Physiology of the spinal cord, reticular formation, spinal shock. Physiology of the spinal cord, reticular formation, spinal shock Extrapyramidal, reflex motor 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) . During the process of evolution, two thickenings were formed in the spinal cord: cervical (segments innervating the upper limbs) and lumbosacral (segments innervating the lower limbs) as a result of increased load on these parts. 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 interneurons, of which some are neurons that belong to the autonomic nervous system.

Classification of spinal cord neurons

Neurons of the spinal cord are classified according to the following characteristics:

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

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

3) by influence (exciting 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 - 70-120 m/s. ά-Motoneurons are divided into two subgroups: ά 1 - fast, innervating fast white muscle fibers, their lability reaches 50 impulses/s, and ά 2 - slow, innervating slow red muscle fibers, their lability is 10-15 impulses/s. The low lability of ά-motoneurons is explained by the long-term trace hyperpolarization that accompanies AP. There are up to 20 thousand synapses on one ά-motoneuron: from skin receptors, proprioceptors and descending pathways of the overlying parts of the central nervous system.

γ-motoneurons are scattered among ά-motoneurons, their activity is regulated by neurons of the overlying parts 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 reactions. These neurons have high lability - up to 200 impulses / s, but their axons are characterized by a low excitation velocity - 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, conducting afferent impulses from muscle, tendon and skin receptors, enter the corresponding segments of the spinal cord and form synaptic contacts either directly on ά-motoneurons (excitatory synapses) or on interneurons.

3. Interneurons (intermediates, interneurons) establish connections with motor neurons of the spinal cord, with sensory neurons, and also provide communication between the spinal cord and the nuclei of the brain stem, and through them with the cerebral cortex. Interneurons can be either excitatory or inhibitory, having 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 discharge frequency is 3-5 impulses/s. 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 are also background active.

5. Associative neurons form their own apparatus of the spinal cord, which establishes connections 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

The spinal cord contains the regulatory centers for 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) by all pelvic organs: the bladder, part of the colon below its left bend, and genitals. In men, parasympathetic innervation provides the reflex component of erection, in women - 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 a segmental principle, the skeletal muscles of the neck (C 1 - C 4), diaphragm (C 3 - C 5), upper extremities (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 causes specific motor and sensory disorders.

Each segment of the spinal cord is involved in the 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 metameres (dermatomes) of the body by brain segments: 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 using descending and ascending pathways.

Afferent information enters the spinal cord through the dorsal 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 consists of many 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 primary afferent neurons localized in the spinal ganglia is, apparently, substance P.

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

1) participation in the coordination activities of the central nervous system to control skeletal muscles. When the afferent impulse from the working organ 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 environmental changes. 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 extension reflexes of a segmental nature. Somatic spinal reflexes can be divided into two groups according to the following characteristics:

Firstly, according to the receptors, the irritation of which causes the 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. Visceroceptive (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 organ:

a) limb reflexes;

b) abdominal reflexes;

c) testicular reflex;

d) anal reflex.

1. Reflexes of the limbs. This group of reflexes is studied most often in clinical practice.

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

Phasic reflexes- this is a single flexion of a 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 and have a protective value. Reflexes arising from proprioceptors can be monosynaptic and polysynaptic. Phasic reflexes from proprioceptors are involved in the formation of the act of walking. Based on the severity of phasic flexion and extension reflexes, the state of excitability of the central nervous system and its possible disorders are determined.

The following flexion phase reflexes are examined in the clinic: elbow and Achilles (proprioceptive reflexes) and plantar reflex (cutaneous). The elbow reflex is expressed in the flexion of the arm at the elbow joint and occurs when the m. tendon is struck with a reflex hammer. biceps brachii (when invoking the reflex, 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 leg; it occurs when the Achilles tendon is struck with a hammer; the reflex arc closes at the level of the sacral segments (S 1 - S 2). Plantar reflex - flexion of the foot and toes with line stimulation of the sole, the reflex arc closes at the level S 1 - S 2.

Tonic flexion, as well as extensor reflexes occur during prolonged muscle stretching; their main purpose is to maintain 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, like flexion, are phasic and tonic, arise from proprioceptors of extensor muscles, and are monosynaptic. Simultaneously with the flexion reflex, a cross-extensor reflex of the other limb occurs.

Phasic reflexes occur in response to a single irritation of muscle receptors. For example, when the quadriceps tendon is struck below the kneecap, a knee extensor reflex occurs due to contraction of the quadriceps femoris muscle. During the extensor reflex, the motor neurons of the flexor muscles are inhibited by Renshaw intercalary inhibitory cells (reciprocal inhibition). The reflex arc of the knee reflex closes in the second – fourth lumbar segments (L 2 – L 4). Phasic 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 the pose. In a standing position, tonic contraction of the extensor muscles prevents flexion of the lower limbs and ensures maintaining an upright position. Tonic contraction of the back muscles ensures human posture. Tonic stretch reflexes of muscles (flexors and extensors) are also called myotatic.

