In the area of ​​the posterior lateral and anterior lateral grooves from spinal cord anterior and posterior roots come off spinal nerves. On the dorsal root there is a thickening that represents the spinal ganglion. The anterior and posterior roots of the corresponding groove are connected to each other in the area of ​​the intervertebral foramen and form the spinal nerve.

Bell-Magendie law

The pattern of distribution of nerve fibers in the roots of the spinal cord is called Bell-Magendie law(named after the Scottish anatomist and physiologist C. Bell and the French physiologist F. Magendie): sensory fibers enter the spinal cord as part of the dorsal roots, and motor fibers exit as part of the anterior ones.

Spinal cord segment

- a section of the spinal cord corresponding to the four roots of the spinal nerves or a pair of spinal nerves located at the same level (Fig. 45).

There are 31-33 segments in total: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1-3 coccygeal. Each section is associated with certain part bodies.

Dermatome- part of the skin innervated by one segment.

Myotome- part of the striated muscle innervated by one segment.

Splanchnotome- part of the internal organs innervated by one segment.

On cross section The spinal cord can be seen with the naked eye that the spinal cord consists of gray matter and surrounding white matter. Gray matter is shaped like the letter H or a butterfly and consists of nerve cell bodies (nuclei). The gray matter of the brain forms the anterior, lateral and rear horns.

White matter formed by nerve fibers. Nerve fibers, which are elements of the pathways, form the anterior, lateral and posterior cords.

Neurons of the spinal cord:- insertion neurons or interneurons(97%) transmit information to interneurons at 3-4 higher and lower segments.

— motor neurons(3%) – multipolar neurons of the intrinsic nuclei of the anterior horns. Alpha motor neurons innervate the striated muscle tissue(extrafusal muscle fibers), gamma motor neurons (innervate intrafusal muscle fibers).

— neurons of the autonomic nerve centers– sympathetic (intermediate lateral nuclei of the lateral horns of the spinal cord C VIII -L II - III), parasympathetic (intermediate lateral nuclei S II - IV)

Conducting systems of the spinal cord

1. ascending pathways (extero-, proprio-, interoceptive sensitivity)
2. descending pathways (effector, motor)
3. own (propriospinal) pathways (associative and commissural fibers)

Conducting function of the spinal cord:

1. Rising
   • The thin fascicle of Gaulle and the wedge-shaped fascicle of Burdach in the posterior cords of the spinal cord (formed by the axons of pseudounipolar cells, transmit impulses of conscious proprioceptive sensitivity)
   • Lateral spinothalamic tract in the lateral cords (pain, temperature) and ventral spinothalamic tract in the anterior cords (tactile sensitivity) - axons of the own nuclei of the dorsal horn)
   • Posterior spinocerebellar tract of Flexig without decussation, axons of cells of the thoracic nucleus and anterior spinocerebellar Gowers axons of cells of the medial intermediate nucleus, partly on their side, partly on the opposite side (unconscious proprioceptive sensitivity)
   • Spinoreticular tract (anterior funiculi)
2. Descending

• Lateral corticospinal (pyramidal) tract (lat.) – 70-80% of the entire pyramidal tract) and anterior corticospinal (pyramidal) tract (anterior cords)
• Rubrospinal tract of Monakov (lateral funiculi)
• Vestibulospinal tract and olivospinal tract (lateral funiculi) (maintaining extensor muscle tone)
• Reticulospinal tract (trans.) (RF of the bridge - maintaining the tone of the extensor muscles, RF of the medulla oblongata - flexors)
• Tectospinal tract (trans.) - decussation in the midbrain. (indicative guard reflexes in response to sudden visual and auditory, olfactory and tactile stimuli)
• Medial longitudinal fasciculus – axons of cells of the nuclei of Cajal and Darkshevich of the midbrain – ensuring combined rotation of the head and eyes

Tonic function of the spinal cord:

Even in sleep, the muscles do not relax completely and remain tense. This minimum tension, which is maintained in a state of relaxation and rest, is called muscle tone. Muscle tone has a reflex nature. The degree of muscle contraction at rest and contraction is regulated by proprioceptors - muscle spindles. Intrafusal muscle fiber with nuclei arranged in a chain.

1. Intrafusal muscle fiber with nuclei located in the nuclear bursa.
2. Afferent nerve fibers.
3. Efferent α-nerve fibers
4. Connective tissue capsule of the muscle spindle.

Muscle spindles(muscle receptors) are located parallel to the skeletal muscle - their ends are attached to the connective tissue membrane of the bundle of extrafusal muscle fibers. The muscle receptor consists of several striated intrafusal muscle fibers, surrounded by a connective tissue capsule (length 4-7 mm, thickness 15-30 µm). There are two morphological types of muscle spindles: with a nuclear bursa and with a nuclear chain.

