Nerves that enter and leave the brain in medicine are defined 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 pairs and the violations that arise in them.
Types of cranial nerves
Each of the mentioned pairs of nerves is indicated by a Roman numeral from the first to the twelfth, according to their location on the basis of the brain. They are arranged in the following order:
1) olfactory;
2) visual;
3) oculomotor;
4) block;
5) trigeminal;
6) discharge;
7) facial;
8) auditory;
9) glossopharyngeal;
10) wandering;
11) incremental;
12) sublingual.
They include vegetative, efferent, and afferent fibers, and their nuclei are located in the gray matter of the brain. Depending on the composition of nerve fibers, all cranial nerves (12 pairs) are divided into sensory, motor and mixed. Consider them in this aspect.
Sensitive species
This group includes olfactory, optic and auditory nerves.
The olfactory nerves have processes located in the nasal mucosa. Starting from the nasal cavity, they cross the ethmoid plate and approach the olfactory bulb, where the first neuron ends and the central path begins.
The visual pair consists of fibers extending from the retina, cones and rods. All nerves enter the same trunk in the cranial cavity. First, they form a cross, and then the optic tract, enveloping the leg of the brain and giving fibers to the visual centers. About one million fibers (axons of neurons of the optic retina) enter one nerve, and, in addition, it has one vagina outside and another 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 vestibule and cochlear root. They depart from the middle ear and enter the cerebellopontine angle.
Motor types
Another group of 12 pairs of cranial nerves includes oculomotor, block, accessory, sublingual and abducent nerves.
The third pair, that is, the oculomotor nerves, contain autonomic, motor and parasympathetic fibers. They are divided into upper and lower branches. Moreover, only the upper branches belong to the motor group. They enter the muscle that raises the eyelid.
The next group includes block nerves that set the eyes in motion. If you compare all the cranial nerves - 12 pairs - then these are the thinnest. They originate from the nucleus on the lid of the midbrain, then bend around the leg of the brain and go into the orbit, innervating the upper oblique muscle of the eye apple.
The abducent nerves are related to the rectus muscle. They have a motor core in the fossa. Leaving the brain, they are directed to the upper orbital fissure, innervating there the rectus muscle.
Additional nerves originate from the medulla oblongata and cervical spinal cord. Separate roots are connected in one trunk, passing through the hole and dividing into the outer and inner branches. The inner 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 is provided for convenience at the end of the article) related to motor nerves are sublingual nerves. The origin of this nerve is spinal. But, over time, his spine moved to the skull. It is clear that this is the motor nerve of the tongue. The roots exit 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 the mixed nerves there are ganglia similar to those of 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 can also just be nearby.
The output of 12 pairs of cranial nerves is different. So, the third, seventh, ninth and tenth pairs have parasympathetic fibers at the exit sites, which are directed to the vegetative ganglia. Many of them are connected by branches, where different fibers pass.
The trigeminal nerve has two roots, where the larger is sensitive, and the smaller is motor. The skin innervation occurs on the parietal, ear and chin areas. Innervation also captures the conjunctiva and apple of the eye, the hard shell of the brain, the mucous membrane of the mouth and nose, teeth and gums, as well as the main part of the tongue.
Trigeminal nerves exit between the cerebellar pedicle, in the middle, and the bridge. Sensitive root fibers belong to the ganglion lying in the temporal pyramid near the apex, which was formed as a result of the 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 cord, which continues into the medulla oblongata, and then goes to the spinal cord. The fibers of the motor nerve root originate from the trigeminal nucleus, which is located in the bridge.
Upper, mandibular and optic nerves depart from the ganglion. The latter is sensitive, dividing into the nasal, frontal and lacrimal. The innervation of 12 pairs of cranial nerves varies not only in the pairs themselves, but also in the derived branches. So, the lacrimal nerve innervates the lateral ocular angle, passing the secretory branches to the lacrimal gland. The frontal nerve, respectively, branches out on the forehead and supplies its mucous membrane. The nasolacrimal innervates the eyeball, and the ethmoid nerves departing from it, innervating the nasal mucosa.
The maxillary nerve, which passes into the pterygo-palatine fossa and exits on the front facial surface, is also sensitive. From it originate the upper alveolar nerves, which pass to the teeth of the upper jaw and gums. The nerve on the cheekbones passes from the ganglion along the posterior nerves of the nose to its mucosa and nasopharynx. Nerve fibers here are sympathetic and parasympathetic.
The mixed type is the mandibular nerve. It consists of a motor root. Its sensitive branches include the buccal nerve, supplying the corresponding mucosa, ear-temporal, innervating the skin on the temples and ears and lingual, which supplies the tip and back of the tongue. The lower alveolar nerve is mixed. Passing in the lower jaw, it ends on the chin, branching here in the skin and mucosa of the lower lip. His branches are associated with vegetative ganglia:
- ear-temporal nerve - with the ear, innervating the parotid gland;
- lingual nerve - with ganglion, giving innervation to the sublingual and submandibular glands.
