Physiology of the reflex activity of the spinal cord. Anatomical and physiological features of the spinal cord

Lecture 19 nervous system

The spinal cord is a nerve cord about 45 cm long in men and about 42 cm in women. It has a segmental structure (31 - 33 segments) - each of its sections is associated with a certain metameric segment of the body. The spinal cord is anatomically divided into five sections: cervical thoracic lumbar sacral and coccygeal.

The total number of neurons in the spinal cord approaches 13 million. Most of them (97%) are interneurons, 3% are efferent neurons.

Efferent neurons spinal cord related to the somatic nervous system are motor neurons. There are α- and γ-motor neurons. α-Motoneurons innervate extrafusal (working) muscle fibers of skeletal muscles, which have a high speed of excitation along axons (70-120 m/s, group A α).

γ -Motoneurons dispersed among α-motor neurons, they innervate the intrafusal muscle fibers of the muscle spindle (muscle receptor).

Their activity is regulated by messages from the overlying parts of the central nervous system. Both types of motoneurons are involved in the mechanism of α-γ-coupling. Its essence is that when the contractile activity of intrafusal fibers changes under the influence of γ-motoneurons, the activity of muscle receptors changes. Impulse from muscle receptors activates α-moto-neurons of the “own” muscle and inhibits α-moto-neurons of the antagonist muscle.

In these reflexes, the role of the afferent link is especially important. Muscle spindles (muscle receptors) are located parallel to the skeletal muscle with their ends attached to the connective tissue sheath of the bundle of extrafusal muscle fibers with tendon-like strips. The muscle receptor consists of several striated intrafusal muscle fibers surrounded by a connective tissue capsule. Around the middle part of the muscle spindle, the end of one afferent fiber wraps several times.

Tendon receptors (Golgi receptors) are enclosed in a connective tissue capsule and are localized in the tendons of skeletal muscles near the tendon-muscle junction. The receptors are non-myelinated endings of a thick myelinated afferent fiber (having approached the Golgi receptor capsule, this fiber loses its myelin sheath and divides into several endings). Tendon receptors are attached sequentially relative to the skeletal muscle, which ensures their irritation when the tendon is pulled. Therefore, tendon receptors send information to the brain that the muscle is contracted (tension and tendon), and muscle receptors that the muscle is relaxed and lengthened. Impulses from tendon receptors inhibit the neurons of their center and excite the neurons of the antagonist center (in flexor muscles, this excitation is less pronounced).

Thus, skeletal muscle tone and motor responses are regulated.

Afferent neurons of the somatic nervous system are localized in the spinal sensory nodes. They have T-shaped processes, one end of which goes to the periphery and forms a receptor in the organs, and the other goes to the spinal cord through the dorsal root and forms a synapse with the upper plates. gray matter spinal cord. The system of intercalary neurons (interneurons) ensures the closure of the reflex at the segmental level or transmits impulses to the suprasegmental areas of the CNS.

Neurons of the sympathetic nervous system are also intercalary; located in the lateral horns of the thoracic, lumbar and partially cervical spinal cord. They are background-active, the frequency of their discharges is 3-5 imp/s. Neurons of the parasympathetic division of the autonomic nervous system are also intercalary, localized in the sacral spinal cord and also background-active.

The spinal cord contains the control centers for most internal organs and skeletal muscles.

Myotatic and tendon reflexes of the somatic nervous system, elements of the stepping reflex, control of the inspiratory and expiratory muscles are localized here.

The spinal centers of the sympathetic division of the autonomic nervous system control the pupillary reflex, regulate the activities of the heart, blood vessels, kidneys, and organs of the digestive system.

The spinal cord has a conductive function.

It is carried out with the help of descending and ascending paths.

Afferent information enters the spinal cord through the posterior roots, efferent impulses and regulation of the functions of various organs and tissues of the body are carried out through the anterior roots (Bell-Magendie law).

Each root is a set nerve fibers. For example, the dorsal root of a cat includes 12 thousand, and the ventral root - 6 thousand nerve fibers.

All afferent inputs to the spinal cord carry information from three groups of receptors:

1) skin receptors - pain, temperature, touch, pressure, vibration receptors;

2) proprioceptors - muscle (muscle spindles), tendon (Golgi receptors), periosteum and joint membranes;

3) receptors of internal organs - visceral, or interoreceptors. reflexes.

In each segment of the spinal cord there are neurons that give rise to ascending projections to the higher structures of the nervous system. The structure of the Gaulle, Burdach, spinocerebellar and spinothalamic pathways are well covered in the course of anatomy.

The spinal cord is the most ancient formation of the CNS. A characteristic feature of the structure is segmentation.

The neurons of the spinal cord form it Gray matter in the form of anterior and posterior horns. They perform a reflex function of the spinal cord.

The posterior horns contain neurons (interneurons) that transmit impulses to the overlying centers, to the symmetrical structures of the opposite side, to the anterior horns of the spinal cord. The posterior horns contain afferent neurons that respond to pain, temperature, tactile, vibration, and proprioceptive stimuli.

The anterior horns contain neurons (motoneurons) that give axons to the muscles, they are efferent. All descending pathways of the CNS for motor reactions terminate in the anterior horns.

In the lateral horns of the cervical and two lumbar segments there are neurons of the sympathetic division of the autonomic nervous system, in the second-fourth segments - of the parasympathetic.

The spinal cord contains many intercalary neurons that provide communication with the segments and with the overlying parts of the CNS; they account for 97% of the total number of spinal cord neurons. They include associative neurons - neurons of the spinal cord's own apparatus, they establish connections within and between segments.

white matter the spinal cord is formed by myelin fibers (short and long) and performs a conductive role.