When a muscle relaxes (lengthens), the muscle receptor, namely its central part. Here the permeability of the membrane to sodium increases, sodium enters the cell, and a receptor potential is generated. Intrafusal muscle fibers have double innervation:

1. From central part an afferent fiber begins, along which excitation is transmitted to the spinal cord, where a switch to the alpha motor neuron occurs, which leads to muscle contraction.
2. TO peripheral parts efferent fibers from gamma motor neurons are suitable. Gamma motor neurons are under constant descending (inhibitory or excitatory) influence from the motor centers of the brain stem (reticular formation, red nuclei of the midbrain, vestibular nuclei of the pons).

The REFLECTOR function of the spinal cord is to perform

all reflexes, the arcs of which (wholly or partially) are located in the spinal cord.

Spinal cord reflexes are classified according to following criteria: a) by the location of the receptor, b) by the type of receptor, c) by the location of the nerve center of the reflex arc, c) by the degree of complexity of the nerve center, d) by the type of effector, e.) by the relationship in the location of the receptor and effector, c) by state of the body, g) for use in medicine.

Spinal cord reflexes

Somatic according to the 1st and 5th sections of the reflex arc are divided into:

1. propriomotor
2. visceromotor
3. cutanomotor

By anatomical regions they are divided into:

1. Limb reflexes

   • Flexion (phase: ulnar C V - VI, Achilles S I - II - propriomotor plantar S I - II - cutanomotor - protective, tonic - maintaining posture)

   • Extensor (phasic - knee L II - IV, tonic, stretch reflexes (myotatic - maintaining posture)

   • Postural - propriomotor (cervicotonic with the obligatory participation of the overlying parts of the central nervous system)

   • Rhythmic – repeated repeated flexion and extension of the limbs (rubbing, scratching, stepping)

2. Abdominal reflexes - cutanomotor (upper Th VIII - IX, middle Th IX - X, lower Th XI - XII)

3. Reflexes of the pelvic organs (creamaster L I - II, anal S II - V)

Autonomic ones according to the 1st and 5th sections of the reflex arc are divided into:

1. propriovisceral
2. viscero-visceral
3. cutanovisceral

Functions of the spinal cord:

1. Conductor
2. Tonic
3. Reflex

Reticular formation.

The RF is a complex of anatomically and functionally connected neurons of the cervical spinal cord and the brainstem (medulla oblongata, pons, midbrain), the neurons of which are characterized by an abundance of collaterals and synapses. Due to this, all information entering the reticular formation loses its specificity, and the number of nerve impulses increases. Therefore, the reticular formation is also called the “energy station” of the central nervous system.

The reticular formation has the following influences: a) descending and ascending, b) activating and inhibitory, c) phasic and tonic. It is also directly related to the work of the body’s biosynchronizing systems.

RF neurons have long, poorly branched dendrites and well-branched axons, which often form a T-shaped branching: one branch is ascending, the other is descending.

Functional features of RF neurons:

1. Multisensory convergence: receive information from several sensory pathways coming from different receptors.
2. RF neurons have a long latent period of response to peripheral impulses (polysynaptic pathway)
3. Neurons of the reticular formation have tonic activity at rest of 5-10 impulses per second
4. High sensitivity to chemical irritants (adrenaline, carbon dioxide, barbiturates, aminazine)

Functions of the Russian Federation:

1. Somatic function: influence on motor neurons of the nuclei of the cranial nerve, motor neurons of the spinal cord and the activity of muscle receptors.
2. Ascending excitatory and inhibitory effects on the cerebral cortex (regulation of the sleep/wake cycle, forms a nonspecific pathway for many analyzers)
3. The Russian Federation is part of the vital centers: cardiovascular and respiratory, swallowing, sucking, chewing centers

Spinal shock

Spinal shock is the name given to sudden changes in the function of the centers of the spinal cord that occur as a result of complete or partial transection (or damage) of the spinal cord no higher than C III - IV. The disturbances that occur in this case are more severe and lasting, the higher the animal is at the evolutionary stage of development. The frog's shock is short-lived - lasting only a few minutes. Dogs and cats recover after 2-3 days, and the recovery of so-called voluntary movements (conditioned motor reflexes) does not occur. During the development of spinal shock, two phases are distinguished: 1 and 2.

In the 1st phase The following symptoms can be distinguished: atony, anesthesia, areflexia, lack of voluntary movements and autonomic disorders below the site of injury.

Autonomic disorders: With shock, vasodilation occurs, falling blood pressure, disturbance of heat generation, increased heat transfer, urinary retention occurs due to sphincter spasm Bladder, the rectal sphincter relaxes, as a result of which the rectum is emptied as feces enter it.

The 1st phase of shock occurs as a result of passive hyperpolarization of motor neurons, in the absence of excitatory influences coming from the overlying parts of the nervous system to the spinal cord.

2nd phase: Anesthesia persists, voluntary movements are absent, hypertension and hyperreflexia develop. Autonomic reflexes in humans are restored after a few months, but voluntary emptying of the bladder and voluntary defecation are not restored when connections with the cerebral cortex are interrupted.

