Nerves entering and leaving the brain are defined in medicine as cranial or cranial nerves (12 pairs). They innervate the glands, muscles, skin and other organs located in the head and neck, as well as in the abdominal and chest cavity.
Let's talk today about these couples and the violations that occur in them.
Types of cranial nerves
Each of the mentioned pairs of nerves is denoted by a Roman numeral from one to twelve, according to their location on the base of the brain. They are in the following order:
1) olfactory;
2) visual;
3) oculomotor;
4) block;
5) ternary;
6) diverting;
7) facial;
8) auditory;
9) glossopharyngeal;
10) wandering;
11) additional;
12) sublingual.
They include autonomic, efferent and afferent fibers, and their nuclei are located in the gray matter of the brain. Depending on the composition of the nervefibers, all cranial nerves (12 pairs) are divided into sensory, motor and mixed. Consider them in this aspect.
Sensitive views
This group includes the olfactory, optic and auditory nerves.
Olfactory nerves have processes located in the nasal mucosa. Starting in the nasal cavity, they cross the lamina cribrosa and reach the olfactory bulb, where the first neuron ends and the central pathway begins.
The visual pair consists of fibers extending from the retina, cones and rods. All nerves enter one trunk in the cranial cavity. First, they form a decussation, and then the optic tract, enveloping the brain stem and giving fibers to the visual centers. One nerve includes about a million fibers (axons of retinal neurons) and, in addition, it has one sheath on the outside and the other on the inside. The nerve enters the skull through the optic canal.
The eighth pair includes auditory cranial nerves - 12 pairs of the rest, except for these three, are motor or mixed. In the auditory nerves, the fibers are directed from the middle ear to the nuclei. Each of them includes the vestibular and cochlear root. They arise from the middle ear and enter the cerebellopontine angle.
Motor types
Another group of 12 pairs of cranial nerves includes the oculomotor, trochlear, accessory, hypoglossal, and abducens nerves.
The third pair, that is, the oculomotor nerves, contain autonomic, motor and parasympathetic fibers. They aredivided into upper and lower branches. Moreover, only the upper branches belong to the motor group. They enter the muscle that lifts the eyelid.
The next group includes trochlear nerves that set the eyes in motion. If we compare all the cranial nerves - 12 pairs - then these are the thinnest. They originate from the nucleus on the tegmentum of the midbrain, then go around the peduncle and go to the orbit, innervating the superior oblique muscle of the apple of the eye.
The abducens nerves are related to the rectus eye muscle. They have a motor nucleus in the fossa. Leaving the brain, they go to the superior orbital fissure, innervating the rectus eye muscle there.
The accessory nerves originate from the medulla oblongata and the cervical regions of the spinal cord. Separate roots are connected into one trunk, passing through the hole and dividing into external and internal branches. The internal branch, in which there are fibers involved in the innervation of the larynx and pharynx, is attached to the vagus nerve.
And the last of the 12 pairs of cranial nerves (a table of which for convenience is presented at the end of the article), related to the motor ones, are the hypoglossal nerves. This nerve has a spinal origin. But, over time, its spine moved into the skull. It is clear that this is the motor nerve of the tongue. The roots emerge from the medulla oblongata, then cross the carotid artery and enter the lingual muscles, dividing into branches.
Mixed Species
This group includes trigeminal, facial, glossopharyngeal and vagus nerves. In mixed nervesthere are ganglia similar to those found in the spinal cord, but they do not have anterior and posterior roots. They have fibers of the motor and sensory types connected into a common trunk. They may also just be around.
The output of 12 pairs of cranial nerves is different. So, the third, seventh, ninth and tenth pairs have parasympathetic fibers in the output areas, which are directed to the autonomic ganglia. Many of them are connected by branches where different fibers pass.
The trigeminal nerve has two roots, where the larger one is sensitive, and the smaller one is motor. The innervation of the skin occurs on the parietal, ear and chin areas. The innervation also captures the conjunctiva and apple of the eye, the dura mater of the brain, the mucous membranes of the mouth and nose, teeth and gums, and also the main part of the tongue.
