home Audience 1 The cerebellum, its connections with the spinal cord and brain. Damage symptoms. What are the ascending and descending pathways of the spinal cord

The cerebellum, its connections with the spinal cord and brain. Damage symptoms. What are the ascending and descending pathways of the spinal cord

Candidate medical sciences Pavel Musienko, Institute of Physiology. I. P. Pavlov RAS (St. Petersburg).

The spinal cord can be "taught" to serve motor functions, even when its connection with the brain is broken as a result of an injury, and moreover, it can be forced to form new connections "bypassing" the injury. This requires electrochemical neuroprostheses, stimulation and training.

Through the introduction of chemicals, they act on neuronal receptors, causing certain effects of excitation or inhibition of neurons. spinal cord below the damage level.

With paralysis, it is possible to stimulate the sensory fibers of the spinal cord with an electric current and, through them, the spinal neurons (A). Due to electrical stimulation (ES), an animal with spinal cord injury can walk (B).

Motor skills for paralysis can be trained using a specially designed robotic system. The robot, if necessary, supports and controls the movement of the animal in three directions (x, y, z) and around the vertical axis (φ

Multisystem neurorehabilitation (specific training + electrochemical stimulation) restores voluntary control of movements due to the formation of new interneuronal connections in the spinal cord and brain stem.

For electrical stimulation of several segments of the spinal cord and multicomponent pharmacological stimulation of specific neuronal receptors on the spinal networks, special neuroprostheses can be created - a set of electrodes and chemotrodes.

Spinal cord injuries are rarely accompanied by a complete anatomical interruption. Remaining intact nerve fibers can contribute to functional recovery.

The traditional neurophysiological picture of movement control assigned to the spinal cord the functions of a channel through which nerve impulses propagate, connecting the brain with the body, and a primitive reflex control. However, recent data accumulated by neurophysiologists force us to reconsider this modest role. New research technologies have made it possible to discover numerous networks of its “own” neurons in the spinal cord, specialized in performing complex motor tasks, such as coordinated walking, maintaining balance, controlling speed and direction when moving.

Could these neuronal systems in the spinal cord be used to restore motor function in people paralyzed as a result of a spinal cord injury?

With a spinal cord injury, the patient loses motor functions because the connection between the brain and the body is disrupted or completely broken: the signal does not pass, and there is no activation of motor neurons below the injury site. Thus, an injury to the cervical spinal cord can lead to paralysis and loss of function of the arms and legs, the so-called tetraplegia, and an injury to the thoracic region can lead to paraplegia, immobilization only lower extremities: as if the units of a certain army, in themselves functional and combat-ready, were cut off from the headquarters and stopped receiving commands.

But the main evil of spinal injury is that any stable connections that connect neurons into stable functional networks degrade if they are not activated again and again. Those who have not ridden a bike or played the piano in a long time are familiar with this phenomenon: many motor skills are lost if they are not used. In the same way, in the absence of activating signals and training, the neural networks of the spinal cord specialized for movement begin to disintegrate over time. Changes become irreversible: the network "unlearns" how to move.

Can this be prevented? The answer given by modern neurophysiology is encouraging.

Neurons interact with each other sequentially, in a chain, producing chemical substances- mediators of various types. At the same time, most of the neurons are concentrated in the brain, using fairly well-studied monoaminergic mediators: serotonin, norepinephrine, dopamine as a signal "language".

Receptors capable of receiving this signal remain on the neural networks of even a damaged spinal cord. Therefore, one can try to activate the spinal networks with appropriate monoaminergic drugs by injecting them into nervous tissue spinal cord from the outside.

This circumstance formed the basis of experiments on chemical stimulation.

In 2008, together with a group of researchers from the University of Zurich (Switzerland), we tried to activate the spinal neural networks responsible for movement by “planting” substances corresponding to monoaminergic mediators on intact spinal neuron receptors. These drugs were supposed to serve as a signal source that activates the neural networks of the spinal cord and prevents their degradation. The result of the experiment was positive, moreover, optimal combinations of monoaminergic drugs were found to improve walking function and balance. The work was published in 2011 in the journal Neuroscience.

The spinal cord is distinguished by high systemic neuronal plasticity: its neural networks are able to gradually “remember” the tasks that they have to perform regularly. Regular exposure to certain sensory and motor pathways during motor training improves the functioning of these neural pathways and restores the ability to perform the trained functions.

But if the neural networks of the spinal cord can be trained, then is it possible to “teach” them something - for example, by stimulating the damaged spinal cord and motor training to achieve such a functional restructuring of its neural networks, which would more or less successfully control motor activity independently, apart from the "headquarters" - the brain?

To answer this question, we tried to combine chemical neurostimulation with electrical stimulation. Back in 2007, joint experiments by Russian and American neurophysiologists showed that if electrodes are placed on the surface of the spinal cord of a rat, then the electric field around the active electrode can excite conductive spinal structures. Since very small currents were used in the experiment, the most excitable tissues near the electrode were activated first of all: thick conducting fibers of the posterior spinal roots, which transmit sensory information from the receptors of the limb tissues to the neurons of the spinal cord. Such electrical stimulation made it possible to activate motor functions in spinal animals.

The combination of electrical stimulation, chemical stimulation and movement training gave excellent results. With a complete break in the connections between the spinal cord and the brain, it was possible to turn dormant spinal neural networks into highly functionally active ones. The paralyzed animals were injected with neuropharmacological drugs, their spinal cord was stimulated in two segments, and the gait function was constantly trained. As a result, after a few weeks, the animals showed movements close to normal and were able to adapt to changes in speed and direction of movement.

In the first experiments, the researchers trained animals using treadmill and a biomechanical system that helped the animal to keep the body on weight, but did not allow to move forward. Recently, in 2012, the results of joint research by the University of Zurich and the Institute of Physiology named after Zurich were published in the journals Science and Nature Medicine. I. P. Pavlov RAS, in which we applied the robotic approach.

A special robot allows the rat to move freely, if necessary, supporting and controlling its movements in three directions (x, y, z). Moreover, the impact force along different axes can vary depending on the experimental task and the animal's own motor abilities. The robotic installation uses soft elastic drives and spirals that eliminate the inertial influence of force effects on a living object. This makes it possible to apply the set in behavioral experiments. The robot was tested on an experimental model of a paralyzed rat with damage to the opposite halves of the spinal cord at the level of different spinal segments. The connection between the brain and spinal cord was completely interrupted, but the possibility of sprouting new nerve fibers between the left and right parts of the spinal cord remained. (This model bears similarities to spinal cord injuries in humans, which are most often anatomically incomplete.) Combining robotic training with multicomponent chemical and electrical spinal cord stimulation allowed these animals to walk forward in a straight line, step over obstacles, and even climb stairs. In rats, new interneuronal connections appeared in the area of spinal cord injury and voluntary control of movements was restored.

This is how the idea of electrochemical neuroprostheses for implantation into the spinal cord and control of spinal networks was born. Through special implant channels, drugs can be injected that act on the corresponding receptors and mimic the modulating nerve signal interrupted after an injury. The array of electrodes stimulates sensory inputs from different segments and through them activates individual populations of neurons to thus induce certain movements.

