Neural organization spinal cord

Neurons of the spinal cord form gray matter in the form of symmetrically located two anterior and two posterior horns in the cervical, lumbar and sacral regions. In the thoracic region, the spinal cord has, in addition to those mentioned, also lateral horns.

The posterior horns perform mainly sensory functions and contain neurons that transmit signals to overlying centers, to symmetrical structures on the opposite side, or to the anterior horns of the spinal cord.

The anterior horns contain neurons that send their axons to the muscles. All descending pathways of the central nervous system that cause motor responses end on the neurons of the anterior horns.

The human spinal cord contains about 13 million neurons, of which 3% are motor neurons, and 97% are intercalary neurons. Functionally, spinal cord neurons can be divided into 5 main groups:

1) motor neurons, or motor neurons, are cells of the anterior horns, the axons of which form the anterior roots. Among the motor neurons, a-motoneurons are distinguished, transmitting signals to muscle fibers, and γ-motoneurons, innervating the intraspindle muscles. muscle fibers;

2) interneurons of the spinal cord include cells that, depending on the course of their processes, are divided into: stial, the processes of which branch within several adjacent segments, and interneurons, the axons of which pass through several segments or even from one part of the spinal cord to another, forming own bundles of the spinal cord;

3) the spinal cord also contains projection interneurons that form the ascending tracts of the spinal cord. Interneurons are neurons that receive information from the genital ganglia and are located in the dorsal horns. These neurons respond to pain, temperature, tactile, vibration, proprioceptive stimulation;

4) sympathetic, parasympathetic neurons are located mainly in the lateral horns. The axons of these neurons exit the spinal cord as part of the ventral roots;

5) associative cells - neurons of the spinal cord’s own apparatus, establishing connections within and between segments.

In the middle zone of the gray matter (between the posterior and anterior horns) and at the apex of the posterior horn of the spinal cord, the so-called gelatinous substance (gelatinous substance of Roland) is formed and performs the functions of the reticular formation of the spinal cord.

Functions of the spinal cord. The first function is reflexive. The spinal cord carries out motor reflexes of skeletal muscles relatively independently. Examples of some motor reflexes of the spinal cord are: 1) elbow reflex - tapping on the tendon of the biceps brachii muscle causes flexion in the elbow joint due to nerve impulses that are transmitted through 5-6 cervical segments; 2) knee reflex - tapping the tendon of the quadriceps femoris muscle causes extension in the knee joint due to nerve impulses that are transmitted through the 2-4 lumbar segments. The spinal cord is involved in many complex coordinated movements - walking, running, labor and sports activities, etc. The spinal cord carries out autonomic reflexes to change the functions of internal organs - cardiovascular, digestive, excretory and other systems.
Thanks to reflexes from proprioceptors in the spinal cord, motor and autonomic reflexes are coordinated. Reflexes are also carried out through the spinal cord from internal organs to skeletal muscles, from internal organs to receptors and other organs of the skin, from an internal organ to another internal organ.
The second function is conductive. Centripetal impulses entering the spinal cord along the dorsal roots are transmitted along short pathways to its other segments, and along long pathways to different parts of the brain.
The main long pathways are the following ascending and descending pathways.

9. PARTICIPATION OF THE SPINAL CORD IN THE REGULATION OF MUSCLE TONE. ROLE OF ALPHA AND GAMA MOTONEURONS IN THIS PROCESS.

Maintenance function muscle tone is provided according to the principle of feedback at various levels of regulation of the body. Peripheral regulation is carried out with the participation of the gamma loop, which includes supraspinal motor pathways, intercalary neurons, descending reticular system, alpha and gamma neurons.

There are two types of gamma fibers in the anterior horn of the spinal cord. Gamma-1 fibers ensure the maintenance of dynamic muscle tone, i.e. tone necessary for the implementation of the movement process. Gamma-2 fibers regulate the static innervation of muscles, i.e. posture, posture of a person. Central regulation of the functions of the gamma loop is carried out by the reticular formation through the reticulospinal tract. The main role in maintaining and changing muscle tone is given to the functional state of the segmental arc of the stretch reflex (myotatic or proprioceptive reflex). Let's take a closer look at it.

Its receptor element is the encapsulated muscle spindle. Each muscle contains a large number of these receptors. The muscle spindle consists of intrafusal muscle fibers (thin) and a nuclear bursa, braided by a spiral-shaped network of thin nerve fibers, which are the primary sensory endings (anulospinal filament). Some intrafusal fibers also have secondary, grape-shaped sensory endings. When intrafusal muscle fibers are stretched, the primary sensory endings strengthen the impulses emanating from them, which are carried through fast-conducting gamma-1 fibers to the alpha-large motor neurons of the spinal cord. From there, through also fast-conducting alpha-1 efferent fibers, the impulse goes to the extrafusal white muscle fibers, which provide rapid (phasic) muscle contraction. From secondary sensory endings that respond to muscle tone, afferent impulses are carried along thin gamma-2 fibers through a system of interneurons to alpha small motor neurons, which innervate the tonic extrafusal muscle fibers (red), which maintain tone and posture.

Intrafusal fibers are innervated by gamma neurons of the anterior horns of the spinal cord. Excitation of gamma neurons, transmitted along gamma fibers to the muscle spindle, is accompanied by contraction of the polar sections of the intrafusal fibers and stretching of their equatorial part, while the initial sensitivity of the receptors to stretch changes (the threshold of excitability of stretch receptors decreases, and tonic tension of the muscle increases).

Gamma neurons are influenced by central (suprasegmental) influences transmitted along fibers that come from motor neurons of the oral parts of the brain as part of the pyramidal, reticulospinal, and vestibulospinal tracts.