Short fibers connect neurons of one or different segments of the spinal cord.

Long fibers (projection) form the pathways of the spinal cord. They form ascending pathways to the brain and descending pathways from the brain.

The spinal cord performs reflex and conduction functions.

The reflex function allows you to realize all the motor reflexes of the body, reflexes of internal organs, thermoregulation, etc. Reflex reactions depend on the location, strength of the stimulus, the area of ​​​​the reflexogenic zone, the speed of the impulse through the fibers, and the influence of the brain.

Reflexes are divided into:

1) exteroceptive (occur when irritated by environmental agents of sensory stimuli);

2) interoceptive (occur when irritated by presso-, mechano-, chemo-, thermoreceptors): viscero-visceral - reflexes from one internal organ to another, viscero-muscular - reflexes from internal organs to skeletal muscles;

3) proprioceptive (own) reflexes from the muscle itself and its associated formations. They have a monosynaptic reflex arc. Proprioceptive reflexes regulate motor activity due to tendon and postural reflexes. Tendon reflexes (knee, Achilles, with the triceps of the shoulder, etc.) occur when the muscles are stretched and cause relaxation or contraction of the muscle, occur with every muscle movement;

4) postural reflexes (occur when the vestibular receptors are excited when the speed of movement and the position of the head relative to the body change, which leads to a redistribution of muscle tone (increase in extensor tone and decrease in flexors) and ensures body balance).

The study of proprioceptive reflexes is performed to determine the excitability and degree of damage to the central nervous system.

The conduction function ensures the connection of the neurons of the spinal cord with each other or with the overlying sections of the central nervous system.

Structural formations of the hindbrain.

1. V–XII pair cranial nerves.

2. Vestibular nuclei.

3. Kernels of the reticular formation.

The main functions of the hindbrain are conductive and reflex.

Descending pathways pass through the hindbrain (corticospinal and extrapyramidal), ascending - reticulo- and vestibulospinal, responsible for the redistribution muscle tone and maintaining body posture.

The reflex function provides:

1) protective reflexes (lacrimation, blinking, coughing, vomiting, sneezing);

3) posture maintenance reflexes (labyrinth reflexes). Static reflexes maintain muscle tone to maintain body posture, statokinetic ones redistribute muscle tone to take a pose corresponding to the moment of rectilinear or rotational movement;

4) centers located in the hindbrain regulate the activity of many systems.

The vascular center regulates vascular tone, the respiratory center regulates inhalation and exhalation, the complex food center regulates the secretion of gastric, intestinal glands, pancreas, liver secretory cells, salivary glands, provides reflexes of sucking, chewing, swallowing.

Damage to the hindbrain leads to loss of sensitivity, volitional motility, thermoregulation, but respiration, magnitude blood pressure, reflex activity is preserved.

Structural units of the midbrain:

1) tubercles of the quadrigemina;

2) red core;

3) black core;

4) nuclei of the III-IV pair of cranial nerves.

The tubercles of the quadrigemina perform an afferent function, the rest of the formations perform an efferent function.

The tubercles of the quadrigemina closely interact with the nuclei of III-IV pairs of cranial nerves, the red nucleus, with the optic tract. Due to this interaction, the anterior tubercles provide an orienting reflex reaction to light, and the posterior tubercles to sound. They provide vital reflexes: a start reflex is a motor reaction to a sharp unusual stimulus (increased flexor tone), a landmark reflex is a motor reaction to a new stimulus (turning the body, head).

The anterior tubercles with the nuclei of the III-IV cranial nerves provide a convergence reaction (convergence eyeballs to midline), movement of the eyeballs.

The red nucleus takes part in the regulation of the redistribution of muscle tone, in restoring the body posture (increases the tone of the flexors, lowers the tone of the extensors), maintains balance, and prepares the skeletal muscles for voluntary and involuntary movements.

The substantia nigra of the brain coordinates the act of swallowing and chewing, breathing, blood pressure (the pathology of the substantia nigra of the brain leads to an increase in blood pressure).

The diencephalon consists of the thalamus and hypothalamus, they connect the brain stem with the cerebral cortex.

thalamus- a paired formation, the largest accumulation of gray matter in the diencephalon.

Topographically, the anterior, middle, posterior, medial and lateral groups of nuclei are distinguished.

By function, they are distinguished:

1) specific:

a) switching, relay. They receive primary information from various receptors. The nerve impulse along the thalamocortical tract goes to a strictly limited area of ​​the cerebral cortex (primary projection zones), due to this, specific sensations arise. The nuclei of the ventrabasal complex receive an impulse from skin receptors, tendon proprioceptors, and ligaments. The impulse is sent to the sensorimotor zone, the body orientation in space is regulated. The lateral nuclei switch the impulse from the visual receptors to the occipital visual zone. Medial nuclei respond to a strictly defined length sound wave and conduct an impulse to the temporal zone;

b) associative (internal) nuclei. The primary impulse comes from the relay nuclei, is processed (an integrative function is carried out), transmitted to the associative zones of the cerebral cortex, the activity of the associative nuclei increases under the action of a painful stimulus;

2) non-specific nuclei. This is a non-specific way of transmitting impulses to the cerebral cortex, the frequency of the biopotential changes (modeling function);

3) motor nuclei involved in the regulation of motor activity. Impulses from the cerebellum, basal nuclei go to the motor zone, carry out the relationship, consistency, sequence of movements, spatial orientation of the body.

The thalamus is a collector of all afferent information, except for olfactory receptors, the most important integrative center.

Hypothalamus located on the bottom and sides of the third ventricle of the brain. Structures: gray tubercle, funnel, mastoid bodies. Zones: hypophysiotropic (preoptic and anterior nuclei), medial (middle nuclei), lateral (outer, posterior nuclei).