→ Posture reflexes– redistribution of muscle tone that 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 posture reflexes are closed. There are two groups of these reflexes - those that occur 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 increases, as a result of which the forelimbs bend and the hind limbs extend. When the head is tilted upward (posteriorly), opposite reactions occur - the forelimbs extend 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 neck muscles and fascia covering the cervical spine. Under conditions of natural behavior, they increase the animal's chance of reaching food located above or below head level.

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

Second group of cervical postural reflexes occurs from the same receptors, but only when turning the head 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 posture, which can be disrupted due to a change in the position of the center of gravity after turning the head. The center of gravity shifts towards the rotation of the head - 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 include the scratching and stepping reflexes.

2. Abdominal reflexes (upper, middle and lower) appear when the abdominal skin is irritated by strokes. Expressed in the contraction of the corresponding areas of the muscles of the abdominal wall. These are protective reflexes. To evoke the upper abdominal reflex, irritation is applied parallel to the lower ribs directly below them, the reflex arc 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 the lower abdominal reflex, irritation is applied parallel to the inguinal fold (next to it), the reflex arc closes at the level of Th 11 - Th 12.

3. The cremasteric (testicular) reflex consists of contraction of m. cremaster and raising the scrotum in response to stroke 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 streak of irritation or a prick of the skin near the anus; the reflex arc closes at the level of S 2 - S 5.

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

IV. Spinal shock

Transection or injury 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, stimuli that would normally trigger reflexes are no longer effective. At the same time, the activity of centers located above the transection is maintained. After transection, not only skeletal-motor reflexes disappear, but also autonomic ones. Blood pressure decreases, vascular reflexes, defecation and urination are absent.

The duration of shock varies among animals at different levels of the evolutionary ladder. In a frog, shock lasts 3-5 minutes, in a dog - 7-10 days, in a monkey - more than 1 month, in humans - 4-5 months. When the shock wears off, 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 a large role belongs to the reticular formation of the brain stem.

Spinal cord

Liquor - the internal environment of the brain:

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

Composition of cerebrospinal fluid (mg%)

The spinal cord performs two main functions:

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

Along the spinal cord there 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 motor neurons to muscle proprioceptors, 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, the ventral and dorsal horns, as well as the intermediate zone, are distinguished. In the thoracic segments of the spinal cord there are also lateral horns. Here in the gray matter there are 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 exteroceptors go here. This is where some upward paths begin.

The anterior horns contain motoneurons that form motor nuclei. Segments with sensory fibers of one pair of dorsal roots form a metamer. The axons of one muscle emerge as part of several ventral roots, which ensures reliable functioning of the muscle if any one axon is disrupted.

Reflex activity of the spinal cord.

The scope of functions performed by the spinal cord is very large. The spinal cord takes part in regulating:

• 1. All motor reflexes (except for head movements).
• 2. Reflexes of the genitourinary system.
• 3. Intestinal reflexes.
• 4. Reflexes of the vascular system.
• 5. Body temperatures.
• 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 interneurons, therefore the path along which they are carried out is called monosynaptic, and the reflexes are called monosynaptic. These reflexes are of great importance in neurology, as they are easily caused by hitting the tendons with a neurological hammer and result in muscle contractions. Clinically, these reflexes are called T-reflexes. They are well expressed in the extensor muscles. For example, knee reflex, Achilles reflex, elbow reflex, etc..

Using 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 move up, then if you know at what level the motor neurons of this reflex are localized, you can determine the level of damage.
• 2. Determine the insufficiency or excess of excitation of 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 some side, then there is a lesion there.

There is a second group of reflexes, carried out with the participation of the synthetic 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. Postural (maintaining a pose).
• 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.

Spinal cord pathways:

• · Associative paths
• · Commissural tracts
• · Projection
• o ascending
• o downstream

Conductive function of the spinal cord

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

• 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 Bun
• o Wedge-shaped bundle of Burdach
• o Lateral spinothalamic tract
• o Ventral spinothalamic tract
• o Flexig's dorsal spinocerebellar tract
• o Ventral spinocerebellar tract of Gowers

The ascending tracts of the spinal cord include:

• 1. Thin beam (Gaull).
• 2. Wedge-shaped bundle (Burdakha). The primary efferents of the thin and cuneate fasciculi, without interruption, go to the medulla oblongata to the Gaulle and Burdach nuclei and are conductors of skin and mechanical sensitivity.
• 3. The spinothalamic tract carries impulses from skin receptors.
• 4. Spinocerebellar tract:
  • a) dorsal
  • b) ventral. These pathways carry impulses to the cerebellar cortex from the skin and muscles.
• 5. Pathway of pain sensitivity. Localized in the ventral columns of the spinal cord.