Moreover, if the role of the pyramidal system is primarily to regulate the phasic (i.e. fast, purposeful) components of voluntary movements, then the extrapyramidal system ensures their smoothness, i.e. predominantly regulates the tonic innervation of the muscular system. Thus, according to J. Noth (1991), spasticity develops after supraspinal or spinal damage to the descending motor systems with the obligatory involvement of the corticospinal tract in the process.

Inhibitory mechanisms also take part in the regulation of muscle tone, without which reciprocal interaction of antagonist muscles is impossible, and therefore, purposeful movements are impossible. They are realized with the help of Golgi receptors located in muscle tendons and Renshaw intercalary cells located in the anterior horns of the spinal cord. Golgi tendon receptors, when the muscle is stretched or significantly strained, send afferent impulses along fast-conducting type 1b fibers to the spinal cord and have an inhibitory effect on the motor neurons of the anterior horns. Renshaw intercalary cells are activated through collaterals when alpha motor neurons are excited, and act on the principle of negative feedback, contributing to the inhibition of their activity. Thus, the neurogenic mechanisms of regulation of muscle tone are diverse and complex.

When the pyramidal tract is damaged, the gamma loop is disinhibited, and any irritation by stretching the muscle leads to a constant pathological increase in muscle tone. In this case, damage to the central motor neuron leads to a decrease in inhibitory effects on motor neurons as a whole, which increases their excitability, as well as on interneurons of the spinal cord, which helps to increase the number of impulses reaching alpha motor neurons in response to muscle stretching.

Other causes of spasticity include structural changes at the level of the segmental apparatus of the spinal cord that arise as a result of damage to the central motor neuron: shortening of the dendrites of alpha motor neurons and collateral sprouting (proliferation) of afferent fibers that make up the dorsal roots.

Secondary changes also occur in muscles, tendons and joints. Therefore, the mechanical-elastic characteristics of muscle and connective tissue, which determine muscle tone, suffer, which further enhances movement disorders.

Currently, an increase in muscle tone is considered as a combined lesion of the pyramidal and extrapyramidal structures of the central nervous system, in particular the corticoreticular and vestibulospinal tracts. Moreover, among the fibers that control the activity of the gamma neuron-muscle spindle system, inhibitory fibers usually suffer to a greater extent, while activating fibers retain their influence on the muscle spindles.

The consequence of this is muscle spasticity, hyperreflexia, the appearance of pathological reflexes, as well as the primary loss of the most subtle voluntary movements.

The most significant component of muscle spasm is pain. Painful impulses activate alpha and gamma motor neurons of the anterior horns, which increases the spastic contraction of the muscle innervated by this segment of the spinal cord. In the same time, muscle spasm, which occurs during the sensorimotor reflex, enhances the stimulation of muscle nociceptors. Thus, according to the negative feedback mechanism, a vicious circle is formed: spasm - pain - spasm - pain.

In addition, local ischemia develops in spasmodic muscles, since algogenic chemicals (bradykinin, prostaglandins, serotonin, leukotrienes, etc.) have a pronounced effect on the vessels, causing vasogenic tissue edema. Under these conditions, substance “P” is released from the terminals of type “C” sensory fibers, as well as the release of vasoactive amines and increased microcirculatory disorders.

Data on the central cholinergic mechanisms of muscle tone regulation are also of interest. Renshaw cells have been shown to be activated by acetylcholine through both motor neuron collaterals and the reticulospinal system.

10. REFLECTOR ACTIVITY OF THE MEDULENA, ITS ROLE IN THE REGULATION OF MUSCLE TONE. DECEREBRATORY RIGIDITY. The medulla oblongata, like the spinal cord, performs two functions - reflex and conductive. Eight pairs of cranial nerves (V to XII) emerge from the medulla oblongata and the pons and it, like the spinal cord, has a direct sensory and motor connection with the periphery. Through sensory fibers it receives impulses - information from receptors of the scalp, mucous membranes of the eyes, nose, mouth (including taste buds), from the organ of hearing, the vestibular apparatus (organ of balance), from receptors of the larynx, trachea, lungs, as well as from interoceptors of the heart -vascular system and digestive system. Through the medulla oblongata, many simple and complex reflexes are carried out, covering not individual metameres of the body, but organ systems, for example, the digestive, respiratory, and circulatory systems.

Reflex activity. The following reflexes occur through the medulla oblongata:

· Protective reflexes: coughing, sneezing, blinking, tearing, vomiting.

· Food reflexes: sucking, swallowing, juice production (secretion) of the digestive glands.

· Cardiovascular reflexes that regulate the activity of the heart and blood vessels.

· The medulla oblongata contains an automatically functioning respiratory center that provides ventilation to the lungs.

· The vestibular nuclei are located in the medulla oblongata.

From the vestibular nuclei of the medulla oblongata begins the descending vestibulospinal tract, which is involved in the implementation of posture reflexes, namely in the redistribution of muscle tone. A bulbar cat can neither stand nor walk, but the medulla oblongata and cervical segments of the spinal cord provide those complex reflexes that are elements of standing and walking. All reflexes associated with the standing function are called positioning reflexes. Thanks to them, the animal, despite the forces of gravity, maintains the posture of its body, as a rule, with the crown upward. The special importance of this part of the central nervous system is determined by the fact that the medulla oblongata contains vital centers - respiratory, cardiovascular, therefore not only removal, but even damage to the medulla oblongata results in death.
In addition to the reflex function, the medulla oblongata performs a conductive function. Conducting pathways pass through the medulla oblongata, connecting the cortex, diencephalon, midbrain, cerebellum and spinal cord with a bilateral connection.

The medulla oblongata plays an important role in the implementation of motor acts and in the regulation of skeletal muscle tone. Influences emanating from the vestibular nuclei of the medulla oblongata increase the tone of the extensor muscles, which is important for the organization of posture.

