Functions of the pathways of the spinal cord. Ascending and descending tracts of the spinal cord

The nerve cell has a large number of processes. The processes removed from the cell body are called nerve fibers. Nerve fibers that do not extend beyond the central nervous system, form the conductors of the head and spinal cord. Fibers that travel outside the central nervous system gather into bundles and form peripheral nerves.

Nerve fibers passing inside the brain and spinal cord have different lengths - some of them come into contact with neurons located close, others with neurons located on greater distance, while others move far away from the body of their cell. In this regard, three types of conductors can be distinguished that carry out the transmission of impulses within the central nervous system.

1. Projection conductors communicate with the overlying sections of the central nervous system with the sections located below. (Fig. 4). Among them, there are two types of paths. Descending conduct impulses from the overlying parts of the brain down and are called centrifugal. They are motor in nature. The paths that direct from the periphery the conductive impulses from the skin, muscles, joints, ligaments, bones to the center have an upward direction and are called centripetal. They are sensitive in nature.

Rice. four.

I - posterior spinal bundle; II - fibers of the posterior cord; III - spinal tuberous bundle; IV - anterior cortical-spinal bundle; V - lateral cortical-spinal bundle; VI - vestibulo-spinal bundle

2. Commissural, or adhesive, conductors connect the hemispheres of the brain. Examples of such connections are the corpus callosum, which connects the right and left hemisphere, anterior commissure, commissure of the uncinate gyrus, and gray commissure of the thalamus that connects both halves of the thalamus.

3. Associative, or associative, conductors connect parts of the brain within the same hemisphere. Short fibers connect various convolutions in one or closely spaced lobes, and long ones stretch from one lobe of the hemisphere to another. For example, an arcuate bundle connects the lower and middle departments frontal lobe, lower longitudinal connects temporal lobe from the occipital. Allocate the fronto-occipital, frontal-parietal bundles, etc. (Fig. 5).

Rice. 5.

I - upper longitudinal (or arcuate) bundle; II - fronto-occipital bundle; III - lower longitudinal beam; IV - waist bun; V - hook-shaped bundle; VI - arcuate fiber; VII - large commissure (corpus callosum)

Consider the course of the main projection conductors of the brain and spinal cord.

centrifugal ways

The pyramidal path starts from large and giant pyramidal cells (Betz cells) located in the fifth layer of the anterior central gyrus and the paracentral lobule. In the upper sections there are paths for the legs, in the middle sections of the anterior central gyrus - for the trunk, below - for the arms, neck and head. Thus, the projection of human body parts in the brain is presented inverted. From the total amount of fibers a powerful bundle is formed, which passes through the inner bag. Then the pyramidal bundle passes through the base of the brain stem, the pons, entering the medulla oblongata, and then into the spinal cord.

At the level of the pons and medulla, part of the fibers of the pyramidal pathway ends in the nuclei of the cranial nerves (trigeminal, abducens, facial, glossopharyngeal, vagus, accessory, hypoglossal). This short bundle of fibers is called the cortical-bulbar pathway. It starts from the lower sections of the anterior central gyrus. Before entering the nuclei, the nerve fibers of the short pyramidal pathway cross over. Another, longer bundle of pyramidal nerve fibers, starting from upper divisions anterior central gyrus, descends into the spinal cord and is called the corticospinal tract. The latter, on the border of the medulla oblongata with the spinal cord, forms an incomplete decussation, and most of nerve fibers (subjected to cross) continue their way in the lateral columns of the spinal cord, and a smaller part (not crossed) goes as part of the anterior columns of the spinal cord of its side. Both segments end in the motor cells of the anterior horn of the spinal cord.

The pyramidal pathway (cortical-spinal and cortical-bulbar) is the central segment of the path that transmits motor impulses from the cells of the cerebral cortex to the nuclei of the cranial nerves and cells of the spinal cord. It does not go beyond the central nervous system.

From the motor nuclei of the cranial nerves and from the cells of the anterior horns of the spinal cord, the peripheral segment of the path along which the impulse is directed to the muscles begins. Consequently, the transmission of a motor impulse is carried out through two neurons. One conducts impulses from the cells of the cortex of the motor analyzer to the cells of the anterior horns of the spinal cord and to the nuclei of the cranial nerves, the other - to the muscles of the face, neck, trunk and limbs (Fig. 6).

When the pyramidal tract is damaged, movements are disturbed on the side opposite to the lesion, which can be expressed by a complete absence of muscle movements (paralysis) or their partial weakening (paresis). Depending on the location of the lesion, there are central and peripheral paralysis or paresis.

Rice. 6.

I - cortical-spinal bundle; II - cortical-bulbar bundle; III - the crossed part of the cortical-spinal bundle; IV - uncrossed part of the cortical-spinal bundle; V - cross of pyramids; VI - caudate nucleus; VII - hillock; VIII - lentil kernel; IX - pale ball; X - leg of the brain; XI - varolian bridge; XII - medulla oblongata; K. VII - core facial nerve; K. XII - core hypoglossal nerve

The Monakovic bundle begins in the midbrain from the red nuclei. Immediately upon exiting the red nucleus, the fibers cross and, having passed the hindbrain, descend into the spinal cord. In the spinal cord, this bundle of nerve fibers is located in the lateral columns near the bundle of the crossed pyramidal tract and gradually ends, like pyramidal path, in the cells of the anterior horns of the spinal cord.