Standard clinical approach treatment of patients with severe spinal injuries is aimed at preventing further secondary damage to the nervous system, somatic complications of paralysis, at providing psychological assistance to paralyzed patients and teaching them how to use the remaining functions. Restorative therapy of lost motor skills in severe spinal cord injuries is not only possible, but necessary.

Experimental work on a chemical neuroprosthesis has not yet taken a step further laboratory research on animals, but in 2011 the respected medical journal The Lancet gave a vivid illustration of what stimulation therapy can do for humans. The journal published the results of clinical and experimental work using electrical spinal cord stimulation. Neurophysiologists and doctors from the US and Russia have shown that regular training of certain motor skills in combination with epidural spinal cord stimulation restored motor abilities in a patient with complete motor paraplegia, that is, a complete loss of control over movement. The treatment improved the functions of standing and maintaining body weight, elements of locomotor activity and partial voluntary control of movements during stimulation.

As a result of training and stimulation, it was possible not only to activate neural networks below the level of damage, but also to some extent restore the connection between the brain and spinal motor centers - the already mentioned neuroplasticity of the spinal cord made possible education new neural connections that "bypass" the site of injury.

Experimental and clinical studies show the high effectiveness of spinal cord stimulation and training after severe vertebral spinal injury. Although successful results have already been obtained with spinal cord stimulation in patients with severe paralysis, the bulk of the research work is still ahead. In addition, it is necessary to develop spinal implants for electrochemical stimulation and find optimal algorithms for their use. The active efforts of the world's leading laboratories are now directed to all this. Hundreds of independent and interlaboratory research projects are dedicated to achieving these goals. It remains to be hoped that as a result of the joint efforts of the world scientific centers into the generally accepted clinical standards more effective methods treatment of paralyzed patients.

Spinal cord(lat. Medulla spinalis) is an organ of the central nervous system of vertebrates located in the spinal canal. The spinal cord is protected soft, gossamer And dura mater. The spaces between the membranes and the spinal canal are filled with cerebrospinal fluid.

The spinal cord is located in the spinal canal and has the form of a rounded cord, expanded in the cervical and lumbar regions and pierced by the central channel. It consists of two symmetrical halves, separated anteriorly by a median fissure, posteriorly by a median sulcus, and is characterized by a segmental structure; each segment is associated with a pair of anterior (ventral) and a pair of posterior (dorsal) roots. In the spinal cord, gray matter is located in its central part, and white matter lies along the periphery.

The gray matter is butterfly-shaped in cross section and includes paired anterior (ventral), posterior (dorsal), and lateral (lateral) horns (actually continuous columns running along the spinal cord). The horns of the gray matter of both symmetrical parts of the spinal cord are connected to each other in the region of the central gray commissure (commissure). The gray matter contains the bodies, dendrites and (partly) axons of neurons, as well as glial cells. Between the bodies of neurons there is a neuropil - a network formed by nerve fibers and processes of glial cells.

ganglion- accumulation nerve cells, consisting of bodies, dendrites and axons of nerve cells and glial cells. Usually the ganglion also has a sheath of connective tissue.

The spinal ganglia contain the bodies of sensory (afferent) neurons.

own apparatus spinal cord- this is the gray matter of the spinal cord with the posterior and anterior roots of the spinal nerves and with its own bundles of white matter bordering the gray matter, composed of associative fibers of the spinal cord. The main purpose of the segmental apparatus, as the phylogenetically oldest part of the spinal cord, is the implementation of innate reactions (reflexes).

24. The cerebral cortex, its connection with the spinal cord.

The cerebral cortex or cortex(lat. cortex cerebri) - the structure of the brain, a layer of gray matter 1.3-4.5 mm thick, located along the periphery of the cerebral hemispheres, and covering them.

molecular layer

outer granular layer

layer of pyramidal neurons

inner granular layer

ganglion layer (inner pyramidal layer; Betz cells)

layer of polymorphic cells

The cerebral cortex also contains a powerful neuroglial apparatus that performs trophic, protective, supporting and delimiting functions.

25. Cerebellum and its connection with the spinal cord.

Cerebellum- part of the brain of vertebrates, responsible for the coordination of movements, the regulation of balance and muscle tone. In humans, it is located behind the medulla oblongata and the bridge, under the occipital lobes of the cerebral hemispheres. Through three pairs of legs, the cerebellum receives information from the cerebral cortex, the basal ganglia of the extrapyramidal system, the brain stem and spinal cord. The cerebellum receives a copy of the afferent information transmitted from the spinal cord to the cerebral cortex, as well as efferent information - from the motor centers of the cerebral cortex to the spinal cord.

The cerebellar cortex consists of three layers.

· molecular a layer containing a relatively small number of small cells;

· ganglion layer, formed by one row of bodies of large pear-shaped cells (Purkinje cells);

· granular layer, with a large number of densely lying cells.

The gray matter contains paired nuclei that lie deep in the cerebellum and form the core of the tent, which belongs to the vestibular apparatus. Lateral to the tent are the spherical and cork-shaped nuclei, which are responsible for the work of the muscles of the body, then the dentate nucleus, which controls the work of the limbs.

PATHWAYS OF THE BRAIN AND SPINAL CORD CONDUCTION PATHWAYS OF THE BRAIN AND SPINAL CORD

PATHWAYS OF THE BRAIN AND SPINAL CORD

Conductive pathways called bundles of functionally homogeneous nerve fibers that connect various centers in the central nervous system, occupy a certain place in the white matter of the brain and spinal cord and conduct identical impulses.

Impulses that occur when exposed to receptors are transmitted through the processes of neurons to their bodies. Due to numerous synapses, neurons contact each other, forming chains along which nerve impulses propagate only in a certain direction - from receptor neurons through intercalary neurons to effector neurons. This is due to the morphofunctional features of synapses that conduct excitation (nerve impulses) in only one direction - from the presynaptic membrane to the postsynaptic one.

In one chain of neurons, the impulse propagates centripetally- from the place of origin in the skin, mucous membranes, organs of movement, vessels to the spinal cord or brain. In other circuits of neurons, the impulse is conducted centrifugally from the brain to the periphery to the working organs - muscles and glands. The processes of neurons are sent from the spinal cord to various structures of the brain, and from them in the opposite direction.

Rice. 44. Location of bundles of associative fibers of the white matter of the right hemisphere of the brain, medial surface (scheme): 1 - cingulate gyrus; 2 - upper longitudinal bundle; 3 - arcuate fibers of the large brain; 4 - lower longitudinal beam

direction - to the spinal cord and form bundles connecting nerve centers. These bundles make up the pathways.

Three groups of nerve fibers (conducting pathways) are distinguished in the spinal cord and brain: associative, commissural, and projection.

