The facial nerve is the seventh cranial nerve. It innervates the facial muscles and is responsible for the reception of taste sensations from the front 2/3 of the tongue. It carries parasympathetic fibers that are responsible for controlling the secretion of saliva. Symptoms of facial nerve damage are rather severe - but what exactly are the problems that may arise in people who develop some pathology of the 7th cranial nerve?
The facial nerve(Englishnervus facialis ) is the seventh cranial nerve. It carries very different types of fibers, because both the motor fibers (which dominate its composition) and the sensory fibers and fibers belonging to the autonomic nervous system (more precisely, the parasympathetic nerves are located within the facial nerve). It is due to the fact that the seventh cranial nerve has such different types of fibers in its composition that this structure performs many different, important functions in the human body.
Facial nerve: fiber sources and location
The nucleus in which the bodies of nerve cells (neurons) are located, from which the fibers within the facial nerve are later derived, can be considered as the beginning of the facial nerve. In the case of sensory fibers, they have their source in the elbow ganglion, from which they go to the nucleus of the solitary strand and the nucleus of the spinal strand.
The motor fibers of the facial nerve originate in the motor nucleus of the facial nerve.
As for parasympathetic fibers, those that run through the facial nerve originate from the superior salivary nucleus.
The facial nerve leaves the brain in the pontocerebellar angle. It goes towards the inner ear canal, and finally reaches the inner ear canal.
Further, the facial nerve runs within the facial nerve canal (located in the temporal bone structures) where the knee ganglion is located, then the nerve runs through the tympanic cavity wall until it finally exits the skull through the stylomastoid foramen .
Facial nerve: branches
The facial nerve - both in its intracranial and extracranial sections - gives off numerous branches. They are:
- greater rocky nerve (originating from the knee of the nerveface)
- stapes nerve
- tympanic string (with both sensory and parasympathetic fibers)
- posterior ear nerve (with two branches - ear and occipital)
An important structure that also originates from the facial nerve is the parotid plexus. It is located in the vicinity of the parotid gland and gives away numerous branches that innervate various muscles within the head - these are the temporal, zygomatic and buccal branches, as well as the mandibular marginal branch and the neck branch.
Facial Nerve: Features
Looking at how many branches the facial nerve gives off, it's not hard to guess that this structure has many important functions.
First of all, it innervates numerous muscles located in the area of the head and neck - the facial nerve supplies the mimic muscles of the face (including the forehead muscles, the frowning muscle and the circular muscle of the eye), but also the smallest muscle in the human body the stapes muscle and the muscles around the auricle, the chin and broad muscles of the neck.
As mentioned above, the facial nerve carries not only the motor but also other types of nerve fibers.
It consists of sensory fibers - here the function of the facial nerve turns out to be very important, because it is responsible for the perception of taste sensations from 2/3 of the front tongue (more precisely, one of the branches of this nerve is responsible for it, which is a drum string).
The facial nerve also includes parasympathetic fibers.
Those within the rocky greater nerve eventually reach the pterygoid ganglion and innervate the mucous glands in the mouth, pharynx and nasal cavity, as well as the lacrimal glands.
The tympanic string, mentioned several times here, also guides the fibers of the autonomic system, which, in turn, reach the submandibular ganglion and then innervate the submandibular and sublingual glands.
Facial nerve: examination
Examination of the facial nerve in many patients arouses … laughter. Well, when during a neurological examination the activity of this nerve is assessed, the patient is asked to perform activities such as:
- teeth bared
- frown
- pouting
- closing eyes
- puffing out cheeks
All these activities should be possible to perform freely, moreover, movements performed by the patient - under correct conditions - should be symmetrical.
The function of the components of the facial nerves is assessed in the manner described abovemovement fibers.
To check whether the sensory functions of this structure are also preserved, the respondents are asked about the possibility of feeling the taste in the front part of the tongue.
The facial nerve function test also includes the evaluation of the corneal reflex.
Here, however, it should be emphasized that the evaluation of the functions of the trigeminal nerve is carried out simultaneously. The fifth cranial nerve is the centripetal arm of this reflex, while the seventh cranial nerve is the centrifugal arm (to put it simply, the trigeminal nerve fibers are responsible for transmitting a signal to the brain that the eye's cornea has been touched, while the facial nerve is responsible for the fact that after such stimulation leads to reflex contracture of both eyelids).
Facial nerve: diseases
Dysfunction of the facial nerve can be caused by many different pathologies.
It happens that the nuclei from which its fibers are derived will be damaged due to the patient having a stroke.
The facial nerve may also be disturbed when the patient develops pathological processes in the vicinity of its fibers, such as otitis media or a cancerous tumor.
Dysfunction of the nerve fibers of the facial nerve can also be caused by pathologies of the parotid gland (e.g. its inflammation or tumors), as well as inflammation of the nerve itself (e.g. caused by the herpes virus).
Sometimes a patient's facial paralysis occurs for no apparent reason, in which case it is referred to as Bell's palsy.
Facial nerve: symptoms of damage
Symptoms of facial nerve damage vary - they depend both on the level of damage to the nerve and on exactly which branches of the nerve will be damaged.
When the defect occurs within the intracranial fibers, the muscles supplied by the nerve are paralyzed or weakened significantly. Apart from that, it may also appear:
- salivation reduction
- loss of taste from the front of the tongue
- hypersensitivity to sounds (with damage to the acoustic nerve)
- reduced tear flow
And then, when damage to the extracranial branches of the facial nerve, patients develop only weakness or paralysis of the muscles innervated by the facial nerve.
Also readNervous system: structure and functions
Facial nerve palsy: causes, symptoms,rehabilitation
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About the authorBow. Tomasz NęckiA graduate of the medical faculty at the Medical University of Poznań. An admirer of the Polish sea (most willingly strolling along its shores with headphones in his ears), cats and books. In working with patients, he focuses on always listening to them and spending as much time as they need.Read more articles by this author