Phase 2 occurs due to the initial partial depolarization of motor neurons in the anterior horns of the spinal cord and the absence of inhibitory influences from the suprasegmental apparatus.

The spinal cord performs conductor and reflex functions.

Conductor function carried out by ascending and descending pathways passing through the white matter of the spinal cord. They connect individual segments of the spinal cord with each other, as well as with the brain.

Reflex function carried out through unconditioned reflexes, which close at the level of certain segments of the spinal cord and are responsible for the simplest adaptive reactions. The cervical segments of the spinal cord (C3 - C5) innervate the movements of the diaphragm, the thoracic segments (T1 - T12) - the external and internal intercostal muscles; cervical (C5 – C8) and thoracic (T1 – T2) are the centers of movement upper limbs, lumbar (L2 – L4) and sacral (S1 – S2) – centers of movement lower limbs.

In addition, the spinal cord is involved in implementation of autonomic reflexes – response of internal organs to irritation of visceral and somatic receptors. The autonomic centers of the spinal cord, located in the lateral horns, are involved in the regulation of blood pressure, heart activity, secretion and motility of the digestive tract and the function of the genitourinary system.

In the lumbar sacral region The spinal cord contains the center of defecation, from which impulses are sent through parasympathetic fibers as part of the pelvic nerve, enhancing the motility of the rectum and ensuring a controlled act of defecation. The voluntary act of defecation is accomplished due to the descending influences of the brain on the spinal center. In the II-IV sacral segments of the spinal cord there is a reflex center for urination, which ensures controlled separation of urine. The brain controls urination and provides voluntary control. In a newborn child, urination and defecation are involuntary acts, and only as the regulatory function of the cerebral cortex matures do they become voluntarily controlled (usually this occurs in the first 2–3 years of a child’s life).

Brain– the most important department of the central nervous system – surrounded meninges and is located in the cranial cavity. It consists of brain stem : medulla oblongata, pons, cerebellum, midbrain, diencephalon, and the so-called telencephalon, consisting of the subcortical, or basal, ganglia and cerebral hemispheres (Fig. 11.4). The upper surface of the brain corresponds in shape to the internal concave surface of the cranial vault, the lower surface (the base of the brain) has a complex relief corresponding to the cranial fossae of the internal base of the skull.

Rice. 11.4.

The brain is intensively formed during embryogenesis, its main parts are distinguished by the 3rd month intrauterine development, and by the 5th month the main grooves of the cerebral hemispheres are clearly visible. In a newborn, the brain weight is about 400 g, its ratio to body weight is significantly different from that of an adult - it is 1/8 of body weight, while in an adult it is 1/40. The most intensive period of growth and development of the human brain occurs in early childhood, then its growth rate decreases somewhat, but continues to remain high until 6-7 years, by which time the brain mass reaches 4/5 of the mass of the adult brain. The final maturation of the brain ends only by the age of 17–20; its mass increases 4–5 times compared to newborns and averages 1400 g in men and 1260 g in women (the mass of the adult brain ranges from 1100 to 2000 g ). The length of the brain in an adult is 160–180 mm, and the diameter is up to 140 mm. Subsequently, the mass and volume of the brain remain maximum and constant for each person. Interestingly, brain mass does not directly correlate with a person’s mental abilities, however, when brain mass decreases below 1000 g, a decrease in intelligence is natural.

Changes in the size, shape and mass of the brain during development are accompanied by changes in its internal structure. The structure of neurons and the form of interneuron connections become more complex, the white and gray matter become clearly demarcated, and various pathways of the brain are formed.

The development of the brain, like other systems, proceeds heterochronically (unevenly). Before others, those structures on which the normal functioning of the body depends at a given stage mature. age stage. Functional usefulness is achieved first by the stem, subcortical and cortical structures that regulate the autonomic functions of the body. These sections in their development approach the adult brain by the age of 2-4 years.

The structure of reflex arcs of spinal reflexes. The role of sensory, intermediate and motor neurons. General principles coordination of nerve centers at the level of the spinal cord. Types of spinal reflexes.

Reflex arcs- These are chains consisting of nerve cells.

The simplest reflex arc includes sensory and effector neurons, along which the nerve impulse moves from the place of origin (from the receptor) to the working organ (effector). Example the simplest reflex can serve knee reflex , which occurs in response to a short-term stretch of the quadriceps femoris muscle by a light blow to its tendon below the kneecap

(The body of the first sensitive (pseudo-unipolar) neuron is located in the spinal ganglion. The dendrite begins with a receptor that perceives external or internal irritation (mechanical, chemical, etc.) and converts it into a nerve impulse that reaches the body of the nerve cell. From the neuron body along the axon, the nerve impulse through the sensitive roots of the spinal nerves are sent to the spinal cord, where they form synapses with the bodies of effector neurons. At each interneuron synapse, with the help of biologically active substances (mediators), impulse transmission occurs. The axon of the effector neuron leaves the spinal cord as part of the anterior roots of the spinal nerves (motor or secretory nerve fibers) and is directed to the working organ, causing muscle contraction and increased (inhibited) gland secretion.)