Associative nerve fibers(short and long) connect groups of neurons (nerve centers) located in one half of the brain (Fig. 44). Short (intralobar) association pathways connect nearby areas gray matter and are located, as a rule, within the same lobe of the brain. Among them are arcuate fibers of the cerebrum (fibrae arcuatae), which bend in an arcuate manner and connect the gray matter of adjacent gyri without going beyond the cortex (intracortical) or passing through the white matter of the hemisphere (extracortical). Long (interlobar) associative bundles connect areas of gray matter located at a considerable distance from each other, usually in different lobes. These include superior longitudinal bundle (fasciculus longitudinalis superior), passing in the upper layers of the white matter of the hemisphere and connecting the cortex of the frontal lobe with the parietal and occipital;

lower longitudinal bundle (fasciculus longitudinalis inferior), lying in the lower layers of the white matter of the hemisphere and connecting the gray matter of the temporal lobe with the occipital, and hook-shaped bundle (fasciculus uncipatus), connecting the cortex in the region of the frontal pole with the anterior part of the temporal lobe. The fibers of the uncinate bundle curve in an arcuate fashion around the islet.

In the spinal cord, association fibers connect neurons located in different segments to each other and form own bundles of the spinal cord(intersegmental bundles), which are located near the gray matter. Short bundles are thrown over 2-3 segments, long bundles connect segments of the spinal cord that are far apart from each other.

Commissural (commissural) nerve fibers connect the same centers (gray matter) of the right and left hemispheres of the large brain, forming the corpus callosum, the commissure of the fornix and the anterior commissure (Fig. 45). corpus callosum connects the new sections of the cerebral cortex of the right and left hemispheres. In each hemisphere, the fibers diverge fan-shaped, forming radiance of the corpus callosum (radiatio corporis callori). Anterior bundles of fibers, passing in the knee and beak of the corpus callosum, connect the cortex of the anterior sections frontal lobes, forming frontal forceps (forceps frontalis). These fibers, as it were, cover the anterior part of the longitudinal fissure of the brain on both sides. The cortex of the occipital and posterior sections of the parietal lobes of the large brain is connected by bundles of fibers passing in the ridge of the corpus callosum. They form the so-called occipital forceps (forceps occipitalis). Curving backwards, the bundles of these fibers, as it were, cover the posterior sections of the longitudinal fissure of the large brain. Fibers passing in the central parts of the corpus callosum connect the cortex of the central gyrus, parietal and temporal lobes of the cerebral hemispheres.

IN anterior commissure fibers pass that connect the sections of the cortex of the temporal lobes of both hemispheres, belonging to the olfactory brain. fibers adhesions of the fornix connect the gray matter of the hippocampus and temporal lobes of both hemispheres.

Projection nerve fibers(conducting paths) are divided into ascending And descending. Ascending connect the spinal cord with the brain, as well as the nuclei of the brain stem with the basal nuclei and the cortex of the cerebral hemispheres. Descending ones go in the opposite direction (Table 1).

Rice. 45. Commissural fibers (radiation) of the corpus callosum, dorsal view. The upper sections of the frontal, parietal and occipital lobes of the large brain are removed: 1 - frontal forceps (large forceps); 2 - corpus callosum; 3 - medial longitudinal strip; 4 - lateral longitudinal strip; 5 - occipital forceps

(small tongs)

Ascending projection pathways are afferent, sensitive. Nerve impulses that arise as a result of exposure to the body of various environmental factors, including impulses coming from the sense organs, the musculoskeletal system, internal organs and vessels. Depending on this, the ascending projection pathways are divided into three groups: exteroceptive, proprioceptive and interoceptive pathways.

exteroceptive pathways carry impulses from skin(pain, temperature, touch and pressure), from the senses (vision, hearing, taste, smell). Pathway of pain and temperature sensitivity (lateral spinothalamic pathway, tractus spinothalamicus lateralis) consists of three neurons (Fig. 46). The receptors of the first (sensitive) neurons that perceive these stimuli are located in the skin and mucous membranes, and the cell bodies lie in the spinal nodes. The central processes in the composition of the posterior root are sent to the posterior horn of the spinal cord and end in synapses on the cells of the second neurons. All axons of the second neurons, whose bodies lie in the posterior horn, pass through the anterior gray commissure to the opposite side of the spinal cord, enter the lateral funiculus, are included in the lateral spinothalamic pathway, which ascends to the medulla oblongata (behind the nucleus of the olive), passes in the tire bridge and in the tire of the midbrain, passing at the outer edge of the medial loop. Axons terminate, forming synapses on cells located in the posterolateral nucleus of the thalamus (the third neuron). The axons of these cells pass through the posterior leg of the internal capsule and as part of fan-shaped divergent bundles of fibers forming l clean crown (corona radiata), sent to the neurons of the internal granular plate of the cortex (layer IV) of the postcentral gyrus, where the cortical end of the general sensitivity analyzer is located. The fibers of the third neuron of the sensitive (ascending) pathway connecting the thalamus with the cortex form thalamocortical bundles (fasciculi thalamocorticales)- thalamoparietal fibers (fibrae thalamoparietales). The lateral spinothalamic pathway is a completely crossed pathway (all fibers of the second neuron pass to the opposite side), therefore, if one half of the spinal cord is damaged, pain and temperature sensitivity on the opposite side of the injury completely disappear.

The conductive path of touch and pressure (anterior spinothalamic path, tractus spinothalamicus anterior) carries impulses from the skin where they lie

Table 1. Pathways of the brain and spinal cord

Continuation of table 1.

Table 1 continued

End of table 1.

Rice. 46. Pathways of pain and temperature sensitivity,

touch and pressure (outline): 1- lateral spinothalamic pathway; 2 - anterior spinothalamic pathway; 3 - thalamus; 4 - medial loop; 5 - cross section of the midbrain; 6 - cross section of the bridge; 7 - cross section of the medulla oblongata; 8 - spinal node; 9 - cross section of the spinal cord. Arrows show the direction of movement of nerve impulses

receptors, to the cells of the cortex of the postcentral gyrus. The bodies of the first neurons (pseudo-unipolar cells) lie in the spinal nodes. The central processes of these cells, as part of the posterior roots of the spinal nerves, are sent to the posterior horn of the spinal cord. The axons of the neurons of the spinal nodes form synapses with the neurons of the posterior horn of the spinal cord (second neurons). Most of the axons of the second neuron also pass to the opposite side of the spinal cord through the anterior commissure, enter the anterior funiculus, and in its composition follow up to the thalamus. Part of the fibers of the second neuron go in the posterior funiculus of the spinal cord and in the medulla oblongata join the fibers of the medial loop. The axons of the second neuron form synapses with the neurons of the posterolateral nucleus of the thalamus (the third neuron). The processes of the cells of the third neuron pass through the posterior leg of the internal capsule, then, as part of the radiant crown, they are sent to the neurons of the IV layer of the cortex of the postcentral gyrus (internal granular plate). Not all fibers that carry impulses of touch and pressure pass to the opposite side in the spinal cord. Part of the fibers of the pathway of touch and pressure goes as part of the posterior cation of the spinal cord (its side) together with the axons of the pathway of the proprioceptive sensitivity of the cortical direction. In this regard, when one half of the spinal cord is affected, the skin sense of touch and pressure on the opposite side does not disappear completely, as pain sensitivity, but only decreases. This transition to the opposite side is partially carried out in the medulla oblongata.

