Pathways of the spinal cord. Features of the neural organization of the spinal cord

It is one of the main divisions of the central nervous system. Its development begins almost from the first minutes of the intrauterine formation of the human body. One of the elements of protection of the spinal cord are the membranes of the spinal cord. It is located in the cavity of the spine. Due to the relative strength of the vertebrae, the spinal cord retains its integrity.

What is the spinal cord?

The cord of the spinal cord is a column. It looks like an elongated cylinder with pointed ends. Surprisingly, such an important element of the human body weighs only up to 40 g. A cord begins at the base of the brain (at the level of the beginning of the cervical spine), near the occipital hole. The border between the medulla oblongata and the spinal cord is close to the foramen magnum. It ends approximately at the level of the first or second vertebrae of the lumbar spine. Approaching the end, it begins to narrow, forming a cone, from which a thin thread of the spinal cord descends - the terminal thread. In this thin thread are nerve fibers. The cone of the spinal cord already resembles a large accumulation of connective tissue, which has three layers. The terminal thread of the dorsal region, which comes from the cone of the spinal cord, ends just below the second vertebra of the lumbar region. There it converges with the periosteum. In this area, a cauda equina is formed - an accumulation of nerve endings of the spinal cord, braiding a thread with connective tissue.

The spinal cord has several spheres that cover it. The main membranes of the spinal cord:

cobweb;
hard;
soft.

The main canal is first covered with a soft layer, then comes the arachnoid layer of the brain membrane. Its processes pass from the main canal through the soft and hard protective layers of the membrane of the spinal cord and brain. The main functions (nutrition and protection) are performed by the membranes of the spinal cord and brain.

Furrows and thickenings

When viewed from the position of the spine, the cervical and lumbar regions are mobile, and the thoracic region is fixed. This is due to the fact that the spine in this place with the ribs protects the lungs, heart and other internal organs from damage. It is in the departments that have mobility that there is a high probability of damage.

For this reason, the spinal cord in these departments has seals. These are zones of cervical thickening and lumbosacral compaction. Moreover, there are additional clusters of nerve endings. Their function is the innervation of the upper and lower extremities.

The spinal cord is divided in half by fissures. These are furrows. These furrows are symmetrical (front and back). The anterior and posterior sulci of the spinal cord are the boundaries. For example, in front of it there is a root of movement, and these grooves are separated by front and third-party ropes. Furrows are very important.

Substance, segments and roots

The spinal cord has anterior and posterior roots. These are also nerve endings. The anterior roots arise from the gray matter of the CNS. The posterior roots are sensitive cells that penetrate the nervous system, intertwining, the anterior and posterior endings form nodes.

There are 62 spines in total. They branch out in different directions throughout the size of the spinal cord. It turns out 31 roots on each side. A segment is already a part of the spinal cord, which is located between the paired "forks" - roots. Accordingly, the number of dorsal segments is 31. There are 8 segments in the cervical region, 12 in the thoracic region, 5 segments in the lumbar region, 5 segments in the sacrum, and the last segment in the coccyx. This is somewhat consistent with the number of vertebrae in the human body, but still the spinal cord is shorter than the spine, so some segments do not correspond to their localization when compared with a vertebra.

The spinal nerve cord includes not only process roots. It also has white and gray matter. At the same time, the uniqueness lies in the fact that the white matter comes only from the nerve fibers of the spinal cord, but the gray matter was formed not only by the cells and fibers of the spinal cord, but also by the nerve endings of the brain.

Gray matter

The white matter covers the gray matter. Inside the gray matter is the main canal. In turn, there is cerebrospinal fluid inside the main channel. If we consider the transverse section of the spinal cord, then the white matter has the shape of a butterfly. The transverse section allows you to study in detail the structure of the spinal cord in the transverse direction. The spinal cord (main canal) and the brain (its ventricles, the place between the membranes) are connected not only by nerve endings, but also by the circular movement of cerebrospinal fluid. Cerebrospinal fluid is regulated by nerve plexuses located in the ventricles of the spinal cord. CSF regulation (its production and reabsorption) occurs in a similar way.

Gray matter is the common name for the columns of the spinal cord. They stick together in one place. This zone is called a plate. This is a gray compound. In the center is visible the main canal in which the spinal cord is located. There are two such zones for fastening the pillars: back and front. They are located in the back and front of the main channel. On a transverse section of the spinal cord, such adhesions resemble a butterfly or the letter H in shape.

When examining the spinal cord, one can see how appearances, which are called the horns of the spinal cord, depart from the gray matter. They are located in front and behind. The protrusions located in front are the anterior horns. There are wide paired horns in front, and narrow paired horns behind. The anterior horns contain movement neurons. The anterior roots themselves are formed from neurites. These are the neurons of motion. In the anterior horn there is a nucleus of the spinal cord, and it is not one. The nuclei are formed from the neurons of the horn. In total, there should be five centers-nuclei: central, lateral (2 pcs.), Medial (2 pcs.). From them, the processes are directed to the muscles.

The posterior paired narrow horns have their own nuclei. They are located in the center. Motor nuclei are formed from auxiliary intercalary neurons. Axons are the roots of these nerve cells. They go to the anterior horn, forming ligaments. They intersect with the anterior fastening (commissure) and then pass to the anterior side of the spinal cord. If the intercalary nerve cells reach a large size compared to other neurons, then the dendrites (their endings) branch significantly, forming another nucleus. This nucleus is located near the base of the posterior horn. The nodes of the spinal cord, which are located between the vertebrae, include neuron cells that have significant processes. They reach the centers of the posterior horns.

