Facial nerve

The facial nerve (n. facialis) unites the facial nerve proper and the intermediate nerve.

The facial nerve proper (n. facialis) is formed by motor nerve fibers. The intermediate nerve (n. intermedius; Wrisberg's nerve) contains sensory taste and autonomic parasympathetic fibers. The sensory fibers end on the neurons of the nucleus of the solitary tract, the motor fibers begin from the cells of the motor nucleus. The autonomic fibers originate from the superior salivary nucleus. The facial nerve emerges at the posterior edge of the pons, lateral to the abducens nerve, lateral to the olive. This nerve is directed forward and laterally and enters the internal auditory canal. On the inferior side of the internal auditory canal, the nerve runs in the facial nerve canal of the temporal bone, initially transversely in relation to the long axis of the pyramid of the temporal bone. Then, at the level of the cleft of the canal of the greater petrosal nerve, the facial nerve forms the first bend almost at a right angle to the back. Then it passes a short distance in the upper part of the medial wall of the tympanic cavity, then turns downwards (second bend). At the first bend (the geniculate canal) is the geniculate ganglion (ganglion geniculi), formed by the bodies of pseudounipolar neurons. The geniculate ganglion refers to the sensitive part of the facial (intermediate) nerve. The facial nerve leaves the canal of the same name through the stylomastoid foramen at the base of the skull and gives off its branches to the facial muscles of the head.

Several branches extend from the facial nerve canal:

1. The great petrosal nerve (n. petrosus major) branches off in the region of the geniculate gland and leaves the facial nerve canal through the cleft of the canal of the great petrosal nerve. Then the great petrosal nerve passes along the anterior surface of the pyramid of the temporal bone, along the groove of the great petrosal nerve, pierces the cartilage in the region of the lacerated foramen and enters the pterygoid canal. In this canal, together with the deep petrosal nerve (n. petrosus profundus, a sympathetic nerve from the internal carotid plexus), it forms the nerve of the pterygoid canal (n. canalis pterygoidei; Vidian nerve), which approaches the pterygoid ganglion (see "Trigeminal nerve"). The great petrosal nerve consists of fibers of the intermediate nerve. These are preganglionic parasympathetic fibers, which are axons of neurons of the superior salivary nucleus;
2. the communicating branch (with the tympanic plexus) [r. соmmunicans (cum plexus tympanico)] departs from the geniculate ganglion or from the greater petrosal nerve and goes to the mucous membrane of the tympanic cavity;
3. the stapedius nerve (n. stapedius) is a motor nerve that originates from the descending part of the facial nerve and penetrates into the tympanic cavity to the stapedius muscle;
4. The chorda tympani is formed by parasympathetic (preganglionic) and sensory (taste) fibers. The sensory fibers are peripheral processes of the pseudounipolar neurons of the geniculate ganglion. The sensory fibers of the chorda tympani originate on the taste buds located in the mucous membrane of the anterior 2/5 of the tongue and soft palate. The chorda tympani separates from the trunk of the facial nerve before it exits the canal of the same name (above the stylomastoid opening) and passes into the tympanic cavity. In the tympanic cavity, the chorda tympani passes under the mucous membrane along the upper part of its medial wall, between the long leg of the incus and the handle of the malleus. Without giving off branches in the tympanic cavity, the chorda tympani exits onto the outer surface of the base of the skull through the petrotympanic fissure. The chorda tympani then goes forward and downward and at an acute angle (between the medial and lateral pterygoid muscles) joins the lingual nerve.

The facial nerve immediately after exiting the stylomastoid foramen gives off the posterior auricular nerve, which runs backwards and upwards along the anterior surface of the mastoid process of the temporal bone and innervates the occipital belly of the epicranial muscle, the posterior auricular and superior auricular muscles (posterior auricular nerve, n. auricularis posterior). Here, the digastric branch (r. digastricus) departs from the facial nerve to the posterior belly of the digastric muscle and the stylohyoid branch (r. stylohyoideus) to the stylohyoid muscle.

The facial nerve then enters the thickness of the parotid salivary gland, where its branches exchange fibers, resulting in the formation of the parotid plexus (plexus intraparotideus). From this plexus, the branches of the facial nerve go up, forward, and down to the facial muscles. Because of its unique location, the parotid plexus and the branches of the facial nerve that extend from it are called the "big goose foot" (pes anserinus major).

The branches of the parotid plexus are the temporal, zygomatic, buccal branches, the marginal branch of the mandible, and the cervical branch.

The temporal branches (rr. temporales) in the amount of two or three go upward and innervate the ear muscles, the frontal belly of the epicranial muscle, the orbicularis oculi muscle, and also the muscle that corrugates the eyebrows.

The zygomatic branches (rr. zygomatici), three or four in number, are directed forward and upward, innervating the orbicularis oculi muscle and the zygomaticus major muscle.

Three or four buccal branches (rr. buccales) are directed forward along the outer surface of the masseter muscle to the large and small zygomatic muscles, the muscle that raises the upper lip, the muscle that raises the angle of the mouth, the orbicularis oris muscle, the buccal muscle, the nasalis muscle, and the laughter muscle.

The marginal branch of the lower jaw (r. marginalis mandibulae) goes forward and downward along the outer surface of the body of the lower jaw to the muscles that lower the lower lip and the corner of the mouth, to the mentalis muscle.

The cervical branch (r. colii) passes behind the angle of the mandible down to the platysma muscle of the neck. This branch joins with the transverse nerve of the neck (from the cervical plexus), forming the superficial cervical loop.

The branches of the facial nerve are connected by fibers from the auriculotemporal nerve (behind the articular process of the mandible), from the supraorbital, infraorbital, and mental nerves. These connecting branches contain sensory fibers that pass from the branches of the trigeminal nerve to the branches of the facial nerve.

[ 1 ], [ 2 ], [ 3 ]