proprioceptive pathways conduct impulses from muscles, tendons, joint capsules, ligaments. They carry information about the position of body parts in space, the volume of movements. Proprioceptive sensitivity allows a person to analyze their own complex movements and carry out their purposeful correction. Proprioceptive pathways of the cortical direction and proprioceptive pathways of the cerebellar direction are distinguished. Cortical pathway of proprioceptive sensitivity carries impulses of muscular-articular feeling to the cortex of the postcentral gyrus of the brain (Fig. 47). Receptors of the first neurons located in muscles, tendons, articular capsules, ligaments, perceive signals about the state of the musculoskeletal system as a whole, muscle tone, the degree of stretching of the tendons, and send these signals along the spinal nerves to the bodies of the first neurons of this path, which lie in the spinal cord. nodes. body

Rice. 47. Pathway of proprioceptive sensation

cortical direction (scheme): 1 - spinal node; 2 - cross section of the spinal cord;

3 - posterior funiculus of the spinal cord;

4 - front outer arcuate fibers; 5 - medial loop; 6 - thalamus; 7 - cross section of the midbrain; 8 - cross section of the bridge; 9 - cross section of the medulla oblongata; 10 - rear outer arcuate fibers. The arrows show the direction of movement

nerve impulses

the first neuron of this pathway also lie in the spinal nodes. The axons of the first neurons in the posterior root, without entering the posterior horn, go to the posterior funiculus, where they form thin And wedge-shaped bundles.

Axons carrying proprioceptive impulses enter the posterior funiculus, starting from the lower segments of the spinal cord. Each next bundle of axons is adjacent from the lateral side to the existing bundles. Thus, the outer sections of the posterior cord (wedge-shaped bundle, Burdach's bundle) are occupied by axons of cells that carry out proprioceptive innervation in the upper thoracic, cervical parts of the body and upper limbs. Axons occupying inner part posterior cord (thin bundle, Gaulle's bundle), conduct proprioceptive impulses from the lower extremities and the lower half of the body.

The fibers in the thin and wedge-shaped bundles go up to the medulla oblongata to the thin and wedge-shaped nuclei, where they end in synapses on the bodies of the second neurons. The axons of the second neurons emerging from these nuclei arcuately bend forward and medially, and at the level of the lower angle of the rhomboid fossa pass to the opposite side in the interstitial layer of the medulla oblongata, forming decussation of the medial loop (decussatio lemniscorum medialium). This internal arcuate fibers (fibrae arcuatae internae), which form the initial sections of the medial loop. Then the fibers of the medial loop pass upward through the tegmentum of the pons and the tegmentum of the midbrain, where they are located dorsal-lateral to the red nucleus. These fibers terminate in the dorsal lateral nucleus of the thalamus with synapses on the bodies of third neurons. The axons of the thalamus cells are directed through the posterior pedicle of the internal capsule as part of the radiant crown in cortex of the postcentral gyrus where they form synapses with neurons of the IV layer of the cortex (inner granular plate).

Another part of the fibers of the second neurons (posterior external arcuate fibers, efibrae arcueatae exteernae posteriores) upon exiting the thin and wedge-shaped nuclei, it goes to the lower cerebellar peduncle of its side and ends with synapses in the cortex of the worm. The third part of the axons of the second neurons (anterior external arcuate fibers, fibrae arcudtae extdrnae anterieores) passes to the opposite side and also through the lower cerebellar peduncle of the opposite side goes to the cortex of the worm. Proprioceptive impulses along these fibers go to the cerebellum to correct subconscious movements of the musculoskeletal system.

So, proprioceptive pathway the cortical direction is also crossed. The axons of the second neuron pass to the opposite side not in the spinal cord, but in the medulla oblongata. When damaged

of the spinal cord on the side of the occurrence of proprioceptive impulses (in case of brain stem injury - on the opposite side), the idea of the state of the musculoskeletal system, the position of body parts in space is lost, and coordination of movements is disturbed.

There are proprioceptive pathways of the cerebellar direction - front And posterior spinal tracts, which carry information about the state of the musculoskeletal system and motor centers of the spinal cord to the cerebellum.

Posterior spinal tract(Flexig bundle) (tractus spinocerebellaris posterior)(Fig. 48) carries impulses from receptors located in muscles, tendons, joint capsules, ligaments to the cerebellum. body first neurons(pseudo-unipolar cells) are located in the spinal nodes. The central processes of these cells, as part of the posterior roots of the spinal nerves, are sent to the posterior horn of the spinal cord, where they form synapses with the neurons of the thoracic nucleus (Clark's column), which lies in the medial part of the base of the posterior horn. (second neurons). The axons of the second neurons pass in the back of the lateral

Rice. 48. Posterior spinocerebellar pathway:

1 - cross section of the spinal cord; 2 - cross section of the medulla oblongata; 3 - cerebellar cortex; 4 - dentate nucleus; 5 - spherical nucleus; 6 - synapse in the cortex of the cerebellar vermis; 7 - lower cerebellar peduncle; 8 - dorsal (posterior) spinal tract; 9 - spinal node

the funiculus of the spinal cord of its side, rise up and through the lower cerebellar peduncle go to the cerebellum, where they form synapses with the cells of the cortex of the cerebellar vermis (posterior-lower sections).

Anterior spinocerebellar pathway (Govers bundle) (tractus spinocerebellaris anterior)(Fig. 49) also carries impulses from receptors located in muscles, tendons, joint capsules to the cerebellum. These impulses along the fibers of the spinal nerves, which are peripheral processes of pseudo-unipolar cells of the spinal nodes (first neurons), are sent to the posterior horn, where they form synapses with neurons of the central intermediate (gray) substance of the spinal cord (second neurons). The axons of these fibers pass through the anterior gray commissure to the opposite side into the anterior part of the lateral funiculus of the spinal cord and rise upward. At the level of the isthmus of the rhomboid brain, these fibers form a second decussation, return to their side and through the superior cerebellar peduncle enter the cerebellum to the cells of the anterior-superior cortex of the worm

Rice. 49. Anterior spinal cerebellar pathway: 1 - transverse section of the spinal cord; 2 - anterior spinal tract; 3 - cross section of the medulla oblongata; 4 - synapse in the cortex of the cerebellar vermis; 5 - spherical nucleus; 6 - cerebellar cortex; 7 - dentate nucleus; 8 - spinal node

cerebellum. Thus, the anterior spinal cerebellar tract, complex and doubly crossed, returns to the same side on which the proprioceptive impulses arose. Proprioceptive impulses that have entered the cortex of the worm along the spinal cerebellar proprioceptive tracts are transmitted to the red nuclei and through the dentate nucleus to the cerebral cortex (into the postcentral gyrus) along the cerebellar-thalamic and cerebellar-tegmental tracts (Fig. 50).

