Functions of the spinal cord. Structure and function of the spinal cord Ascending pathways

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 have formed in the spinal cord: cervical (segments innervating the upper limbs) and lumbosacral (segments innervating the lower limbs) as a result of an 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 the 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. Intercalary neurons (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, the regulation of heart activity - Th 1 - Th 5, salivation - Th 2 - Th 4, the 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 limbs (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 the internal organs and are manifested in the contraction of the muscles of the 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 the 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 proprioceptors of the muscles of the neck and fascia covering the cervical 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. Blood pressure decreases, 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.

Spinal cord consists of 31-33 segments: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1-3 coccygeal.

Segment- This is a section of the spinal cord associated with one pair of anterior and a pair of posterior roots.

The posterior (dorsal) roots of the spinal cord are formed by the central processes of afferent sensory neurons. The bodies of these neurons are localized in the spinal and cranial nerve nodes (ganglia). The anterior (ventral) roots are formed by axons of efferent neurons.

According to Bell Magendie law , the anterior roots are efferent - motor or autonomic, and the posterior - afferent sensitive.

On a transverse section of the spinal cord, a centrally located Gray matter, which is formed by the accumulation of nerve cells. It borders white matter, which is formed by nerve fibers. The nerve fibers of the white matter form the dorsal (posterior), lateral and ventral (anterior) cords of the spinal cord containing the pathways of the spinal cord. In the posterior cords there are ascending, in the anterior - descending, and in the lateral - both ascending and descending pathways.

The gray matter is divided into dorsal (posterior) and ventral (anterior) horns. In addition, there are lateral horns in the thoracic, lumbar, and sacral segments.

All gray matter neurons can be divided into three main groups:

1) interneurons located mainly in the posterior horns of the spinal cord,

2) efferent motor neurons located in the anterior horns,

3) efferent preganglionic neurons of the autonomic nervous system, located in the lateral and anterior horns of the spinal cord.

A segment of the spinal cord, together with the innervated parts of the body, is called metamer . A group of muscles innervated by one segment of the spinal cord is called myotome . The area of ​​skin from which sensory signals travel to a specific segment of the spinal cord is called dermatome .

There are three main functions of the spinal cord:

1) reflex,

2) trophic,

3) conductive.

reflex function spinal cord may be segmental and intersegmental. Reflex segmental function of the spinal cord lies in the direct regulatory influence of the efferent neurons of the spinal cord on the effectors innervated by them upon stimulation of the receptors of a certain dermatome.

Reflexes whose arc switches in the spinal cord are called spinal . The simplest spinal reflexes are tendon reflexes , which provide contraction of skeletal muscles when their proprioreceptors are irritated due to rapid short-term stretching of the muscle (for example, when a neurological hammer strikes a tendon). Tendon spinal reflexes are clinically important because each of them closes in certain segments of the spinal cord. Therefore, by the nature of the reflex reaction, one can judge the functional state of the corresponding segments of the spinal cord.

Depending on the localization of the receptors and the nerve center in humans, elbow, knee and Achilles tendon spinal reflexes are distinguished.

elbow flexion reflex occurs when the tendon of the biceps muscle of the shoulder (in the region of the ulnar fossa) is struck and manifests itself in flexion of the arm in the elbow joint. The nerve center of this reflex is localized in the 5-6 cervical segments of the spinal cord.

Elbow extensor reflex occurs when the tendon of the triceps muscle of the shoulder (in the region of the ulnar fossa) is struck and manifests itself in the extension of the arm in the elbow joint. The nerve center of this reflex is localized in the 7-8 cervical segments of the spinal cord.

knee jerk occurs when the tendon of the quadriceps femoris muscle is struck below the patella and manifests itself in the extension of the leg at the knee joint. The nerve center of this reflex is localized in 2-4 lumbar segments of the spinal cord.

Achilles reflex occurs when hitting the calcaneal tendon and manifests itself in flexion of the foot at the ankle joint. The nerve center of this reflex is localized in 1-2 sacral segments of the spinal cord.

There are two types of fibers in skeletal muscle - extrafusal and intrafusal that are connected in parallel. Intrafusal muscle fibers perform a sensory function. They consist of connective tissue capsule in which proprioreceptors are located, and peripheral contractile elements.

A sharp, quick blow to the tendon of the muscle leads to its tension. As a result, the connective tissue capsule of the intrafusal fiber is stretched and proprioceptors are irritated. Therefore, there is a pulsed electrical activity of motor neurons localized in the anterior horns of the spinal cord. The discharge activity of these neurons is the direct cause of the rapid contraction of extrafusal muscle fibers.