Nonspecific parts of the medulla oblongata, on the contrary, have a depressing effect on the tone of skeletal muscles, reducing it in the extensor muscles. The medulla oblongata is involved in the implementation of reflexes to maintain and restore body posture, the so-called positioning reflexes.

Decerebrate rigidity is a plastic, pronounced increase in the tone of all muscles that function with resistance to gravity (extensor spasticity), and is accompanied by fixation in the position of extension and inward rotation of the arms and legs. and also often opisthotonos. This condition is also called apallic syndrome. It is based on damage to the midbrain, especially herniation into the tentorial foramen due to supratentorial processes, primarily neoplasia in the temporal lobes, cerebral hemorrhage with blood escaping into the ventricles, severe brain contusions, hemorrhage into the brainstem, encephalitis, anoxia, and poisoning. The pathology may initially manifest itself in the form of “cerebral spasms” and be provoked by external stimuli. With the complete cessation of the influence of descending impulses in the spinal cord, spasticity develops in the flexors. Rigidity is a sign of damage to the extrapyramidal system. It is observed in various etiological variants of parkinsonism syndrome (accompanied by akinesia, the “cogwheel” phenomenon and often tremor, which first appear on one side) and in other degenerative diseases accompanied by parkinsonism, for example, olivopontocerebellar atrophy, orthostatic hypotension, Creutzfeldt-Jakob disease, etc. .

Characteristic posture for decerebrate rigidity

The anterior horns of the spinal cord contain motor neurons - large and small cells. The neurons of the anterior horns are multipolar. Their dendrites have multiple synaptic connections with various afferent and efferent systems.

Large α cells with thick and fast conductive axon is carried out fast contractions muscles and associated with giant cells of the cortex cerebral hemispheres. Small a-cells with a thinner axon perform tonic function and receive information from the extrapyramidal system. α-Cells with a thin and slowly conducting axon innervate proprioceptive muscle spindles, regulating their functional state. α-Motoneurons are located under the influence of descending pyramidal, reticular-spinal, vestibulospinal s ways. The efferent influences of α-fibers provide fine regulation of voluntary movements and the ability to regulate the strength of the receptor response to stretching (α-motoneuron-spindle system).

For the nervous system to function, it is necessary not only to excite neurons or nerve centers, but also slow down their work when the need for their operation decreases. Consequently, inhibition is an active nervous process, the result of which is the cessation, prevention or weakening of excitation. Inhibition performs the following functions: protective, information processing in the central nervous system and coordination.

Inhibition can develop as an independent process with its own mechanisms (presynaptic and postsynaptic inhibition), or it can be the result of active excitation (pessimal inhibition).

There are three nerve centers main types of direction of braking actions in nerve networks:

return braking

lateral inhibition

· reciprocal inhibition.

In some cases, sequential and direct mutual inhibition is distinguished.

Return braking – this is the inhibition of neurons by their own impulses arriving through return collaterals to the inhibitory cells. The most striking example of recurrent inhibition is the inhibition of spinal cord neurons through Renshaw inhibitory intercalary cells who have synapses on the same neurons. Thus, a circuit with negative feedback is formed from two neurons. Parallel braking plays a similar role.

Lateral inhibition – this is the inhibition of elements of neighboring nerve chains in competing communication channels. Intercalary cells form inhibitory synapses on neighboring neurons, blocking the lateral pathways of excitation. In such cases, excitation is directed only along a strictly defined path. Such inhibition is observed in neighboring retinal elements, as well as in visual, auditory and other sensory centers. Lateral inhibition contrasts (highlights) significant signals.

Reciprocal inhibition – this is mutual (conjugate) inhibition of the centers of antagonistic reflexes, ensuring the coordination of these reflexes. An example of reciprocal inhibition is the inhibition of motor neurons that control antagonist muscles. It is carried out using special inhibitory interneurons.

Gamma motor neurons constitute approximately 30% of all cells of the anterior horns of the spinal cord; their axons are directed to the intrafusal muscle fibers that are part of the proprioceptors - muscle spindles.

The muscle spindle consists of several thin intrafusal muscle fibers enclosed in a fusiform connective tissue capsule. The axons of gamma motor neurons end on the intrafusal fibers, affecting the degree of their tension. Stretching or contraction of intrafusal fibers leads to changes in the shape of the muscle spindle and irritation of the spiral fiber surrounding the equator of the spindle. In this fiber, which is the beginning of the dendrite of a pseudounipolar cell, a nerve impulse arises, which is directed to the body of this cell, located in the spinal ganglion, and then along the axon of the same cell to the corresponding segment of the spinal cord. The terminal branches of this axon directly or through interneurons reach the alpha motor neuron, exerting an excitatory or inhibitory effect on it.

Thus, with the participation of gamma cells and their fibers, a gamma loop is created, which ensures the maintenance of muscle tone and the fixed position of a certain part of the body or the contraction of the corresponding muscles. In addition, the gamma loop ensures the transformation of the reflex arc into a reflex ring and takes part in the formation, in particular, of tendon or myotatic reflexes.

Complex movements can only be carried out if the effector impulses are constantly adjusted to take into account the changes that occur every moment in the muscle during its contraction. Therefore, the muscular system is a source of numerous afferent impulses. The spinal cord constantly receives information about the degree of tension of muscle fibers and their length.

The receptor part of the motion analyzer is muscle spindles and Golgi tendon organs.

Muscle spindles. In muscles, mainly extensors, that perform anti-gravity function is muscle fibers, thin and short others. They are placed in small bundles (from 2 to 12 fibers) in a connective tissue capsule. Due to their shape, such structures are called muscle spindles (Figure 4.8). Muscle fibers located in the capsule, called intrafusal(lat. Fusus- spindle), while ordinary fibers, which account for the bulk of the muscle, called extrafusal, or working fibers. Probably one end is attached to the perimysium of the extrafusal muscle fiber, the other - to the tendon. The central part of the intrafusal fibers is the actual receptor part.