An intermediate section is formed between the horns of the anterior and posterior sections of the spinal cord. In this zone, the lateral branches (the horns of the spinal cord) diverge from the gray matter. This phenomenon can be seen from the eighth cervical region to the second lumbar segment of the spinal cord.

These branches have a substance that consists exclusively of nerve cells. Their uniqueness lies in the fact that they are calculated exclusively by the autonomic nervous system.

White matter in the brain

The cords of the spinal cord (three pairs: anterior, lateral and posterior) create white matter. The anterior cords are located between the lateral and medial fissures. This is where the front shoots come out. The lateral cords are located between the two lateral fissures. The posterior funiculus can be seen between the lateral and median fissures.

Nerve impulses travel along nerve fibers. These fibers are formed from white matter. Impulses pass in two directions: up (to the brain) and down (in).

The gray matter also has nerve endings that are located between the segments. These short endings connect only closely located neighboring departments. The segmental apparatus of the spinal cord is what they form together. Their purpose is to establish communication between the parts of the spinal cord.

Ganglion neurons form the posterior roots of the spinal cord. Some of them are connected with the posterior horn, and the rest are located on the sides. Another part of the endings goes to the posterior cords. Then they go to the brain. These are the ascending pathways of the spinal organ.

Conduction functions of nerves

The spinal cord performs several very important functions, one of them is conduction. This means that impulses with information move along the spinal cord to the brain and other organs (and vice versa).

This function is performed by the white matter, the neurons and nerve fibers that make it up. The evolutionary development of the spinal cord has led to the fact that the reflex arc is constantly becoming more complex as the basis of the nervous system. Development made it possible that where there could previously be only one neuron, knots of nerve fibers began to gradually appear, each of which consisted of an accumulation of nerve cells.

The pathways of the spinal organ are a collection of nerve endings that have common functions and a similar structure and development. These fibers connect either the spinal cord and the brain, or different segments of the spinal cord.

All pathways of the spinal cord, depending on their functions, are classified as projection, associative and commissural. Projection pathways can be efferent and afferent. These pathways are the main ones in the central nervous system. They can be ascending and descending. Descending paths are called motor and centrifugal. The ascending paths are called sensitive and centripetal. Ascending fibers use the currents that come from the receptors and are responsible for the factors of the external and internal environment.

The conductive paths of ascent are divided into paths of intero-extero- and proprioceptive sensitivity. There are several main bundles: the path of Gaulle and Burdakh, lateral, dorsal, ventral. Thin and wedge-shaped bundles respond to touch, simple movements, the state of the body in space. The dorsolateral pathway and the thalamic pathway are responsible for temperature and pain control. The Gowers and Flexig bundles are directed to skin receptors and receptors of muscles and ligaments. In addition, they are responsible for the transmission of impulses when pressure is sensed.

The descending fiber conducts electrical currents from the brain to the spinal cord, more precisely, they pass to the nuclei of movement, then the reaction follows.

Operations on the spinal cord

Basically, operations on the brain and spine are open, only in some, extremely rare cases, closed interventions can be performed.

The most common surgical intervention when it is necessary to open the back surface of the spinal cord (this is a laminectomy).

Laminotopias are also often needed - these are operations in which you can expose the spine not in a small segment, but in a large area.

If fixation of the vertebrae is necessary, then various plates and structures are used, but a cut must be made in that place.

When performing operations on the peripheral nervous system, the usual principles are used. A cut is made, a special microscope is used, which allows you to stitch the nerve endings if they have been torn or broken.

Now it is possible to use prostheses for some, not the most significant segments of the spinal cord.

Operations are performed under anesthesia. In some cases, local anesthesia is used. Depending on the operation, gaseous anesthesia, inhalation, electric anesthesia, etc. can be used.

Rehabilitation after surgery may take a different period depending on the severity. The following postoperative associated problems may occur:

itching and burning in the incision area for surgery;
headaches and dizziness;
violations in speech, swallowing, seizures, seizures, convulsions.

You need to see a doctor to solve problems. The main ones are listed below.

Symptoms and consequences of atrophy

Spinal cord atrophy is a process in which nerve fibers and cells die, and nerve connections are destroyed. This phenomenon can pass from the spinal cord to the brain.

Statistics show that brain atrophy most often occurs in women after 50 years of age. For several decades, a person can go to dementia. But the disease can also take hold of very young children. The basis of the disease is that the brain mass decreases over time. Scientists believe that the cause is heredity.

Symptoms depend on which spinal region is affected. A person first ceases to be active, becomes lethargic. Sometimes there may be a disregard for moral standards. Then there may be problems with memory, speech, sensory organs, motor skills, over time, the ability to analyze and create one's own opinion is lost.

Despite the development of new treatment methods, the prognosis for patients is not favorable enough. The best solution for treatment will be communication and good relationships in the family. Of the drugs prescribe vitamins and drugs for blood vessels.

You need to try to maintain an active lifestyle, healthy and proper nutrition.

Signs of a meningioma

Meningioma of the brain is a tumor that is located on the spinal canal. It usually arises from the vascular tissues of the layers of the brain. It is most often located almost at the base of the skull. Often it practically does not grow for a long period. Spinal cord meningioma is small and occupies no more than a few vertebrae. But then it can increase in length along the spine. In most cases, meningioma is benign, but it can become malignant or atypical.

It has been established that a tumor can arise and begin to develop from ionizing radiation during pregnancy, and increase during the menstrual cycle.