Facial include motor and sensory cranial nerves. Mixed fibers create a taste. Here, some fibers innervate the lacrimal and salivary glands, while others - the front two-thirds of the tongue.
The facial nerve consists of motor fibers starting in the upper fossa. The intermediate nerve with taste and parasympathetic fibers belongs to it. 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 next to the motor nucleus.
The facial nerve begins in the cerebellar cerebellar corner 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 leaves the bones of the temples and passes into the parotid gland, intertwining there. From here the branches diverge in a fan-shaped manner. At this time, all muscles related to the mimic are innervated, and some others. A branch on the neck from the facial nerve branches on it in the subcutaneous muscle.
The lingo-pharyngeal pair realizes the innervation of the lacrimal glands, the posterior part of the tongue, the inner ear and pharynx. The motor fibers are directed to the stylo-pharyngeal muscle and the pharyngeal compressors, and the sensitive ones - for the parotid gland to the ear ganglion. The nuclei of these nerves, in contrast to 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 begin in the salivary nucleus. The glossopharyngeal nerve, moving away from the medulla oblongata, extends to the base of the tongue. From the ganglion begins the tympanic nerve, which has parasympathetic fibers, continuing to the ear ganglion. Next, the lingual, tonsil and pharyngeal nerves begin. Lingual nerves innervate the root of the tongue.
A wandering couple 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 biggest innervation. The vagus nerve has a double core:
Going behind the olive on the neck, he moves with a neurovascular bundle, and then branches.
Violations
All cranial nerves can have impaired functions - 12 pairs. The anatomy of the lesion sites appears at different levels of the 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, however, studies the symptoms on the opposite side. Then the lesion of the pathways is diagnosed. It also happens that nerve dysfunction is associated with a tumor, an arachnoid cyst, an abscess, vascular malformations, and other similar processes.
The simultaneous defeat of 12 pairs of cranial nerves, that is, the hyoid, as well as the vagus and glossopharyngeal, was called bulbar paralysis. This is a very dangerous disease, since there is a possibility of pathology of the most important centers of the brain stem.
Knowing the topographic location of the cranial nerves allows you to correctly identify a narrow area of damage to each of them. To conduct research, use special techniques. With the appropriate equipment, today it is possible to identify all the details of the condition of the fundus, optic nerve, diagnose the field of vision and foci of loss. A computerized study allows highly accurate localization of the lesion site.
Ophthalmological examination
This technique allows to identify violations in the oculomotor, block and abduction pairs of nerves, to identify the 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. Diagnostics of the upper slit of the orbit, as well as various openings of the skull.
Vertebral and carotid angiography
This method is important in the recognition of vascular malformations and intracranial processes. However, more detailed information on these issues will provide computed tomography. She visualizes the trunks of the cranial nerves, diagnoses a tumor of the visual and auditory pair and other pathologies.
Electromyography
The deepening of the study of cranial nerves became possible thanks to the development of this method. It determines the state of spontaneous muscle chewing and facial expression, muscles of the tongue, soft palate and other muscles. Electromyography also allows you to calculate the speed of the impulse along the trunks of the facial, accessory and sublingual nerves. For this, the reflex blinking response, which is provided by trigeminal and facial nerves, is examined.
Neurological examination and symptoms of disorders of individual cranial nerves
This technique is carried out in a specific order. Examination begins with the olfactory nerve. The cotton wool soaked in the stimulus is brought to the nostrils in turn. The optic nerve is examined at an ophthalmological examination, on the basis of which, in addition to direct damage, even secondary changes can be detected. Pathology can be stagnant, dystrophic, inflammatory, or the nerve can be completely destroyed.
Lesions of the following three of the 12 pairs of cranial nerves (oculomotor, abduction and block) cause diplopia and strabismus. Lowering of the upper eyelid, dilated pupil, double vision may also occur.
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. 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.
In case of violation of the auditory nerve, hearing is worsened, 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
The functions of nerve fibers can be impaired both in isolation and in combination, together 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 Garsen's syndrome. With a tumor of the orbital bones and soft tissues, there is a syndrome of the upper orbital fissure. With the defeat of both the olfactory and optic nerves, Kennedy syndrome occurs.
These and other diseases occur both in adulthood and in childhood. For children, nerve damage that is associated with a malformation is especially common.
Below is a structure by which you can better understand how the cranial nerves act (12 pairs). Anatomy (the table is based on her knowledge) will help you navigate the intricacies of the functioning of their various groups.
Conclusion
We examined all cranial nerves - 12 pairs. The anatomy, table, and functions described in the article demonstrate that all the cranial nerves have a complex structure that is 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. Using this data, and also thanks to special modern equipment, neurology has made significant progress in the possibilities of timely diagnosis and effective treatment of patients.