The trigeminal nerves exit between the cerebellar peduncle, in the middle, and the pons. The fibers of the sensitive root belong to the ganglion, which lies in the temporal pyramid near the apex, which was formed as a result of splitting of the hard shell of the brain. They end in the nucleus of this nerve, which is located in the fossa, as well as the nucleus of the spinal tract, continuing into the medulla oblongata, and then heading to the spinal cord. The fibers of the motor nerve root originate from the trigeminal nucleus, which is located in the bridge.
The upper, mandibular and ophthalmic nerves depart from the ganglion. The latter is sensitive, divided into nasociliary, frontal and lacrimal. Innervation of 12 pairs of cranial nerves variesnot only for the pairs themselves, but also for the derived branches. Thus, the lacrimal nerve innervates the lateral ophthalmic angle, passing secretory branches to the lacrimal gland. The frontal nerve, accordingly, branches on the forehead and supplies its mucous membrane. The nasociliary innervates the eyeball, and the ethmoid nerves depart from it, innervating the nasal mucosa.
The maxillary nerve is also sensitive, passing into the pterygopalatine fossa and exiting to the anterior facial surface. From it originate the upper alveolar nerves, which pass to the teeth of the upper jaw and gums. The nerve on the cheekbones runs from the ganglion along the posterior nerves of the nose to its mucosa and nasopharynx. The nerve fibers here are sympathetic and parasympathetic.
The mandibular nerve belongs to the mixed type. It consists of a motor root. Its sensory branches include the buccal nerve, which supplies the corresponding mucosa, the ear-temporal nerve, which innervates the skin at the temples and ears, and the lingual, which supplies the tip and back of the tongue. The inferior alveolar nerve is mixed. Passing in the lower jaw, it ends on the chin, branching here in the skin and mucous membrane of the lower lip. Its branches are connected with autonomic ganglia:
- Auricular-temporal nerve - with the auricular, innervating the parotid gland;
- lingual nerve - with a ganglion that gives innervation to the sublingual and submandibular glands.
Facial include motor and sensory cranial nerves. Mixed fibers create a taste sensation. Some fibers here innervate the lacrimal and salivary glands, while others - the anterior two-thirdsparts of the language.
The facial nerve consists of motor fibers starting in the upper part of the fossa. It includes the intermediate nerve with taste and parasympathetic fibers. Some are processes of the ganglion, ending with the taste fibers of the vagus and glossopharyngeal nerves. And others begin in the salivary and lacrimal nuclei located near the motor nucleus.
The facial nerve originates in the cerebellopontine angle of the brain and then passes into the facial canal through the ear canal. Here is the drum string and, passing through the cavity, connects to the lingual nerve. It includes taste and parasympathetic fibers that reach the submandibular ganglion.
The facial nerve emerges from the bone of the temples and passes into the parotid gland, intertwining there. From here, the branches diverge in a fan-shaped fashion. At this time, all the muscles related to mimic and some others are innervated. A branch on the neck from the facial nerve branches on it in the subcutaneous muscle.
Glossopharyngeal pair realizes the innervation of the lacrimal glands, the back of the tongue, the inner ear and pharynx. The motor fibers are directed to the stylo-pharyngeal muscle and constrictors of the pharynx, and the sensory fibers are directed to the parotid gland to the ear ganglion. The nuclei of these nerves, unlike where the other nuclei of 12 pairs of cranial nerves are located, are located in the fossa - the triangle of the vagus nerve.
Parasympathetic fibers originate in the salivary nucleus. Glossopharyngeal nerve, moving away from the medulla oblongata, stretches to the base of the tongue. From the ganglion, the tympanic nerve begins, which has parasympathetic fibers that continue to the ear ganglion. Next, the lingual, amygdala and pharyngeal nerves begin. The lingual nerves innervate the root of the tongue.
The wandering pair implements parasympathetic innervation in the abdominal cavity, as well as in the chest and neck. This nerve includes motor and sensory fibers. Here is the greatest innervation. The vagus nerve has a double nucleus:
- dorsal;
- single path.
Coming out behind the olive on the neck, it moves with the neurovascular bundle, and then forks.
Violations
Disturbances of functions can have all cranial nerves - 12 pairs. The anatomy of the lesions is manifested at different levels of nuclei or trunks. To make a diagnosis, an in-depth analysis of intracranial pathological processes is carried out. If the lesion affects one side of the nuclei and fibers, then most likely it is a violation of the functions of any of the affected 12 pairs of cranial nerves.