Physiological role - the highest subcortical integrative center of the autonomic nervous system, which has an effect on:

1) thermoregulation. The anterior nuclei are the center of heat transfer, where the process of sweating, respiratory rate and vascular tone are regulated in response to an increase in temperature. environment. The posterior nuclei are the center of heat production and the preservation of heat when the temperature drops;

2) pituitary. Liberins promote the secretion of hormones of the anterior pituitary gland, statins inhibit it;

3) fat metabolism. Irritation of the lateral (nutrition center) nuclei and ventromedial (satiation center) nuclei leads to obesity, inhibition leads to cachexia;

4) carbohydrate metabolism. Irritation of the anterior nuclei leads to hypoglycemia, the posterior nuclei to hyperglycemia;

5) cardiovascular system. Irritation of the anterior nuclei has an inhibitory effect, the posterior nuclei - an activating one;

6) motor and secretory functions of the gastrointestinal tract. Irritation of the anterior nuclei increases motility and secretory function of the gastrointestinal tract, while the posterior nuclei inhibit sexual function. The destruction of the nuclei leads to a violation of ovulation, spermatogenesis, a decrease in sexual function;

7) behavioral responses. Irritation of the starting emotional zone (front nuclei) causes a feeling of joy, satisfaction, erotic feelings, the stop zone (rear nuclei) causes fear, a feeling of anger, rage.

Reticular formation of the brain stem- accumulation of polymorphic neurons along the brain stem.

Physiological feature of neurons of the reticular formation:

1) spontaneous bioelectrical activity. Its causes are humoral irritation (increase in the level of carbon dioxide, biologically active substances);

2) sufficiently high excitability of neurons;

3) high sensitivity to biologically active substances.

The reticular formation has wide bilateral connections with all parts of the nervous system, according to its functional significance and morphology it is divided into two parts:

1) rastral (ascending) department - reticular formation of the diencephalon;

2) caudal (descending) - the reticular formation of the posterior, midbrain, bridge.

The physiological role of the reticular formation is the activation and inhibition of brain structures.

limbic system- a collection of nuclei and nerve tracts.

Structural units of the limbic system:

1) olfactory bulb;

2) olfactory tubercle;

3) transparent partition;

4) hippocampus;

5) parahippocampal gyrus;

6) almond-shaped nuclei;

7) piriform gyrus;

8) dentate fascia;

9) cingulate gyrus.

The main functions of the limbic system:

1) participation in the formation of food, sexual, defensive instincts;

2) regulation of vegetative-visceral functions;

3) the formation of social behavior;

4) participation in the formation of the mechanisms of long-term and short-term memory;

5) performance of the olfactory function;

6) inhibition of conditioned reflexes, strengthening of unconditioned ones;

7) participation in the formation of the wake-sleep cycle.

Significant formations of the limbic system are:

1) hippocampus. Its damage leads to a disruption in the process of memorization, information processing, a decrease in emotional activity, initiative, a slowdown in the speed of nervous processes, irritation - to an increase in aggression, defensive reactions, and motor function. Hippocampal neurons are characterized by high background activity. In response to sensory stimulation, up to 60% of neurons react, the generation of excitation is expressed in a long-term reaction to a single short impulse;

2) almond-shaped nuclei. Their damage leads to the disappearance of fear, inability to aggression, hypersexuality, reactions of care for offspring, irritation - to a parasympathetic effect on the respiratory and cardiovascular, digestive system. The neurons of the amygdala nuclei have a pronounced spontaneous activity, which is inhibited or enhanced by sensory stimuli;

3) olfactory bulb, olfactory tubercle.

The limbic system has a regulatory effect on the cerebral cortex.

The highest department of the central nervous system is the cerebral cortex, its area is 2200 cm 2.

The cerebral cortex has a five-, six-layer structure. Neurons are represented by sensory, motor (Betz cells), interneurons (inhibitory and excitatory neurons).

The cerebral cortex is built according to the columnar principle. Columns are functional units of the cortex, divided into micromodules that have homogeneous neurons.

According to IP Pavlov's definition, the cerebral cortex is the main manager and distributor of body functions.

The main functions of the cerebral cortex:

1) integration (thinking, consciousness, speech);

2) ensuring the connection of the organism with the external environment, its adaptation to its changes;

3) clarification of the interaction between the body and systems within the body;

4) coordination of movements (the ability to carry out voluntary movements, to make involuntary movements more accurate, to carry out motor tasks).

These functions are provided by corrective, triggering, integrative mechanisms.

I. P. Pavlov, creating the doctrine of analyzers, distinguished three sections: peripheral (receptor), conductive (three-neural pathway for transmitting impulses from receptors), brain (certain areas of the cerebral cortex, where the processing of a nerve impulse takes place, which acquires a new quality ). The brain section consists of the analyzer nuclei and scattered elements.

According to modern ideas On the localization of functions during the passage of an impulse in the cerebral cortex, three types of fields arise.

1. The primary projection zone lies in the region of the central section of the analyzer nuclei, where the electrical response (evoked potential) first appeared, disturbances in the region of the central nuclei lead to a violation of sensations.

2. The secondary zone lies in the environment of the nucleus, is not associated with receptors, the impulse comes through the intercalary neurons from the primary projection zone. Here, a relationship is established between phenomena and their qualities, violations lead to a violation of perceptions (generalized reflections).

3. The tertiary (associative) zone has multisensory neurons. The information has been revised to meaningful. The system is capable of plastic restructuring, long-term storage of traces of sensory action. In case of violation, the form of abstract reflection of reality, speech, purposeful behavior suffer.

