The facial nerve is the name given to the facial nerve in humans. It forms the 7th cranial nerve.
What is the facial nerve?
The facial nerve is also known as the facial nerve, 7th cranial nerve, VII nerve or intermediofacial nerve. This refers to the 7th cranial nerve. What is meant by this is a gill arch nerve that arises from the nerves of the 2nd gill arch. It is responsible for visceromotor innervation of all muscles that form from the muscular anlage of the gill arch.
Anatomy and structure
The facial nerve is the only cranial nerve in which sensory, parasympathetic, sensory, and motor fibers are present simultaneously. The nerve arises from approximately 10,000 nerve cells. 7000 of these cells give rise to medullary motor fibers. The remaining 3000 cells belong to the intermedius nerve. They have medullary sensory, sensory and parasympathetic fibers. The motor components of the facial nerve primarily innervate the muscles of the facial expression and the posterior segments of the muscles of the floor of the mouth. These are the stylohyoid muscle and the ventor posterior of the digastric muscle. There are also fibers that lead toward the stapedius muscle. They serve for the fine regulation of the auditory system. Together with the chorda tympani (tympanic cord), the sensory fibers of the facial nerve take a course via the nucleus tractus solitarii. In this way, the anterior segment of the tongue provides functional supply to the taste buds in the lingual papillae region. In the direction of the skin of the meatus acusticus externis as well as the tympanic membrane, the sensitive facial nerve fibers are located. There they undertake the transmission of temperature sensations as well as touch and pain stimuli. Parasympathetic nerve fibers, which originate from the nucleus salivatorius superior, are supplied to the facial nerve via the nervus intermedius. With the chorda tympani, they travel toward the oral cavity and take care of the innervation of the oral salivary glands. Other parasympathetic facial nerve parts lead to the lacrimal gland, which is supplied by them. The facial nerve has its main centers in the region of the medulla oblongata. After circumnavigating the abducens nucleus, facial nerve fibers exit the brain at the cerebellopontine angle. Subsequently, the 7th cranial nerve continues to the petrous bone or its meatus acusticus internus via the porus acusticus. There it enters the canali nervi facialis at the fundus. The geniculate ganglion is also formed at the petrous bone section. The perikarya of the afferent fibers are found there. In addition, a second so-called “knee” is formed by the facial nerve, which is called the geniculum nervi facialis. Three branches of the facial nerve form from the petrous bone. These are the greater petrosal nerve, which innervates the lacrimal gland, the stapedius nerve, which supplies the stapedius muscle, and the tympanic cord. From the stylomastoid foramen comes the exit of other branches such as the posterior auricular nerve.
Function and Tasks
Various perceptions are transmitted through the facial nerve. These include sensations from the external auditory canal, the auricle, and the tongue toward the brain. Furthermore, the facial nerve takes over the control of the facial muscles, the salivary, lacrimal and nasal glands, the tongue muscles as well as a middle ear muscle. The facial nerve is considered a mixed nerve because it has both efferent and afferent nerve fibers. From the efferent fibers, commands from the brain are transmitted to the affected organ of success. This may be a muscle, for example. The afferent fibers, on the other hand, transmit information from the organ of success to the brain. These include, for example, temperature sensations from the skin.
Diseases
Various diseases can affect the facial nerve. First and foremost, this includes facial nerve palsy (facial paralysis). In this case, individual or all muscles of the facial nerve on one side of the head are paralyzed. In most cases, facial nerve palsy is caused by circulatory disturbances of the facial nerve within the bony canal, inflammations of the ear or space constrictions in the petrous bone region. Typical symptoms of facial nerve palsy are drooping of the lower eyelid, incomplete closure of the eyelid, and increases in hearing sensation.In addition, the patient is unable to frown and suffers from disturbances in tear secretion as well as taste disorders. Another disorder of the facial nerve is facial myokymia. These are wave-like contractions along the muscle that occur involuntarily and do not end even during sleep. They are caused by injuries to the central nuclei of the facial nerve within the brainstem. Inflammation of the facial nerve, which occurs in the geniculate ganglion, also sometimes causes impairments. The geniculate ganglion is the name given to a nerve switching center located along the course of the facial nerve close to the brainstem. The inflammation marks a special form of facial paresis and mostly includes all nerve functions. Only the eyebrows can still be raised. Another disease of the facial nerve is facial spasm (tonic facial spasm). This refers to tonic synchronous spasms of all muscles supplied by the facial nerve. The most common cause is nerve compression in the immediate vicinity of the brain stem caused by a vein, artery or vascular malformation. Likewise, multiple sclerosis or a tumor may be responsible for the compression. Another impairment of the facial nerve is Melkersson-Rosenthal syndrome, the causes of which are unknown. This is a mixture of facial nerve palsy, swelling of the oral mucosa and face, and pain in the outer ear region.