Monakov's bundle conducts motor impulses that regulate muscle tone.

The roof-spinal bundle connects the anterior colliculus of the midbrain with the anterior and partly lateral columns of the spinal cord. Participates in the implementation of visual and auditory orienting reflexes.

The vestibulospinal bundle originates in the nuclei vestibular apparatus(in the Deiters kernel). The fibers descend into the spinal cord and pass in the anterior and partly lateral columns. The fibers end in the cells of the anterior horns. Since the nucleus of Deiters is connected with the cerebellum, impulses from the vestibular system and the cerebellum to the spinal cord follow this path; participates in the balance function.

The reticular-spinal bundle starts from the reticular formation of the medulla oblongata, passes in different bundles in the anterior and lateral columns of the spinal cord. It ends in the cells of the anterior horn; conducts vital impulses from the coordinating center of the hindbrain.

The posterior longitudinal bundle consists of ascending and descending fibers. It travels through the brainstem to the anterior columns of the spinal cord. Impulses from the brain stem and segments of the spinal cord, from the vestibular apparatus and nuclei pass along this path. eye muscles, as well as from the cerebellum.

As already noted, there are a number of neurons in the spinal cord that give rise to long ascending pathways to various brain structures. A large number of descending tracts formed by axons also enter the spinal cord. nerve cells, localized in the cerebral cortex, on average and medulla oblongata. All these projections, along with the pathways connecting the cells of various spinal segments, form a system of pathways shaped like white matter, where each path occupies a well-defined position.

Major ascending tracts of the spinal cord shown in fig. 81 and in table. 4. Some of them are fibers of primary afferent (sensitive) neurons that run without interruption. These fibers are thin (gaulle bundle) and wedge-shaped (Burdach's bundle) the bundles go as part of the dorsal cords of the white matter and end in the medulla oblongata near the neuronal relay nuclei, called the nuclei of the dorsal cord, or the nuclei of Gaulle and Burdach. The fibers of the dorsal funiculus are conductors of the skin-mechanical senses. 81. Localization of the main ascending pathways in white vitality. substance of the spinal cord (diagram). Explanation in the text.

The remaining ascending pathways start from neurons located in the gray matter of the spinal cord. Since these neurons receive synaptic inputs from primary afferent neurons, they are commonly referred to as second-order neurons, or secondary afferent neurons. The bulk of the fibers from the secondary afferent neurons pass through the lateral funiculus of the white matter. Here is located spinothalamic pathway. The axons of the spinothalamic neurons cross and reach without interruption through the oblong and midbrain to the thalamic nuclei, where they form synapses with thalamic neurons. The spinothalamic pathways receive impulses from skin receptors.

Fibers run in the lateral cords dorsal tracts, dorsal and ventral conducting impulses from skin and muscle receptors to the cerebellar cortex.

As part of the lateral funiculus, there are also fibers of the spinocervical tract, the endings of which form synapses with relay neurons. cervical spinal cord - neurons

cervical nucleus. After switching in the cervical nucleus, this pathway is directed to the cerebellum and the brainstem nuclei.

The path of pain sensitivity is localized in the ventral columns of the white matter. In addition, the spinal cord's own pathways pass through the posterior, lateral, and anterior columns, ensuring the integration of functions and the reflex activity of its centers.

Descending tracts of the spinal cord also divided into several independent tracts, occupying a certain position in the lateral and ventral cords of the white matter (Fig. 82).

Evolutionarily older descending paths originate from neurons whose nuclei are located within the medulla oblongata and the bridge. it reticulospinal and vestibulospinal tracts. The reticulospinal tract is formed by axons of neurons of the reticular formation of the hindbrain.

Reticulospinal fibers are part of the lateral and ventral funiculi of the spinal cord and end on many gray matter neurons, including a- and y-motor neurons. The fibers of the vestibulospinal tract, which are mainly axons of neurons of the lateral vestibular nucleus, or Deiters' nucleus, have a similar localization. Both of these paths do not intersect.

Evolutionarily younger downstream is rubrospinal tract, reaching greatest development only in mammals. Rubrospinal fibers are axons of neurons in the red nucleus located in the midbrain. The rubrospinal tract crosses and goes as part of the lateral cords of the white matter.

The endings of the rubrospinal fibers occupy a more dorsal position in the gray matter of the spinal cord than the endings of the fibers of the reticulo- and vestibulospinal tracts. Nevertheless, some of these fibers form synapses directly on motor neurons.

The most important downward path is cortico-spinal, or pyramidal, tract, whose neurons are located in the motor area of ​​the cerebral hemispheres. The pyramidal tract is evolutionarily the youngest. It appears only in mammals and is most developed in primates and humans. The fibers of the pyramidal tract decussate and run as part of the dorsolateral cords above the rubrospinal tract. The endings of the cortico-spinal fibers are found mainly on the intercalary neurons of the spinal cord. Pyramidal axons, which establish direct connections with motor neurons, are myelinated fibers of large diameter and conduct impulses at high speed.

