What are the ascending and descending tracts of the spinal cord. Conducting ascending and descending tracts of the spinal cord
To control the functioning of the entire body or separate body, motor apparatus, leading paths are needed spinal cord. Their main task is to deliver impulses sent by the human “computer” to the body and limbs. Any failure in the process of sending or receiving impulses or reflex sympathetic nature threatens with serious pathologies of health and all life activities.
What are the pathways in the spinal cord and brain?
The pathways of the brain and spinal cord act as a complex of neural structures. In the course of their work, impulses are sent to specific areas of the gray matter. Essentially, impulses are signals that prompt the body to act upon the call of the brain. Multiple groups nerve fibers, different according to functional features, are the conductive tracts of the spinal cord. These include:
In addition, the performance of spinal conductors necessitates the following classification, according to which they can be:
Sensory perception and motor activity of a person
The sensory or sensitive pathways of the spinal cord and brain serve as an indispensable element of contact between these two complex systems in the body. They send an impulsive message to every organ, muscle fiber, arms and legs. The instantaneous sending of an impulse signal is the main point in a person’s implementation of coordinated body movements, which are performed without the use of any conscious effort. Impulses sent by the brain can be recognized by nerve fibers through touch, pain, temperature regime body, joint and muscle motility.
The motor pathways of the spinal cord determine the quality of a person’s reflex response. By ensuring the sending of impulse signals from the head to the reflex endings of the spine and muscular system, they endow a person with the ability to self-control motor skills - coordination. Also, these leading pathways are responsible for transmitting impulses towards the visual and auditory organs.
Where are the pathways located?
Having become familiar with the anatomical distinctive features spinal cord, it is necessary to understand where the very conductive tracts of the spinal cord are located, because this term implies a lot of nerve matter and fibers. They are located in specific vital necessary substances: gray and white. By connecting the spinal horns and the cortex of the left and right hemispheres, conducting pathways with neural connection provide contact between these two departments. Functions of chief executives human organs consist in the implementation of assigned tasks with the help of specific departments. In particular, the spinal cord pathways are located within the upper vertebrae and head; this can be described in more detail as follows:
System of ascending and descending conductors
The ascending pathways of the spinal cord fulfill the human need for vision, hearing, motor functions and their contact with important systems body. The receptors for these connections are located in the space between the hypothalamus and the first segments spinal column. The ascending tracts of the spinal cord are capable of receiving and sending further impulses coming from the surface upper layers epidermis and mucous membranes, life support organs.
In turn, the descending pathways of the spinal cord include the following elements in their system:
It is quite difficult for an ordinary person who does not specialize in neurosurgery to understand the system represented by the complex pathways of the spinal cord. The anatomy of this department is truly an intricate structure consisting of neural impulse transmissions. But it is thanks to it that the human body exists as a single whole. Due to the double direction along which the spinal cord pathways act, instant transmission of impulses is ensured, which carry information from the controlled organs.
Conductors of deep sensory
The structure of the nerve connections that act in the ascending direction is multi-component. These leading pathways of the spinal cord are formed by several elements:
Inside the intervertebral nodes there are neuron cells with a deep degree of sensitivity. The processes localized in peripheral areas terminate in the most appropriate muscle tissue, tendons, osteochondral fibers and their receptors.
In turn, the central processes of the cells, located behind, are directed towards the spinal cord. Conducting deep sensitivity, the posterior nerve roots do not go deep into the gray matter, forming only the posterior spinal columns. Where such fibers enter the spinal cord, they are divided into short and long. Next, the pathways of the spinal cord and brain are sent to the hemispheres, where their radical redistribution occurs. The main part of them remains in the areas of the anterior and posterior central gyri, as well as in the region of the crown. It follows that these pathways conduct sensitivity, thanks to which a person can feel how his muscular-articular apparatus works, feel any vibration movement or tactile touch. The Gaulle bundle, which is located right in the center of the spinal cord, distributes sensation from the lower torso. Burdach's bundle is located higher and serves as a conductor of sensitivity of the upper extremities and the corresponding part of the body.
How to find out about the degree of sensory?