There are two types of intrafusal muscle fibers that differ in the location of their nuclei: nuclear chain fiber nuclei and nuclear bursa fiber nuclei. Obviously, these two types of fibers are functionally different.

Afferent innervation. Each spindle is penetrated by a thick myelinated nerve fiber; it sends a branch to each intrafusal fiber and ends on its middle part, spiraling around it and creating the so-called annulo-spiral endings. These afferents are fibers 1a (Aa), and their endings are called primary sensory endings. An adequate stimulus for them is the change and rate of change in the length of the muscle fiber (Fig. 4.9). Some spindles are innervated afferent fibers of group II (Ab). These sensory fibers “serve” exclusively the intrafusal fibers with the nuclear chain and are called secondary sensory endings; They are located with their processes peripherally from the anulospiral endings. their excitability is lower, and their sensitivity to dynamic parameters is less.

Efferent innervation intrafusal muscle fibers are carried out by nerve fibers of group A-y. The nerve cell from which they arise is γ-motoneuron.

Rice. 4.8. Diagram of the structure of the muscle spindle (according to R. Schmidt, G. Tevs, 1985)

Rice. 4.9. Scheme of the myotatic reflex

Golgi tendon organs - special receptors, which consist of tendon filaments extending from approximately 10 extrafusal muscle fibers and are fixed in the muscle tendons sequentially, in the foredeck chain. An adequate stimulus for them is a change in muscle tension.

Thick myelin fibers of group and b (Αβ) fit into the Golgi organs. In the tendon organ they branch into thinner, numerous branches and lose myelin. Such receptors are common in skeletal muscles.

The nature of excitation of muscle spindles and tendon organs depends on their placement: the muscle spindles are connected in parallel, and the tendon organs are connected in series relative to the extrafusal muscle fibers. So, as a consequence, muscle spindles perceive mainly the length of the muscle, and tendon organs - his tension.

The sensitive endings of muscle spindles can be excited not only under the influence of muscle stretching, but also as a result contraction of intrafusal muscle fibers upon excitation of γ-motoneurons. This mechanism is called γ-loops(Fig. 4.10). When only the intrafusal fibers contract, the length or tension of the muscle does not change, but the central part of these fibers is stretched and therefore the sensory endings are excited.

Thus there is two excitation mechanisms muscle spindles: 1) muscle stretching and 2) contraction of intrafusal fibers; these two mechanisms may act synergistically.

Lecture: “Physiology of the spinal cord”

Lecture outline:

4. Spinal reflexes

5. Spinal shock. Characteristics of the spinal animal. Consequences of complete and partial transection of the spinal cord

The spinal cord is the most ancient formation of the central nervous system; it first appears in the lancelet. The spinal cord has a segmental structure.

^ 1. General characteristics of the functions of the spinal cord

The main functions of the spinal cord include: sensory, conductive and reflex functions.

At the level of neurons of the spinal cord occurs primary information analysis from proprioceptors and skin receptors of the trunk, limbs and a number of visceroreceptors. Proprioceptors include muscle receptors, tendon receptors, periosteum, and joint membranes. Skin receptors are receptors located on the surface and in the thickness of the skin: pain, temperature, tactile and pressure receptors.

Ascending and descending fibers (white matter) form the spinal cord pathways, through which information coming from receptors is transmitted and impulses come from the overlying parts of the central nervous system.

Due to the functional diversity of spinal cord neurons, the presence of numerous segmental, intersegmental connections and connections with brain structures, conditions are created for reflex activity spinal cord.

^ 2. Neural organization of the spinal cord. Segmental and intersegmental principles of operation of the spinal cord.

The human spinal cord contains about 13 million neurons, of which 3% are motor neurons, 97% are intercalary neurons. Functionally, spinal cord neurons can be divided into 4 groups:

^ 1. Motor neurons are cells of the anterior horns of the spinal cord, the axons of which form the anterior horns.

2. Interneurons receive information from the spinal ganglia and are located in the dorsal horns. These are sensitive neurons that respond to pain, temperature, tactile, vibration and proprioceptive stimulation.

^ 3. Sympathetic (lateral horns of the spinal cord) and parasympathetic (sacral department).

4. Associative neurons of the spinal cord’s own apparatus establish connections within and between segments.

^ Motor neurons of the spinal cord.

Motor neurons are divided into α- and gamma motor neurons. The size of alpha motor neurons ranges from 40-70 microns, gamma motor neurons - 30-40 microns. 1/3 of the diameter of the anterior root is occupied by the axons of gamma motor neurons. The motor neuron axon innervates muscle fibers. Skeletal muscles have 2 types of fibers: intrafusal and extrafusal. The intrafusal fiber is located inside the so-called muscle spindle - this is a specialized muscle receptor located deep in the skeletal muscle. This fiber is necessary to regulate receptor sensitivity. It is controlled by the gamma motor neuron. All muscle fibers belonging to a given muscle and not part of the muscle spindle are called extrafusal.

Alpha motor neurons innervate skeletal muscle fibers (extrafusal fibers) to produce muscle contractions. Gamma motor neurons innervate intrafusal fibers, muscle spindles, which are stretch receptors. There is a combined activation of alpha and gamma motor neurons. The alpha motor neuron axon is the only channel connecting nervous system with skeletal muscle. Only the excitation of the alpha motor neuron leads to the activation of the corresponding muscle fibers.

There are 3 ways of connecting fibers of the descending pathways with alpha motor neurons:

^ 1. Direct descending influence on alpha motor neuron

2 Indirectly through an interneuron

3. Activation of gamma motor neuron and through intrafusal fiber to alpha motor neuron

Gamma loop:

Gama motor neurons activate infrafusal muscle fibers, as a result of which afferent nerve fibers are activated and the flow of impulses goes to alpha motor neurons or intercalary motor neurons, and from them to alpha motor neurons - this is called the gamma loop.