Radiation treatments or surgery can be used for treatment. Chemotherapy will not give a positive result if the tumor is benign. The treatment method is chosen depending on the location and size of the tumor. Most often, traditional methods are used at the beginning to reduce swelling in the area of the neoplasm.

Signs of angioma

Angioma of the spinal cord is a strong local expansion of blood vessels. From the outside, it looks like a red ball of tangled threads. Such an anomaly could arise due to heredity. Angioma can develop at the birth of a person, as well as in old age. The reason for its sudden appearance can be injuries and infections.

Angioma is manifested by such symptoms as:

headaches and dizziness;
visual impairment, memory, movement coordination;
noises in the head;
convulsions.

Angioma is divided into the following types: venous, capillary, tricky (a tangle of different vessels with thin walls).

If the angioma is small and does not interfere, then it can not be removed. Otherwise, the vessels are specially clogged and removed, so their development will not be observed.

Signs and consequences of a spinal cord rupture

A brain rupture is very difficult to diagnose. The place of the rupture is determined due to the fact that the spinal cord is protected not only by the spine, but also by the muscular base. The occurrence of such a disorder in the functioning of the nervous system as a rupture of the spinal cord can lead to very unpleasant, severe and unpredictable consequences for a person.

Rupture leads to loss of sensation, activity and partial or complete paralysis. The gap can lead to complete or partial disability, which complicates the normal life of a person. Car accidents, domestic injuries and falls from great heights can lead to rupture. A person can experience spinal shock when the whole body refuses to work. This often leads to death.

The spinal cord is an important element of the human body. It is better to immediately carry out the prevention of any diseases and, if you are afraid, consult a doctor.

Conducting paths	Columns of the spinal cord	Physiological significance
A. Ascending (sensory) pathways
1. Thin beam (Gaul's beam)	Dorsal	Tactile sensitivity, sense of body position, passive body movements,
2. Wedge-shaped (Burdach's bundle)	«	Same
3. Dorsolateral	Side	Ways of pain and temperature sensitivity
4. Dorsal dorsal cerebellar tract (Flexig's bundle)	«	Impulses from proprioceptors of muscles, tendons, ligaments; feeling of pressure and touch from the skin
5. Ventral dorsal cerebellar tract (Govers bundle)	«	Same
thalamic pathway	«	Pain and temperature sensitivity
7. Spino-tectal tract thalamic tract	«	Sensory pathways of visual-motor reflexes (?) and pain sensitivity (?)
Ventral	Tactile sensitivity

1. Lateral corticospinal (pyramidal) pathway	Side	Impulses to skeletal muscles. Arbitrary movements
2. Red nuclear-spinal (Monakov) path	«	Impulses that maintain skeletal muscle tone
spinal tract	«	body posture and balance
4. Olivospinal (Gelweg) path "	«	Function unknown. Possibly involved in thalamospinal reflexes
5. Reticular-spinal tract	Ventral	Impulses that maintain skeletal muscle tone, regulate the state of the spinal autonomic centers and the sensitivity of muscle spindles of skeletal muscle proprioreceptors
6. Ventral vestibulospinal tract	«	Impulses that maintain body posture and balance
7. Tectospinal (cover-spinal) path	«	Impulses that ensure the implementation of visual and auditory motor reflexes
8. Ventral corticospinal (pyramidal) pathway	Ventral	Impulses to skeletal muscles, voluntary movements

nerve fibers, characterized by a common structure and functions. They connect different parts of the spinal cord or spinal cord and brain. All nerve fibers of one path start from homogeneous neurons and end on neurons that perform the same function.

In accordance with the functional features, there are associative, commissural and projection (afferent and efferent) nerve fibers. association fibers, or bundles carry out unilateral connections between individual parts of the spinal cord. Linking different segments, they form their own bundles, which are part of the segmental apparatus of the spinal cord. Commissural fibers connect functionally homogeneous opposite sections of different parts of the spinal cord. Projection fibers connect the spinal cord with the overlying departments. These fibers form the main pathways, which are ascending (centripetal, afferent, sensory) and descending (centrifugal, efferent, motor) pathways.

Ascending pathways. They carry impulses from receptors that receive information from the outside world and the internal environment of the body. Depending on the kind of sensitivity they carry out, they are divided into paths extero-, proprio- And interoceptive sensitivity. descending paths transmit impulses from the structures of the brain to the motor nuclei, which carry out responses to external and internal stimuli.

Main ascending paths spinal cord are thin bundle, sphenoid bundle, lateral and ventral spinal-thalamic pathways, dorsal and ventral spinal-cerebellar pathways.

thin beam(Goll) and wedge-shaped bundle(Burdaha) make up the posterior funiculi of the spinal cord. These fiber bundles are processes of sensitive cells of the spinal ganglia, which conduct excitation from the proprioreceptors of muscles, tendons, partially tactile skin receptors, and visceroreceptors. The fibers of the thin and wedge-shaped bundles are myelinated, they carry out excitation at a speed of 60-100 m/s. The short axons of both bundles establish synaptic connections with motor neurons and interneurons of their segment, while the long ones go to the medulla oblongata. Along the way, they give off a large number of branches to the neurons of the overlying segments of the spinal cord, thus forming intersegment connections.