It is possible to trace the fiber systems along which the impulse from the cortex of the worm reaches the red nucleus, the cerebellar hemisphere and even the overlying parts of the brain - the cortex of the cerebral hemispheres. From the cortex of the worm, through the corky and spherical nuclei, the impulse through the superior cerebellar peduncle is directed to the red nucleus of the opposite side (cerebellar-tegmental path). The cortex of the worm is connected by associative fibers with the cortex of the cerebellar hemisphere, from where impulses enter the dentate nucleus of the cerebellum.

With the development of higher centers of sensitivity and voluntary movements in the cortex of the cerebral hemispheres, connections between the cerebellum and the cortex also arose, through the thalamus. Thus, from the dentate nucleus, the axons of its cells through the superior cerebellar peduncle exit into the tegmentum pons, pass to the opposite side and go to the thalamus. Switching in the thalamus to the next neuron, the impulse follows in the cerebral cortex, in the postcentral gyrus.

Interoceptive pathways conduct impulses from internal organs, vessels, body tissues. Their mechano-, baro-, chemoreceptors perceive information about the state of homeostasis (intensity metabolic processes, chemical composition tissue fluid and blood, vascular pressure, etc.).

Impulses enter the cortex of the cerebral hemispheres along direct ascending sensory pathways and from the subcortical centers.

From the cortex of the cerebral hemispheres and subcortical centers (from the nuclei of the brain stem), descending paths originate that control the motor functions of the body (voluntary movements).

Descending motor pathways conduct impulses to the underlying parts of the central nervous system - to the nuclei of the brain stem and to the motor nuclei of the anterior horns of the spinal cord. These paths are divided into pyramidal and extrapyramidal. Pyramidal pathways are the main avenues.

Rice. 50. Cerebellar-thalamic and cerebellar-tegmental conduction

1 - cerebral cortex; 2 - thalamus; 3 - cross section of the midbrain; 4 - red core; 5 - cerebellar-thalamic path; 6 - cerebellar-cover path; 7 - globular nucleus of the cerebellum; 8 - cerebellar cortex; 9 - dentate nucleus; 10 - cork nucleus

Through the consciously controlled motor nuclei of the brain and spinal cord, they carry impulses from the cerebral cortex to the skeletal muscles of the head, neck, trunk, and limbs. carry impulses from subcortical centers and various departments cortex also to the motor and other nuclei of the cranial and spinal nerves.

main motor, or pyramidal pathway is a system of nerve fibers through which arbitrary motor impulses from the pyramidal form of neurocytes (Betz pyramidal cells) located in the cortex of the precentral gyrus (layer V) are sent to the motor nuclei of the cranial nerves and to the anterior horns of the spinal cord, and from them to the skeletal muscles . Depending on the direction and location of the fibers, the pyramidal tract is divided into the cortical-nuclear tract, which goes to the nuclei of the cranial nerves, and the cortical-spinal tract. In the latter, the lateral and anterior cortical-spinal (pyramidal) pathways leading to the nuclei of the anterior horns of the spinal cord are distinguished (Fig. 51).

Corticonuclear pathway(tractus corticonuclearis) is a bundle of axons of giant pyramidal cells located in the lower third precentral gyrus. The axons of these cells (first neuron) pass through the knee of the internal capsule, the base of the brain stem. Then the fibers of the cortical-nuclear pathway pass to the opposite side to motor nuclei of the cranial nerves: III and IV - in the midbrain; V, VI, VII - in the bridge; IX, X, XI and XII - in the medulla oblongata, where they end with synapses on their neurons (second neurons). The axons of the motor neurons of the cranial nerve nuclei leave the brain as part of the corresponding cranial nerves and are sent to the skeletal muscles of the head and neck. They control the conscious movements of the muscles of the head and neck.

Lateral And anterior corticospinal (pyramidal) pathways (tractus corticospinales (pyramidales) anterior et lateralis) control the conscious movements of the muscles of the trunk and limbs. They start from the pyramidal form of neurocytes (Betz cells) located in the V layer of the cortex of the middle and upper thirds of the precentral gyrus. (first neurons). The axons of these cells are sent to the internal capsule, pass through the anterior part of its posterior leg, behind the fibers of the cortical-nuclear pathway. Then the fibers through the base of the brain stem (lateral to the fibers of the cortical-nuclear pathway) pass

Rice. 51. Scheme of the pyramidal pathways:

1 - precentral gyrus; 2 - thalamus; 3 - cortical-nuclear pathway; 4 - cross section of the midbrain; 5 - cross section of the bridge; 6 - cross section of the medulla oblongata; 7 - cross of pyramids; 8 - lateral cortical-spinal tract; 9 - cross section of the spinal cord; 10 - anterior cortical-spinal path. Arrows show the direction of movement of nerve impulses

across the bridge to the pyramid of the medulla oblongata. At the border of the medulla oblongata with the spinal cord, part of the fibers of the corticospinal tract passes to the opposite side at the border of the medulla oblongata with the spinal cord. The fibers then continue into the lateral funiculus of the spinal cord. (lateral corticospinal pathway) and gradually end in the anterior horns of the spinal cord with synapses on the motor cells (radicular neurocytes) of the anterior horns (second neuron).

The fibers of the cortical-spinal pathway, which do not cross to the opposite side at the border of the medulla oblongata with the spinal cord, descend down as part of the anterior funiculus of the spinal cord, forming anterior cortico-spinal tract. These fibers pass segmentally to the opposite side through the white commissure of the spinal cord and end in synapses on the motor (radicular) neurocytes of the anterior horn of the opposite side of the spinal cord. (second neurons). The axons of the cells of the anterior horns exit the spinal cord as part of the anterior roots and, being part of the spinal nerves, innervate the skeletal muscles. So, all pyramidal pathways are crossed. Therefore, with unilateral damage to the spinal cord or brain, paralysis of the muscles of the opposite side develops, which are innervated from the segments located below the damage zone.

Extrapyramidal pathways have connections with the nuclei of the brain stem and with the cortex of the cerebral hemispheres, which controls the extrapyramidal system. The influence of the cerebral cortex is carried out through the cerebellum, red nuclei, the reticular formation associated with the thalamus and the striatum, through the vestibular nuclei. One of the functions of the red nuclei is to maintain muscle tone, which is necessary to involuntarily keep the body in balance. The red nuclei, in turn, receive impulses from the cerebral cortex, from the cerebellum. From the red nucleus, nerve impulses are sent to the motor nuclei of the anterior horns of the spinal cord (red nuclear spinal cord) (Fig. 52).

Red nuclear-spinal tract (tractus rubrospinalis) maintains skeletal muscle tone and controls automatic habitual movements. First neurons of this path lie in the red nucleus of the midbrain. Their axons cross over to the opposite side in the midbrain (Forel's chiasm), pass through the tegmentum pedunculi,

Rice. 52. Red nuclear-spinal pathway (scheme): 1 - section of the midbrain; 2 - red core; 3 - red nuclear-spinal path; 4 - cerebellar cortex; 5 - dentate nucleus of the cerebellum; 6 - section of the medulla oblongata; 7 - section of the spinal cord. The arrows show the direction of movement

nerve impulses

pontine tegmentum and medulla oblongata. Next, the axons follow as part of the lateral funiculus of the spinal cord of the opposite side. The fibers of the red nuclear-spinal tract form synapses with the motor neurons of the nuclei of the anterior horns of the spinal cord (second neurons). The axons of these cells are involved in the formation of the anterior roots of the spinal nerves.