Collaboration of the cerebral hemispheres and their asymmetry.

There are morphological prerequisites for the joint work of the hemispheres. The corpus callosum provides a horizontal connection with the subcortical formations and the reticular formation of the brain stem. Thus, the friendly work of the hemispheres is carried out and reciprocal innervation when working together.

functional asymmetry. Speech, motor, visual and auditory functions dominate in the left hemisphere. The thinking type of the nervous system is left hemisphere, and the artistic type is right hemisphere.

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

The posterior roots are formed by 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 is a set of nerve fibers.

Rice. 3.11.

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

Rice. 3.12.

• 1 - anterior horn of 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 the movement of a person or animal in the 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 stimuli, as a rule, on the skin surface, causes a protective reaction, which leads to the removal of the stimulus from the surface of the body or the removal of the body or its parts from the stimulus. Protective reactions are expressed in the withdrawal of a limb or running away from a 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. Vegetative reflexes are provided nerve cells located in the lateral horns of the spinal cord, which are the centers of the sympathetic nervous system. Here, vasomotor, urethral reflexes, defecation reflexes, sweating, etc.
• 3. Very importance have tonic reflexes. They provide the formation and maintenance of skeletal muscle tone. Tone is a constant, invisible contraction (tension) of the muscles without fatigue. The tone provides the posture and position of the body in space. A posture is a fixed position of the body (head and other parts of the body) of a person or animals in space under the 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). As part of the conducting paths, both afferent and efferent fibers pass. Since some of these fibers conduct interoceptive impulses from the 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

The conduction pathways of the spinal cord and their physiological significance

Age features of the spinal cord

The spinal cord develops earlier than other parts of the CNS. During fetal 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 lasts up to 20 years. It grows most intensively in the first year of life. However, the rate of its growth 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 as 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 maximum 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 their smaller size and lack of pigment. In a newborn child, in the 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 the level of adults by the age of 7, however, functionally 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 the adult level.

The amount of cerebrospinal fluid in newborns is less than in adults (40-60 g), and the protein content is higher. In the future, from 8-10 years old, 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 has generalized movements of the arms and legs (simultaneous contraction of the flexors and extensors) with skin irritation. The tonic contraction of the flexor muscles predominates and forms the posture of the fetus, providing 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, which gradually disappear in ontogenesis:

• stepping reflex (movement of the legs when taking the child under the armpits);
• Babinski's reflex (abduction thumb legs with irritation of the foot, disappears at the beginning of the 2nd year of life);
• knee jerk (flexion knee joint due to the predominance of flexor tone; is transformed into extensor on the 2nd month);
• grasping reflex (grasping and holding an object when touching the palm, disappears on the 3-4th month);
• the grasping reflex (bringing the arms to the sides, then bringing them together with the rapid lifting and lowering of the child, disappears after the 4th month);
• crawling reflex (in the position lying on his stomach, the child raises his head and makes crawling movements; if you put your palm on the soles, the child will begin to actively push off the obstacle with his feet, disappears by the 4th month);
• labyrinth reflex (in the position of the child on the back, when the position of the head in space changes, the tone of the muscles of the extensor muscles of the neck, back, legs increases; when turning over on the stomach, the tone of the flexors of the neck, back, arms and legs increases);
• torso-rectifying (when the child's feet come into contact with the support, the head is straightened, it is formed by the 1st month);
• Landau reflex (upper - a child in a position on his stomach raises his head and upper body, leaning on a plane with his hands; lower - in a position on his stomach, the child unbends and raises his legs; these reflexes are formed by the 5-6th month), etc.

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

With the aging of the body, there is a decrease in the strength and an increase in the latent period of reflex reactions, the cortical control of spinal reflexes decreases (the Babinski reflex appears again, the proboscis labial reflex), coordination of movements worsens due to a decrease in the strength and mobility of the main nervous processes.

The spinal cord is the most important element of the nervous system, located inside the spinal column. Anatomically, the upper end of the spinal cord is connected to the brain, providing its peripheral sensitivity, and at the other end there is a spinal cone that marks the end of this structure.

The spinal cord is located in the spinal canal, which reliably protects it from external damage, and in addition, it allows normal stable blood supply to all tissues of the spinal cord along its entire length.

Anatomical structure

The spinal cord is perhaps the most ancient nervous formation inherent in all vertebrates. The anatomy and physiology of the spinal cord make it possible not only to ensure the innervation of the whole body, but also the stability and security of this element of the nervous system. In humans, the spine has a lot of features that distinguish it from all other vertebrate creatures living on the planet, which is largely due to the processes of evolution and the acquisition of the ability to walk upright.

In adult men, the length of the spinal cord is about 45 cm, while in women the length of the spine is on average 41 cm. The average mass of the spinal cord of an adult ranges from 34 to 38 g, which is approximately 2% of the total mass of the brain .

The anatomy and physiology of the spinal cord is complex, so any injury has systemic consequences. The anatomy of the spinal cord includes a significant number of elements that provide the function of this nervous formation. It should be noted that, despite the fact that the brain and spinal cord are conditionally different elements of the human nervous system, it should still be noted that the border between the spinal cord and the brain, passing at the level of pyramidal fibers, is very conditional. In fact, the spinal cord and brain are an integral structure, so it is very difficult to consider them separately.

The spinal cord has a hollow canal inside, which is commonly called the central canal. The space that exists between the membranes of the spinal cord, between the white and gray matter, is filled with cerebrospinal fluid, which is known in medical practice as cerebrospinal fluid. Structurally, the organ of the central nervous system in the context has the following parts and structure:

• white matter;
• Gray matter;
• back spine;
• nerve fibers;
• front spine;
• ganglion.