Scheme of the reflex arc of the tendon spinal reflex

1) intrafusal muscle fiber, 2) proprioceptor, 3) afferent sensory neuron, 4) spinal motoneuron, 5) extrafusal muscle fibers.

The total time of the tendon spinal reflex is small, because its reflex arc is monosynaptic. It includes rapidly adapting receptors, phasic a-motor neurons, FF and FR type motor units.

Reflex intersegmental function of the spinal cord is the implementation of intersegmental integration of spinal reflexes, which is provided by intraspinal pathways that connect different segments of the spinal cord.

Trophic function of the spinal cord is reduced to the regulation of metabolism and nutrition of those organs and tissues that are innervated by the neurons of the spinal cord. It is associated with the impulseless activity of neurons capable of synthesizing many trophotropic biologically active substances. These substances slowly move to the nerve endings, from where they are released into the surrounding tissue.

Conductor function of the spinal cord is to provide bilateral connections between the spinal cord and the brain. It is provided by its ascending and descending pathways - groups of nerve fibers.

There are three main groups of ascending pathways:

1) Goll and Burdakh,

2) spinothalamic,

3) spinocerebellar.

The ways of Gaulle and Burdakh are conductors of skin-mechanical sensitivity from tactile receptors and proprioceptors to the sensory zones of the posterior central gyrus of the cerebral cortex. The Gaull path carries information from the lower body, and the Burdakh path carries information from the upper.

Spinothalamic pathway is a conductor of tactile, temperature and pain sensitivity. This pathway ensures the transmission of information about the quality of the stimulus to the posterior central gyrus.

Spinal tracts carry information from tactile receptors, as well as proprioreceptors of muscles, tendons and joints to the cerebellar cortex.

Descending pathways form pyramidal and extrapyramidal systems. pyramid system includes pyramidal corticospinal tract. It is formed by the axons of large pyramidal neurons ( betz cells), which are located in the motor (motor) zone of the precentral gyrus of the cerebral cortex.

In humans, the pyramidal tract has a direct triggering activating effect on the spinal motor neurons that innervate the flexor muscles (flexors) of the distal extremities. Thanks to this path, arbitrary conscious regulation of precise phase movements is ensured.

Extrapyramidal system includes:

1) rubrospinal path,

2) reticulospinal path,

3) vestibulospinal pathways.

Rubrospinal path is formed by the axons of the neurons of the red nucleus of the midbrain, activating the spinal motor neurons of the flexors. reticulospinal pathway It is formed by axons of neurons of the reticular formation of the hindbrain, which have both an activating and inhibitory effect on the motor neurons of the flexors. Vestibulospinal pathways are formed by axons of neurons of the vestibular nuclei of Deiters, Schwalbe and Bekhterev, which are located in the hindbrain. These pathways have an activating effect on spinal extensor motor neurons (extensors).

An animal in which the spinal cord is separated from the brain is called spinal. Immediately after injury or separation of the spinal cord from the brain, spinal shock - the reaction of the body, which manifests itself in a sharp drop in excitability and inhibition of reflex activity or areflexia.

The main mechanisms of spinal shock (according to Sherrington) are:

1) elimination of descending activating influences entering the spinal cord from the higher parts of the central nervous system,

2) activation of intraspinal inhibitory processes.

There are two main factors that determine the severity and duration of spinal shock:

1) the level of organization of the body (in a frog, a spinal shock lasts 1-2 minutes, and in a person - months and years),

2) the level of damage to the spinal cord (the higher the level of damage, the more severe and longer the spinal shock).

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, 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 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 conduction functions is carried out by different types of neurons that are part of 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 of the working group, that is, skeletal muscles.
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 the 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.

Spinal cord

Liquor - the internal environment of the brain:

• 1. Maintains the salt composition of the brain
• 2. Maintains osmotic pressure
• 3. Is a mechanical protection of neurons
• 4. Is a brain nutrient

CSF composition (mg%)

The spinal cord has two main functions:

• 1. Reflex
• 2. Conductor (innervates all muscles, except for the muscles of the head).

Along the spinal cord are roots (ventral and dorsal), of which 31 pairs can be distinguished. The ventral (anterior) roots contain efferents where the axons of the following neurons pass: b-motoneurons to skeletal muscles, gamma-motoneurons to muscle proprioreceptors, preganglionic fibers of the autonomic nervous system, etc. Dorsal (posterior) roots are processes of neurons whose bodies are located in spinal ganglia. This arrangement of nerve fibers in the ventral and dorsal roots is called the Bell-Magendie law. The ventral roots perform a motor function, while the dorsal roots are sensitive.