Segmental and intersegmental principles of operation of the spinal cord:

The spinal cord is characterized by a segmental structure, reflecting the segmental structure of the body of vertebrates. Two pairs of ventral and dorsal roots arise from each spinal segment. 1 sensory and 1 motor root innervates its transverse layer of the body, i.e. metamer. This is the segmental principle of the spinal cord. The intersegmental principle of operation is the innervation by the sensory and motor roots of its metamere, the 1st overlying and 1st underlying metamer. Knowledge of the boundaries of body metameres makes it possible to carry out topical diagnosis of spinal cord diseases.

^ 3. Conductive organization of the spinal cord

Axons of the spinal ganglia and gray matter of the spinal cord go into its white matter, and then into other structures of the central nervous system, thereby creating the so-called pathways, functionally divided into proprioceptive, spinocerebral (ascending) and cerebrospinal (descending).

^ Propriospinal tract connect neurons of the same or different segments of the spinal cord. The function of such connections is associative and consists in coordinating posture, muscle tone, and movements of various metameres of the body. One metamer includes 1 pair of spinal nerves and the area of ​​the body innervated by them.

^ Spinocerebral tracts connect segments of the spinal cord with brain structures. They are represented by proprioceptive, spinothalamic, spinocerebellar and spinoreticular pathways/

a) The proprioceptive pathway (thin fascicle of Gaulle and wedge-shaped fascicle of Burdach) starts from the deep sensitivity receptors of the periosteum, joint membranes, tendons and muscles. Through the spinal ganglion it goes to the dorsal roots of the spinal cord, into the white matter of the posterior cords and, without switching to a new neuron at the level of the spinal cord, rises to the Gaulle and Burdach nuclei of the medulla oblongata. Here a switch to a new neuron occurs, then the path goes to the lateral nuclei of the thalamus of the opposite hemisphere of the brain, here it switches to a new neuron (second switch). From the thalamus, the pathway ascends to the neurons of the somatosensory cortex. Along the way, the fibers of these tracts give off collaterals in each segment of the spinal cord, which creates the possibility of correcting the posture of the entire body.

b) The spinothalamic pathway begins from pain, temperature, and baroreceptors of the skin. The signal from the skin receptors goes to the spinal ganglion, then through the dorsal root to the dorsal horn of the spinal cord, here it switches to a new neuron (first switch). Sensory neurons in the dorsal horn send axons to the opposite side of the spinal cord and ascend along the lateral funiculus to the thalamus. Here the second switch occurs and rises to the sensory cortex. Some of the fibers of the skin receptors go to the thalamus along the anterior cord of the spinal cord.

c) The spinocerebellar tracts begin from the receptors of muscles, ligaments, and internal organs and are represented by the non-crossing Gowers fascicle and the double-crossing Flexig fascicle. Therefore, the right and left cerebellum receive information only from their side of the body. This information comes from Golgi tendon receptors, proprioceptors, pressure and touch receptors.

d) Spinoreticular tract – starts from the interneurons of the spinal cord and reaches the RF of the brain stem. Carries information from visceroreceptors.

Thus, through the conductive tracts of the spinal cord, impulses are carried out from the receptors of the trunk and limbs to the neurons of the spinal cord and overlying structures of the central nervous system.

^ Cerebrospinal tracts start from the neurons of the brain structures and end on the neurons of the spinal cord segments. These include the following pathways: the corticospinal tract, which provides regulation of voluntary movements, the rubrospinal, vestibulospinal and reticulospinal tracts, which regulate muscle tone. What these pathways have in common is that they end at the motor neurons of the anterior horns of the spinal cord.

^ 4. Spinal reflexes

The reflex activity of the spinal cord is based on a reflex, the structural and functional basis of which is the reflex arc. There are monosynaptic and polysynaptic reflex arcs.

^ Spinal reflexes are divided into into somatic (motor) and autonomic.

Motor reflexes, in turn, are divided into tonic(aimed at maintaining muscle tone, maintaining the limbs and the entire torso in a certain static position) and phasic(provide movement of the limbs and torso).

Tonic ones include: myotatic reflex, cervical tonic reflexes of position, support reflex (they were first described by the Dutch physiologist Rudolf Magnus, 1924), flexion tonic reflex.

Phasic reflexes include: tendon reflexes, shortening reflexes from Golgi bodies, plantar, abdominal, flexion protective, extensor crossed, rhythmic.

^ Myotatic reflex – stretch reflex, for example, when a person takes a vertical position, due to gravitational forces he can fall (bending at the joints lower limbs), but this does not happen with the participation of myotatic reflexes, because When a muscle is stretched, muscle spindles are activated, which are located parallel to the extrafusal fibers of the skeletal muscle. The impulse from the muscle receptors goes through the afferent neuron and enters the alpha motor neurons of the given muscle. As a result, shortening of the extrafusal water pipes occurs. Thus, the length of the muscle returns to its original length. The myotatic reflex is characteristic of all muscles, is well expressed and easily evoked in the flexor muscles, directed against gravitational forces, to maintain balance and muscle tone. It should be noted that impulses from the receptors simultaneously through the Renshaw intercalary inhibitory cells enter the alpha motor neurons of the antagonist of this muscle, therefore, when the agonist is shortened, the antagonist muscle does not interfere with this process.

Receptive field cervical tonic reflexes positions are the proprioceptors of the neck muscles and fascia covering the cervical spine. The central part of the reflex arc is polysynaptic in nature, i.e. includes interneurons. The reflex reaction involves the muscles of the trunk and limbs. In addition to the spinal cord, it also involves the motor nuclei of the brain stem, which innervate the muscles of the eyeballs. Cervical tonic reflexes occur when turning and tilting the head, which causes stretching of the neck muscles and activates the receptive field of the reflex.