Considering the anatomical features of the spinal cord, it is necessary to note a rather powerful defense system that does not end at the level of the spine. The spinal cord has its own protection, consisting of 3 membranes at once, which, although it looks vulnerable, still ensures the preservation of not only the entire structure from mechanical damage, but also various pathogenic organisms. The organ of the central nervous system is covered with 3 shells, which have the following names:

• soft shell;
• arachnoid;
• hard shell.

The space between the uppermost hard shell and the hard bone and cartilage structures of the spine surrounding the spinal canal is filled with blood vessels and adipose tissue, which helps maintain the integrity of neurons during movement, falls and other potentially dangerous situations.

In cross section, sections taken in different parts of the column make it possible to reveal the heterogeneity of the spinal cord in different parts of the spine. It is worth noting that, considering the anatomical features, one can immediately note the presence of a certain segmentation comparable to the structure of the vertebrae. The anatomy of the human spinal cord has the same division into segments, like the entire spine. The following anatomical parts are distinguished:

• cervical;
• chest;
• lumbar;
• sacral;
• coccygeal.

The correlation of one or another part of the spine with one or another segment of the spinal cord does not always depend on the location of the segment. The principle of determining one or another segment to one or another part is the presence of radicular branches in one or another part of the spine.

In the cervical part, the human spinal cord has 8 segments, in the thoracic part - 12, in the lumbar and sacral parts there are 5 segments each, while in the coccygeal part - 1 segment. Since the coccyx is a rudimentary tail, anatomical anomalies in this area are not uncommon, in which the spinal cord in this part is located not in one segment, but in three. In these cases, a person has a greater number of dorsal roots.

If there are no anatomical developmental anomalies, in an adult, exactly 62 roots depart from the spinal cord, and 31 on one side of the spinal column and 31 on the other. The entire length of the spinal cord has a non-uniform thickness.

In addition to the natural thickening in the area of ​​​​the connection of the brain with the spinal cord, and in addition, the natural decrease in thickness in the coccyx area, thickenings are also distinguished in the cervical region and the lumbosacral joint.

Basic physiological functions

Each of the elements of the spinal cord performs its own physiological functions and has its own anatomical features. Consideration of the physiological characteristics of the interaction of different elements is best to start with the cerebrospinal fluid.

The cerebrospinal fluid, known as cerebrospinal fluid, performs a number of extremely important functions that support the vital activity of all elements of the spinal cord. Liquor performs the following physiological functions:

• maintenance of somatic pressure;
• maintenance of salt balance;
• protection of spinal cord neurons from traumatic injury;
• creation of a nutrient medium.

The spinal nerves are directly connected to the nerve endings that provide innervation to all tissues of the body. Control over reflex and conductive functions is carried out different types neurons that make up the spinal cord. Since the neuronal organization is extremely complex, a classification of the physiological functions of various classes of nerve fibers was compiled. Classification is carried out according to the following criteria:

1. Department of the nervous system. This class includes neurons of the autonomic and somatic nervous systems.
2. By appointment. All neurons located in the spinal cord are divided into intercalary, associative, afferent efferent.
3. In terms of influence. All neurons are divided into excitatory and inhibitory.

Gray matter

white matter

• posterior longitudinal beam;

• wedge-shaped bundle;
• thin bundle.

Features of the blood supply

The spinal cord is the most important part of the nervous system, so this organ has a very powerful and branched blood supply system that provides it with all the nutrients and oxygen. The blood supply to the spinal cord is provided by the following large blood vessels:

• vertebral artery originating in the subclavian artery;
• branch of the deep cervical artery;
• lateral sacral arteries;
• intercostal lumbar artery;
• anterior spinal artery;
• posterior spinal arteries (2 pcs.).

In addition, the spinal cord literally envelops a network of small veins and capillaries that contribute to the continuous nutrition of neurons. With a cut of any segment of the spine, one can immediately note the presence of an extensive network of small and large blood vessels. Nerve roots have blood arterial veins accompanying them, and each root has its own blood branch.

The blood supply to the branches of the blood vessels originates from the large arteries that supply the column. Among other things, the blood vessels that feed the neurons also feed the elements of the spinal column, so all these structures are connected by a single circulatory system.

When considering the physiological characteristics of neurons, one has to admit that each class of neurons is in close interaction with the other classes. So, as already noted, there are 4 main types of neurons according to their purpose, each of which performs its function in the overall system and interacts with other types of neurons.

1. Insertion. Neurons belonging to this class are intermediate and serve to ensure interaction between afferent and efferent neurons, as well as with the brain stem, through which impulses are transmitted to the human brain.
2. Associative. Neurons belonging to this species are an independent operating apparatus that provides interaction between different segments within the existing spinal segments. Thus, associative neurons are controlling for such parameters as muscle tone, coordination of body position, movements, etc.
3. Efferent. Neurons belonging to the efferent class perform somatic functions, since their main task is to innervate the main organs working group i.e. skeletal muscle.
4. Afferent. Neurons belonging to this group perform somatic functions, but at the same time provide innervation of tendons, skin receptors, and, in addition, provide sympathetic interaction in efferent and intercalary neurons. Most of the afferent neurons are located in the ganglia of the spinal nerves.

Different types of neurons form entire pathways that serve to maintain the connection of the human spinal cord and brain with all tissues of the body.

In order to understand exactly how the transmission of impulses occurs, one should consider the anatomical and physiological features of the main elements, that is, gray and white matter.