The degree of deep sensitivity can be determined using a few simple tests. To perform them, the patient's eyes are closed. Its task is to determine the specific direction in which the doctor or researcher makes passive movements in the joints of the fingers, arms or legs. It is also advisable to describe in detail the posture of the body or the position taken by its limbs. Using a tuning fork, the spinal cord pathways can be examined for vibration sensitivity. The functions of this device will help to accurately determine the time during which the patient clearly feels vibration. To do this, take the device and press it to make a sound. At this point, it is necessary to expose to any bony prominence on the body. In the case when such sensitivity disappears earlier than in other cases, it can be assumed that the posterior columns are affected. The test for the sense of localization involves the patient, with his eyes closed, accurately pointing to the place where the researcher touched him a few seconds before. The indicator is considered satisfactory if the patient makes an error within one centimeter.
Sensory sensitivity of the skin
The structure of the spinal cord pathways makes it possible to determine the degree of skin sensitivity at the peripheral level. The fact is that the nerve processes of the protoneuron are involved in skin receptors. The processes are located centrally as part of the posterior processes and go straight to the spinal cord, as a result of which the Lisauer area is formed there.
Just like the path of deep sensitivity, the cutaneous one consists of several sequentially united nerve cells. Compared to the spinothalamic bundle of nerve fibers, information impulses transmitted from the lower extremities or lower torso are slightly above and in the middle. Skin sensitivity varies according to criteria based on the nature of the irritant. It happens:
In this case, the latter type of skin sensitivity, as a rule, is transmitted by conductors of deep sensitivity.
How to find out about the pain threshold and temperature differences?
To determine the level pain, doctors use the method of incantation. In the most unexpected places for the patient, the doctor applies several light injections using a hairpin. The patient's eyes should be closed, because he should not see what is happening. The temperature sensitivity threshold is easy to determine. At in good condition a person experiences different sensations at temperatures whose difference was about 1-2°. To identify a pathological defect in the form of impaired skin sensitivity, doctors use a special device - a thermoesthesiometer. If it is not there, you can test for warm and hot water.
Pathologies associated with disruption of conduction pathways
In the ascending direction, the spinal cord pathways are formed in a position due to which a person can feel tactile touch. For the study, you need to take something soft, tender and, in a rhythmic manner, conduct a fine examination to identify the degree of sensitivity, as well as check the reaction of hairs, bristles, etc.
Sensitivity disorders are currently considered to be:
Features of the structure of descending conductors
The descending pathways of the brain and spinal cord include several groups, including:
All of the above elements are motor pathways of the spinal cord, which are components of neural connections in the descending direction. The so-called pyramidal tract begins from huge cells of the same name located in the upper layer of the cerebral hemisphere, mainly in the area of the central gyrus. The path of the anterior cord of the spinal cord is also located here - this is important element system is directed downward and passes through several sections of the posterior femoral capsule. At the point of intersection of the medulla oblongata and the spinal cord, an incomplete decussation can be found, forming a straight pyramidal fasciculus. In the tegmentum of the midbrain there is a rubrospinal tract. It starts from red kernels. Upon exiting, its fibers intersect and pass into the spinal cord through the varoli and medulla oblongata. The rubrospinal tract allows impulses to be transmitted from the cerebellum and subcortical ganglia. Pathways white matter spinal cord begin in Deiters' nucleus. Located in the brain stem, the vestibulo-spinal tract continues in the spinal tract and ends in its anterior horns. The passage of impulses from vestibular apparatus to the motor neuron peripheral system. In the cells of the reticular formation of the hindbrain, the reticulospinal tract begins, which is in the white matter of the spinal cord, scattered in separate bundles mainly from the side and in front. In fact, this is the main connecting element between the reflex brain center and the musculoskeletal system. The posterior longitudinal ligament is also involved in the connection motor structures with the brain stem. The work of the oculomotor nuclei and the vestibular apparatus as a whole depends on it. Rear longitudinal beam located in the cervical spine.
Consequences of spinal cord diseases
Thus, the spinal cord pathways are vital connecting elements that give a person the ability to move and feel. The neurophysiology of these pathways is associated with the structural features of the spine. It is known that the structure of the spinal cord, surrounded by muscle fibers, has a cylindrical shape. Within the substances of the spinal cord, associative and motor reflex pathways control the functionality of all body systems.
If a spinal cord disease occurs, mechanical damage or developmental defects, the conductivity between the two main centers may be significantly reduced. Disruption of the pathways threatens a person with a complete cessation of motor activity and loss of sensory perception. The main reason for the lack of impulse conduction is the death nerve endings. The most complex degree of conduction disturbance between the brain and spinal cord is paralysis and lack of sensation in the limbs. Then there may be problems in operation internal organs connected to the brain by damaged neural connections. For example, violations in lower section The spinal trunk carries with it the processes of urination and defecation that are uncontrollable by humans.