10. ascending and descending pathways of the spinal cord and brain

Pathways that connect the spinal cord with the brain and brain stem with bark big brain, is usually divided into ascending and descending. The ascending nerve pathways carry sensory impulses from the spinal cord to the brain. Descending - conduct motor impulses from the cerebral cortex to the reflex-motor structures of the spinal cord, as well as from the centers extrapyramidal system to prepare muscles for motor acts and to correct actively performed movements.

Ascending paths. 1. Path for superficial (pain, temperature and tactile) sensitivity. Information is perceived by receptors embedded in the skin. Through the sensitive fibers of the peripheral nerves, impulses are transmitted to the spinal nodes, where the cells of the first sensitive neuron are laid. Next, the excitation is directed along back roots in the posterior horns of the spinal cord.

2. Path for conducting deep (muscle-articular, vibration) and tactile sensitivity. Receptors that perceive irritations are embedded in the tissues of the musculoskeletal system (for tactile sensitivity - in the skin). Excitation is transmitted along the sensitive fibers of the peripheral nerves to the cells of the spinal nodes, i.e. to the cells of the first sensitive neuron.

3. Anterior dorsal cerebellar path (Govers) originates from cells back horns from the spinal cord and along the lateral cords of its own and opposite sides through the upper cerebellar peduncles it enters the cerebellum, where it ends in the region of its worm.

4. The posterior spino-cerebellar path (Flexiga) also begins in the region of the posterior horns of the spinal cord and is sent as part of the lateral cords of its side through the lower cerebellar peduncles to the cerebellar vermis.

The anterior and posterior spinal cerebellar tracts conduct impulses from proprioreceptors.

descending paths.

1. Pyramidal pathways - descending nerve fibers, including cortical-spinal cord (anterior and lateral) pathways and cortical-nuclear fibers.

The cortical-spinal tract begins from large pyramidal (motor) cells of the cerebral cortex in the region of the precentral gyrus; the face is represented in its lower third, the hand in the middle, the leg in the upper. The fibers of the lateral pyramidal pathway innervate the muscles of the limbs, and the anterior pyramidal pathway innervates the muscles of the neck, trunk, and perineum. Due to the peculiarities of the course of the pyramidal tracts, the muscles of the limb receive innervation from the opposite hemisphere, and the muscles of the neck, trunk, and perineum receive innervation from both hemispheres.

Cortical-nuclear fibers also serve to conduct impulses of voluntary movements.

2. The cortical-cerebellar pathway provides coordination of movements (consistency). Its first neurons are located in the cortex of the frontal, parietal, occipital and temporal lobes of the brain. The descending pathways also include the posterior longitudinal bundle, which connects the brain stem with the spinal cord. These descending pathways terminate in the cells of the anterior horns of the spinal cord or the motor nuclei of the cranial nerves. Here are peripheral motor neurons that conduct impulses to the muscles and are at the same time the efferent part reflex arcs.

Functional systems P.K. Anokhin. The principle of heterochrony of development. Intrasystem and intersystem heterochrony.

Having considered the ontogeny of sensorimotor structures, we turn to the formation functional systems described by Academician P.K. Anokhin. The theory of functional systems considers the organism as a complex integrative structure consisting of many functional systems, each of which has its own dynamic activity provides beneficial results for the body. PC. Anokhin evaluates systemogenesis as the selective maturation of functional systems and their individual components in ontogenesis. Along with the leading genetic and embryological aspects of the maturation of functional systems in pre- and postnatal periods development of systemogenesis includes patterns of formation of behavioral functions. The main process that selects functional systems for existence in a new (external) environment is accelerated (heterochronous) and selective maturation of central and peripheral structures. These adaptive reactions of the body are hereditarily fixed in phylo- and embryogenesis. This multi-temporal maturation of various structures of the embryo is necessary for the concentration nutrients and energy in certain systems in given age periods. A person has his own early maturing set of functional systems, i.e. its systemogenesis. In this case, the system can begin to function without receiving yet full development. For its formation, signals (irritations) coming from the external environment are necessary. The sequence of maturation of the parts of the central nervous system is genetically determined. The spinal cord begins to differentiate earlier than the brain and independently of it. The readiness of the nerve cell and the entire neuron for activity is due to the accumulation of nutrients and the presence of the myelin sheath, the formation of synapses. Thus, as a result of a series of successive inclusions, accumulation and jumps, with the leading participation of higher frontal structures, a multilevel functional system is formed.

Symptoms and prophets of the development of other organs and systems. Sometimes the detection of pathology in NSG is an accidental finding. III. Systematics of methods of B-scanning of the brain from the standpoint of pediatric neuropathology and neurosurgery Depending on the sensors used, linear scanning or sectoral scanning is performed. Depending on the ultrasonic window used, there are ...

Laryngospasm. Pain radiates to the ear, provoked by eating and swallowing. pain point is determined on the lateral surface of the neck, slightly above the thyroid cartilage. Giving help. Urgent care similar to that which turns out to be a patient with neuralgia trigeminal nerve. Glossalgia. Clinic. Glossalgia is caused by the defeat of peripheral somatic formations of the oral cavity, but the main ...

Activity and sound-producing side of speech. These children have a quiet, poorly modulated voice with a nasal tinge. The study of the neck-tonic reflex in cerebral palsy with symptoms of torticollis Depending on the severity and prevalence, the following forms of children's cerebral palsy: spastic diplegia, spastic hemiplegia, double hemiplegia, ...

