слёзную железу.

Анатомо-физиологические условия, которые представляют ход лицевого нерва, дают возможность по клинической картине очень точно диагностировать место, где произошёл перерыв проводимости этих систем:

Повреждение лицевого нерва в пирамиде височной кости

• Проксимально относительно барабанной струны ( лат. chorda tympani ) – периферический паралич лицевого нерва, отсутствие вкусовой чувствительности на передних 2/3 языка . У больных часто отмечается сухость во рту за счёт расстройства секреции подчелюстной и подъязычной слюнных желёз.
• Проксимально относительно стременного нерва ( лат. n.stapedius ) - периферический паралич лицевого нерва, отсутствие вкусовой чувствительности на передних 2/3 языка. У больных часто отмечается сухость во рту за счёт расстройства секреции подчелюстной и подъязычной слюнных желёз, гиперакузия – ненормально тонкий слух и особенная чувствительность к низким тонам

• Проксимально относительно большому каменистому нерву лат. n.petrosus major - периферический паралич лицевого нерва, отсутствие вкусовой чувствительности на передних 2/3 языка. У больных часто отмечается сухость во рту за счёт расстройства секреции подчелюстной и подъязычной слюнных желёз; часто нервная глухота вследствие сочетанного повреждения преддверно-улиткового нерва лат. n.vestibulocochlearis ; только когда она отсутствует – гиперакузия; отсутствие слёзоотделения – ксерофтальмия.

Могут возникать следующие синдромы:

• Синдром внутреннего слухового прохода (синдром Ляница), состоящий из признаков поражения слухового и лицевого нервов на стороне патологического очага. При этом могут отмечаться шум в ухе, снижение слуха по звуковоспринимающему типу, признаки периферического паралича лицевого нерва. Чаще отмечается в ранней стадии роста невриномы VIII нерва .

• Синдром боковой цистерны моста или синдром мосто-мозжечкового угла состоит из сочетания признаков поражения черепных нервов, проходящих через боковую цистерну варолиева моста, то есть VIII, VII и V черепных нервов. Этот синдром чаще всего возникает при невриномах VIII нерва.

Повреждение лицевого нерва в полости черепа

Вышеперечисленные симптомы. Нередко двусторонний паралич лицевого нерва (базальный менингит). В большинстве случаев также поражаются другие нервы, а также имеются общемозговые симптомы.

Повреждение ядра лицевого нерва

Ядра могут страдать при дегенеративных заболеваниях (прогрессивный бульбарный паралич, сирингобульбия), дисциркуляторных и воспалительных процессах (полио энцефалит ), опухоли варолиева моста или кровоизлияниях в варолиев мост. Клинически поражения ядра лицевого нерва проявляется его периферическим параличом. Так как патологические процессы редко изолированно затрагивают только ядро лицевого нерва, то выделяют следующие синдромы

• Синдром Мийяра-Гюблера, состоящий из сочетания признаков периферического паралича лицевого нерва на стороне патологического очага, обусловленных поражением ядра или корешка лицевого нерва, и центрального гемипаралича или гемипареза на противоположной патологическому очагу стороне, возникшего в связи с поражением пирамидных путей
• Синдром Фовилля, проявляющийся параличом мышц, иннервируемых лицевым и отводящим нервами на стороне патологического очага, и центральным гемипараличом или гемипарезом, а иногда и гемианестезией или гемигипестезией на противоположной стороне. Синдромы Фовилля и Мийяра-Гюблера возникают при обструкции циркумферентных ветвей основной артерии.

• Синдром каудальных отделов покрышки моста – причиной является обструкция коротких и длинных циркумферентных ветвей основной артерии. Симптоматика – ипсилатеральный ядерный паралич лицевого и отводящего нервов; нистагм (вследствие поражения медиального продольного пучка); паралич взора в сторону очага поражения; ипсилатеральная гемиатаксия и асинергия (вследствие поражения средней мозжечковой ножки); контралатеральная анальгезия и терманестезия (вследствие поражения латерального спиноталамического пути); гипестезия тактильной, вибрационной, чувствительности, чувства положения (вследствие поражения медиальной петли); ипсилатеральные миоритмии мягкого нёба и глотки (вследствие поражения центрального покрышечного пути).

Центральный паралич лицевого нерва

При локализации патологического очага в коре мозга или по ходу кортико-нуклеарных путей, имеющих отношение к системе лицевого нерва, развивается центральный паралич лицевого нерва. При этом центральный паралич или чаще парез развивается на стороне, противоположной патологическому очагу, лишь в мышцах нижней части лица, иннервация которых обеспечивается через посредство нижней части ядра лицевого нерва. Парез мимических мышц по центральному типу обычно сочетается с гемипарезом.

При сугубо ограниченном очаге в корковой проекционной зоне лицевого нерва отставание угла рта на противоположной половине лица по отношению к патологическому очагу констатируется лишь при произвольном оскале зубов. Эта асимметрия полностью нивелируется при эмоционально-выразительных реакциях (при смехе и плаче ), ибо рефлекторное кольцо этих реакций замыкается на уровне лимбико-подкорково-ретикулярного комплекса. В связи с этим несмотря на существование надъядерного паралича, мускулатура лица способна на непроизвольные движения в виде клонического тика, или тонического лицевого спазма, поскольку сохраняются связи лицевого нерва с экстрапирамидной системой. Возможно сочетание изолированного надъядерного паралича с приступами джексоновской эпилепсии .

Начиная осмотр больного, прежде всего необходимо отметить наличие или отсутствие нарушений мимики и движения мимических мышц.

При поражении лицевого нерва происходит сглаживание природных складок на лбу, носогубной складки. Обращают внимание на ширину глазной щели, расположение бровей и т.д.

Больному предлагается выполнить ряд тестов:

1. закрыть глаза
2. закрыть попеременно сначала один, а потом другой глаз
3. зажмурить глаза
4. поднять брови
5. нахмурить брови
6. поморщить нос
7. оскалить зубы
8. надуть щёки
9. подуть, посвистеть
10. образовать складку на шее

Следует проследить, выполняются ли движения одинаково с обеих сторон.

Также у больного необходимо проверить вкусовую чувствительность на передних 2/3 языка.

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