Do they treat diseases of the spinal cord and pathways?
Just appeared degenerative changes almost instantly affect the conductive activity of the spinal cord. Suppression of reflexes leads to pronounced pathological changes caused by the death of neuron fibers. It is impossible to completely restore damaged areas of conductivity. The disease occurs rapidly and progresses at lightning speed, so severe conduction disorders can only be avoided if you start in a timely manner. drug treatment. The sooner this is done, the greater the chances of stopping pathological development. Nonconductivity of the spinal cord pathways requires treatment, the primary task of which will be to stop the processes of death of nerve endings. This can only be achieved if the factors that influenced the onset of the disease cease. Only after this can you begin therapy with the goal of maximizing possible restoration sensitivity and motor functions. Treatment with medications is aimed at stopping the process of cell death. Their task is also to restore impaired blood supply to the damaged area of the spinal cord. During treatment, doctors take into account age characteristics, nature and severity of damage and progression of the disease. In pathway therapy, it is important to maintain constant stimulation of nerve fibers using electrical impulses. This will help maintain satisfactory muscle tone.
Surgical intervention is carried out to restore the conductivity of the spinal cord, so it is carried out in two directions:
The operation is preceded by a complete medical examination of the entire body. This will allow us to determine the localization of the processes of degeneration of nerve fibers. In cases of severe spinal injuries, the causes of compression must first be addressed.
In its physiology it is highly organized and specialized. It is he who conducts many signals from peripheral sensory receptors to the brain and back from top to bottom. This is possible due to the fact that there are well-organized pathways in the spinal cord. We will look at some of their types, tell you where the spinal cord pathways are located and what they contain.
The back is the area of our body where the spine is located. The soft and delicate trunk of the spinal cord is securely hidden in the depths of the strong vertebrae. It is in the spinal cord that there are unique pathways that consist of nerve fibers. They are the main conductors of information from the periphery to the central nervous system. They were first discovered by the outstanding Russian physiologist, neurologist, psychologist Sergei Stanislavovich Bekhterev. He described their role for animals and humans, their structure, and their participation in reflex activity.
The spinal cord tracts are either ascending or descending. They are presented in the table.
Kinds
Rising:
- Posterior cords. They form a whole system. These are the sphenoid and inferior fasciculi, through which skin-mechanical afferent and motor signals pass to the medulla oblongata.
- Spinothalamic tracts. Through them, signals from all receptors are sent to the brain to the thalamus.
- The spinocerebellar conducts impulses to the cerebellum.
Descending:
- Corticospinal (pyramidal).
- Extrapyramidal pathways that provide communication between the central nervous system and skeletal muscles.
Functions
The conductive tracts of the spinal cord are formed by axons - the endings of neurons. Their anatomy is that the axon is very long and connects to other nerve cells. The projection pathways of the brain and spinal cord conduct a huge number of nerve signals from receptors to the central nervous system.
In that complex process Nerve fibers located almost along the entire length of the spinal cord are involved. The signal is transmitted between neurons and from different parts of the central nervous system to organs. The conductive tracts of the spinal cord, the circuit of which is quite intricate, ensure the unhindered passage of signals from the periphery to the central nervous system.
They consist mainly of axons. These fibers are capable of creating connections between segments of the spinal cord; they are located only in it and do not extend beyond its limits. This ensures control of effector organs.
The simplest neural network is reflex arcs, which provide vegetative and somatic processes. Initially, the nerve impulse occurs at the end of the receptor. Next, sensory, intercalary and motor neuron fibers are involved.
Neurons conduct a signal in their segment, and also ensure its processing and the response of the central nervous system to irritation of a specific receptor.
In our muscles, organs, tendons, and receptors, signals arise every second that require immediate processing by the central nervous system. They are carried there along special cords of the spinal cord. These pathways are called sensory or ascending pathways. The ascending tracts of the spinal cord connect to receptors around the periphery of the entire body. They are formed by the axons of neurons sensitive type. The bodies of these axons are located in spinal ganglia. Interneurons are also involved. Their bodies are located in the dorsal horns (spinal cord).