U. M., Belova L. V. "Some issues of psychotherapy in dermatology" - "Bulletin of dermatology and venereology" 1982, 11, 62-66. 605. Mirzamukhamedov M. A., Suleimanov A. S., Pak S. T., Shamirzaeva M. Kh. “The effectiveness of hypnosis and acupuncture in some functional diseases in children" - " medical journal Uzbekistan" 1987, 1, 52-54. 606. Mirzoyan A. S. “Step-by-step psychotherapy of sexual...

The nerve cell has a large number of processes. The processes removed from the cell body are called nerve fibers. Nerve fibers that do not extend beyond the central nervous system form conductors of the brain and spinal cord. Fibers that travel outside the central nervous system gather into bundles and form peripheral nerves.

Nerve fibers passing inside the brain and spinal cord have different lengths - some of them come into contact with neurons located close, others with neurons located at a greater distance, and still others are far removed from the body of their cell. In this regard, three types of conductors can be distinguished that carry out the transmission of impulses within the central nervous system.

1. Projection conductors communicate with the overlying sections of the central nervous system with the sections located below. Among them, there are two types of paths. Descending conduct impulses from the overlying departments of the go-

To MOUSE

Rice. 47. Projection fibers of the spinal cord:

1 - posterior spinal bundle; II - fibers of the posterior cord; III - spinal tuberous bundle; IV - anterior cortical-spinal bundle; V - lateral cortical-in-spinal bundle; VI - vestibulo-spinal bundle

I - upper longitudinal (or arcuate) bundle; II - fronto-occipital bundle; III - lower longitudinal beam; IV - waist bun; V - hook-shaped bundle; VI - arcuate fiber; VII - large commissure (corpus callosum)

brain down and are called centrifugal. They are motor in nature. The paths that direct from the periphery the conductive impulses from the skin, muscles, joints, ligaments, bones to the center have an upward direction and are called centripetal. They are sensitive in nature.

Commissural, or adhesive, conductors connect the hemispheres of the brain. Examples of such connections are the corpus callosum, connecting the right and left hemispheres, the anterior commissure, the uncinate gyrus commissure, and the gray commissure of the thalamus, connecting both halves of the thalamus.

Associative, or associative, conductors connect parts of the brain within the same hemisphere. Short fibers connect various convolutions in one or closely spaced lobes, and long ones stretch from one lobe of the hemisphere to another. For example, the arcuate bundle connects the lower and middle sections of the frontal lobe, the lower longitudinal connects the temporal lobe with the occipital lobe. Allocate the fronto-occipital, fronto-parietal bundles, etc. (Fig. 48).

Consider the course of the main projection conductors of the brain and spinal cord.

centrifugal ways

pyramid path begins from large and giant pyramidal cells (Betz cells) located in the fifth layer of the anterior central gyrus and paracentral lobule. In the upper sections there are paths for the legs, in the middle sections of the anterior central gyrus - for the trunk, below - for the arms, neck and head. Thus, the projection of human body parts in the brain is presented inverted. A powerful bundle is formed from the total amount of fibers, which passes through the inner bag (in Fig. 36 - see the knee and the front two-thirds of the back of the thigh). Then the pyramidal bundle passes through the base of the brain stem, the pons, entering the medulla oblongata, and then into the spinal cord.

At the level of the pons and medulla, part of the fibers of the pyramidal pathway ends in the nuclei of the cranial nerves (trigeminal, abducens, facial, glossopharyngeal, vagus, accessory, hypoglossal). This short bundle of fibers is called the cortical-bulbar pathway. It starts from the lower sections of the anterior central gyrus. Before entering the nuclei, the nerve fibers of the short pyramidal pathway cross over. Another, longer bundle of pyramidal nerve fibers, starting from the upper sections of the anterior central gyrus, descends down into the spinal cord and is called the cortical-spinal path. The latter, on the border of the medulla oblongata with the spinal cord, forms an incomplete decussation, and most of the nerve fibers (subjected to decussation) continue their way in the lateral columns of the spinal cord, and a smaller part (not crossed) goes as part of the anterior columns of the spinal cord of its side. Both segments end in the motor cells of the anterior horn of the spinal cord.

The pyramidal pathway (cortical-spinal and cortical-bulbar) is the central segment of the path that transmits motor impulses from the cells of the cerebral cortex to the nuclei of the cranial nerves and cells of the spinal cord. It does not go beyond the central nervous system.

From the motor nuclei of the cranial nerves and from the cells of the anterior horns of the spinal cord, the peripheral segment of the path along which the impulse is directed to the muscles begins. Consequently, the transmission of a motor impulse is carried out through two neurons. One conducts impulses from the cells of the cortex of the motor analyzer to the cells of the anterior horns of the spin

leg brain and to the nuclei of the cranial nerves, the other - to the muscles of the face, neck, trunk and limbs.

When the pyramidal tract is damaged, movements are disturbed on the side opposite to the lesion, which can be expressed by a complete absence of muscle movements (paralysis) or their partial weakening (paresis). Depending on the location of the lesion, central and peripheral paralysis or paresis are distinguished. The characteristics of these violations are given in the corresponding section.