More complex reflex arcs have one or more interneurons.

(The body of the interneuron in three-neuron reflex arcs is located in the gray matter rear pillars(horns) of the spinal cord and contacts the axon of the sensory neuron that comes as part of the posterior (sensitive) roots of the spinal nerves. The axons of interneurons are directed to the anterior columns (horns), where the bodies of effector cells are located. The axons of effector cells are directed to muscles and glands, affecting their function. The nervous system contains many complex multineural reflex arcs, which have several interneurons located in the gray matter of the spinal cord and brain.)

Intersegmental reflex connections. In the spinal cord, in addition to the reflex arcs described above, limited by one or several segments, ascending and descending intersegmental reflex pathways operate. The interneurons in them are the so-called propriospinal neurons , the bodies of which are located in the gray matter of the spinal cord, and the axons ascend or descend at various distances in the composition propriospinal tracts white matter, never leaving the spinal cord.

Intersegmental reflexes and these programs contribute to the coordination of movements triggered by different levels spinal cord, particularly the fore and hind limbs, limbs and neck.

Types of neurons.

Sensory (sensitive) neurons receive and transmit impulses from receptors “to the center”, i.e. central nervous system. That is, through them the signals go from the periphery to the center.

Motor (motor) neurons. They carry signals coming from the brain or spinal cord to the executive organs, which are muscles, glands, etc. in this case, the signals go from the center to the periphery.

Well, intermediate (intercalary) neurons receive signals from sensory neurons and send these impulses further to other intermediate neurons, or directly to motor neurons.

Principles of coordination activity of the central nervous system.

Coordination is ensured by selective excitation of some centers and inhibition of others. Coordination is the unification of the reflex activity of the central nervous system into a single whole, which ensures the implementation of all functions of the body. The following basic principles of coordination are distinguished:
1. The principle of irradiation of excitations. Neurons of different centers are interconnected by interneurons, so impulses arriving during strong and prolonged stimulation of receptors can cause excitation not only of the neurons of the center of a given reflex, but also of other neurons. For example, if you irritate one of the hind legs of a spinal frog, it contracts (defensive reflex); if the irritation is increased, then both hind legs and even the front legs contract.
2. The principle of a common final path. Impulses arriving in the central nervous system through different afferent fibers can converge to the same intercalary, or efferent, neurons. Sherrington called this phenomenon the “common final path principle.”
For example, motor neurons that innervate the respiratory muscles are involved in sneezing, coughing, etc. On the motor neurons of the anterior horns of the spinal cord, innervating the muscles of the limb, fibers of the pyramidal tract, extrapyramidal tracts, from the cerebellum, reticular formation and other structures end. The motor neuron, which provides various reflex reactions, is considered as their common final path.
3. The principle of dominance. It was discovered by A.A. Ukhtomsky, who discovered that irritation of the afferent nerve (or cortical center), which usually leads to contraction of the muscles of the limbs when the animal's intestines are full, causes an act of defecation. In this situation, the reflex excitation of the defecation center suppresses and inhibits the motor centers, and the defecation center begins to react to signals that are foreign to it. A.A. Ukhtomsky believed that at every given moment of life a defining (dominant) focus of excitation arises, subordinating the activity of the entire nervous system and determining the nature of the adaptive reaction. Excitations from various areas of the central nervous system converge to the dominant focus, and the ability of other centers to respond to signals coming to them is inhibited. Under natural conditions of existence, dominant excitation can cover entire systems of reflexes, resulting in food, defensive, sexual and other forms of activity. The dominant excitation center has a number of properties:
1) its neurons are characterized by high excitability, which promotes the convergence of excitations from other centers to them;
2) its neurons are able to summarize incoming excitations;
3) excitement is characterized by persistence and inertia, i.e. the ability to persist even when the stimulus that caused the formation of the dominant has ceased to act.
4. Principle feedback. The processes occurring in the central nervous system cannot be coordinated if there is no feedback, i.e. data on the results of function management. The connection between a system's output and its input with a positive gain is called positive feedback, and with a negative gain is called negative feedback. Positive feedback is mainly characteristic of pathological situations.
Negative feedback ensures the stability of the system (its ability to return to its original state). There are fast (nervous) and slow (humoral) feedbacks. Feedback mechanisms ensure the maintenance of all homeostasis constants.
5. The principle of reciprocity. It reflects the nature of the relationship between the centers responsible for the implementation of opposite functions (inhalation and exhalation, flexion and extension of the limbs), and lies in the fact that the neurons of one center, when excited, inhibit the neurons of the other and vice versa.
6. The principle of subordination(subordination). The main trend in the evolution of the nervous system is manifested in the concentration of the main functions in the higher parts of the central nervous system - cephalization of the functions of the nervous system. There are hierarchical relationships in the central nervous system - highest center regulation is the cerebral cortex, the basal ganglia, the middle, medulla oblongata and spinal cord obey its commands.
7. Function compensation principle. The central nervous system has a huge compensatory capacity, i.e. can restore some functions even after the destruction of a significant part of the neurons that form the nerve center. If individual centers are damaged, their functions can transfer to other brain structures, which is carried out when mandatory participation cerebral cortex.