How the sense of touch is born
The fibers that provide sensitivity pass different path. For example, from proprioceptors the pathways go to the cerebellum and cortex. They send a signal to this area about the condition of the joints, tendons, and muscles.
This path is made up of axons of sensory type neurons. The afferent neuron processes the received signal and, using an axon, conducts it to the thalamus. After processing in the thalamus, information about the motor system is sent to the postcentral cortex. Here the formation of sensations occurs about how tense the muscles are, in what position the limbs are, at what angle the joints are bent, whether there is vibration, passive movements.
The thin bundle also contains fibers that are associated with skin receptors. They conduct a signal that generates information about tactile sensitivity during vibration, pressure, and touch.
The axons of the second interneurons form other sensory pathways. The area where the cell bodies of these neurons are located is the dorsal horn (spinal cord). In their segments, these axons create a cross, then they go on the opposite side to the thalamus.
There are fibers in this path that provide temperature, pain sensitivity. Also here are fibers that are involved in tactile sensitivity. located in the spinal cord, they perceive information from brain structures.
Extrapyramidal neurons participate in the formation of the rubrospinal, reticulospinal, vestibulospinal, and tectospinal tracts. Nerve efferent impulses pass along all of these paths. They are responsible for maintaining muscle tone, performing various involuntary movements, and posture. These processes involve acquired or innate reflexes. In these pathways, the conditions for performing all voluntary movements controlled by the cerebral cortex are formed.
The spinal cord conducts all signals that come from the centers of the ANS to the neurons that make up the sympathetic nervous system. These neurons are located in the lateral horns of the spinal cord.
Also involved in the process are neurons from the parasympathetic nervous system, which are also localized in the spinal cord (sacral region). These pathways are entrusted with the function of maintaining the tone of the sympathetic nervous system.
Sympathetic and parasympathetic nervous systems
The importance of the sympathetic nervous system cannot be overestimated. Without it, the functioning of blood vessels, the heart, the gastrointestinal tract, and all internal organs is impossible.
The parasympathetic system ensures the functioning of the pelvic organs.
The feeling of pain is one of the most important for our life. Let's understand how the process of signal transmission through the trigeminal nerve occurs.
Where the motor fibers of the corticospinal tract intersect, the spinal nucleus of one of the largest nerves, the trigeminal, passes to the cervical spine. Through the region of the medulla oblongata, axons of sensory neurons descend to its neurons. It is from them that a signal about pain in the teeth, jaws, and oral cavity is sent to the nucleus. Signals from the face, eyes, and orbits pass through the trigeminal nerve.
The trigeminal nerve is extremely important for receiving tactile sensations from the facial area and sensing temperature. If it is damaged, the person begins to suffer from severe pain, which constantly returns. The trigeminal nerve is very large, it consists of many afferent fibers and a nucleus.
Conduction disorders and their consequences
It happens that the signal paths may be disrupted. The causes of such disorders are different: tumors, cysts, injuries, diseases, etc. Problems can be observed in different areas of the SM. Depending on which area is affected, a person loses sensation in a certain part of his body. Malfunctions of the musculoskeletal system may also appear, and with severe lesions the patient can be paralyzed.
It is extremely important to know the structure afferent pathways, because this allows you to determine in which area the fiber damage occurred. It is enough to determine in which part of the body sensitivity or movement is impaired in order to conclude in which brain pathway the problem occurred.
We have described the anatomy of the spinal cord tracts quite schematically. It is important to understand that they are the ones responsible for conducting signals from the periphery of our body to the central nervous system. Without them, it is impossible to process information from visual, auditory, olfactory, tactile, motor and other receptors. Without the locomotor function of neurons and pathways, it would be impossible to perform the simplest reflex movement. They are also responsible for the functioning of internal organs and systems.
The spinal cord tracts run along the entire spine. They are capable of forming complex and very effective system on processing huge amount incoming information, take the most Active participation in brain activity. The most important role at the same time, axons directed downwards, upwards and to the sides perform. These processes predominantly make up the white matter.
Ascending tracts of the spinal cord
Medial lemniscal tracts formed by two ascending tracts: 1) thin Gaulle bundle; 2) wedge-shaped bundle of Burdach (Fig. 4.14).