I - cortical-spinal bundle; II - cortical-bulbar bundle; III - the crossed part of the cortical-spinal bundle; IV - uncrossed part of the cortical-spinal bundle; V - cross of pyramids; VI - caudate nucleus; VII - hillock; VIII - lentil kernel; IX - pale ball; X - leg of the brain; XI - varolian bridge; XII - medulla oblongata; K. VII - the nucleus of the facial nerve; K. XII - the nucleus of the hypoglossal nerve

Monakov's bundle conducts motor impulses that regulate muscle tone.

Roof-spinal bundle connects the anterior colliculus of the midbrain with the anterior and partly lateral columns of the spinal cord. Participates in the implementation of visual and auditory orienting reflexes.

vestibulo-spinal bundle begins in the nuclei of the vestibular apparatus (in the nucleus of Deiters). The fibers descend into the spinal cord and pass in the anterior and partly lateral columns. The fibers end in the cells of the anterior horns. Since the nucleus of Deiters is connected with the cerebellum, impulses from the vestibular system and the cerebellum to the spinal cord follow this path; participates in the balance function.

Retico-spinal bundle starts from the reticular formation of the medulla oblongata, passes in different bundles in the anterior and lateral columns of the spinal cord. It ends in the cells of the anterior horn; conducts vital impulses from the coordinating center of the hindbrain.

Posterior longitudinal beam consists of ascending and descending fibers. It travels through the brainstem to the anterior columns of the spinal cord. Impulses from the brain stem and segments of the spinal cord, from the vestibular apparatus and nuclei of the eye muscles, as well as from the cerebellum pass along this path.

centripetal paths

Pathway of superficial skin sensitivity carries pain, temperature and, in part, tactile sensations (the main path of touch passes with fibers of deep sensitivity). The path begins in the intervertebral node from cells that have two processes, one of them goes to the periphery to the skin receptors, and the other goes to the spinal cord and ends in the cells dorsal horn spinal cord. This is the so-called first neuron of the sensory pathway. From the cells of the posterior horn, the second neuron of the skin sensitivity pathway begins. It passes to the opposite side and rises along the lateral columns of the spinal cord, passes through the medulla oblongata, and in the pons varolii and in the region of the midbrain it enters the medial loop and goes to the outer nucleus of the thalamus. From the thalamus begins the third neuron of the sensory pathway; it passes the internal pouch (at the back of the thigh) and travels to the cerebral cortex. It ends in the region of the posterior central gyrus (parietal lobe).

Path of deep sensitivity It also starts from the nerve cells of the intervertebral node, where impulses are suitable not only from the skin and mucous membranes, but also from muscles, joints, bones, tendons and ligaments. The path of deep sensitivity, carrying irritations from all these formations, enters the spinal cord as part of the posterior columns. Then it rises up along the spinal cord to the oblong, in the nuclei of which the first neuron of this path ends. From the nuclei of the medulla oblongata begins the second neuron of deep sensitivity. Upon exiting the nuclei, the fibers cross, then form a medial loop and go to the lateral nucleus of the visual mound. The third neuron of deep sensitivity begins from the visual hillock, it passes through the internal bag and also ends in the cells of the posterior central gyrus (parietal lobe) (Fig. 50).

I- nuclei of the posterior pillars; II - posterior columns of the spinal cord, III - spinal tuberous bundle; IV - trigeminal nerve: P. - median loop: 3. bug. - visual tubercle: M. t. - corpus callosum; Ch. i. - lentil kernel; V. s. - inner bag

The ascending pathways include sensory pathways that carry olfactory, visual and auditory stimuli. These will be discussed below in the section on cranial nerves.

With the defeat of sensitive conductors, disorders of all types of sensitivity of the corresponding area are observed. So, with the defeat of the corresponding paths of the lateral column, skin (pain and temperature) and partly tactile sensitivity on the opposite side suffers.

In connection with the defeat of the fibers of the cerebellar pathways, disorders of coordination of movements occur. With the defeat of the posterior pillars, deep sensitivity is disturbed - a sense of the position of the organs of movement, localization, a two-dimensional spatial sense. In this regard, the gait is also disturbed, which becomes uncertain, the movements are sweeping, inaccurate.

cranial nerves

The cranial nerves originate in the brainstem, where their nuclei are located. The exceptions are the olfactory, auditory and optic nerves, the first neuron of which is located outside the brain stem.

Most cranial nerves are mixed, i.e. contain both sensory and motor fibers, with sensory predominating in some, and motor in others.

In total there are twelve 12 cranial nerves (Fig. 51).

/ pair - olfactory nerve. It begins in the nasal mucosa in the form of thin nerve threads that pass through ethmoid bone skulls, go to the base of the brain and are collected in the olfactory bulb. From the olfactory bulb comes the secondary olfactory pathway - olfactory tract. The fibers of the olfactory tract partly diverge, forming a triangle. Most of the olfactory fibers end in the central nucleus of the olfactory analyzer, located in the uncinate gyrus on the inner surface of the cortex.

The sense of smell is examined with a set of odorous substances.

The olfactory disorder can be expressed in different ways: in the form total absence perception of odors - anosmia, or a decrease in the perception of odors - hyposmia. Sometimes there is a particularly hypersensitivity to odorous substances - hyperosmia (in childhood almost never seen).