Support (push-off) reflex– when standing on the surface, the tone of the extensor muscles increases.

Flexion tonic reflex observed, for example, in a frog or a rabbit, in which a tucked position of the limbs is characteristic. This reflex is aimed at maintaining a certain posture, which is possible if there is a certain muscle tone.

Tendon reflex– shortening reflex from Golgi bodies

Plantar reflex– irritation of the skin of the foot leads to plantar flexion of the fingers and toes of the lower limb.

Abdominal reflexes- voltage abdominal muscles, arising from nociceptive afferent influences. This is a protective reflex.

Flexion defensive reflexes- occur when pain receptors in the skin, muscles and internal organs are irritated and are aimed at avoiding various damaging effects.

^ Extensor cross reflex: reflex flexion of one of the limbs is often accompanied by a contraction of the contralateral limb, onto which additional body weight is transferred under natural conditions (when walking).

^ To rhythmic reflexes in mammals this refers to the scratching reflex. Its analogue in amphibians is the rubbing reflex. Rhythmic reflexes are characterized by the coordinated work of the muscles of the limbs and torso, the correct alternation of flexion and extension of the limbs, along with tonic contraction of the adductor muscles, which establish the limb in a certain position to the skin surface.

^ Step reflex – coordinated motor activity of the upper and lower extremities. To implement this reflex, intersegmental interaction of the muscles of the arms, legs and torso is necessary. The mechanisms of stepping movements are located in the spinal cord, but the spinal mechanism is activated from the midbrain.

^ Autonomic spinal reflexes : vascular, sweating, urination, defecation. Autonomic reflexes ensure the reaction of internal organs and the vascular system to irritation of visceral, muscle, and skin receptors.

^ 5. Spinal shock. Characteristics of the spinal animal. Consequences of complete and partial transection of the spinal cord.

Spinal shock(shock) occurs after complete transection of the spinal cord. It lies in the fact that all centers below the transection cease to organize their inherent reflexes. Spinal shock is characterized by a temporary disappearance of the reflex functions of the spinal cord. Disruption of reflex activity after transection of the spinal cord lasts for different times in different animals. In monkeys, the first signs of recovery of reflexes after transection of the spinal cord appear within a few days; in a frog it takes minutes; in humans, the first spinal reflexes are restored after several weeks, or even months.

^ The cause of shock is a violation of the regulation of reflexes on the part of the overlying structures of the central nervous system.

With a spinal cord injury, a person may develop a group of spinal motor reflexes that are normally present only in the first days and months of postnatal development. Disinhibition of these primitive reflexes is a clinical sign of spinal cord dysfunction.

^ Spinal animal - this is an animal in which the spinal cord is separated from the brain; the spinal cord is transected below the 3rd cervical vertebra. Transection above the 3rd cervical vertebra is incompatible with life, because at the level of 1-2 cervical vertebrae there are nerve centers of the respiratory muscles and, if they are destroyed, the animal will die from paralysis of the respiratory muscles, i.e. asphyxia.

When a person is injured, in some cases, a complete or half transection of the spinal cord occurs. With half-lateral damage to the spinal cord, Brown-Séquard syndrome develops. It manifests itself in the fact that paralysis develops in half of the lesion (below the lesion site) motor system due to damage to the pyramidal tracts. On the opposite side the movements are preserved.

On the affected side (below the lesion site), proprioceptive sensitivity is impaired (from the deep sensitivity receptors of the periosteum, joint membranes, tendons and muscles). This is due to the fact that the ascending pathways of deep sensitivity go along their side of the spinal cord to the medulla oblongata, where they cross (bundle of Gaulle and Burdach).

On the opposite side of the body (relative to the damage), pain and temperature sensitivity (spinothalamic tract) is impaired, because ascending pathways of deep sensitivity go from the spinal ganglion to the dorsal horn of the spinal cord, where they switch to a new neuron, the axon of which passes to the opposite side. As a result, if the left half of the spinal cord is damaged, then pain and temperature sensitivity of the right half of the body below the damage disappears.

After a spinal cord injury, a person experiences distortion of spinal reflexes: weakening of myotatic and musculocutaneous motor reflexes, increased tendon reflexes, and distortion of the plantar reflex.

References:

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Lecture No. 2

Topic: “Physiology of the hindbrain”

Lecture outline

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3. Reflex function of the hindbrain. Concept of a bulbar animal

^ 4.1. Structure and afferent connections of the reticular formation

4.2. Characteristics of efferent connections of the reticular formation

1. General characteristics of the hindbrain functions

The hindbrain includes the medulla oblongata and the pons (pons). Together with the midbrain, they form the brain stem, which includes a large number of nuclei, ascending and descending pathways.

^ The functions of the hindbrain include:

1) primary analysis of information from vestibuloreceptors and auditory receptors

2) primary analysis of information from proprioceptors and skin receptors of the head

3) primary analysis of information from the body’s visceroreceptors

4) conductive function: pathways that connect the structures of the central nervous system pass through the hindbrain: the vestibulospinal, olivospinal and reticulospinal pathways, which provide tone and coordination of muscle reactions, originate here; the pathways of proprioceptive sensitivity of the spinal cord - thin and wedge-shaped - end here.

5) reflex function: the hindbrain carries out reflexes, the reflex arc of which closes at the level of the medulla oblongata and the pons

^ 2. Basic motor and autonomic nuclei of the hindbrain

The nuclei of the V-XII pairs of h.m.n. are localized in the hindbrain. (in the medulla oblongata these are the nuclei of VIII-XII pairs of h.m.n., in the pons - the nuclei of V-VIII pairs of h.m.n.).