Predverno-spinal tract (tractus vestibulospinalis, or Leventhal's bundle), maintains the balance of the body and head in space, provides adjusting reactions of the body in case of imbalance. First neurons this path lies in the lateral nucleus (Deiters) and the lower vestibular nucleus of the medulla oblongata and bridge (predvernocochlear nerve). These nuclei are connected to the cerebellum and the posterior longitudinal fasciculus. The axons of the neurons of the vestibular nuclei pass in the medulla oblongata, then as part of the anterior cord of the spinal cord at the border with the lateral cord (of its own side). The fibers of this pathway form synapses with the motor neurons of the nuclei of the anterior horns of the spinal cord (second neurons), the axons of which are involved in the formation of the anterior (motor) roots of the spinal nerves. Posterior longitudinal bundle (fasciculus longitudinalis posterior), in turn, is associated with the nuclei of the cranial nerves. This keeps the position eyeball with movements of the head and neck.

Reticulo-spinal tract (tractus reticulospinalis) maintains the tone of skeletal muscles, regulates the state of the spinal autonomic centers. First neurons of this path lie in the reticular formation of the brain stem (the intermediate nucleus of Cajal, the nucleus of the epithalamic (posterior) commissure of Darkshevich, etc.). The axons of the neurons of these nuclei pass through the midbrain, bridge, medulla oblongata. The axons of the neurons of the intermediate nucleus (Cajal) do not cross, they pass as part of the anterior funiculus of the spinal cord of their side. The axons of the cells of the nucleus of the epithalamic commissure (Darshkevich) pass to the opposite side through the epithalamic (posterior) commissure and go as part of the anterior funiculus of the opposite side. The fibers form synapses with the motor neurons of the nuclei of the anterior horns of the spinal cord. (second neurons).

Covering-spinal path (tractus tectospinalis) connects the quadrigemina with the spinal cord, transmits the influence of the subcortical centers of vision and hearing on the tone of skeletal muscles, and participates in the formation of protective reflexes. First neurons lie in the nuclei of the upper

and inferior colliculi of the quadrigemina of the midbrain. The axons of these cells pass through the pons, the medulla oblongata, pass to the opposite side under the aqueduct of the brain, forming a fountain-like, or Meynertian, cross. Further, the nerve fibers pass as part of the anterior funiculus of the spinal cord of the opposite side. The fibers form synapses with the motor neurons of the nuclei of the anterior horns of the spinal cord. (second neurons). Their axons are involved in the formation of the anterior (motor) roots of the spinal nerves.

Cortico-cerebellar pathway (tractus corticocerebellaris) controls the functions of the cerebellum, which is involved in the coordination of movements of the head, trunk and limbs. First neurons of this path lie in the cortex of the frontal, temporal, parietal and occipital lobes of the brain. Axons of frontal lobe neurons (frontal bridge fibers- Arnold's bundle) are sent to the internal capsule and pass through its anterior leg. Axons of neurons of the temporal, parietal and occipital lobes (parietal-temporal-occipital-bridge fibers- Türk's bundle) pass as part of the radiant crown, then through the posterior leg of the internal capsule. All fibers follow through the base of the brain stem to the bridge, where they end in synapses on the neurons of the own nuclei of the bridge of their side (second neurons). The axons of these cells pass to the opposite side in the form of transverse fibers of the bridge, then, as part of the middle cerebellar peduncle, they follow into the cerebellar hemisphere of the opposite side.

Thus, the pathways of the brain and spinal cord establish connections between afferent and efferent (effector) centers, close complex reflex arcs in the human body. Some reflex paths close on the nuclei that lie in the brain stem and provide functions with a certain automatism, without the participation of consciousness, although under the control of the cerebral hemispheres. Other reflex pathways close with the participation of the functions of the cerebral cortex, higher departments central nervous system and provide arbitrary actions of the organs of the apparatus of movement.

The spinal cord is part of the central nervous system. It is located in the spinal canal. It is a thick-walled tube with a narrow channel inside, somewhat flattened in the anterior-posterior direction. Has quite complex structure and ensures the transmission of nerve impulses from the brain to the peripheral structures of the nervous system, and also carries out its own reflex activity. Without the functioning of the spinal cord, it is impossible normal breathing, heartbeat, digestion, urination, sexual activity, any movement in the limbs. From this article you can learn about the structure of the spinal cord and the features of its functioning and physiology.

The spinal cord is laid on the 4th week of intrauterine development. Usually a woman does not even suspect that she will have a child. Throughout pregnancy, differentiation of various elements occurs, and some parts of the spinal cord completely complete their formation after birth during the first two years of life.

What does the spinal cord look like externally?

The beginning of the spinal cord is conditionally determined at the level of the upper edge of I cervical vertebra and foramen magnum of the skull. In this area, the spinal cord is gently rebuilt into the brain, there is no clear separation between them. In this place, the intersection of the so-called pyramidal paths is carried out: the conductors responsible for the movements of the limbs. The lower edge of the spinal cord corresponds to the upper edge of the second lumbar vertebra. Thus, the length of the spinal cord is less than the length of the spinal canal. It is this feature of the location of the spinal cord that makes it possible to perform a spinal puncture at the level of the III-IV lumbar vertebrae (it is impossible to damage the spinal cord during a lumbar puncture between the spinous processes of the III-IV lumbar vertebrae, since it simply does not exist there).

The dimensions of the human spinal cord are as follows: length approximately 40-45 cm, thickness - 1-1.5 cm, weight - about 30-35 g.

There are several sections of the spinal cord along the length:

cervical;
chest;
lumbar;
sacral;
coccygeal.

The spinal cord is thicker in the region of the cervical and lumbosacral levels than in other parts, because in these places there are clusters of nerve cells that provide movement of the arms and legs.

The last sacral segments, together with the coccygeal, are called the conus of the spinal cord due to the corresponding geometric shape. The cone passes into the terminal (end) thread. The thread no longer has nerve elements in its composition, but only connective tissue, and is covered by the membranes of the spinal cord. The terminal thread is fixed to the II coccygeal vertebra.

The spinal cord is covered throughout its entire length by 3 meninges. The first (inner) shell of the spinal cord is called soft. It carries arterial and venous vessels that provide blood supply to the spinal cord. The next shell (middle) is arachnoid (arachnoid). Between the inner and middle shells is the subarachnoid (subarachnoid) space containing cerebrospinal fluid(liquor). When conducting spinal tap the needle must fall into this space so that the cerebrospinal fluid can be taken for analysis. outer shell spinal cord - solid. The dura mater continues to the intervertebral foramina, accompanying the nerve roots.

Inside the spinal canal, the spinal cord is fixed to the surface of the vertebrae with the help of ligaments.