Afferent fibers of these pathways transmit information from tactile receptors in the skin and proprioceptors, in particular joint receptors. They enter the gray matter of the posterior horns of the spinal cord, should not be interrupted and pass in the posterior funiculi to the thin and cuneate nuclei (Gaull and Burdach), where information is transmitted to the second neuron. The axons of these neurons cross, pass to the opposite side and, as part of the medial loop, rise to specific switching nuclei of the thalamus, where switching occurs to third neurons, the axons of which transmit information in the posterior central gyrus, which ensures the formation of tactile sensation, sense of body position, passive movements, vibrations.
Spinocerebellar tract They also have 2 tracts: 1) posterior Flexig and 2) anterior Govers. their afferent fibers transmit information from proprioceptors of muscles, tendons, ligaments and tactile pressure receptors on the skin. They are characterized by a switch to the second neuron in the gray matter of the spinal cord and a transition to the opposite side. They then pass through the lateral cords of the spinal cord and carry information to the cerebellar cortex.
Spinothalamic tract(lateral, anterior), their afferent fibers transmit information from skin receptors - cold, heat, pain, tactile - about gross deformation and pressure on the skin. They switch to the second neuron in the gray matter of the dorsal horns of the spinal cord, move to the opposite side and rise in the lateral and anterior cords to the nuclei of the thalamus, where they switch to third neurons that transmit information to the posterior central gyrus.
RICE. 4.14.
Descending tracts of the spinal cord
Receiving information from the ascending conduction system about the state of activity of the effector organs, the brain sends impulses (“instructions”) through descending conductors to the working organs, among which is the spinal cord, and plays a leading-executive role. This happens with the following systems(Fig. 4.15).
Cortinospinal or pyramidal tracts(ventral, lateral) pass through the medulla oblongata, where most intersect at the level of the pyramids, and are called pyramidal. They carry information from the motor centers of the motor zone of the cerebral cortex to the motor centers of the spinal cord, due to which they carry out voluntary movements. The ventral corticospinal tract runs in the anterior cords of the spinal cord, and the lateral tract runs in the lateral cords.
Rubrospinal tract- its fibers are axons of neurons of the red nucleus of the midbrain, cross and go as part of the lateral cords of the spinal cord and transmit information from the red nuclei to the lateral interneurons of the spinal cord.
Stimulation of the red nuclei leads to activation of flexor motor neurons and inhibition of extensor motor neurons.
Medial retinulospinal tract (pontoretiulospinal) starts from the pons nuclei, goes to the anterior funiculi of the spinal cord and transmits information to the ventromedial parts of the spinal cord. Stimulation of the pontine nuclei leads to the activation of motor neurons in both flexors and extensors, with a predominant effect on the activation of motor neurons in the extensors.
Lateral retinulospinal tract (medulore tinulospinal) starts from the reticular formation of the medulla oblongata, goes to the anterior funiculi of the spinal cord and transmits information to the interneurons of the spinal cord. Its stimulation causes a general inhibitory effect, mainly on motor neurons in the extensors.
Vestibulospinal tract starts from the Deiters nuclei, goes to the anterior funiculi of the spinal cord, transmits information to interneurons and motor neurons on the same side. Stimulation of Deiters' nuclei leads to activation of extensor motor neurons and inhibition of flexor motor neurons.
RICE. 4.15.
RICE. 4.16.
Tectospinal tract starts from the superior colliculus and quadrigeminal and transmits information to the motor neurons of the cervical spinal cord, providing regulation of the functions of the cervical muscles. The topography of the spinal cord pathways is shown in Fig. 4.16.
Reflex function The spinal cord is that it contains reflex centers. Alpha motor neurons of the anterior horns constitute motor centers skeletal muscles torso, limbs, as well as the diaphragm, and β-motoneurons are tonic, maintaining tension and a certain length of these muscles. Motor neurons of the thoracic and cervical (CIII-CIV) segments that innervate respiratory muscles, constitute the "spinal respiratory center". In the lateral horns of the thoracolumbar part of the spinal cord there are bodies of sympathetic neurons, and in the sacral part - parasympathetic ones. These neurons make up the centers vegetative functions: vasomotor, regulation of cardiac activity (TI-TV), pupil dilation reflex (TI-TII), sweat secretion, heat generation, regulation of smooth muscle contraction of the pelvic organs (in the lumbosacral region).
The reflex function of the spinal cord is studied experimentally after its isolation from the higher parts of the brain. To preserve breathing due to the diaphragm, cuts are made between the V and VI cervical segments. Immediately after cutting, all functions are suppressed. A state of areflexia occurs, which is called spinal shock.