Nuclei of the XII pair h.m.s. (hypoglossal nerve) and XI pair of h.m.n. (accessory nerve) are purely motor. Axons located in these motor neuron nuclei innervate, respectively, the muscles of the tongue and the muscles that move the head.

Nuclei of mixed X (vagus) and IX (glossopharyngeal) pairs h.m.n. less isolated into separate nuclear structures. Axons motor nuclei X-IX pairs h.m.s. innervate the muscles of the pharynx and larynx. Viscerosensory nucleusX- IXsteam h.m.s.(called the nucleus of the solitary fasciculus) receives sensory fibers from afferent neurons whose bodies are located in the jugular, fascicular and petrosal ganglia (these nodes correspond to the spinal ganglia). Impulses from the receptors of the tongue, larynx, trachea, esophagus, and internal organs arrive here. The viscerosensory nucleus is connected through interneurons with the visceromotor nuclei of the vagus and glossopharyngeal nerves. The neurons located in these nuclei innervate the parotid gland, glandular and smooth muscle cells of the trachea, bronchi, stomach, intestines, as well as the heart and blood vessels.

^VIIIa couple of h.m.s. is sensitive, it contains 2 branches - vestibular and auditory. Auditory branch formed by afferent fibers coming from the organ of Corti of the cochlea. Auditory afferent fibers enter the medulla oblongata and reach the ventral and dorsal auditory nuclei.

Substantial part vestibular fibers, coming from the receptors of the semicircular canals, ends on the neurons of the vestibular nuclei: medial (Schwalbe's nucleus), prevesticular superior (Bechterew's nucleus), prevesticular lateral (Deiters' nucleus) and descending (Roller's nucleus). In addition, part of the vestibular fibers is sent to the cerebellum. When the vestibular nuclei are excited under the influence of adequate stimuli, impulses along the vestibulospinal tract, originating from the Deiters nucleus, excite the alpha motor neurons of the extensors and, at the same time, through the mechanism of reciprocal innervation, inhibit the alpha motor neurons of the extensors. Thanks to this, when the vestibular apparatus is excited, a change in the muscle tone of the limbs ensures the preservation of balance.

Neurons of the vestibular nuclei also give rise to the vestibulocerebellar and vestibulospinal tracts. At the same time, from the vestibular nuclei of the medulla oblongata there is a path to the so-called medial longitudinal fasciculus, which starts from the Darkshevich nucleus and the intermediate nucleus located in the midbrain. The medial longitudinal fascicle connects all the nuclei of the nerves involved in regulating the activity of the muscles of the eyeball (III, IV and VI pairs of the eyeball) into a single functional ensemble. Thanks to this, the movement of the eyeballs occurs normally synchronously.

In the brain bridge the nuclei of the facial (VII pair), abducens (VI pair) and trigeminal (V) nerves are located.

Facial nerve is mixed, the afferent fibers in its composition transmit signals from the taste buds of the anterior part of the tongue. Efferent fibers facial nerve innervate the facial muscles.

Abducens nerve is motor, its motor neurons innervate the external rectus muscle of the eye.

Trigeminal nerve is also mixed. Its neurons innervate the muscles of mastication, the muscles of the velum palatine, and the tensor tympani muscle. The sensory nucleus of the trigeminal nerve, starting at the lower (caudal) end of the medulla oblongata, extends across the entire pons, up to the upper (rostral) end of the midbrain. Axons from afferent neurons of the semilunar ganglion approach the sensitive nucleus of the trigeminal nerve, delivering signals from receptors in the skin of the face, parietal, temporal region, conjunctiva, nasal mucosa, periosteum of the skull bones, teeth, dura mater, and tongue.

^ 3. Reflex function of the hindbrain. Characteristics of the bulbar animal

A) strengthening of myotatic spinal reflexes, which are directed against gravitational forces, play a role in maintaining muscle tone and balance.

^ B) strengthening of cervical spinal reflexes(posture-tonic). They lead to changes in muscle tone when the position of the head and neck changes (called Magnus rivers).

IN) vestibular position reflexes, the main component of which is represented by reflex effects on the neck muscles. Thanks to the redistribution of the tone of the neck muscles, when moving, the head constantly maintains its natural position.

^ Cervical and vestibular reflexes provide a relatively stable standing posture when turning and tilting the head.

D) posture maintenance reflexes: information from the vestibuloreceptors is sent to the vestibular nuclei, which take part in determining the muscle groups and segments of the spinal cord that should take part in changing the posture, and then the command is sent to the spinal cord.

e) Autonomic reflexes - most are realized through the nuclei of the vagus nerve, which receive information about the state of activity of the heart, blood vessels, digestive tract, lungs, digestive glands, etc. In response, the nuclei organize the motor and secretory reactions of these organs.

- digestive reflexes:

e) Protective reflexes. The medulla oblongata organizes and implements a number of protective reflexes (vomiting, sneezing, coughing, lacrimation, closing the eyelids with the participation of nuclei V, VII, IX, X, pairs of h.m.n.).

g) organization and implementation of reflexes of eating behavior: sucking, chewing and swallowing, where various groups of neurons are involved, which are covered by excitation in a certain order, respectively, the muscles of the pharynx, larynx and tongue contract in a certain sequence.

^ Bulbar animal - this is an animal in which a transection has been made between the medulla oblongata and midbrain (below the posterior tubercles of the quadrigeminal). The bulbar animal has all spinal reflexes and reflexes that close at the level of the hindbrain. The bulbar animal, which has a medulla oblongata and pons, is capable of carrying out more complex reactions to external influences than the spinal animal. All the basic vital functions of these animals are united by more advanced control and are more coordinated.