In the middle of the spinal cord, along its entire length, there is a narrow tube, the central canal. It also contains cerebrospinal fluid.

From all sides deep into the spinal cord recesses protrude - cracks and furrows. The largest of them are the anterior and posterior median fissures, which delimit the two halves of the spinal cord (left and right). Each half has additional recesses (furrows). Furrows split the spinal cord into cords. The result is two anterior, two posterior and two lateral cords. Such an anatomical division has a functional basis - in different cords there are nerve fibers that carry various information (about pain, about touch, about temperature sensations, about movements, etc.). Blood vessels penetrate into the furrows and fissures.

Segmental structure of the spinal cord - what is it?

How is the spinal cord connected to the organs? In the transverse direction, the spinal cord is divided into special sections, or segments. Roots emerge from each segment, a pair of anterior and a pair of posterior ones, which communicate the nervous system with other organs. The roots exit the spinal canal, form nerves that go to various structures of the body. The anterior roots transmit information mainly about movements (stimulate muscle contraction), therefore they are called motor. back roots they carry information from receptors to the spinal cord, that is, they send information about sensations, therefore they are called sensitive.

The number of segments in all people is the same: 8 cervical segments, 12 thoracic, 5 lumbar, 5 sacral and 1-3 coccygeal (usually 1). Roots from each segment rush into the intervertebral foramen. Since the length of the spinal cord is shorter than the length of the spinal canal, the roots change their direction. IN cervical region they are directed horizontally, in the chest - obliquely, in the lumbar and sacral departments almost vertically down. Due to the difference in the length of the spinal cord and spine, the distance from the exit of the roots from the spinal cord to the intervertebral foramen also changes: in the cervical region, the roots are the shortest, and in the lumbosacral region, the longest. The roots of the four lower lumbar, five sacral and coccygeal segments form the so-called ponytail. It is he who is located in the spinal canal below the II lumbar vertebra, and not the spinal cord itself.

Each segment of the spinal cord is assigned a strictly defined zone of innervation on the periphery. This zone includes a patch of skin, certain muscles, bones, and part of the internal organs. These zones are almost the same in all people. This feature of the structure of the spinal cord allows you to diagnose the location pathological process with illness. For example, knowing that the sensitivity of the skin in the umbilical region is regulated by the 10th thoracic segment, with the loss of sensations of touching the skin below this area, it can be assumed that the pathological process in the spinal cord is located below the 10th thoracic segment. A similar principle works only taking into account the comparison of the innervation zones of all structures (both skin, muscles, and internal organs).

If you cut the spinal cord in the transverse direction, it will look uneven in color. On the cut you can see two colors: gray and white. Gray color is the location of the bodies of neurons, and White color- these are peripheral and central processes of neurons (nerve fibers). There are over 13 million nerve cells in the spinal cord.

The bodies of gray neurons are arranged in such a way that they have a bizarre butterfly shape. This butterfly has clearly visible bulges - the front horns (massive, thick) and the hind horns (much thinner and smaller). Some segments also have lateral horns. In the region of the anterior horns there are bodies of neurons responsible for movement, in the region of the posterior horns - neurons that perceive sensitive impulses, in the lateral horns - neurons of the autonomic nervous system. In some parts of the spinal cord, the bodies of nerve cells responsible for the functions of individual organs are concentrated. The localization sites of these neurons have been studied and clearly defined. So, in the 8th cervical and 1st thoracic segments there are neurons responsible for the innervation of the pupil of the eye, in the 3rd - 4th cervical segments - for the innervation of the main respiratory muscle (diaphragm), in the 1st - 5th thoracic segments - for regulation of cardiac activity. Why do you need to know? This is used in clinical diagnostics. For example, it is known that the lateral horns of the 2nd - 5th sacral segments of the spinal cord regulate the activity of the pelvic organs (bladder and rectum). In the presence of a pathological process in this area (hemorrhage, tumor, destruction during trauma, etc.), a person develops urinary and fecal incontinence.

The processes of the bodies of neurons form connections with each other, with different parts spinal cord and brain, respectively tend up and down. These nerve fibers, which are white in color, make up the white matter in the cross section. They also form cords. In the cords, the fibers are distributed in a special pattern. In the posterior cords there are conductors from the receptors of muscles and joints (articular-muscular feeling), from the skin (recognition of an object by touch with closed eyes, sensation of touch), that is information is coming in the upward direction. In the lateral cords, fibers pass that carry information about touch, pain, temperature sensitivity to the brain, to the cerebellum about the position of the body in space, muscle tone (ascending conductors). In addition, the lateral cords also contain descending fibers that provide body movements programmed in the brain. In the anterior cords, both descending (motor) and ascending (sensation of pressure on the skin, touch) paths pass.

The fibers can be short, in which case they connect the segments of the spinal cord to each other, and long, then they communicate with the brain. In some places, the fibers may cross over or simply cross over to the opposite side. Crossing of different conductors occurs on different levels(for example, the fibers responsible for the feeling of pain and temperature sensitivity cross 2-3 segments above the level of entry into the spinal cord, and the fibers of the articular-muscular sense go uncrossed to the uppermost parts of the spinal cord). The result of this is the following fact: in the left half of the spinal cord there are conductors from the right parts of the body. This does not apply to all nerve fibers, but is especially characteristic of sensitive processes. The study of the course of nerve fibers is also necessary for the diagnosis of the lesion site in the disease.

Blood supply to the spinal cord

The spinal cord is nourished by blood vessels coming from vertebral arteries and from the aorta. The uppermost cervical segments receive blood from the system of vertebral arteries (as well as part of the brain) through the so-called anterior and posterior spinal arteries.

Along the entire spinal cord, additional vessels that carry blood from the aorta, the radicular-spinal arteries, flow into the anterior and posterior spinal arteries. The latter also come in front and rear. The number of such vessels is due to individual characteristics. Usually there are about 6-8 anterior radicular-spinal arteries, they are larger in diameter (the thickest ones approach the cervical and lumbar thickenings). The inferior radicular-spinal artery (the largest) is called the Adamkevich artery. Some people have an additional radicular-spinal artery coming from the sacral arteries, the Desproges-Gotteron artery. The zone of blood supply of the anterior radicular-spinal arteries occupies the following structures: the anterior and lateral horns, the base of the lateral horn, the central sections of the anterior and lateral cords.

There are an order of magnitude more posterior radicular-spinal arteries than the anterior ones - from 15 to 20. But they have a smaller diameter. The zone of their blood supply is the posterior third of the spinal cord in a transverse section (posterior cords, the main part of the posterior horn, part of the lateral cords).

In the system of radicular-spinal arteries, there are anastomoses, that is, the places where the vessels connect to each other. It's playing important role in the nutrition of the spinal cord. In the event that a vessel ceases to function (for example, a blood clot blocked the lumen), then blood flows through the anastomosis, and the neurons of the spinal cord continue to perform their functions.

The veins of the spinal cord accompany the arteries. The venous system of the spinal cord has extensive connections with the vertebral venous plexuses, the veins of the skull. Blood from the spinal cord through a whole system of vessels flows into the superior and inferior vena cava. In the place where the veins of the spinal cord pass through the dura mater, there are valves that do not allow blood to flow in the opposite direction.