TO ascending tracts of the spinal cord include (Fig. 23):
1-2. Thin and wedge-shaped beams. They are located in the posterior cord: the thin bundle is located medially, and the wedge-shaped bundle is located laterally. The boundary between these bundles is the intermediate sulcus, passing between the posterior median and posterior lateral sulci. Both of these bundles are formed by the axons of pseudounipolar sensory neurons of the spinal ganglia, heading to the nuclei of the same name in the medulla oblongata. These neurons are the first link lemniscal sensory system . By subtle and wedge-shaped fasciculi impulses are carried out from the receptors of the skin, joints and muscles of the corresponding parts of the body, ultimately arriving in the sensory cortex of the brain and providing conscious proprioceptive*, skin stereognostic sensitivity**, as well as tactile sensitivity. A thin bundle conducts impulses from receptors lower limb and lower half of the body (up to the V thoracic segment), wedge-shaped - from receptors upper limb And upper half bodies.
3. Posterior spinocerebellar tract (tract) passes in the back of the lateral funiculus. Its constituent fibers begin from the cells of the thoracic nucleus, located on the side of the same name in the medial part of the base of the posterior horn.
4. Anterior spinocerebellar tract (tract) passes in the anterior part of the lateral funiculus. This pathway consists of processes of interneurons of the medial intermediate nucleus, located on the opposite side.
Both spinocerebellar tracts carry proprioceptive impulses from skeletal muscles to the cerebellum (cortical neurons of the vermis). Based on this information, the cerebellum carries out unconscious*** coordination of movements.
5. Anterior spinothalamic tract (tract) passes in the anterior cord of the spinal cord lateral to the vestibule-spinal tract. This path is formed by the axons of the cells of the nucleus of the dorsal horn, located on the opposite side of the spinal cord. The pathway carries impulses of tactile sensitivity (touch and pressure) to the thalamus.
6. Lateral spinothalamic tract (tract) passes in the lateral funiculus medial to the anterior spinocerebellar tract. This path consists of fibers of interneurons of the nucleus of the dorsal horn, located on the opposite side. Neurons, the processes of which form the lateral spinothalamic tract, are the first link extralemniscal sensory system, conducting impulses of pain and temperature sensitivity to diencephalon and further to the cortex cerebral hemispheres.
7. Spinal-tegmental tract located in the lateral funiculus anterior to the lateral spinothalamic tract. It conducts proprioceptive impulses to the midbrain tegmentum, used by the midbrain to reflex regulation movements and maintaining posture.
Descending tracts of the spinal cord
TO descending tracts of the spinal cord include (see Fig. 23):
1. Lateral corticospinal (lateral corticospinal) tract is also called the main crossed pyramidal tract, since it contains most of the fibers of the pyramidal system. It passes in the lateral funiculus medial to the posterior spinocerebellar tract. This path is formed by the axons of cells located on the opposite side in the motor cortex big brain(in the precentral gyrus). Along the way pyramid path its gradual thinning occurs, since in each segment of the spinal cord some of its fibers end on the motor neurons of the anterior horn. Along the pyramidal tracts, impulses are carried from the cortex, causing voluntary (conscious) movements.
2. Anterior corticospinal tract (straight or uncrossed pyramidal tract) lies in the anterior cord of the spinal cord. It, like the lateral pyramidal tract, consists of axons of cells of the motor cortex of the hemisphere, only located ipsilaterally. These axons first descend to “their” segment, then move on as part of anterior commissure of the spinal cord to the opposite side and end here on the motor neurons of the anterior horn. This path performs the same function as the lateral pyramidal path, and together with it forms a common pyramid system.
3. Red nuclear spinal tract (rubrospinal tract). It originates from the red nucleus of the midbrain and descends in the lateral funiculus of the opposite side of the spinal cord to the motor neurons of the anterior horns. This pathway conducts unconscious (involuntary) motor impulses.
4. Tectospinal tract (tectospinal tract) lies in the anterior funiculus medial to the anterior pyramidal tract. This path begins in the superior and inferior colliculi of the midbrain roof and ends on the motor neurons of the anterior horns. Thanks to this pathway, reflex (involuntary) protective and orientation movements are carried out during visual and auditory stimulation.