Types of spinal reflexes.

Ch. Sherrington (1906) established the basic patterns of his reflex activity and identified the main types of reflexes he performs.

Actually muscle reflexes (tonic reflexes) occur when the stretch receptors of muscle fibers and tendon receptors are irritated. They appear in long-term stress muscles when they are stretched.

Defensive reflexes are represented by a large group of flexion reflexes that protect the body from the damaging effects of excessively strong and life-threatening stimuli.

Rhythmic reflexes manifest themselves in the correct alternation of opposite movements (flexion and extension), combined with tonic contraction of certain muscle groups (motor reactions of scratching and stepping).

Position reflexes (postural) are aimed at long-term maintenance of contraction of muscle groups that give the body posture and position in space.

The consequence of a transverse section between the medulla oblongata and the spinal cord is spinal shock. It is manifested by a sharp drop in excitability and inhibition of the reflex functions of all nerve centers located below the site of transection

Spinal cord. The spinal canal contains the spinal cord, which is conventionally divided into five sections: cervical, thoracic, lumbar, sacral and coccygeal.

31 pairs of spinal nerve roots arise from the SC. The SM has a segmental structure. A segment is considered to be a segment of CM corresponding to two pairs of roots. There are 8 segments in the cervical part, 12 in the thoracic part, 5 in the lumbar part, 5 in the sacral part, and from one to three in the coccygeal part.

The central part of the spinal cord contains gray matter. When cut, it looks like a butterfly or the letter H. The gray matter consists mainly of nerve cells and forms protrusions - the posterior, anterior and lateral horns. The anterior horns contain effector cells (motoneurons), the axons of which innervate skeletal muscles; in the lateral horns there are neurons of the autonomic nervous system.

Surrounding the gray matter is the white matter of the spinal cord. It is formed by nerve fibers of the ascending and descending tracts that connect different parts of the spinal cord with each other, as well as the spinal cord with the brain.

The white matter consists of 3 types of nerve fibers:

Motor - descending

Sensitive - ascending

Commissural - connects the 2 halves of the brain.

All spinal nerves are mixed, because formed from the fusion of the sensory (posterior) and motor (anterior) roots. On the sensory root before its merger with the motor root there is spinal ganglion, in which they are located sensory neurons, whose dendrites come from the periphery, and the axon enters the SC through the dorsal roots. The anterior root is formed by axons of motor neurons of the anterior horns of the SC.

Functions of the spinal cord:

1. Reflex – consists in the fact that reflex arcs of motor and autonomic reflexes are closed at different levels of the SC.

2. Conductive – ascending and descending pathways pass through the spinal cord, which connect all parts of the spinal cord and brain:

Ascending, or sensory, pathways pass in the posterior cord from tactile, temperature receptors, proprioceptors and pain receptors to various departments CM, cerebellum, brain stem, CGM;

Descending pathways that run in the lateral and anterior cords connect the cortex, brainstem, and cerebellum with motor neurons of the SC.

Reflex is the body's response to an irritant. The set of formations necessary for the implementation of the reflex is called a reflex arc. Any reflex arc consists of afferent, central and efferent parts.

Structural and functional elements of the somatic reflex arc:

Receptors are specialized formations that perceive the energy of stimulation and transform it into the energy of nervous excitation.

Afferent neurons, the processes of which connect receptors with nerve centers, provide centripetal conduction of excitation.

Nerve centers are a collection of nerve cells located at different levels of the central nervous system and involved in the implementation of a certain type of reflex. Depending on the level of location of the nerve centers, reflexes are distinguished: spinal (nerve centers are located in segments of the spinal cord), bulbar (in the medulla oblongata), mesencephalic (in the structures of the midbrain), diencephalic (in the structures of the diencephalon), cortical (in various areas of the cerebral cortex). brain).

Efferent neurons are nerve cells from which excitation spreads centrifugally from the central nervous system to the periphery, to the working organs.

Effectors, or executive organs, are muscles, glands, internal organs involved in reflex activity.

Types of spinal reflexes.

Most motor reflexes are carried out with the participation of spinal cord motor neurons.

Muscle reflexes themselves (tonic reflexes) occur when stretch receptors in muscle fibers and tendon receptors are stimulated. They manifest themselves in prolonged muscle tension when they are stretched.

Protective reflexes are represented by a large group of flexion reflexes that protect the body from the damaging effects of excessively strong and life-threatening stimuli.

