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Facial nerve

Facial nerve (nervus facialis) - VII pair of cranial nerves, mixed nerve.

Most of the facial nerve - its motor portion - originates in the nucleus, located in the tire of the bridge. The fibers emanating from the nucleus go first in the dorsal direction and bend around the nucleus of the abducent nerve, then stretch in the ventral direction and exit from the bridge to the cerebellar gland. Here, the facial nerve is located medially, from the auditory nerve in the form of a more powerful root of the facial nerve itself and a thin root of the intermediate nerve [n. intermedins (wrisbergi)]. Together with the auditory nerve, it enters the internal auditory opening of the temporal bone. At the beginning of the facial nerve canal (canalis facialis), it bends at a right angle, forming the external knee, and exits the skull through the awl-mastoid (Fig.). Then the facial nerve penetrates the parotid gland, passes through it and forms a plexus in front of the external auditory canal, from which branches for the facial muscles of the facial muscles. The largest branches of the facial nerve on the face are the temporal, buccal, zygomatic, as well as the mandible branch; on the neck comes a branch innervating the skin muscle of the neck.

facial nerve
The facial nerve and its core (schematically): a - motor fibers, b - sensitive fibers, c - vegetative fibers; 1 - ganglion sphenopalatine; 2 - n. petrosus superficialis major; 3 - n. intermedins; 4 - nucleus n. facialis; 5 - genu internum; 6 - nucleus salivatorius sup .; 7 - nucleus tractus solitarii; 8 - genu externum; 9 - chorda tympani; VIII - n. acusticus; IX - n. glosscpharyngeus.

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Directly adjacent to the facial nerve is an intermediate nerve, which is anatomically part of the facial nerve and contains afferent and efferent fibers. In the external knee of the facial nerve, the sensitive part of the intermediate nerve forms a thickening containing cells (ganglion genicyli). Its sensitive fibers are part of the drum string (chorda tympani), which joins the lingual branch of the trigeminal nerve, which carries taste impulses from the anterior 2/3 of the tongue. The central branches are directed to a single bundle in the brain stem.

The cortical center of the facial nerve is located in the lower quarter of the anterior central gyrus. The axons of the cells of the cortical center descend downward, pass through the inner capsule. Partly not reaching the nucleus of the facial nerve in the bridge, partially already at their level, the cortical fibers cross in the seam of the bridge and approach the cells of the nucleus of the facial nerve of the opposite side. Part of the uncrossed fibers ends in the core of its side. In addition to voluntary motor innervation of the facial muscles, most facial reflexes are realized through the facial nerve - sucking, flashing, corneal, conjunctival, sneezing, nasal.

Paralysis of the facial nerve is one of the most frequent peripheral paralysis and is mostly due to hypothermia or infection. It develops mainly on one side. At the same time, on the side of paralysis, half of the forehead does not have folds, the eyebrow is lower, the upper eyelid becomes narrower, the eyeball is wider and slightly protrudes forward. The eye slit always remains open (lagophthalmos); when you try to close the eye, the eyeball goes up (Bell's symptom), the eye is constantly watering. The nasolabial fold on the paralyzed side is smoothed, the angle of the mouth is lowered. With a grin, the corner of the mouth is pulled to a healthy side. Food gets stuck between the teeth and cheek. The addition of a taste disorder in the front 2/3 of the tongue to the facial paralysis of the facial muscles indicates a lesion of the facial nerve in its bone channel and involvement of the drum string in the process. The appearance of herpes on the auricle and in the external auditory canal indicates a lesion of the facial nerve at the level of the ganglion geniculi.

The disease usually develops acutely. Often, before the disease or in the first days, pain appears under the lower jaw and behind the auricle. In severe forms, paralysis lasts 6 weeks or more. The presence of electrical excitability of the nerve and the absence of a reaction of rebirth allow us to hope for recovery even with a long course of the disease. In some patients, residual effects remain in the form of muscle contracture on the side of the former paralysis.

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From the peripheral paralysis of the facial nerve, one should distinguish its central, or supranuclear, paralysis. In the latter, only the lower branch of the facial nerve is paralyzed; the muscles of the forehead and the closure of the eye are not paralyzed, as they have bilateral innervation.

The defeat of the facial nerve is also observed in many diseases: poliomyelitis, polyneuritis, neurosyphilis, injuries of the skull base and temporal bone, vascular diseases of the brain stem. Paralysis of the facial nerve may occur with purulent damage to the middle ear and caries of the temporal bone. Purulent lesion of the parotid gland and surgery on it often entail facial nerve paralysis. Isolated lesions of its individual branches are found in superficial wounds of the face. Rarely, paralysis occurs in the newborn when the forceps are applied or pressure is applied to the erupting face from the side of the mother’s normal or pathologically changed lumbar joint.

Sometimes there are single or bilateral spasms of the facial muscles innervated by the facial nerve. Twitching or jerking of muscles does not depend on volitional effort, distraction of attention or emotions. A spasm is often limited to a part of the facial muscles (for example, a muscle that compresses the eyelids) and gradually engulfs the entire half of the face. In addition, each twitching begins with 1 convulsive contraction of individual muscles and then quickly spreads to all the facial muscles of half of the face.

Treatment of paralysis of the facial nerve is primarily reduced to the treatment of the underlying disease (otitis media, syphilis , neoplasms, etc.). With the "rheumatic" paralysis of the facial nerve, salicylates are shown (acetylsalicylic acid, amidopirin, analgin 0.5 g three times a day), vitamin B1 (0.01 g intramuscularly once a day, only 20-30 injections), vitamin B12 (intramuscularly 500-1000 mcg for 7-10 days), prozerin (0.05% 1 ml under the skin 1-2 times a day for 15-20 days). With signs of infection - penicillin (300 000 IU twice a day, only 6 000 000 IU). From the first days should be appointed massage facial muscles. In the acute period - thermal procedures (UHF, quartz, paraffin). When lagophthalmos often need to wash the eyes with a weak solution of boric acid or albucide and instill 1-2 drops of sterile vaseline or peach oil. After 2 weeks, iono-galvanization with sodium iodide is recommended. If signs of contracture appear, electrical procedures are contraindicated. In the recovery period - therapeutic exercises. If therapeutic treatment is unsuccessful, surgical treatment can be recommended, but not earlier than after 6 months. after the onset of the disease. Different types of operations have been proposed: stitching the peripheral end of the facial nerve with the central end of the hypoglossal nerve, nerve decompression, muscular plasty.

Prevention of facial paralysis in persons who have already had it, is reduced to protecting the face from cooling.