5. Vestibulospinal tract (vestibular tract) passes in the anterior cord of the spinal cord. It goes from the vestibular nuclei of the pons to the anterior horns of the spinal cord. It carries impulses that ensure the balance of the body.
6. Reticulospinal tract (reticulospinal tract) passes in the middle part of the anterior cord. It carries excitatory impulses from the reticular formation to the motor neurons of the spinal cord. Due to this, the susceptibility of motor neurons to all regulatory stimuli increases.
Brain
General overview of the brain
Brain located in the cranial cavity. The brain has a complex shape that matches the topography of the cranial vault and cranial fossae (Fig. 24, 25, 26). The upper lateral parts of the brain are convex, the base is flattened and has many irregularities. In the base region, 12 pairs extend from the brain cranial nerves.
The weight of the brain in an adult varies from 1100 to 2000. On average, it is 1394 g for men, 1245 g for women. This difference is due to the lower body weight of women.
The brain consists of five sections: oblong, posterior, middle, intermediate And telencephalon.
During an external examination of the brain, it is distinguished as consisting of the medulla oblongata, pons and midbrain. brain stem(Fig. 27, 28, 29), cerebellum And big brain(see Fig. 24, 26) . In humans cerebral hemispheres cover the remaining parts of the brain in front, above and on the sides, they are separated from each other longitudinal fissure of the cerebrum. In the depths of this gap there is corpus callosum, which connects both hemispheres (see Fig. 25). The corpus callosum, like the medial surfaces of the hemispheres, can be seen only after separating the upper edges of the hemispheres and, accordingly, expanding the longitudinal fissure of the cerebrum. In the normal state, the medial surfaces of the hemispheres are quite close to each other; in the skull they are separated only by a large crescent of dura. meninges. The occipital lobes of the cerebral hemispheres are separated from the cerebellum transverse fissure of the cerebrum.
The surfaces of the cerebral hemispheres are streaked with grooves (see Fig. 24, 25,26). Deep primary grooves divide the hemispheres into lobes (frontal, parietal, temporal, occipital), small secondary grooves separate narrower areas - convolutions. In addition, there are also non-constant and very variable different people tertiary grooves, which divide the surface of the convolutions and lobules into smaller areas.
During an external examination of the brain from the side(see Fig. 24) the cerebral hemispheres are visible; the cerebellum (dorsally) and the pons (ventrally) are adjacent to them below. Below them is visible the medulla oblongata, which passes down into the spinal cord. If you bend the temporal lobe of the cerebrum down, then in the depths of the lateral (Sylvian) fissure you can see the smallest lobe of the cerebrum - insula (islet).
On the undersurface of the brain(see Fig. 26) structures belonging to all five of its departments are visible. In the front part there are frontal lobes protruding forward, on the sides there are temporal lobes. In the middle part between temporal lobes(see Fig. 26) the lower surface of the diencephalon, midbrain and medulla oblongata, which passes into the spinal cord, is visible. On the sides of the pons and medulla oblongata the lower surface of the cerebellar hemispheres is visible.
The following anatomical structures are visible on the lower surface (base) of the brain (see Fig. 26). IN olfactory grooves frontal lobes are located olfactory bulbs, which pass posteriorly into olfactory tracts And olfactory triangles. 15–20 are suitable for the olfactory bulbs olfactory filaments ( olfactory nerves) – I pair of cranial nerves. Posterior to the olfactory triangles on both sides is visible anterior perforated substance, through which they pass deep into the brain blood vessels. Between both sections of the perforated substance is located cross optic nerves(visual chiasm), which are the second pair of cranial nerves.
Posterior to the optic chiasm is gray bump, turning into funnel, connected to pituitary gland (cerebral appendage). Behind the gray mound there are two mastoid bodies. These formations belong to the diencephalon, its ventral section - hypothalamus. The hypothalamus is followed by cerebral peduncles(structures of the midbrain), and behind them, in the form of a transverse ridge, is the ventral part of the hindbrain - brain bridge. Between the peduncles of the brain opens interpeduncular fossa, the bottom of which is perforated by vessels penetrating deep into the brain - posterior perforated substance. The cerebral peduncles lying on the sides of the perforated substance connect the pons with the cerebral hemispheres. On inner surface each cerebral peduncle emerges near the anterior edge of the pons oculomotor nerve (III pair), and on the side of the cerebral peduncle – trochlear nerve(IV pair of cranial nerves).