^ 4. Physiology of the reticular formation

4.1.Structure and afferent connections of the Russian Federation

The reticular or reticular formation (named by Deiters, 1855) is located in the medial part of the brain stem; the RF is a cluster of neurons separated by many fibers passing in different directions. This interweaving of neurons and fibers continues in the pons and midbrain. The network structure ensures high reliability of the functioning of the Russian Federation and resistance to damaging influences, since local damage is always compensated by the surviving network elements. On the other hand, the high reliability of the functioning of the Russian Federation is ensured by the fact that irritation of any of its parts is reflected in the activity of the entire Russian Federation of a given structure due to the diffuseness of connections.

At the level of the medulla oblongata, the nuclei of the Russian Federation are distinguished: reticular giant cell, reticular small cell, reticular lateral. The giant cell nucleus is the beginning of the reticulospinal tract.

RF neurons are highly sensitive to chemical stimuli: hormones and some metabolic products. RF cells are the beginning of both ascending and descending pathways, giving numerous collaterals ending on neurons of different nuclei of the central nervous system. The respiratory and vasomotor centers are located in the Russian Federation.

^ To the main afferent connections of the Russian Federation (i.e., coming from different structures of the central nervous system to the RF) include afferent pathways from the CBP, cerebellum, motor nuclei of the brainstem (medulla oblongata, midbrain, diencephalon), as well as RF neurons of the medulla oblongata receive numerous collaterals from fibers of all ascending tracts of the spinal cord .

^ 4.2. Characteristics of efferent connections of the Russian Federation

Efferent connections of the Russian Federation (starting from the Russian Federation) - go in an ascending direction to the overlying structures and in a descending direction. Rising influences of the Russian Federation are directed to the cbp (reticulo-cortical path), to the thalamus and to the hypothalamus (reticulothalamic and reticulo-hypothalamic paths), through which sensory information is transmitted from the body. Ascending influences to the cerebral cortex are divided into activating (tonic) and hypnogenic (inhibiting). Yes, during experimental research On animals, the American physiologist Magoon and the Italian researcher Moruzzi showed that when the hypnogenic effects of the RF brain are stimulated, animals fall asleep. When activating ascending influences of the Russian Federation were excited, Moruzzi and Magun (1948) observed an awakening reaction on the EEG.

Descending influences The Russian Federation (Megun, 50s of the last century) is divided into 2 groups:

A) influences on motor centers

^ B) influences on the vegetative centers

A) Influences on motor centers, in turn, are divided into specific and nonspecific. Specific reticulospinal pathways: activate flexor and inhibit extensor alpha motor neurons of the trunk muscles.

Nonspecific reticulospinal pathways are divided into activating and inhibitory pathways.

Activating pathways come from the lateral part of the Russian Federation, exert a generalized activating effect on all spinal neurons, and cause facilitation of spinal reflexes. For example, the temporary absence of spinal reflexes during spinal shock is associated with the absence of the facilitating effects of the RF.

Inhibitory - start from the inhibitory zone of the medulla oblongata in the medial part of the Russian Federation, reach the gamma motor neurons of the spinal cord, innervating the muscle spindles, causing inhibition of spinal reflexes.

^ B) Influences on the vegetative centers. The structure of the Russian Federation contains the vasomotor center (VMC) and the respiratory center (RC).

SDC. Afferent impulses in the SDC come from vascular receptors and, through other brain structures, from bronchioles, heart, from abdominal organs, and from receptors of the somatic system. The efferent pathways of reflexes go along the reticulospinal tract to the lateral horns of the spinal cord. The effect of changing blood pressure depends not only on which neurons fire, but also on the frequency at which they fire. High-frequency impulses increase, and low-frequency impulses decrease blood pressure. This is due to the fact that low-frequency stimulation of the sympathetic neurons of the spinal cord, where the reticulospinal tracts from the vasomotor center end, reduces vascular tone, and high-frequency stimulation increases it. Excitation of the SDC changes the respiratory rhythm, tone of the bronchi, intestinal muscles, bladder, etc. This is due to the fact that the RF of the medulla oblongata is closely connected with the hypothalamus and other nerve centers. In addition, SDC neurons are characterized by high chemical sensitivity. As a result, the frequency of their rhythm is determined by changes in the chemical composition of the blood.

The DC is divided into the center of inhalation and exhalation; accordingly, the DC neurons are divided into inspiratory and expiratory. Neurons of the respiratory center have the ability to self-excite, i.e. are able to rhythmically issue volleys of impulses without the influx of irritation to them from the structures of the respiratory organs. DC neurons respond to changes in the levels of oxygen, carbon dioxide and blood pH.

Thus, the Russian Federation has bilateral connections with all structures of the central nervous system; RF neurons have chemical sensitivity. In the RF region, interaction of both ascending and descending impulses occurs; circulation through closed circular neural circuits is also possible, which determines a constant level of excitation of RF neurons, thereby ensuring tone and a certain degree of readiness for the activity of various parts of the central nervous system. It should be emphasized that the degree of excitation of the Russian Federation regulates the bp.

Thus, in the hindbrain there are centers of both relatively simple and more complex reflexes, in the implementation of which various muscle groups, blood vessels and many internal organs. Brainstem RF regulates the level of activity of almost all parts of the central nervous system.

References:

^ 1.Human physiology /Ed. V.M. Pokrovsky, G.F. Briefly. T.1. M., 1998

2. Human physiology Agadzhanyan N.A., Tel L.Z., Tsirkin V.I., Chesnokova S.A. – M.: Medical Book, N. Novgorod: Publishing House of NGMA, 2001. – 526 p.

^ 3. Human physiology / Ed. G.I. Kositsky. - M., 1985

4. Fundamentals of human physiology / Ed. B.I. Tkachenko. T.1.- St. Petersburg, 1994

5. Guide to practical exercises in physiology. /Ed. G.I. Kositsky, V.A. Polyantseva. M., 1988

^ 6. General course of human and animal physiology in 2 books/Ed. HELL. Nozdracheva.-M., “Higher School”, 1991