Through the fibers of the thin bundle, excitation is carried out from the caudal part of the body and pelvic limbs, through the fibers of the wedge-shaped bundle - from the cranial part of the body and thoracic limbs. In the spinal cord, both of these paths go without interruption and without crossing, and end in the medulla oblongata at the nuclei of the same name, where they form a synaptic switch to the second neuron. The processes of the second neuron are sent to the specific nuclei of the thalamus of the opposite side, thereby forming a kind of cross. Here they switch to the third neuron, the axons of which reach the neurons of layer IV of the cerebral cortex.

It is believed that information of finely differentiated sensitivity is carried out through this system, which makes it possible to determine the localization, the contour of peripheral irritation, as well as its changes over time.

By lateral dorsal thalamic tract pain and temperature sensitivity, ventral dorsal-thalamic - tactile. There is evidence that the transmission of excitation from proprio- and visceroceptors is also possible along these pathways. The speed of excitation in the fibers is 1-30 m/s. The spinal thalamic pathways are interrupted and cross either at the level of the segment into which they have just entered, or at first they pass several segments on their side, and then pass to the opposite one. From here come fibers that terminate in the thalamus. There they form synapses on nerve cells, the axons of which are sent to the cerebral cortex.

It is believed that information about the qualitative nature of stimuli is mainly transmitted through the fiber system of these pathways.

Dorsal dorsal cerebellar tract or Flexig's bundle - phylogenetically, this is the most ancient sensory pathway of the spinal cord. The location of the nerve cells, the axons of which form the fibers of this path, is the base of the dorsal horn of the spinal cord. Without crossing, the path reaches the cerebellum, where each fiber occupies a certain area. The speed of conduction along the fibers of the spinal-cerebellar tract is about 110 m/s. They carry information from the receptors of the muscles and ligaments of the limbs. This path reaches its greatest development in ungulates.

ventral spinocerebellar tract, or the Gowers bundle, is also formed by the axons of the interneurons of the opposite side of the spinal cord. Through the medulla oblongata and cerebellar peduncles, the fibers are directed to the cerebellar cortex, where they occupy vast areas. Impulses with conduction speed up to 120 m/s come from tendon, skin and visceroreceptors. They are involved in maintaining muscle tone to perform movements and maintain posture.

Descending pathways. These pathways connect the higher parts of the CNS with the effector neurons of the spinal cord. The main ones are the pyramidal, red nuclear-spinal and reticular-spinal tracts.

pyramid path formed by axons of the cells of the motor zone of the cerebral cortex. Heading towards the medulla oblongata, these axons give off a large number of collaterals to the structures of the diencephalon, midbrain, medulla oblongata and the reticular formation. In the lower part of the medulla oblongata, most of the fibers of the pyramidal tract pass to the opposite side (the intersection of the pyramids), forming lateral pyramidal tract. in the dorsal

brain, it is located in the lateral funiculus. The other part of the fibers goes, without crossing, to the spinal cord and only at the level of the segment in which it ends does it pass to the opposite side. It's straight ventral pyramidal tract. Both end on the motor neurons of the anterior horns of the gray matter of the spinal cord. The composition of the fibers of this pathway is heterogeneous, it includes myelinated and unmyelinated fibers of different diameters with excitation conduction velocities from 1 to 100 m/s.

The main function of the pyramidal tracts is the transmission of impulses to perform arbitrary movements. Reliability in the implementation of this function is increased due to the duplication of the connection of the brain with the spinal cord through two paths - crossed and direct. In the evolutionary series, the pyramidal tract developed in parallel with the development of the cerebral cortex and reached the greatest perfection in humans.

Red nuclear-spinal tract(Monakov) is formed by the axons of the cells of the red nucleus of the midbrain. After leaving the nucleus, the fibers completely pass to the opposite side. Some of them go to the cerebellum and the reticular formation, others - to the spinal cord. In the spinal cord, the fibers are located in the lateral columns in front of the crossed pyramidal pathway and terminate on the interneurons of the corresponding segments. The red nuclear-spinal path carries impulses from the cerebellum, the nucleus of the vestibular nerve, and the striatum.

The main purpose of the red nuclear-spinal tract is to control muscle tone and involuntary coordination of movements. In the process of evolution, this path arose early. It is of great importance in animals, less developed in humans.

Vestibulo-spinal tract formed by fibers that are processes of cells of the lateral pre-door nucleus (Deiters nucleus), which lies in the medulla oblongata. This tract has the most ancient evolutionary origin. It transmits impulses from the vestibular apparatus and the cerebellum to the motor neurons of the ventral horns of the spinal cord, which regulate muscle tone, coordination of movements, and balance. If the integrity of this path is violated, disorders of coordination of movements and orientation in space are observed.

In the spinal cord, in addition to the main long ones, there are also short descending paths connecting its individual segments to each other.

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 pathways, depending on their structure and functional significance, various groups of nerve fibers are distinguished: 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 V 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 pathways are formed from giant pyramidal neurons (Betz cells), as well as large pyramidal neurons localized in layer V 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, starting in the cortex of the right and left hemispheres, they move to the opposite side of the 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 the 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 the motor nuclei of the 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.

Ascending (afferent) pathways originating in the spinal cord

The bodies of the first neurons - conductors of all types of sensitivity to the spinal cord - lie in the spinal nodes. The axons of the cells of the spinal ganglions as part of the posterior roots enter the spinal cord and are divided into two groups: medial, consisting of thick, more myelinated fibers, and lateral, formed by thin, less myelinated fibers.