Thick veins diverge posteriorly and laterally from the bridge middle cerebellar peduncle. From the thickness middle pedicle cerebellum comes out trigeminal nerve(V pair).
Posterior to the pons is the medulla oblongata. From the transverse groove separating the medulla oblongata from the pons, it emerges medially abducens nerve(VI pair), and lateral from it - facial nerve (VII pair) and vestibular nerve(VIII pair of cranial nerves). On each side of median sulcus medulla oblongata, running longitudinally, longitudinal thickenings are visible - pyramids, and on the side of each of them are olives. From the groove behind the olive, the cranial nerves emerge successively from the medulla oblongata - glossopharyngeal(IX pair), wandering*(X pair), additional(XI pair), and from the groove between the pyramid and the olive - hypoglossal nerve (XII pair cranial nerves).
The pathways of the central nervous system are built from functionally homogeneous groups of nerve fibers; they represent internal connections between nuclei and cortical centers located in different parts and sections of the brain, and serve for their functional unification (integration). The pathways, as a rule, run in the white matter of the spinal cord and brain, but can also be localized in the tectum of the brain stem, 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 are nerve fibers - the axons of neurons, which transmit information in the form of a nerve impulse in a strictly defined direction, namely from the cell body. Among the conducting pathways, depending on their structure and functional significance, there are various groups nerve fibers: fibers, bundles, tracts, radiances, commissures (commissures).
Projection paths consist of neurons and their fibers that provide connections between the spinal cord and brain. Projection pathways also connect the nuclei of the brainstem with the basal ganglia and the cerebral cortex, as well as the nuclei of the brainstem with the cortex and nuclei of the cerebellum. Projection paths can be ascending and descending.
Ascending (sensory, sensory, afferent) projection pathways conduct nerve impulses from extero-, proprio- and interoreceptors (sensitive nerve endings in the skin, musculoskeletal system, internal organs), as well as from the sensory organs in an ascending direction to the brain, mainly 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, to midbrain and into 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 programming the body's movements in specific situations, therefore they are motor pathways.
A common feature of downstream motor pathways is that they necessarily pass through the internal capsule - a layer of white matter in the cerebral hemispheres, separating the thalamus from the basal ganglia. In the brainstem, most of the descending tracts to the spinal cord and cerebellum originate at its base.
35. Pyramidal and extrapyramidal systems
The pyramidal system is a collection of motor centers of the cerebral cortex, motor centers of the 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 connecting them to each other.
The pyramidal tracts ensure the conduction of impulses in the process of conscious regulation of movements.
Pyramidal tracts 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 motor analyzer; about 20% - from the postcentral gyrus, and the remaining 40% - from the posterior parts of the superior and middle lobar gyri, and from the supramarginal gyrus of the inferior parietal lobule, in which the center of praxia is located, which controls complex coordinated goal-directed movements.
The pyramidal tracts are divided into corticospinal and corticonuclear. Their common feature is that they, starting in the cortex of the right and left hemispheres, 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 emotions. A distinctive feature of the extrapyramidal system is the multi-stage, with many switchings, transmission of nervous influences from various parts of the brain to the executive centers - the motor nuclei of the spinal cord and cranial nerves.
The extrapyramidal pathways transmit motor commands during protective motor reflexes that occur unconsciously. For example, thanks to the extrapyramidal pathways, information is transmitted when restoring the vertical position of the body as a result of loss of balance (vestibular reflexes) or during motor reactions to sudden light or sound exposure (protective reflexes that close in the roof of the midbrain), etc.
The extrapyramidal system is formed by the nuclear centers of the hemispheres ( basal ganglia: caudate and lenticular), diencephalon (medial nuclei of the thalamus, subthalamic nucleus) and brainstem (red nucleus, substantia nigra), as well as pathways connecting it with the cerebral cortex, with the cerebellum, with the reticular formation and, finally, with executive centers located in the motor nuclei of the cranial nerves and in the anterior horns of the spinal cord.
There is also a somewhat expanded interpretation when E.S. include the cerebellum, nuclei of the quadrigeminal midbrain, 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 onto the basal ganglia. The basal ganglia themselves are closely connected with each other by numerous internal connections, as well as with the nuclei of the thalamus and 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 rubrospinal tract and through the nuclei of the reticular formation (reticulospinal tract). Also, through the red nucleus, the influences of the cerebellum are transmitted to the work of the spinal motor centers.