It should be borne in mind that sometimes local damage to the nasal mucosa (for example, with a runny nose) disrupts the perception of odors, which is not at all associated with damage to the olfactory tract itself.

2 pair - optic nerve. The visual path (Fig. 52) begins in the retina. The retina of the eye has a very complex

From the cells of the external geniculate body, the visual path is directed to the cerebral cortex. This segment of the path is called the Graziole bundle.

The visual path ends in the cortex of the occipital lobe, where the central nucleus of the visual analyzer is located.

Visual acuity in children can be checked using a special table. Color perception is checked by a set of color pictures.

structure, it consists of cells called rods and cones. These cells are receptors that perceive various light and color stimuli. In addition to these cells, there are ganglionic nerve cells in the eye, the dendrites of which end in cones and rods, and the axons form the optic nerve. The optic nerves enter the cranial cavity through the bony opening and pass along the bottom of the base of the brain. Based on the brain optic nerves form a half cross - chiasm. Not all nerve fibers are crossed, but only fibers coming from the inner halves of the retina; the fibers coming from the outer halves do not cross.

massive beam neural pathways, which is formed after the intersection of the optic fibers, is called the optic tract. Thus, in the optic tract of each side, nerve fibers pass not from one eye, but from the same halves of the retinas of both eyes. For example, in the left optic tract from both left halves of the retinas, and in the right - from both right halves (Fig. 52).

Most of the nerve fibers of the optic tract go to the external geniculate bodies, a small part

Visual pathway lesion may occur in Fig. 52. Scheme of the visual pathways

1 - „ (according to Bing)

any segment. AT depending on this, a different clinical picture of visual impairment will be observed.

Basically, it is necessary to distinguish three areas of the lesion: before the chiasm, in the region of the chiasm itself (chiasm) and after the optic chiasm. More on this will be discussed below.

L / (oculomotor nerve), IV (trochlear nerve) and VI (abducens nerve) pairs of nerves carry out the movements of the eyeball and are, therefore, oculomotors. These nerves send impulses to the muscles that move eyeball. With the defeat of these nerves, paralysis of the corresponding muscles and restrictions on the movements of the eyeball - strabismus are observed.

In addition, with the defeat of the III pair of cranial nerves, ptosis (drooping of the upper eyelid) and inequality of the pupils are also observed. The latter is also associated with damage to the branch of the sympathetic nerve, which is involved in the innervation of the eye.

V pair - the trigeminal nerve leaves the skull on the front surface, forming three branches: a) orbital, b) zygomatic, c) mandibular.

The first two branches are sensitive. They innervate the skin of the upper facial region, the mucous membranes of the nose, eyelids, as well as the eyeball, upper jaw, gums and teeth. Part of the nerve fibers supplies the meninges.

The third branch of the trigeminal nerve is mixed in terms of fiber composition. Its sensory fibers innervate lower section skin surface of the face, anterior two-thirds of the tongue, oral mucosa, teeth and gums mandible. The motor fibers of this branch innervate the masticatory muscles.

The sympathetic nerve plays an important role in the system of innervation of the trigeminal nerve.

With the defeat of the peripheral branches of the trigeminal nerve, the skin sensitivity of the face is upset. Sometimes there are excruciating attacks of pain (trigeminal neuralgia), due to the inflammatory process in the nerve. Disorders of the motor portion of the fibers cause paralysis of the masticatory muscles, as a result of which the movements of the lower jaw are sharply limited, which makes it difficult to chew food.

VII pair - the facial nerve (motor) is suitable for all the facial muscles of the face. With a unilateral lesion of the facial nerve, which often occurs as a result of a cold, nerve paralysis develops, in which the following picture is observed: low position eyebrows, palpebral fissure is wider than on the healthy side, the eyelids do not close tightly, the nasolabial fold is smoothed, the corner of the mouth sags, voluntary movements are difficult, it is not possible to frown and lift them up, evenly inflate the cheeks, it is not possible to whistle with lips or pronounce the sound "y". Patients at the same time feel numbness in the affected half of the face, experience pain. Due to the fact that the composition of the facial nerve includes secretory and taste fibers, salivation is disturbed, taste is upset. The fibers of the trigeminal nerve are also involved in the implementation of the function of taste.

VIII pair - auditory nerve begins in the inner ear with two branches. The first - the auditory nerve itself - departs from the spiral ganglion located in the cochlea of ​​the labyrinth. The cells of the spiral ganglion are bipolar, i.e. have two processes, and one group of processes (peripheral) goes to the hair cells of the organ of Corti, the others form the auditory nerve. The second branch of the mixed auditory nerve is called the vestibular nerve, departing from the vestibular apparatus, also located in the inner ear. It consists of three bony tubules and two sacs. A fluid circulates inside the canals - endolymph, in which calcareous pebbles - otoliths float. The inner surface of the sacs and canals is equipped with sensory nerve endings coming from the Scarpov nerve ganglion, which lies at the bottom of the internal auditory canal. The long processes of this node form the vestibular nerve branch. When exiting inner ear auditory and vestibular branches join.

Having entered the cavity of the medulla oblongata, these nerves approach the nuclei lying here, after which they are again disconnected, each following its own direction.