The medial group of fibers of the posterior root is sent to the posterior funiculus of the white matter, where each fiber divides in a T-shape into ascending and descending branches. The ascending branches, following upward, come into contact with the cells of the gray matter of the spinal cord in the gelatinous substance and in the posterior horn, and some of them reach the medulla oblongata, forming thin and wedge-shaped bundles, fasciculi gracilis et cuneatus(see Fig.,,), spinal cord.

The descending branches of the fibers go down and come into contact with the cells of the gray matter of the posterior columns for six to seven underlying segments. Some of these fibers form a bundle in the thoracic and cervical sections of the spinal cord, which has the form of a comma on the cross section of the spinal cord and is located between the wedge-shaped and thin bundles; in the lumbar region - a type of medial cord; in the sacral region - a view of an oval bundle of the posterior funiculus adjacent to the medial surface of a thin bundle.

The lateral group of fibers of the posterior root goes to the marginal zone, and then to the posterior column of gray matter, where it comes into contact with the cells of the posterior horn located in it.

The fibers extending from the cells of the nuclei of the spinal cord go up partly along the lateral funiculus of their side, and partly pass as part of the white commissure to the opposite side of the spinal cord and also go up in the lateral funiculus.

The ascending pathways (see Fig.,,), starting in the spinal cord, include the following:

Posterior spinocerebellar tract, tractus spinocerebellaris dorsalis, - direct cerebellar path, conducts impulses from muscle and tendon receptors to the cerebellum. The bodies of the first neurons lie in the spinal ganglion, the bodies of the second neurons lie throughout the spinal cord in the thoracic column (thoracic nucleus) of the posterior horn. The long processes of the second neurons go outwards; reaching the posterior part of the spinal cord of the same side, they wrap up and rise along the lateral funiculus of the spinal cord, and then follow the lower cerebellar pedicle to the cortex of the cerebellar vermis.
Anterior spinocerebellar tract, tractus spinocerebellaris ventralis, conducts impulses from muscle and tendon receptors to the cerebellum. The bodies of the first neurons lie in the spinal ganglion, and the second neurons lie in the medial nucleus of the intermediate zone and send part of their fibers through the white commissure to the lateral cords of the opposite side, and part to the lateral cords of their side. These fibers reach the anterolateral parts of the lateral cords, located anterior to the posterior spinal cerebellar tract. Here, the fibers wrap up, go along the spinal cord, and then along the medulla oblongata and, having passed the bridge, along the upper cerebellar peduncles, having made the second cross, they reach the cerebellar vermis.
Spinal tract, tractus spinoolivaris, originates from the cells of the posterior horns of the gray matter. The axons of these cells cross and rise near the surface of the spinal cord at the border of the lateral and anterior cords, ending in the nuclei of the olive. The fibers of this pathway carry information from skin, muscle and tendon receptors.
Anterior and lateral spinal thalamic pathways, tractus spinothalamici ventralis et lateralis(see Fig.), conduct impulses of pain, temperature (lateral path) and tactile (anterior path) sensitivity. The bodies of the first neurons lie in the spinal ganglia. The processes of the second neurons from the cells of the own nucleus of the posterior horn are sent through the white commissure to the anterior and lateral cords of the opposite side. Rising up, the fibers of these pathways pass in the posterior sections of the medulla oblongata, the bridge and legs of the brain and reach the thalamus as part of spinal loop, lemniscus spinalis. The bodies of the third neurons of these pathways lie in the thalamus, and their processes are directed to the cerebral cortex as part of the central thalamic radiations through the posterior leg of the internal capsule (Fig.,).
Spinal reticular path, tractus spinoreticularis, make up fibers that pass as part of the spinal-thalamic pathways, do not intersect and form bilateral projections to all sections of the stem reticular formation.
Spinal tract, tractus spinotectalis, along with the spinal-thalamic pathway, passes in the lateral cords of the spinal cord and ends in the plate of the roof of the midbrain.
Thin bundle, fasciculus gracilis, And wedge-shaped bundle, fasciculus cuneatus(see Fig.), conduct impulses from muscles, joints and tactile sensitivity receptors. The bodies of the first neurons of these pathways are localized in the corresponding spinal nodes. Axons go as part of the posterior roots and, having entered the posterior columns of the spinal cord, take an upward direction, reaching the nuclei of the medulla oblongata.

A thin bundle occupies a medial position and conducts the corresponding impulses from the lower extremities and lower parts of the body - below the 4th thoracic segment.

The wedge-shaped bundle is formed by fibers starting from the cells of all spinal nodes lying above the 4th thoracic segment.

Having reached the medulla oblongata, the fibers of the thin bundle come into contact with the cells of the nucleus of this bundle, which lies in the tubercle of the thin nucleus; the fibers of the wedge-shaped bundle end in the wedge-shaped tubercle. The cells of both hillocks are the bodies of the second neurons of the described pathways. Their axons are internal arcuate fibers, fibrae arcuatae internae, - go forward and up, go to the opposite side and, forming decussation of medial loops (sensitive decussation), decussatio lemniscorum medialium (decussatio sensoria), with fibers of the opposite side, are part of medial loop, lemniscus medialis.

Having reached the thalamus, these fibers come into contact with its cells - the bodies of the third pathway neurons, which send their processes through the internal capsule to the cerebral cortex.

Ascending (afferent) pathways originating in the brainstem

The medial loop, the trigeminal loop, the ascending path of the auditory analyzer, visual radiance, and thalamic radiance begin in the brain stem.

1. medial loop as a continuation of the thin and wedge-shaped bundles described earlier.