Rhythmic reflexes are manifested in the correct alternation of opposite movements (flexion and extension), combined with tonic contraction of certain muscle groups (motor reactions of scratching and stepping).

Positional reflexes (postural) are aimed at long-term maintenance of contraction of muscle groups that give the body posture and position in space.

The consequence of a transverse section between the medulla oblongata and the spinal cord is spinal shock. It is manifested by a sharp drop in excitability and inhibition of the reflex functions of all nerve centers located below the site of transection.

The spinal cord is the most ancient department CNS. It is located in the spinal canal and has a segmental structure. The spinal cord is divided into cervical, thoracic, lumbar and sacral sections, each containing a different number of segments. Two pairs of roots extend from the segment - posterior and anterior (Fig. 3.11).

The dorsal roots are formed by the axons of primary afferent neurons, the bodies of which lie in the spinal sensory ganglia; the anterior roots consist of processes of motor neurons, they are directed to the corresponding effectors (Bell-Magendie law). Each root consists of many nerve fibers.

Rice. 3.11.

On cross section spinal cord (Fig. 3.12) it is clear that in the center there is gray matter, consisting of neuron bodies and resembling the shape of a butterfly, and along the periphery lies white matter, which is a system of neuronal processes: ascending (nerve fibers are directed to different departments brain) and descending (nerve fibers are sent to certain parts of the spinal cord).

Rice. 3.12.

• 1 - anterior horn gray matter; 2 - posterior horn of gray matter;
• 3 - lateral horn of gray matter; 4 - anterior root of the spinal cord; 5 - posterior root of the spinal cord.

The appearance and complication of the spinal cord is associated with the development of locomotion (movement). Locomotion, providing movement of a person or animal in environment, creates the possibility of their existence.

The spinal cord is the center of many reflexes. They can be divided into 3 groups: protective, vegetative and tonic.

• 1. Protective pain reflexes are characterized by the fact that the action of irritants, usually on the skin surface, causes a defensive reaction, which leads to the removal of the irritant from the surface of the body or the removal of the body or its parts from the irritant. Defensive reactions are expressed in withdrawing a limb or running away from the stimulus (flexion and extension reflexes). These reflexes are carried out segment by segment, but with more complex reflexes, such as scratching in hard-to-reach places, complex multi-segment reflexes arise.
• 2. Autonomic reflexes are provided by nerve cells located in the lateral horns of the spinal cord, which are the centers of the sympathetic nervous system. Here vasomotor, urinary reflexes, defecation reflexes, sweating, etc. are carried out.
• 3. Very important have tonic reflexes. They ensure the formation and preservation of skeletal muscle tone. Tone is a constant, invisible contraction (tension) of muscles without the phenomenon of fatigue. Tone ensures the posture and position of the body in space. Pose is fixed position body (head and other parts of the body) of a person or animal in space under conditions of gravity.

In addition, the spinal cord performs a conductive function, which is carried out by ascending and descending fibers of the white matter of the spinal cord (Table 3.1). The pathways contain both afferent and efferent fibers. Since some of these fibers conduct interoceptive impulses from internal organs, this allows them to be used for pain relief during intracavitary operations by introducing an anesthetic into the spinal canal (spinal anesthesia).

Table 3.1

Conducting tracts of the spinal cord and their physiological significance

Posterior spinocerebellar (Flexig's bundle)	Conducts impulses from proprioceptors of muscles, tendons, ligaments to the cerebellum; impulse is not conscious
Anterior spinocerebellar (Gowers bundle)
Lateral spinothalamic	Pain and temperature sensitivity
Anterior spinothalamic	Tactile sensitivity, touch, pressure
Descending (motor) tracts	Physiological significance
Lateral corticospinal (pyramidal)	Impulses to skeletal muscles, voluntary movements
Anterior corticospinal (pyramidal)
Rubrospinal (Monakov's bundle), runs in the lateral columns	Impulses that support tone skeletal muscles
Reticulospinal, runs in the anterior columns	Impulses that maintain skeletal muscle tone through excitatory and inhibitory effects on a- and umotoneurones, as well as regulating the state of spinal autonomic centers
Vestibulospinal, runs in the anterior columns	Impulses that maintain body posture and balance
Rectospinal, passes in the anterior columns	Impulses that ensure the implementation of visual and auditory motor reflexes (reflexes of the quadrigeminal region)

Age-related features of the spinal cord

The spinal cord develops before other parts of the central nervous system. During prenatal development and in the newborn, it fills the entire cavity of the spinal canal. The length of the spinal cord in a newborn is 14-16 cm. The growth in length of the axial cylinder and myelin sheath continues up to 20 years. It grows most intensively in the first year of life. However, its growth rate lags behind the growth of the spine. Therefore, by the end of the 1st year of life, the spinal cord is located at the level of the upper lumbar vertebrae, just like in an adult.

The growth of individual segments is uneven. The thoracic segments grow most intensively, the lumbar and sacral segments grow weaker. Cervical and lumbar thickenings appear already in the embryonic period. By the end of the 1st year of life and after 2 years, these thickenings reach their greatest development, which is associated with the development of the limbs and their motor activity.