Gray matter

The gray matter is the most functional. When the column is cut, it is clear that the gray matter is located inside the white and has the appearance of a butterfly. In the very center of the gray matter is the central channel, through which the circulation of cerebrospinal fluid is observed, providing its nutrition and maintaining balance. Upon closer examination, 3 main departments can be distinguished, each of which has its own special neurons that provide certain functions:

1. Front area. This area contains motor neurons.
2. Back area. The posterior region of the gray matter is a horn-shaped branch that has sensory neurons.
3. Side area. This part of the gray matter is called the lateral horns, since it is this part that branches out strongly and gives rise to the spinal roots. The neurons of the lateral horns give rise to the autonomic nervous system, and also provide innervation to all internal organs and chest, abdominal cavity and pelvic organs.

The anterior and posterior regions do not have clear boundaries and literally merge with each other, forming a complex spinal nerve.

Among other things, the roots extending from the gray matter are components of the anterior roots, the other component of which is the white matter and other nerve fibers.

white matter

White matter literally envelops gray matter. The mass of white matter is about 12 times the mass of gray matter. The grooves present in the spinal cord serve to symmetrically divide the white matter into 3 cords. Each of the cords provides its physiological functions in the structure of the spinal cord and has its own anatomical features. The cords of the white matter received the following names:

1. Posterior funiculus of white matter.
2. Anterior funiculus of white matter.
3. Lateral funiculus of white matter.

Each of these cords includes combinations of nerve fibers that form bundles and paths necessary for the regulation and transmission of certain nerve impulses.

The anterior funiculus of the white matter includes the following pathways:

• anterior cortical-spinal (pyramidal) path;
• reticular-spinal path;
• anterior spinothalamic pathway;
• occlusal-spinal tract;
• posterior longitudinal beam;
• vestibulo-spinal tract.

The posterior funiculus of the white matter includes the following pathways:

• medial spinal tract;
• wedge-shaped bundle;
• thin bundle.

The lateral funiculus of the white matter includes the following pathways:

• red nuclear-spinal path;
• lateral cortical-spinal (pyramidal) path;
• posterior spinal cerebellar path;
• anterior dorsal tract;
• lateral dorsal-thalamic pathway.

There are other ways of conducting nerve impulses of different directions, but at present, not all atomic and physiological features of the spinal cord have been studied well enough, since this system is no less complex than the human brain.

I. Structural and functional characteristics.

The spinal cord is a cord 45 cm long in men and about 42 cm in women. It has a segmental structure (31-33 segments). Each of its segments is associated with a specific part of the body. The spinal cord includes five sections: cervical (C 1 -C 8), thoracic (Th 1 -Th 12), lumbar (L 1 -L 5), sacral (S 1 -S 5) and coccygeal (Co 1 -Co 3) . In the process of evolution, two thickenings formed in the spinal cord: cervical (segments innervating upper limbs) and lumbosacral (segments innervating the lower limbs) as a result of increased load on these departments. In these thickenings, the somatic neurons are the largest, there are more of them, in each root of these segments there are more nerve fibers, they have the greatest thickness. The total number of spinal cord neurons is about 13 million. Of these, 3% are motor neurons, 97% are intercalary neurons, of which some are neurons that belong to the autonomic nervous system.

Classification of spinal cord neurons

Spinal cord neurons are classified according to the following criteria:

1) in the department of the nervous system (neurons of the somatic and autonomic nervous system);

2) by appointment (efferent, afferent, intercalary, associative);

3) by influence (excitatory and inhibitory).

1. Efferent neurons of the spinal cord, related to the somatic nervous system, are effector, since they directly innervate the working organs - effectors (skeletal muscles), they are called motor neurons. There are ά- and γ-motoneurons.

ά-motoneurons innervate extrafusal muscle fibers (skeletal muscles), their axons are characterized by a high speed of excitation conduction - 70-120 m/s. ά-Motoneurons are divided into two subgroups: ά 1 - fast, innervating fast white muscle fibers, their lability reaches 50 imp/s, and ά 2 - slow, innervating slow red muscle fibers, their lability is 10-15 imp/s. The low lability of ά-motoneurons is explained by the long-term trace hyperpolarization that accompanies PD. On one ά-motoneuron, there are up to 20 thousand synapses: from skin receptors, proprioreceptors and descending pathways of the overlying parts of the CNS.

γ-motoneurons are scattered among ά-motoneurons, their activity is regulated by neurons of the overlying sections of the central nervous system, they innervate the intrafusal muscle fibers of the muscle spindle (muscle receptor). When the contractile activity of intrafusal fibers changes under the influence of γ-motoneurons, the activity of muscle receptors changes. Impulse from muscle receptors activates ά-motoneurons of the antagonist muscle, thereby regulating skeletal muscle tone and motor responses. These neurons have a high lability - up to 200 pulses / s, but their axons are characterized by a low speed of excitation conduction - 10-40 m / s.

2. Afferent neurons of the somatic nervous system are localized in spinal ganglia and ganglia of the cranial nerves. Their processes, which conduct afferent impulses from muscle, tendon, and skin receptors, enter the corresponding segments of the spinal cord and form synaptic contacts either directly on ά-motor neurons (excitatory synapses) or on intercalary neurons.

3. Interneurons(intermediate, interneurons) establish a connection with the motor neurons of the spinal cord, with sensory neurons, and also provide a connection between the spinal cord and the nuclei of the brain stem, and through them - with the cerebral cortex. Interneurons can be both excitatory and inhibitory, with high lability - up to 1000 impulses / s.

4. Neurons of the autonomic nervous system. The neurons of the sympathetic nervous system are intercalary, located in the lateral horns of the thoracic, lumbar and partially cervical spinal cord (C 8 -L 2). These neurons are background-active, the frequency of discharges is 3-5 pulses/s. The neurons of the parasympathetic part of the nervous system are also intercalary, localized in the sacral part of the spinal cord (S 2 -S 4) and also background-active.