From the nuclei of the medulla oblongata, the auditory nerve goes already under the name of the auditory pathway. Moreover, part of the fibers crosses at the level of the bridge and passes to the other side. The other part goes along its side, including neurons from some nuclear formations (trapezoid body, etc.). This segment of the auditory pathway is called the lateral loop; it ends in the posterior tubercles of the quadrigemina and the internal geniculate bodies. The crossed auditory pathway also fits here. From the internal geniculate bodies, the third segment of the auditory pathway begins, which passes through the internal bag and approaches the temporal lobe, where the central nucleus of the auditory analyzer is located.

With unilateral damage to the auditory nerve and its nuclei, deafness develops in the ear of the same name. With unilateral injury auditory tract(in particular, the lateral loop), as well as the cortical auditory zone, there are no pronounced auditory disorders, there is some hearing loss in the opposite ear (due to double innervation). Complete cortical deafness is possible only with bilateral foci in the corresponding auditory zones.

The vestibular nerve, starting from the Scarp's node and having traveled some distance together with the auditory branch, enters the cavity of the medulla oblongata and approaches the angular nucleus. The angular nucleus consists of the lateral nucleus of Deiters, the superior nucleus of Bekhterev and inner core. From the angular nucleus, the conductors go to the cerebellar vermis (dentate and roofing nuclei), to the spinal cord along the fibers of the vestibulo-spinal and posterior longitudinal bundle. Through the latter, a connection is made with the oculomotor nuclei of the midbrain. There is a connection with the thalamus.

With the defeat of the vestibular apparatus, as well as the vestibular nerve and its nuclei, the balance is upset, dizziness, nausea, and vomiting appear.

IX pair - glossopharyngeal nerve includes sensory, motor, and secretory fibers. The glossopharyngeal nerve originates from four nuclei located in the medulla oblongata, some nuclei are common with the vagus nerve. This pair of nerves is closely related to the X pair (vagus nerve). The glossopharyngeal nerve supplies sensory (gustatory) fibers to the posterior third of the tongue and palate, and together with the vagus nerve innervates the middle ear and pharynx. The motor fibers of this nerve, together with the branches of the vagus nerve, supply the muscles of the pharynx. Secretory fibers innervate the parotid salivary gland.

With the defeat of the glossopharyngeal nerve, a number of disorders are observed, for example, taste disorders, a decrease in sensitivity in the pharynx, as well as the presence of mild spasms of the pharyngeal muscles. In some cases, salivation may be impaired.

X pair - the vagus nerve departs from the nuclei located in the medulla oblongata, some of the nuclei are common with the IX pair. The vagus nerve performs a number of complex functions of a sensitive, motor and secretory nature. So, it supplies motor and sensory fibers to the muscles of the pharynx (together with the IX pair), soft palate, larynx, epiglottis, vocal cords. Unlike other cranial nerves, this nerve extends far beyond the skull and innervates the trachea, bronchi, lungs, heart, gastrointestinal tract and some other internal organs, as well as blood vessels. Thus, the further course of its fibers takes part in the autonomic innervation, forming the parasympathetic nervous system.

In case of dysfunction vagus nerve, especially with bilateral partial damage, a number of severe disorders can occur, such as swallowing disorders, voice changes (nasality, dysphonia, aphonia); there is a series severe violations from the cardiovascular and respiratory systems. With full you-

If the function of the vagus nerve is turned off, death may occur due to paralysis of the heart and respiratory activity.

XI pair - accessory nerve, is a motor nerve. Its nuclei are located in the spinal cord and medulla oblongata. The fibers of this nerve innervate the muscles of the neck and shoulder girdle, in connection with which such movements as turning the head, raising the shoulders, bringing the shoulder blades to the spine are carried out.

With damage to the accessory nerve, atrophic paralysis of these muscles develops, as a result of which it is difficult to turn the head, the shoulder is lowered. Nerve irritation can cause tonic convulsions. neck muscles, causing the head to be forcibly tilted to the side (torticollis). Clonic spasm in these muscles (bilateral) causes violent nodding movements.

XII pair - hypoglossal nerve. These are the motor nerves of the tongue. The fibers start from the nucleus located at the bottom of the rhomboid fossa. Fibers of the XII pair innervate the muscles of the tongue, giving it maximum flexibility and mobility. With damage to the hypoglossal nerve, atrophic phenomena can develop in the muscles of the tongue, its ability to move is weakened, which is necessary to perform the speech function and the function of eating. In such cases, speech becomes unclear, it becomes impossible to pronounce complex words. With bilateral damage to the hypoglossal nerve, anarthria develops. A typical picture of speech and phonation disorders is observed with a combined lesion of the IX, X and XII pairs of nerves, known as bulbar palsy. In these cases, the nuclei of the medulla oblongata or the roots and nerves extending from them are affected. There is paralysis of the tongue, severe speech disorders, as well as swallowing disorders, choking, liquid food pours out through the nose, the voice becomes nasal. Such paralysis is accompanied by muscle atrophy and bears all the signs of peripheral paralysis. More often there are cases of lesions of the central pathway (cortical-bulbar). In childhood, with bilateral lesions of the cortical-bulbar tract, for example, after suffering parainfectious encephalitis, phenomena develop that are outwardly similar to bulbar paralysis, but differing in the nature of localization. Since this paralysis is central, there is no muscle atrophy. This type of disorder is known as pseudobulbar palsy.