2. Trigeminal loop, lemniscus trigeminalis, is formed by processes of nerve cells that make up the sensory nuclei of the trigeminal nerve (V pair), facial nerve (VII pair), glossopharyngeal nerve (IX pair) and vagus nerve (X pair).

The axons of afferent neurons located in the trigeminal ganglion approach the sensory nuclei of the trigeminal nerve. The axons of afferent neurons located in the node of the knee (VII pair) and in the upper and lower nodes of the IX and X pairs of nerves approach the common sensory nucleus of the other three nerves - the nucleus of the solitary pathway. In the listed nodes, the bodies of the first neurons are localized, and in the sensitive nuclei, the bodies of the second neurons of the path along which impulses are transmitted from the receptors of the head are localized.

The fibers of the trigeminal loop pass to the opposite side (some of the fibers follow on their side) and reach the thalamus, where they end in its nuclei.

The nerve cells of the thalamus are the bodies of the third neurons of the ascending pathways of the cranial nerves, the axons of which, as part of the central thalamic radiances, through the internal capsule are sent to the cerebral cortex (postcentral gyrus).

3. The ascending path of the auditory analyzer has as the first neurons cells that lie in the node of the cochlear part of the vestibulocochlear nerve. The axons of these cells approach the cells of the anterior and posterior cochlear nuclei (second neurons). The processes of the second neurons, moving to the opposite side, form a trapezoid body, and then take an upward direction and get the name lateral loop, lemniscus lateralis. These fibers end on the bodies of the third neurons of the auditory pathway, which lie in the lateral geniculate body. The processes of the third neurons form auditory radiance, radiatio acustica, which goes from the medial geniculate body through the posterior leg of the internal capsule to the middle part of the superior temporal gyrus.

4. Visual radiance, radiatio optica(see Fig.), connects the subcortical centers of vision with the cortex of the spur groove.

The structure of visual radiation includes two systems of ascending fibers:

geniculate-cortical optic tract, which starts from the cells of the lateral geniculate body;
cushion-cortical tract, starting from the cells of the nucleus, which lies in the pillow of the thalamus; man is underdeveloped.

The collection of these fibers is referred to as posterior thalamic radiations, radiationes thalamicae posteriores.

Rising to the cerebral cortex, both systems pass through the posterior leg of the internal capsule.

5. Thalamic radiations, radiationes thalamicae(see fig.), are formed by processes of thalamus cells and make up the final sections of the ascending pathways of the cortical direction.

The composition of the thalamic radiances includes:

anterior thalamic radiations, radiationes thalamicae anteriores, - radially extending fibers of the white matter of the cerebral hemispheres. They start from the superior medial nucleus of the thalamus and go through the anterior leg of the internal capsule to the cortex of the lateral and inferior surfaces of the frontal lobe. Part of the fibers of the anterior thalamic radiations connects the anterior group of thalamic nuclei with the cortex of the medial surface of the frontal lobes and the anterior part of the cingulate gyrus;
central thalamic radiations, radiationes thalamicae centrales, - radial fibers connecting the ventrolateral group of the thalamic nuclei with the cortex of the pre- and postcentral gyrus, as well as with the adjacent sections of the cortex of the frontal and parietal lobes. Pass as part of the posterior leg of the internal capsule;
lower leg of the thalamus, pedunculus thalami inferior, contains radial fibers that connect the thalamic cushion and medial geniculate bodies with areas of the temporal choir;
posterior thalamic radiations(see earlier).

The spinal cord (medulla spinalis) is the initial section of the CNS. It is located in the spinal canal and is a cylindrical cord flattened from front to back, 40–45 cm long and weighing 34–38 grams. From above, it passes into the medulla oblongata, and from below it ends with a sharpening - a cerebral cone at the level of 1-2 lumbar vertebrae. Here, a thin terminal (terminal) thread departs from it - this is a vestige of the caudal (tail) end of the spinal cord. The diameter of the spinal cord in different parts is different. In the cervical and lumbar regions, it has thickenings (accumulations of gray matter) due to the innervation of the upper and lower extremities. On the anterior surface of the spinal cord there is an anterior median fissure, on the posterior surface - the posterior median sulcus. They divide the spinal cord into right and left halves, which are interconnected. On each half, the anterior lateral and posterior lateral grooves are distinguished. The anterior is the exit point of the anterior motor roots from the spinal cord, the posterior is the entry point of the posterior sensory roots of the spinal nerves. These lateral grooves are the boundary between the anterior, lateral, and posterior cords of the spinal cord. Inside the spinal cord there is a gap filled with cerebrospinal fluid (CSF) - the central canal. From above, it passes into the 4th ventricle, and from below it blindly ends (terminal ventricle). In an adult, it partially or completely overgrows.

Parts of the spinal cord:

cervical

Thoracic

Lumbar

sacral

coccygeal

Each part has segments - a section of the spinal cord corresponding to 2 pairs of roots (2 anterior and 2 posterior).

Throughout the spinal cord, 31 pairs of roots depart. Accordingly, 31 pairs of spinal nerves in the spinal cord are divided into 31 segments:

8 - cervical

12 - chest

5 - lumbar

5 - sacral

1-3 - coccygeal

The lower spinal nerves descend downward to form a ponytail.

As the body grows, the spinal cord does not keep pace with the spinal canal in length, and therefore the nerves are forced to descend, leaving the corresponding openings. Newborns do not have this formation.