In the gray matter of the spinal cord, ventral and dorsal horns, as well as an intermediate zone, are distinguished. In the thoracic segments of the spinal cord, there are also lateral horns. Here in the gray matter there is a large number of interneurons, Renshaw cells. The lateral and anterior horns contain preganglionic autonomic neurons, the axons of which go to the corresponding autonomic ganglia. The entire apex of the dorsal horn (posterior) forms the primary sensory area, since fibers from the exteroreceptors go here. Some ascending paths start from here.

Motor neurons are concentrated in the anterior horns, which form the motor nuclei. Segments with sensory fibers of one pair of dorsal roots form a metamere. The axons of one muscle come out as part of several ventral roots, which ensures the reliability of the functioning of the muscle in the event of a violation of any one axon.

Reflex activity of the spinal cord.

The range of functions that the spinal cord performs is very large. The spinal cord is involved in the regulation of:

• 1. All motor reflexes (with the exception of head movement).
• 2. Reflexes of the genitourinary system.
• 3. Intestinal reflexes.
• 4. Reflexes of the vascular system.
• 5. Body temperature.
• 6. Breathing movements, etc.

The simplest reflexes of the spinal cord are tendon reflexes or stretch reflexes. The reflex arc of these reflexes does not contain intercalary neurons, therefore the path along which they are carried out is called monosynaptic, and the reflexes are monosynaptic. These reflexes are of great importance in neurology, as they are easily caused by the impact of the neurological hammer on the tendons and, as a result, muscle contractions occur. In the clinic, these reflexes are called T-reflexes. They are well expressed in the extensor muscles. For example, knee reflex, achilles reflex, elbow reflex, etc..

With the help of these reflexes in the clinic, you can determine:

• 1. At what level of the spinal cord is the pathological process localized? So, if you perform tendon reflexes starting from the plantar and gradually rise up, then if you know at what level the motor neurons of this reflex are localized, you can set the level of damage.
• 2. Determine the insufficiency or excess of excitation of the nerve centers. spinal cord conduction reflex
• 3. Determine the side of the spinal cord lesion, i.e. if you determine the reflex on the right and left legs and it falls out on one side, then there is a lesion.

There is a second group of reflexes carried out with the participation of the blue brain, which are more complex, since they include many interneurons and therefore they are called polysynaptic. There are three groups of these reflexes:

• 1. Rhythmic (for example, the scratching reflex in animals and walking in humans).
• 2. Posture (maintaining posture).
• 3. Neck or tonic reflexes. They occur when turning or tilting the head, resulting in a redistribution of muscle tone.

In addition to somatic reflexes, the spinal cord performs a number of autonomic functions (vasomotor, genitourinary, gastrointestinal motility, etc.), in the implementation of which the autonomic ganglia located in the spinal cord take part.

Pathways of the spinal cord:

• · Associative Paths
• · Commissural paths
• · projection
• o ascending
• o descending

Conductive function of the spinal cord

The conductive function of the spinal cord is associated with the transmission of excitation to and from the brain through the white matter, which consists of fibers. A group of fibers of a general structure and performing a common function forms conducting paths:

• 1. Associative (connect different segments of the spinal cord on one side).
• 2. Commissural (connect the right and left halves of the spinal cord at the same level).
• 3. Projection (connect the underlying parts of the central nervous system with the higher ones and vice versa):
  • a) ascending (sensory)
  • b) descending (motor).

Ascending tracts of the spinal cord

• o Thin Gaulle beam
• o Wedge-shaped bundle of Burdakh
• o Lateral spinothalamic tract
• o Ventral spinothalamic tract
• o Dorsal spinocerebellar tract of Flexig
• o Ventral spinocerebellar tract of Gowers

The ascending tracts of the spinal cord include:

• 1. Thin beam (Gaul).
• 2. Wedge-shaped bundle (Burdaha). The primary efferents of the thin and wedge-shaped bundles, without interruption, go to the medulla oblongata to the nuclei of Gaulle and Burdach and are conductors of skin and mechanical sensitivity.
• 3. The spinothalamic pathway conducts impulses from skin receptors.
• 4. Spinal tract:
  • a) dorsal
  • b) ventral. These pathways conduct impulses to the cerebellar cortex from the skin and muscles.
• 5. Path of pain sensitivity. Localized in the ventral columns of the spinal cord.