Spinal cord cells begin to develop in utero, but development does not end after birth. In a newborn, the neurons that form the nuclei of the spinal cord are morphologically mature, but differ from an adult in being smaller in size and lacking pigment. In a newborn child, on a transverse section of the segments, the posterior horns predominate over the anterior horns. This indicates more developed sensory functions compared to motor ones. The ratio of these parts reaches adult levels by 7 years, but functional motor and sensory neurons continue to develop.

The diameter of the spinal cord is associated with the development of sensitivity, motor activity and pathways. After 12 years, the diameter of the spinal cord reaches adult levels.

Quantity cerebrospinal fluid in newborns it is less than in adults (40-60 g), and the protein content is higher. Subsequently, from 8-10 years, the amount of cerebrospinal fluid in children is almost the same as in adults, and the amount of proteins already from 6-12 months corresponds to the level of adults.

The reflex function of the spinal cord is formed already in the embryonic period, and its formation is stimulated by the movements of the child. From the 9th week, the fetus experiences generalized movements of the arms and legs (simultaneous contraction of the flexors and extensors) due to skin irritation. Tonic contraction of the flexor muscles predominates and forms the fetal position, ensuring its minimum volume in the uterus; periodic generalized contractions of the extensor muscles, starting from the 4-5th month of intrauterine life, are felt by the mother as fetal movement. After birth, reflexes appear that disappear gradually during ontogenesis:

• step reflex (movement of the legs when taking the child under the armpits);
• Babinski reflex (abduction thumb legs with irritation of the foot, disappears at the beginning of the 2nd year of life);
• knee reflex (flexion of the knee joint due to the predominance of flexor tone; converted to extensor in the 2nd month);
• grasping reflex (grasping and holding an object when touching the palm, disappears in the 3-4th month);
• grasping reflex (abducting the arms to the sides, then bringing them together when quickly raising and lowering the child, disappears after the 4th month);
• crawling reflex (when lying on the stomach, the child raises his head and makes crawling movements; if you place your palm on the soles, the child will begin to actively push off the obstacle with his feet, disappears by the 4th month);
• labyrinthine reflex (in the position of the child on his back, when the position of the head in space changes, the tone of the extensor muscles of the neck, back, legs increases; when turning over onto his stomach, the tone of the flexors of the neck, back, arms and legs increases);
• trunk-rectifier (when the child’s feet touch the support, straightening of the head is observed, which is formed by the 1st month);
• Landau reflex (upper - a child in a prone position raises his head and top part torso, resting on the plane with hands; lower - in the position on the stomach, the child extends and raises his legs; these reflexes are formed by the 5th-6th month), etc.

At first, the spinal cord reflexes are very imperfect, uncoordinated, generalized, the tone of the flexor muscles prevails over the tone of the extensors. Periods of physical activity prevail over periods of rest. Reflexogenic zones narrow towards the end of the 1st year of life and become more specialized.

As the body ages, the strength of reflex reactions decreases and the latent period increases, the cortical control of spinal reflexes decreases (the Babinski reflex and proboscis labial reflex appear again), and coordination of movements deteriorates due to a decrease in the strength and mobility of the main nervous processes.

Receptor fields of the spinal cord. Types of transmitted information. Main centers of the spinal cord. Spinal cord reflexes. Reflex arcs of simple and complex somatic reflexes of the spinal cord.

"All the endless variety external manifestations brain activity comes down to just one phenomenon - muscle movement."

THEM. Sechenov

The human spinal cord is the most ancient and primitive part of the central nervous system, retaining its morphological and functional segmentation in the most highly organized animals. In phylogenesis, there is a decrease in the specific weight of the spinal cord in relation to the total mass of the central nervous system. If in primitive vertebrates specific gravity spinal cord is almost 50%, then in humans its specific gravity is 2%. This is explained by the progressive development of the cerebral hemispheres, cephalization and corticalization of functions. In phylogeny, a stabilization of the number of spinal cord segments is also observed.

The reliability of the segmental functions of the spinal cord is ensured by the multiplicity of its connections with the periphery. The first feature of segmental innervation is that each segment of the spinal cord innervates 3 metameres (body segments) - its own, half of the overlying and half of the underlying segment. It turns out that each metamer receives innervation from three segments of the spinal cord. This ensures that the spinal cord performs its functions in case of damage to the brain and its roots. The second feature of segmental innervation is the excess of sensory fibers in the dorsal roots of the spinal cord compared to the number of motor fibers of the anterior roots (“Sherrington’s funnel”) in humans in a ratio of 5:1. With a large variety of incoming information from the periphery, the body uses a small number of executive structures to respond.

The total number of afferent fibers in humans reaches 1 million. They carry impulses from receptor fields:

1 - skin of the neck, torso and limbs;

2 - muscles of the neck, trunk and limbs;

3 - internal organs.

