Nerves extending from and entering the brain are called cranial nerves. The distribution and brief description of them individually is considered in the next article.
Types of Nerves and Pathology
There are several types of nerves:
Neurology of the motor cranial nerves, as sensitive and mixed, has pronounced manifestations that experts can easily diagnose. In addition to an isolated lesion of individual nerves, those that belong to different groups at the same time can be affected. Thanks to the knowledge of their location and functions, it is possible not only to understand which nerve is broken, but also to localize the affected area. This becomes achievable due to special techniques using high-tech equipment. For example, in ophthalmic practice, using modern technology, it is possible to find out the condition of the fundus, optic nerve, and determine the field of vision and foci of prolapse.
Good values are revealed by carotid and vertebral angiography. But more detailed information can be obtained using computed tomography. With it, you can see the individual trunks of nerves and identify tumors and other changes in the auditory, optic and other nerves.
Investigating the trigeminal and auditory nerves became possible thanks to the method of cortical somatosensory potentials. Also in this case, audiography and nystagmography are used.
The development of electromyography has expanded the possibilities for obtaining more detailed information about the cranial nerves. Now you can examine, for example, the reflexive blinking response, spontaneous muscle activity during facial expressions and chewing, muscles of the tongue, palate, and so on.
Let us dwell on each of these pairs of nerves. In total, there are 12 pairs of cranial nerves. A table where they are all given is indicated at the end of the article. In the meantime, consider each of the pairs separately.
1 pair. Description
This includes the olfactory nerve from the sensitive group. Moreover, receptor cells are scattered in the epithelium of the nasal cavity in the olfactory part. Thin nerve cell processes are concentrated in the olfactory filaments, which are the olfactory nerves. From the nasal nerve it enters the cranial cavity through the openings of the plate of the ethmoid bone, and ends in the bulb, from where the central olfactory pathways originate.
2 pair. Optic nerve
This pair includes the optic nerve, which belongs to the sensitive group. Axons of neurons here go through the trellis of the eyeball with one trunk that enters the cranial cavity. At the base of the brain, the fibers of these nerves converge on both sides and create visual crosshairs and tracts. The tracts go to the cranked body and the thalamus of the pillow, after which the central visual pathway is directed to the occipital lobe of the brain.
3 pair. Motor nerve
The oculomotor (motor) created by the fibers of the nerve passes from those nerves that are in the gray matter under the water supply to the brain. To the base, it passes between the legs, after which it enters the orbit and innervates the eye muscles (except for the upper oblique and external straight, other cranial nerves, 12 pairs, the table with the indication of which clearly illustrates all of them together) are responsible for their innervation. This occurs due to parasympathetic fibers contained in the nerve.
4 pair. Block nerve
This pair includes a block nerve (motor), originating from the nucleus under the aqueduct of the brain and reaching the surface in the area of the brain sail. In this part, a cross is obtained, the bending of the legs and penetration into the orbit. This pair is innervated by the superior oblique muscle.
5 pairs of 12 pairs of cranial nerves
The table continues with the trigeminal nerve, which is already mixed. In its trunk there are sensory and motor nuclei, and on the base there are their roots and branches. Sensitive fibers originate from the cells of the trigeminal ganglion, whose dendrites create peripheral branches that innervate the skin of the scalp in front, as well as the face, gum with teeth, ocular conjunctiva, mucous membranes of the nose, mouth, and tongue.
The motor fibers (from the root of the trigeminal nerve) connect to the mandibular nerve branch, pass and innervate the masticatory muscles.
6 pair. Abduction nerve
The next pair included in 12 pairs of cranial nerves (the table assigns it to the group of motor nerves), the pair includes a diverting nerve. It starts from the cell nuclei in the warolium bridge, penetrates the base and moves forward to the orbital fissure from above and further to the orbit. She innervates the rectus muscle (external).
7 pair. Facial nerve
This pair consists of the facial nerve (motor) created from the cellular processes of the motor nucleus. The fibers begin their path in the trunk at the bottom of the fourth ventricle, pass around the nucleus of the fourth nerve, descend to the base and exit into the bridge-cerebellar angle. Then it moves to the auditory opening, into the canal of the facial nerve. After the parotid gland, it is divided into branches innervating the facial facial expressions and muscles, as well as a number of others. In addition, one branch extending from its trunk innervates the muscle located in the middle ear.
8 pair. Auditory nerve
The eighth pair of 12 pairs of cranial nerves (the table lists it as sensitive nerves) consists of the auditory, or vestibule-cochlear nerve, which includes two parts: the vestibular and cochlear. The cochlear part consists of dendrites and axons of the spiral node located in the bone cochlea. And the other part moves away from the vestibular node at the bottom of the ear canal. A nerve on both sides connects in the ear canal to the auditory nerve.
Fibers of the vestibular part end in those nuclei that are in the rhomboid fossa, and cochlear - in the cochlear nuclei of the Varoliev bridge.
9 pair. Glossopharyngeal nerve
The cranial nerve table continues with the ninth pair, which is the glossopharyngeal nerve. It includes sensitive, motor, secretory and taste fibers. There are close connections with the vagus and intermediate nerves. Many nuclei of the nerve in question are located in the medulla oblongata. They are common with the tenth and twelfth pairs.
The nerve fibers of the pair are combined into a trunk leaving the cranial cavity. For the posterior third of the palate and tongue, it is a taste and sensory nerve, for the inner ear and pharynx - sensitive, for the pharynx - motor, for the parotid gland - secretory.
10 pair. Nervus vagus
Further, the cranial nerve table continues with a pair consisting of a vagus nerve, which is endowed with different functions. The trunk begins from the roots in the medulla oblongata. After leaving the cranial cavity, the nerve innervates the striated muscles in the pharynx, as well as in the larynx, palate, trachea, bronchi and digestive organs.
Sensitive fibers innervate the occipital region of the brain, the auditory meatus from the outside, and other organs. Secretory fibers go to the stomach and pancreas, vasomotor - to the vessels, parasympathetic - to the heart.
11 pair. Description of the Additional Nerve
The accessory nerve presented in this pair consists of the upper and lower sections. The first leaves the motor nucleus of the medulla oblongata, and the second - from the nucleus in the horns of the spinal cord. The roots connect with each other and exit the skull with the tenth pair. Some of them go to this vagus nerve.
It innervates the muscles - sternocleidomastoid and trapezius.
12 pair
The summary table of the cranial nerves ends with a pair with the hyoid nerve. Its core is located below the medulla oblongata. Coming out of the skull, he innervates the lingual muscles.
These are approximate schemes of 12 pairs of cranial nerves. To summarize the above.
Look at the list of cranial nerves, 12 pairs. The table is as follows.
Conclusion
Such is the structure and function of these nerves. Each pair plays its most important role. Each nerve is a part of a huge system and depends on it just like the whole system - on the functioning of individual nerves.