Inside the spinal cord is gray and white matter. Gray - neurons that form 3 gray columns in each half of the spinal cord: anterior, posterior and lateral. In cross section, the pillars look like gray horns. There are wide anterior and narrow posterior horns. The lateral horn corresponds to the intermediate vegetative column of gray matter. In the gray matter of the anterior horns, motor neurons pass, in the posterior - sensitive, and in the lateral - intercalary vegetative. Intercalary inhibitory neurons are also located here - Renshaw cells, which inhibit the motor neurons of the anterior horns. The white matter surrounds the gray matter and forms the cords of the spinal cord. There are anterior, posterior and lateral cords in each half of the spinal cord. They consist of longitudinally running nerve fibers, collected in bundles - pathways. The white matter of the anterior cords contains descending pathways (pyramidal and extrapyramidal), in the lateral cords - descending and ascending pathways:

anterior and posterior spinocerebellar tracts (Govers and Flexig)

lateral spinothalamic pathway

lateral cortical-spinal tract (pyramidal)

Red nuclear spinal tract

In the white matter of the posterior cords there are ascending pathways:

thin (gentle) Gaulle's bundle

wedge-shaped bundle of Burdach

The connection of the spinal cord with the periphery is carried out with the help of nerve fibers passing in the spinal roots. The anterior roots contain centrifugal motor fibers, the posterior roots contain centripetal sensory fibers. This fact is called the law of distribution of afferent and efferent fibers in the spinal roots - Francois Magendie's law. Therefore, with a bilateral transection of the posterior roots of the spinal cord, the dog loses sensitivity, and the anterior roots lose muscle tone below the site of the transection.

The spinal cord is covered on the outside by 3 meninges:

inner - soft

medium - arachnoid

external - solid

Between the hard shell and the periosteum of the spinal canal is the epidural space filled with fatty tissue and venous plexuses. Between the hard and arachnoid - subdural space, penetrated by thin connective tissue crossbars. The arachnoid membrane is separated from the soft one by the subarachnoid subarachnoid space containing the cerebrospinal fluid. It is formed in the choroid plexuses of the ventricles of the brain (protective and trophic functions). In the spinal cord there are special inhibitory cells - Renshaw cells - that protect the central nervous system from overexcitation.

Functions of the spinal cord.

1. Reflex: carried out by the nerve centers of the spinal cord, which are segmental working centers of unconditioned reflexes. Their neurons communicate with receptors and working organs. Each metamere (transverse section) of the body receives sensitivity from 3 roots. Skeletal muscles also receive innervation from 3 neighboring segments of the spinal cord. Efferent impulses go to the skeletal muscles, respiratory muscles, internal organs, vessels and glands. The overlying parts of the CNS control the periphery with the help of segmental parts of the spinal cord.

2. Conduction: carried out due to the ascending and descending pathways of the spinal cord. Ascending pathways transmit information from tactile, pain, temperature and proprioceptors of muscles and tendons through spinal cord neurons to other parts of the central nervous system to the cerebellum and cerebral cortex.

Pathways of the spinal cord.

Ascending tracts of the spinal cord.

They carry out the transmission of pain, temperature, tactile sensitivity and proprioceptive sensitivity from receptors to the cerebellum and CBM.

1. anterior spinothalamic pathway - afferent pathway of touch and pressure

2. lateral spinothalamic path - the path of pain and temperature sensitivity

3. anterior and posterior spinal tracts - Gowers and Flexig paths - afferent paths of musculo-articular sensitivity of the cerebellar direction

4. thin (delicate) Gaulle's bundle and the wedge-shaped Burdach's bundle - afferent pathways of muscle-articular sensitivity of the cortical direction from the lower limbs and lower half of the body and from the upper limbs and upper half of the body, respectively

Descending tracts of the spinal cord.

They carry out the transmission of nerve impulses (commands) from the KBM and underlying departments to the working organs. They are divided into pyramidal and extrapyramidal.

Pyramidal pathways of the spinal cord.

They conduct impulses of voluntary motor reactions from the CBM to the anterior horns of the spinal cord (control of conscious movements).

1. anterior cortical - spinal tract

2. lateral corticospinal tract

Extrapyramidal pathways of the spinal cord.

They control involuntary movements. An example of their work is the maintenance of balance by a person in the event of a fall.

1. reticular - spinal path (reticulospinal): from the reticular formation of the brain

2. Tire-spinal tract (tetospinal): from the pons

3. vestibulospinal (vestibulospinal): from the organs of balance

4. red nuclear - spinal (rubrospinal): from the midbrain

Spinal nerves and nerve plexuses.

The human spinal cord has 31 segments, hence 31 pairs of spinal nerves.

8 pairs of neck

12 pairs of chest

5 pairs of lumbar

5 pairs of sacral

1 pair of coccygeal

Formation of the spinal nerve.

Each spinal nerve is formed by connecting the anterior motor and posterior sensory roots. When leaving the intervertebral foramen, the nerve divides into 2 main branches: anterior and posterior. Their functions are mixed. In addition, the meningeal branch departs from the nerve, which returns to the spinal canal and innervates the hard shell of the spinal cord and the white connecting branch, suitable for the nodes of the sympathetic trunk. With various curvature of the spinal column (pathological lordosis, kyphosis and scoliosis), the intervertebral foramens are deformed and pinch the spinal nerves, which leads to dysfunction, neuritis and neuralgia. These nerves supply the spinal cord with:

1. sensitive: torso, limbs, part of the neck

2. motor: all muscles of the trunk, limbs and part of the neck

3. sympathetic: all organs that have it

4. parasympathetic: pelvic organs

The posterior branches of all spinal nerves have a segmental arrangement and pass along the posterior surface of the trunk, where they are divided into skin and muscle branches that innervate the skin and muscles of the occiput, neck, back and pelvis. These branches are named after the corresponding nerves: the posterior branch of the first thoracic nerve, the second, etc. Some have names: the posterior branch of the first cervical nerve is the suboccipital nerve, the second cervical is the great occipital nerve. All anterior branches of the SMN are thicker than the posterior ones. 12 pairs of thoracic SMNs have a segmental arrangement and run along the lower edges of the ribs - the intercostal nerves. They innervate the skin and muscles of the anterior and lateral walls of the chest and abdomen. May become inflamed - intercostal neuralgia. The anterior branches of the remaining SMNs form plexuses (pleksus), the inflammation of which is plexitis.