The thickest myelin fibers come from muscle and tendon receptors. Fibers of medium thickness come from tactile receptors of the skin, some muscle receptors and receptors of internal organs. Thin myelinated and unmyelinated fibers extend from pain and temperature receptors.

The total number of efferent fibers in humans is about 200 thousand. They carry impulses from the central nervous system to the executive organs (muscles and glands). the muscles of the neck, trunk, and limbs receive motor information, and the internal organs receive autonomic motor and secretory information.

The connection between the spinal cord and the periphery is ensured through the roots (posterior and anterior), which contain the fibers discussed above. The dorsal roots, which are sensitive in function, provide information input to the central nervous system. The anterior roots are motor and provide information output from the central nervous system.

The functions of the spinal roots have been elucidated using cutting and irritation methods. Bell and Magendie found that with unilateral transection of the dorsal roots, there is a loss of sensitivity, but motor function is preserved. Transection of the anterior roots leads to paralysis of the limbs of the corresponding side, and sensitivity is completely preserved.

Motor neurons in the spinal cord are excited by afferent impulses coming from receptor fields. The activity of motor neurons depends not only on the flow of afferent information, but also on complex intracentral relationships. Important role here the descending influences of the cerebral cortex, subcortical nuclei and reticular formation play, which correct spinal reflex reactions. Also great importance have numerous contacts of interneurons, among which a special role belongs to Renshaw inhibitory cells. By forming inhibitory synapses, they control the functioning of motor neurons and prevent their overexcitation. The flow of reverse afferentation impulses coming from muscle proprioceptors also interferes with the functioning of neurons.

The gray matter of the spinal cord contains about 13.5 million neurons. Of these, motor neurons make up only 3%, and the remaining 97% are interneurons. Among the spinal neurons there are:

1 - large a-motoneurons;

2 - small g-motoneurons.

From the former, thick fast-conducting fibers go to the skeletal muscles and cause motor acts. From the latter, thin, non-velocity fibers extend to muscle proprioceptors (Golgi spindles) and increase the sensitivity of muscle receptors that inform the brain about the execution of these movements.

The group of a-motoneurons that innervates a single skeletal muscle is called the motor nucleus.

Interneurons of the spinal cord, due to the richness of synaptic connections, provide their own integrative activities spinal cord, including control of complex motor acts.

The nuclei of the spinal cord are functionally the reflex centers of spinal reflexes.

In the cervical spinal cord is the center of the phrenic nerve, the center of pupil constriction. In the cervical and thoracic regions There are motor centers for the muscles of the upper limbs, chest, abdomen and back. In the lumbar region there are centers of the muscles of the lower extremities. The sacral region contains the centers for urination, defecation and sexual activity. In the lateral horns of the thoracic and lumbar regions there are sweating centers and vasomotor centers.

The reflex arcs of individual reflexes are closed through certain segments of the spinal cord. By observing a disturbance in the activity of certain muscle groups, certain functions, it is possible to determine which part or segment of the spinal cord is affected or damaged.

Spinal reflexes can be studied in pure form after separation of the spinal cord and brain. Spinal laboratory animals immediately after transection fall into a state of spinal shock, which lasts several minutes (in a frog), several hours (in a dog), several weeks (in a monkey), and in humans lasts for months. In lower vertebrates (frogs), spinal reflexes ensure the preservation of posture, movements, defensive, sexual and other reactions. In higher vertebrates, without the participation of the centers of the brain and the Russian Federation, the spinal cord is not able to fully perform these functions. A spinal cat or dog cannot stand or walk on its own. They experience a sharp drop in excitability and depression of the functions of centers lying below the site of transection. This is the price of cephalization of functions, the subordination of spinal reflexes to the centers of the brain. After recovery from spinal shock, skeletal muscle reflexes, regulation of blood pressure, urination, defecation, and a number of sexual reflexes are gradually restored. Voluntary movements, sensitivity, body temperature and breathing are not restored - their centers lie above the spinal cord and are isolated when cut. Spinal animals can only live under conditions of mechanical ventilation (artificial ventilation).

Studying the properties of reflexes in spinal animals, Sherrington in 1906 established the patterns of reflex activity and identified the main types of spinal reflexes:

1 - protective (defensive) reflexes;

2 - muscle stretch reflexes (myotatic);

3 - intersegmental reflexes of coordination of movements;

4 - autonomic reflexes.

Despite the functional dependence of the spinal centers on the brain, many spinal reflexes occur autonomously, with little subordination to the control of consciousness. For example, tendon reflexes, which are used in medical diagnostics:

All these reflexes have a simple two-neuron (homonymous) reflex arc.

Skin-muscular reflexes have a three-neuron (heteronymous) reflex arc.

Conclusion: The spinal cord has important functional significance. Performing conductive and reflex functions, it is a necessary link in the nervous system in coordinating complex movements (human movement, work activity) and autonomic functions.