5. Associative neurons form their own apparatus of the spinal cord, which establishes a connection between segments and within segments. The associative apparatus of the spinal cord is involved in the coordination of posture, muscle tone, and movements.

Reticular formation of the spinal cord consists of thin bars of gray matter intersecting in different directions. RF neurons have a large number of processes. The reticular formation is found at the level of the cervical segments between the anterior and posterior horns, and at the level of the upper thoracic segments between the lateral and posterior horns in the white matter adjacent to the gray.

Nerve centers of the spinal cord

In the spinal cord are the centers of regulation of most internal organs and skeletal muscles.

1. The centers of the sympathetic department of the autonomic nervous system are localized in the following segments: the center of the pupillary reflex - C 8 - Th 2, regulation of heart activity - Th 1 - Th 5, salivation - Th 2 - Th 4, regulation of kidney function - Th 5 - L 3 . In addition, there are segmentally located centers that regulate the functions of sweat glands and blood vessels, smooth muscles of internal organs, and centers of pilomotor reflexes.

2. Parasympathetic innervation is received from the spinal cord (S 2 - S 4) to all organs of the small pelvis: bladder, part of the large intestine below its left bend, genitals. In men, parasympathetic innervation provides the reflex component of erection, in women, the vascular reactions of the clitoris and vagina.

3. Skeletal muscle control centers are located in all parts of the spinal cord and innervate, according to the segmental principle, the skeletal muscles of the neck (C 1 - C 4), diaphragm (C 3 - C 5), upper limbs (C 5 - Th 2), trunk (Th 3 – L 1) and lower extremities(L 2 - S 5).

Damage to certain segments of the spinal cord or its pathways cause specific motor and sensory disorders.

Each segment of the spinal cord is involved in sensory innervation of three dermatomes. There is also duplication of motor innervation of skeletal muscles, which increases the reliability of their activity.

The figure shows the innervation of the metameres (dermatomes) of the body by segments of the brain: C - metameres innervated by the cervical, Th - thoracic, L - lumbar. S - sacral segments of the spinal cord, F - cranial nerves.

II. The functions of the spinal cord are conductive and reflex.

Conductor function

The conductive function of the spinal cord is carried out with the help of descending and ascending pathways.

Afferent information enters the spinal cord through the posterior roots, efferent impulsation and regulation of the functions of various organs and tissues of the body is carried out through the anterior roots (Bell-Magendie law).

Each root is a set of nerve fibers.

All afferent inputs to the spinal cord carry information from three groups of receptors:

1) from skin receptors (pain, temperature, touch, pressure, vibration);

2) from proprioceptors (muscle - muscle spindles, tendon - Golgi receptors, periosteum and joint membranes);

3) from receptors of internal organs - visceroreceptors (mechano- and chemoreceptors).

The mediator of the primary afferent neurons localized in the spinal ganglia is, apparently, substance R.

The meaning of afferent impulses entering the spinal cord is as follows:

1) participation in the coordination activity of the central nervous system for the control of skeletal muscles. When the afferent impulse from the working body is turned off, its control becomes imperfect.

2) participation in the processes of regulation of the functions of internal organs.

3) maintaining the tone of the central nervous system; when afferent impulses are turned off, a decrease in the total tonic activity of the central nervous system occurs.

4) carries information about changes in the environment. The main pathways of the spinal cord are shown in Table 1.

Table 1. Main pathways of the spinal cord

III. Spinal cord reflexes

The spinal cord performs reflex somatic and reflex autonomic functions.

The strength and duration of all spinal reflexes increase with repeated stimulation, with an increase in the area of ​​the irritated reflexogenic zone due to the summation of excitation, and also with an increase in the strength of the stimulus.

Somatic reflexes of the spinal cord in their form are mainly flexion and extensor reflexes of a segmental nature. Somatic spinal reflexes can be combined into two groups according to the following features:

Firstly, according to the receptors, the irritation of which causes a reflex: a) proprioceptive, b) visceroceptive, c) skin reflexes. Reflexes arising from proprioceptors are involved in the formation of the act of walking and the regulation of muscle tone. Visceroreceptive (visceromotor) reflexes arise from the receptors of internal organs and manifest themselves in muscle contraction abdominal wall, chest and back extensors. The emergence of visceromotor reflexes is associated with the convergence of visceral and somatic nerve fibers to the same interneurons of the spinal cord.

Secondly, by organs:

a) limb reflexes;

b) abdominal reflexes;

c) testicular reflex;

d) anal reflex.

1. Limb reflexes. This group of reflexes is most frequently studied in clinical practice.

→ Flexion reflexes. Flexion reflexes are divided into phasic and tonic.

Phase reflexes- this is a single flexion of the limb with a single irritation of the skin or proprioceptors. Simultaneously with the excitation of the motor neurons of the flexor muscles, reciprocal inhibition of the motor neurons of the extensor muscles occurs. Reflexes arising from skin receptors are polysynaptic, they have a protective value. Reflexes arising from proprioreceptors can be monosynaptic and polysynaptic. Phase reflexes from proprioreceptors are involved in the formation of the act of walking. According to the severity of phase flexion and extensor reflexes, the state of excitability of the central nervous system and its possible violations are determined.

The clinic examines the following flexion phase reflexes: elbow and Achilles (proprioceptive reflexes) and plantar reflex (skin). Elbow reflex is expressed in flexion of the arm in elbow joint, occurs when a reflex hammer strikes the tendon m. viceps brachii (when the reflex is called, the arm should be slightly bent at the elbow joint), its arc closes in the 5-6th cervical segments of the spinal cord (C 5 - C 6). The Achilles reflex is expressed in plantar flexion of the foot as a result of contraction of the triceps muscle of the lower leg, occurs when the hammer hits the Achilles tendon, the reflex arc closes at the level of the sacral segments (S 1 - S 2). Plantar reflex - flexion of the foot and fingers with dashed stimulation of the sole, the arc of the reflex closes at the level S 1 - S 2.