Neurology studies, however, the symptoms on the opposite side. Then the lesion of the conductive pathways is diagnosed. It also happens that nerve dysfunctions are also associated with a tumor, arachnoid cyst, abscess, vascular malformations and other similar processes.
Simultaneous defeat of the 12th pair of cranial nerves, that is, the hypoglossal, as well as the vagus and glossopharyngeal, is called bulbar palsy. This is a very dangerous disease, as there is a possibility of pathologythe most important centers of the brain stem.
Knowing the topographic location of the cranial nerves allows you to correctly identify the narrow area of the lesion of each of them. To conduct research, special techniques are used. With the appropriate equipment, today it is possible to reveal all the details of the state of the fundus, the optic nerve, to diagnose the field of view and foci of prolapse. Computerized examination allows highly accurate localization of the affected area.
Ophthalmic examination
This technique allows you to identify disorders in the work of oculomotor, trochlear and abducent pairs of nerves, to identify limited motor activity of the eyeballs, the degree of exophthalmos, and more. The pathology of the optic and auditory nerves can be caused by a narrowing of the canal in the bone or, conversely, by its expansion. Diagnosis is made of the upper fissure of the orbit, as well as various openings of the skull.
Verterbal and carotid angiography
This method is important in the recognition of vascular malformations and intracranial processes. However, computed tomography will provide more detailed information on these issues. It visualizes the trunks of cranial nerves, diagnoses a tumor of the visual and auditory pair and other pathologies.
Electromyography
Deepening of the study of cranial nerves became possible due to the development of this method. It determines the state of spontaneous muscular chewing and mimic activity, muscles of the tongue, soft palate and other muscles. Also, electromyography allows you to calculate the speedconducting an impulse along the trunks of the facial, accessory and hypoglossal nerves. For this, the reflex blinking response is examined, which is provided by the trigeminal and facial nerves.
Neurological examination and symptoms of individual cranial nerve disorders
This technique is carried out in a certain order. The examination begins with the olfactory nerve. The cotton wool soaked in the irritant is brought to the nostrils in turn. The optic nerve is examined during an ophthalmological examination, on the basis of which, in addition to a direct lesion, even secondary changes can be detected. Pathology can be congestive, dystrophic, inflammatory, or the nerve can be completely destroyed.
Losses in the next three of the 12 pairs of cranial nerves (oculomotor, abducens, and trochlear) cause diplopia and strabismus. There may also be drooping of the upper eyelid, pupil dilation, double vision.
Violations in the fifth pair, that is, in the trigeminal nerves, lead to a deterioration in sensitivity in that part of the face where they are present. This can be observed both in the temples, forehead, and cheekbones, eyes, chin and lips. It happens that severe pain is felt, rashes and other reactions appear. Due to the fact that the facial nerves have many connections, this pair is characterized by a wide variety of pathological reactions.
When the auditory nerve is disturbed, hearing deteriorates, glossopharyngeal - sensitivity in the inner ear is disturbed, sublingual - the movement of the tongue is limited. In the case of the vagus nerve, paralysis of the soft palate or vocal cord develops. In addition, the rhythm of the heart, respiration, and other visceral-vegetative functions may be disturbed.
Complex disorders and cranial nerves (12 pairs): anatomy, table
Functions of nerve fibers can be disturbed both in isolation and in combination, along with various pathologies of the lower skull. So, if all the nerves on one half of the cranial base are affected, then they talk about Garcin's syndrome. With a tumor of the orbital bones and soft tissues, there is a syndrome of the superior orbital fissure. With damage to both the olfactory and optic nerves, Kennedy syndrome occurs.
These and other diseases occur both in adulthood and in childhood. For children, nerve lesions are especially common, which are associated with a malformation.
Below is a structure to better understand how the cranial nerves work (12 pairs). Anatomy (the table is based on her knowledge) will help you navigate the intricacies of the functioning of their different groups.
Conclusion
We examined all the cranial nerves - 12 pairs. Anatomy, table, functions given in the article demonstrate that all cranial nerves have a complex structure, closely related to each other. And if any function is implemented with a restriction or is not performed at all, then there are violations.
It helps to master all the cranial nerves (12 pairs) table. Neurology, using these data, as well as thanks to special modern equipment, has made significant progress in the possibilities of timely diagnosis andeffective treatment of patients.