1. cervical plexus: formed by the anterior branches of the four superior cervical nerves. located in the region of 4 upper cervical vertebrae on the deep muscles of the neck. From the front and side it is covered by the sternocleidomastoid muscle. Sensory, motor and mixed nerves depart from this plexus.

Sensory nerves: small occipital nerve, large ear, transverse nerve of the neck, supraclavicular nerves (innervate the skin of the lateral part of the occiput, auricle, external auditory canal, anterolateral neck, skin in the collarbone and below it)

Muscular branches innervate the deep muscles of the neck, trapezius, sternocleidomastoid and subhyoid muscles

· Mixed branches: phrenic nerve, which is the largest nerve plexus. Its motor fibers innervate the diaphragm, and its sensory fibers innervate the pericardium and pleura.

2. Brachial plexus: formed by the anterior branches of the four lower cervical, part of the anterior branch of the fourth cervical and first thoracic SMN. In the plexus, supraclavicular (short) and subclavian (long) branches are distinguished. Short branches innervate the muscles and skin of the chest, all the muscles of the shoulder girdle and the muscles of the back.

The shortest branch is the axillary nerve, which innervates the deltoid, teres minor, and capsule of the shoulder joint. Long branches innervate the skin and muscles of the free upper limb.

Medial cutaneous nerve of the shoulder

medial cutaneous nerve of the forearm

Muscular - cutaneous nerve (muscles - shoulder flexors and skin of the anterolateral surface of the forearm)

Median nerve (anterior group of muscles of the forearm, except for the ulnar flexor of the wrist, on the hand, the muscles of the elevation of the thumb, with the exception of the adductor muscle, 2 worm-shaped muscles and the skin of the lateral part of the palm)

Ulnar nerve (flexor carpi ulnaris, muscles of the little finger elevation, all interosseous, 2 vermiform, adductor thumb, and skin of the medial hand)

Radial nerve - the largest nerve of this plexus (muscles - extensors of the shoulder and forearm, skin of the back of the shoulder and forearm)

3. Lumbar plexus: formed by the anterior branches of the upper 3 lumbar nerves and partly by the anterior branches of the 12 thoracic and 4 lumbar nerves. Located in the thickness of the lumbar muscle. Short branches of the plexus innervate the square muscle of the lower back, iliac psoas, abdominal muscles and skin of the lower parts of the abdominal wall and external genital organs (muscular branches, ilio-hypogastric and ilio-inguinal and femoral-genital nerves). Long branches innervate the free lower limb.

Lateral cutaneous nerve of thigh

Femoral nerve (anterior thigh muscle group and skin above it). The largest nerve of this plexus. Its large subcutaneous branch is the saphenous nerve (descends along the medial surface of the lower leg of the foot)

The obturator nerve descends into the small pelvis through the obturator canal, exits to the medial surface of the thigh and innervates the medial thigh muscle group, the skin above them and the hip joint

4. sacral plexus: formed by the anterior branches of the 4th - 5th lumbar nerves and the upper 4th sacral. It is located in the pelvic cavity on the anterior surface of the piriformis muscle. Short branches:

upper gluteal

Lower gluteal

sexual

internal obturator

pear-shaped

quadratus femoris nerve

Long branches:

Posterior femoral cutaneous nerve

sciatic nerve

Both nerves exit through the piriformis foramen, where the posterior femoral cutaneous nerve innervates the skin of the perineum, gluteal region and posterior thigh, and the sciatic (the largest in the body) the entire posterior thigh muscle group. It then splits into 2 branches:

1. tibial

2. common peroneal

The tibial nerve behind the lateral malleolus divides into the plantar nerves, and the common peroneal divides into the superficial and deep nerves. They go to the back of the foot. Combining on the posterior surface of the lower leg, both nerves form the sural nerve, which innervates the skin of the lateral edge of the foot.

Neuritis - inflammation of the nerve

Radiculitis - inflammation of the roots of the spinal cord

Plexitis - inflammation of the nerve plexus

Polyneuritis - multiple nerve damage

Neuralgia - soreness along the course of the nerve, not accompanied by dysfunction of the organ

Causalgia - burning pain along the nerve that occurs after damage to the nerve trunks

Lumbago - acute pain that occurs in the lumbar region at the time of physical exertion (weight lifting)

Discogenic radiculopathy - pain motor disorders caused by damage to the roots of the spinal cord due to osteochondrosis of the spine

Myelitis - inflammation of the spinal cord

Epiduritis - purulent inflammation of the tissue in the epidural space of the spinal cord

Syringomyelia - the formation of cavities in the gray matter of the spinal cord

Poliomyelitis is an acute viral disease characterized by damage to the cells of the anterior horns of the spinal cord and the motor nuclei of the cranial nerves.