Tonic flexion, as well as extensor reflexes occur with prolonged stretching of the muscles, their main purpose is to maintain the posture. Tonic contraction of skeletal muscles is the background for the implementation of all motor acts carried out with the help of phasic muscle contractions.

→ extensor reflexes, as flexion, are phasic and tonic, arise from the proprioreceptors of the extensor muscles, are monosynaptic. Simultaneously with the flexion reflex, a cross-extension reflex of the other limb occurs.

Phase reflexes occur in response to a single stimulation of muscle receptors. For example, when hitting the tendon of the quadriceps femoris below the patella, a knee extensor reflex occurs due to the contraction of the quadriceps femoris. During the extensor reflex, the motor neurons of the flexor muscles are inhibited by the intercalary inhibitory Renshaw cells (reciprocal inhibition). The reflex arc of the knee jerk closes in the second - fourth lumbar segments (L 2 - L 4). Phase extensor reflexes are involved in the formation of walking.

Tonic extensor reflexes represent a prolonged contraction of the extensor muscles during prolonged stretching of the tendons. Their role is to maintain posture. In the standing position, tonic contraction of the extensor muscles prevents flexion of the lower extremities and maintains an upright position. The tonic contraction of the back muscles provides a person's posture. Tonic reflexes to muscle stretch (flexors and extensors) are also called myotatic.

→ Posture reflexes- redistribution of muscle tone, which occurs when the position of the body or its individual parts changes. Posture reflexes are carried out with the participation of various parts of the central nervous system. At the level of the spinal cord, cervical postural reflexes are closed. There are two groups of these reflexes - arising when tilting and when turning the head.

The first group of cervical postural reflexes exists only in animals and occurs when the head is tilted down (anteriorly). At the same time, the tone of the flexor muscles of the forelimbs and the tone of the extensor muscles of the hind limbs increase, as a result of which the forelimbs bend and the hind limbs unbend. When the head is tilted up (posteriorly), opposite reactions occur - the forelimbs unbend due to an increase in the tone of their extensor muscles, and the hind limbs bend due to an increase in the tone of their flexor muscles. These reflexes arise from the proprioreceptors of the muscles of the neck and fascia covering cervical region spine. Under conditions of natural behavior, they increase the animal's chance to get food that is above or below head level.

Reflexes of the posture of the upper limbs in humans are lost. Reflexes of the lower extremities are expressed not in flexion or extension, but in the redistribution of muscle tone, which ensures the preservation of a natural posture.

The second group of cervical postural reflexes arises from the same receptors, but only when the head is turned to the right or left. At the same time, the tone of the extensor muscles of both limbs on the side where the head is turned increases, and the tone of the flexor muscles on the opposite side increases. The reflex is aimed at maintaining a posture that can be disturbed due to a change in the position of the center of gravity after turning the head. The center of gravity shifts in the direction of head rotation - it is on this side that the tone of the extensor muscles of both limbs increases. Similar reflexes are observed in humans.

Rhythmic reflexes - repeated repeated flexion and extension of the limbs. Examples are the scratching and walking reflexes.

2. Abdominal reflexes (upper, middle and lower) appear with dashed irritation of the skin of the abdomen. They are expressed in the reduction of the corresponding sections of the muscles of the abdominal wall. These are protective reflexes. To call the upper abdominal reflex, irritation is applied parallel to the lower ribs directly below them, the arc of the reflex closes at the level of the thoracic segments of the spinal cord (Th 8 - Th 9). The middle abdominal reflex is caused by irritation at the level of the navel (horizontally), the arc of the reflex closes at the level of Th 9 - Th10. To obtain a lower abdominal reflex, irritation is applied parallel to the inguinal fold (next to it), the arc of the reflex closes at the level of Th 11 - Th 12.

3. The cremasteric (testicular) reflex consists in the contraction of m. cremaster and raising the scrotum in response to a dashed irritation of the upper inner surface of the skin of the thigh (skin reflex), this is also a protective reflex. Its arc closes at the level L 1 - L 2.

4. The anal reflex is expressed in the contraction of the external sphincter of the rectum in response to a dashed irritation or prick of the skin near the anus, the arc of the reflex closes at the level S 2 - S 5.

Vegetative reflexes of the spinal cord are carried out in response to irritation of the internal organs and end with a contraction of the smooth muscles of these organs. Vegetative reflexes have their own centers in the spinal cord, which provide innervation to the heart, kidneys, bladder, etc.

IV. spinal shock

Severing or trauma to the spinal cord causes a phenomenon called spinal shock. Spinal shock is expressed in a sharp drop in excitability and inhibition of the activity of all reflex centers of the spinal cord located below the site of transection. During spinal shock, the stimuli that would normally elicit reflexes are rendered ineffective. At the same time, the activity of the centers located above the transection is preserved. After transection, not only skeletal-motor reflexes disappear, but also vegetative ones. Decreases blood pressure, there are no vascular reflexes, acts of defecation and urination.

The duration of the shock is different in animals standing on different steps of the evolutionary ladder. In a frog, the shock lasts 3-5 minutes, in a dog - 7-10 days, in a monkey - more than 1 month, in a person - 4-5 months. When the shock passes, reflexes are restored. The cause of spinal shock is the shutdown of the upstream parts of the brain, which have an activating effect on the spinal cord, in which the reticular formation of the brain stem plays a large role.