Descending tracts of the spinal cord

• o Direct anterior corticospinal pyramidal tract
• o Lateral corticospinal pyramidal tract
• o Rubrospinal tract of Monakov
• o Vestibulospinal tract
• o Reticulospinal tract
• o Tectospinal tract
• 1. Pyramidal path. It begins in the motor cortex of the cerebral hemispheres. Part of the fibers of this path go to the medulla oblongata, where they cross over and go to the lateral trunks (lateral path) of the spinal cord. The other part goes straight and reaches the corresponding segment of the spinal cord (straight pyramidal path).
• 2. Rubrospinal path. It is formed by the axons of the red nucleus of the midbrain. Some of the fibers go to the cerebellum and reticulum, and the other goes to the spinal cord, where it controls muscle tone.
• 3. Vestibulospinal path. OH is formed by the axons of neurons in the nucleus of Deiters. Regulates muscle tone and coordination of movements, participates in maintaining balance.
• 4. Reticulospinal path. It starts from the reticular formation of the hindbrain. Regulates the processes of coordination of movements.

Violation of the connections between the spinal cord and the brain leads to a disorder of spinal reflexes and spinal shock occurs, i.e. the excitability of the nerve centers falls sharply below the level of the gap. With spinal shock, motor and autonomic reflexes are inhibited, which can be restored after a long period of time.

Normal physiology: lecture notes Svetlana Sergeevna Firsova

1. Physiology of the spinal cord

1. Physiology of the spinal cord

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.

1. Physiology of the spinal cord 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 its gray matter in the form of anterior and posterior horns. They perform the reflex function of the spinal cord. Posterior

LECTURE No. 9. Blood supply to the brain and spinal cord. Syndromes of vascular disorders in the vascular pools of the brain and spinal cord Blood supply to the brain is carried out by the vertebral and internal carotid arteries. From the last in the cranial cavity

Chapter 2 ANATOMO-PHYSIOLOGICAL FEATURES OF THE STRUCTURE OF THE SPINAL CORD. POSSIBILITY OF INFORMATION TRANSMISSION WHEN THE SPINAL CORD IS DAMAGED ANATOMICAL AND PHYSIOLOGICAL FEATURES OF THE STRUCTURE OF THE SPINAL CORD

Closed injuries of the spine and spinal cord. Classification of closed spine and spinal cord injuries

Neurons of the spinal cord There is a functional division of neurons into 4 groups. The first group includes motor neurons, or motor neurons, located in the anterior horns, and their axons form the anterior roots. The second group consists of interneurons - intermediate

1.3.1. Peripheral nerves of the spinal cord The spinal nerves are a continuation to the periphery of the anterior and posterior roots of the spinal cord, which, connecting with each other, form the cervical, brachial and lumbosacral plexus. Cervical plexus

MEANS OF THE SPINAL CORD The spinal cord, like the brain, is surrounded by three membranes: the pia mater, adjacent directly to the spinal cord, the arachnoid, located between the pia and dura mater, and the dura mater, located outside the spinal cord.

SPINAL CORD INJURIES The focus of rehabilitation measures for spinal cord injury depends on many factors, the main of which include the following: type and nature of spinal cord injury; stability of spinal injury; type, degree and level

Tumors of the spinal cord Tumors interfere with blood circulation, compress and thereby destroy the spinal cord. They occur most often in people between the ages of 20 and 60. The first sign of the disease is the appearance of back pain, which usually increases with prolonged

Diseases of the spinal cord. Tumors of the spinal cord Spinal cord tumors are divided into benign (meningiomas arising from meningeal cells and schwannomas arising from Schwann (auxiliary) cells) and malignant (gliomas arising from

Spinal cord injuries The main task of exercise therapy for traumatic injuries of the spine and spinal cord is to normalize the patient's motor activity or mobilize compensatory capabilities.

Anatomy of the spinal cord (Fig. 9) The spinal cord is part of the central nervous system. The length of the spinal cord in an adult of average height is about 45-50 cm - from the brain to the sacrum, where the last remaining nerves branch in the lumbar region. This

Disease of the spinal cord - 1 teaspoon topped with fresh vine flowers, pour a glass of boiling water, leave for 1 hour, strain, add 1 tbsp. a spoonful of apple cider vinegar. Sip 1-2 glasses throughout the day

Meridians of the brain (pericardium) and spinal cord (triple warmer) Anyone who is more or less familiar with the literature on traditional Chinese medicine, probably immediately noticed some discrepancy in the names of these meridians. The point is that in

Strengthening the brain-spinal cord I am the Spirit of God, cheerful-cheerful-happy Spirit, mighty gigantic, instantly healing Spirit, cheerful-cheerful-happy. I am the Spirit of God, I ask You, my Heavenly Father, dearly beloved, help me now, strengthen my will,