Spinal Cord Functions

Basically, the spinal cord has only two functions:

reflex;
conductive.

Let's take a closer look at each of them.

Reflex function of the spinal cord

The reflex function of the spinal cord consists in the response of the nervous system to irritation. Did you touch something hot and involuntarily pull your hand away? This is a reflex. Did you get something down your throat and cough? This is also a reflex. Many of our daily activities are based precisely on the reflexes that are carried out thanks to the spinal cord.

So, a reflex is a response. How is it reproduced?

To make it clearer, let's take as an example the hand withdrawal response to touching a hot object (1). In the skin of the hand there are receptors (2) that perceive heat or cold. When a person touches hot, then from the receptor along the peripheral nerve fiber (3) an impulse (signaling about "hot") tends to the spinal cord. At the intervertebral foramen there is a spinal ganglion, in which the body of the neuron (4) is located, along the peripheral fiber of which the impulse came. Further along the central fiber from the body of the neuron (5), the impulse enters the posterior horns of the spinal cord, where it “switches” to another neuron (6). The processes of this neuron are sent to the anterior horns (7). In the anterior horns, the impulse switches to motor neurons (8) responsible for the work of the arm muscles. The processes of motor neurons (9) exit the spinal cord, pass through the intervertebral foramen, and, as part of the nerve, are sent to the muscles of the arm (10). The “hot” impulse causes the muscles to contract, and the hand pulls away from the hot object. Thus, a reflex ring (arc) was formed, which provided a response to the stimulus. At the same time, the brain did not participate in the process at all. The man withdrew his hand without thinking about it.

Each reflex arc has obligatory links: an afferent link (a receptor neuron with peripheral and central processes), an intercalary link (a neuron connecting an afferent link with an executor neuron) and an efferent link (a neuron that transmits an impulse to a direct executor - an organ, a muscle).

On the basis of such an arc, the reflex function of the spinal cord is built. Reflexes are congenital (which can be determined from birth) and acquired (formed in the process of life during learning), they close on various levels. For example, the knee jerk closes at the level of the 3rd-4th lumbar segments. Checking it, the doctor is convinced of the safety of all elements reflex arc, including segments of the spinal cord.

For a doctor, checking the reflex function of the spinal cord is important. This is done at every neurological examination. Most often, superficial reflexes are checked, which are caused by touch, stroke irritation, a prick of the skin or mucous membranes, and deep ones, which are caused by a blow of a neurological hammer. The surface reflexes carried out by the spinal cord include abdominal reflexes (dashed irritation of the skin of the abdomen normally causes contraction of the abdominal muscles on the same side), plantar reflex (dashed irritation of the skin of the outer edge of the sole in the direction from the heel to the fingers normally causes flexion of the toes) . Deep reflexes include flexion-elbow, carporadial, extensor-ulnar, knee, Achilles.

The conduction function of the spinal cord

The conductive function of the spinal cord is to transmit impulses from the periphery (from the skin, mucous membranes, internal organs) to the center (the brain) and vice versa. The conductors of the spinal cord, which make up its white matter, carry out the transmission of information in the ascending and descending direction. An impulse about external influences is sent to the brain, and a certain sensation is formed in a person (for example, you stroke a cat, and you get a feeling of something soft and smooth in your hand). Without the spinal cord, this is impossible. This is evidenced by cases of spinal cord injuries, when the connections between the brain and spinal cord are broken (for example, rupture of the spinal cord). Such people lose sensitivity, touch does not form sensations in them.

The brain receives impulses not only about touches, but also about the position of the body in space, the state of muscle tension, pain, and so on.

Downward impulses allow the brain to “rule” the body. Thus, what a person has conceived is carried out with the help of the spinal cord. Do you want to catch up with the departing bus? The idea is immediately realized - the necessary muscles are set in motion (and you don’t think about which muscles you need to contract and which to relax). This is done by the spinal cord.

Of course, the realization of motor acts or the formation of sensations require a complex and well-coordinated activity of all structures of the spinal cord. In fact, you need to use thousands of neurons to get the result.

The spinal cord is very important anatomical structure. Its normal functioning ensures the entire life of a person. It serves as an intermediate link between the brain and various parts of the body, transmitting information in the form of impulses in both directions. Knowledge of the features of the structure and functioning of the spinal cord is necessary for the diagnosis of diseases of the nervous system.

Video on the topic "The structure and functions of the spinal cord"

Scientific and educational film of the times of the USSR on the topic "Spinal Cord"

Spinal cord injuries in most cases lead to paralysis of the legs or the entire lower body of a person due to the fact that the connection between the brain and the spinal cord is broken, even if both mentioned parts of the nervous system remain in full functional state. And recently, researchers from the Swiss Ecole Polytechnique Federale de Lausanne (EPFL), Brown University, and the Medtronic and Fraunhofer ICT-IMM Institute, Germany, have developed a system that allows you to bypass damaged areas of the nervous system, restoring connection between the motor region of the brain and the spinal cord. At the same time, the entire system works with the help of wireless technologies, and as a demonstration, a specially paralyzed monkey was presented to the attention of the public, which was able to move almost with its normal gait.

Behind last years neurobiologists and physicians have made significant progress towards restoring limb mobility in people paralyzed as a result of a spinal injury. In some cases, implants were used for this, stimulating the local nerve networks of the spinal cord. This technology does not require a direct connection to the brain, and the necessary control signals are obtained by processing a number of indirect data. This approach is the simplest, but it only allows for a small number of movements that are abrupt and not very precise.

More high quality control of the limbs of paralyzed people is provided by technologies that require direct connection of the implant to the human brain. Control signals are drawn directly from the corresponding areas of the brain and are used to directly stimulate the muscles of the limbs. However, this approach is not very practical, as it requires the implant to be connected to a high-speed computer via a fairly thick cable protruding from the patient's skull.

To solve the last of the problems described above, scientists have developed a special neurosensor that communicates with a computer using wireless technology. The computer processes the incoming data, extracts the appropriate images from them, and again, using wireless technology, transmits them to a device connected directly to the spinal cord. This whole chain is organized in such a way that the spinal cord receives exactly the same signals as from the brain, telling which muscles and with what force it is necessary to "work" in this moment time.

The entire system was calibrated by inserting appropriate implants into the nervous system of healthy monkeys. The processing of a huge array of collected information allowed scientists to identify the necessary images of brain activity and correlate them with the control commands for each element. muscular system. Then, having ready-made templates and other necessary information, scientists implanted implants into the nervous system of two monkeys with damage to the upper part of the spine. After a while, the paralyzed monkeys could already move their hind limbs, and after a month they began to walk, moving their legs almost as they do naturally.

Although the researchers have been able to get the wireless system to work, they still have a lot of work to do before such a system can be used to restore limb mobility in paralyzed people. Currently, the system provides only one-way communication and cannot relay sensory information back from the spinal cord to the brain. It is the implementation of feedback that scientists plan to do in the near future.