The CNS pathways are built from functionally homogeneous groups of nerve fibers; they represent internal connections between the nuclei and cortical centers located in different parts and departments of the brain, and serve for their functional association (integration). The pathways, as a rule, pass through the white matter of the spinal cord and brain, but can also be localized in the tegmentum of the brainstem, where there are no clear boundaries between the white and gray matter.

The main conducting link in the system of transmitting information from one center of the brain to another is nerve fibers - the axons of neurons that transmit information in the form of a nerve impulse in a strictly defined direction, namely from the cell body. Among the conducting pathways, depending on their structure and functional significance, there are various groups nerve fibers: fibers, bundles, tracts, radiances, adhesions (commissures).

Projection pathways consist of neurons and their fibers that provide connections between the spinal cord and the brain. Projection paths also connect the nuclei of the trunk with the basal nuclei and the cerebral cortex, as well as the nuclei of the trunk with the cortex and nuclei of the cerebellum. Projection paths can be ascending and descending.

Ascending (sensory, sensitive, afferent) projection pathways conduct nerve impulses from extero-, proprio- and interoreceptors (sensory nerve endings in the skin, organs of the musculoskeletal system, internal organs), as well as from the sense organs in an upward direction to the brain, predominantly to the cerebral cortex, where they mainly end at the level of the IV cytoarchitectonic layer.

A distinctive feature of the ascending pathways is the multi-stage, sequential transmission of sensory information to the cerebral cortex through a number of intermediate nerve centers.

In addition to the cerebral cortex, sensory information is also sent to the cerebellum, the midbrain, and the reticular formation.

Descending (efferent or centrifugal) projection pathways conduct nerve impulses from the cerebral cortex, where they originate from the pyramidal neurons of the fifth cytoarchitectonic layer, to the basal and stem nuclei of the brain and further to the motor nuclei of the spinal cord and brain stem.

They transmit information related to the programming of body movements in specific situations, therefore they are motor pathways.

A common feature of the descending motor pathways is that they necessarily pass through the internal capsule - a layer of white matter in the cerebral hemispheres that separates the thalamus from the basal ganglia. In the brainstem, most of the descending pathways to the spinal cord and cerebellum go at its base.

35. Pyramidal and extrapyramidal systems

The pyramidal system is a combination of motor centers of the cerebral cortex, motor centers of cranial nerves located in the brain stem, and motor centers in the anterior horns of the spinal cord, as well as efferent projection nerve fibers that connect them together.

Pyramidal pathways provide the conduction of impulses in the process of conscious regulation of movements.

Pyramidal paths are formed from giant pyramidal neurons (Betz cells), as well as large pyramidal neurons localized in the fifth layer of the cerebral cortex. Approximately 40% of the fibers originate from pyramidal neurons in the precentral gyrus, where the cortical center of the motor analyzer is located; about 20% - from the postcentral gyrus, and the remaining 40% - from the posterior sections of the upper and middle lobar gyrus, and from the supramarginal gyrus of the lower parietal lobule, in which the center of praxia is located, which controls complex coordinated purposeful movements.

Pyramidal pathways are divided into corticospinal and cortical-nuclear. Their common feature is that they, starting in the cortex of the right and left hemispheres, pass to opposite side brain (i.e., cross) and ultimately regulate the movements of the contralateral half of the body.

The extrapyramidal system combines phylogenetically more ancient mechanisms for controlling human movements than the pyramidal system. It carries out predominantly involuntary, automatic regulation of complex motor manifestations of emotions. A distinctive feature of the extrapyramidal system is a multi-stage, with many switches, transmission of nerve influences from various parts of the brain to the executive centers - the motor nuclei of the spinal cord and cranial nerves.

Through the extrapyramidal pathways, motor commands are transmitted during protective motor reflexes that occur unconsciously. For example, thanks to the extrapyramidal pathways, information is transmitted when the vertical position of the body is restored as a result of a loss of balance (vestibular reflexes) or during motor reactions to a sudden light or sound effect (protective reflexes that close in the roof of the midbrain), etc.

The extrapyramidal system is formed by the nuclear centers of the hemispheres (basal nuclei: caudate and lenticular), diencephalon (medial nuclei of the thalamus, subthalamic nucleus) and brain stem (red nucleus, black matter), as well as pathways connecting it with the cerebral cortex, with the cerebellum , with the reticular formation and, finally, with the executive centers lying in motor nuclei cranial nerves and in the anterior horns of the spinal cord.

There is also a somewhat extended interpretation, when to E.S. they include the cerebellum, the nuclei of the quadrigemina of the midbrain, the nuclei of the reticular formation, etc.

Cortical pathways originate from the precentral gyrus, as well as other parts of the cerebral cortex; these pathways project the influence of the cortex to the basal ganglia. The basal nuclei themselves are closely connected with each other by numerous internal connections, as well as with the nuclei of the thalamus and with the red nucleus of the midbrain. The motor commands formed here are transmitted to the executive motor centers of the spinal cord mainly in two ways: through the red nuclear-spinal (rubrospinal) tract and through the nuclei of the reticular formation (reticulospinal tract). Also, through the red nucleus, the influence of the cerebellum on the work of the spinal motor centers is transmitted.