Descending tracts of the spinal cord

• o Straight anterior corticospinal pyramidal tract
• o Lateral corticospinal pyramidal tract
• o Rubrospinal tract of Monakov
• o Vestibulospinal tract
• o Reticulospinal tract
• o Tectospinal tract
• 1. Pyramid path. Begins in the motor zone of the cerebral cortex. Some of the fibers of this path go to the medulla oblongata, where they cross and go in the lateral trunks (lateral tract) of the spinal cord. The other part goes straight and reaches the corresponding segment of the spinal cord (direct pyramidal tract).
• 2. Rubrospinal tract. Formed by 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 tract. The OH is formed by the axons of neurons in the Deiters nucleus. Regulates muscle tone and coordination of movements, participates in maintaining balance.
• 4. Reticulospinal tract. Starts from the reticular formation of the hindbrain. Regulates the processes of coordination of movements.

Disruption of 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 drops sharply below the level of the gap. With spinal shock, motor and autonomic reflexes are inhibited, which can recover after a long period of time.

How does the human spinal cord work, where is it located and how does it function? In short, this is the main organ of the central nervous system. With its help, signals from the periphery enter the central part and vice versa. Its anatomy is quite complex; it has many nerve endings, substances and membranes. To better study the features and role played by this body, we suggest staying with us and reading the article.

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Anatomical features

A rather thick tourniquet, white in color, located in the spinal canal - this is the human spinal cord. Its diameter is about 1-1.5 cm, and its length almost reaches half a meter (up to 45 cm). This organ weighs about 38 g.

The narrow spinal canal is not only the location of an important organ, but also its protection. The core of the organ consists of a gray substance. It is covered by a white substance, which is also covered with protective and nourishing shells for the core. This is the general plan of the structure of the spinal cord.

Topography

The structure and functions of the spinal cord are quite complex. Neurosurgeon students study it in detail. Experts very carefully consider the development of the spinal cord. Ordinary people are interested in the question of what its topography is and familiarity with the leading role of this organ.

So, it is quite simple to describe the essence and goals that this body serves. The cervical spinal cord at the level of the back of the head in the area of ​​the foramen passes into the cerebellum. The spinal cord ends at the level of the first 2 lumbar vertebrae. The conus spinal cord is located where a pair of vertebrae are located in the lumbar region. Next is the well-known “terminal thread”.

But this fragment is considered atrophied. It is called the “end” region. Nerve endings called “roots” are distributed along the entire circumference of the thread. The filum terminale is equipped with a substance containing a small proportion of nervous system tissue. But the outer part is not even equipped with a similar fabric.

The topography of the organ includes a pair of thickenings where the innervating processes emerge (cervical thickening of the spinal cord and lumbar). The outer and rear surfaces of the bundle are separated by slits called “middle”. The one in front is deeper, the back one is smoothed.

External structure

The general structure of the spinal cord suggests its division into a number of surfaces: posterior, anterior and two lateral. The spinal cord has faint grooves on the lateral surface. They are located longitudinally, and nerves extend from the grooves. They are also called “roots”. In the lumbar area, together with the terminal filament, they form a tail, which is commonly called a horse's tail. The grooves divide half of this cord into the following structures:

• front;
• lateral;
• posterior (cords).

The grooves of the spinal cord extend along the canal. The roots are divided into anterior ones - they are formed by efferent neurons, and posterior ones, created by afferent neurons. Their bodies converge into a knot. The roots unite and form a nerve. So, on all sides of the tourniquet there are over 30 nerve endings, forming exactly the same number of pairs. This is the external structure of the spinal cord.

Anatomically, it consists of 2 types of substances: white and gray. The first is the processes of the neural type, and the gray is their bodies.

White matter

All cords are made entirely of white matter of the spinal cord. They consist of longitudinal nerve fibers. These threads converge, forming peculiar conductors. Based on their functional purpose, fibers are divided into 3 types:

• motor;
• associative;
• sensitive.

The first are represented by short bundles and combine all parts into a single system. The second ones are called ascending. They give signals to the centers. Still others are descending. They provide signals from central structures to areas of the horns.

Gray matter

It structurally resembles grouped longitudinal plates consisting of homogeneous neurons. It contains not only neuronal bodies, but also neuropil, glial cells and capillaries. Along the entire spine it forms 2 columnar types, left and right. They are connected by gray adhesions.

The anterior horns contain the largest neurons. They form the motor nuclei of the spinal cord and inhibitory neurons. The structure of the gray matter of the background horns is not the same. It contains a huge number of intercalary type neurons.

The lateral horns of the spinal cord fill the centers of the ANS, the dilation of the pupil, the bases of innervation of the digestive system and other important organs of the human body. In the nucleus of the gray matter of the spinal cord there is a canal that neurosurgeons call “central.” It is filled with liquor. In adults, in some places it is filled with cerebrospinal fluid, and in others it is overgrown.

Shells

Anatomy of the spinal cord describes the membranes of the spinal cord:

• vascular soft;
• hard;
• avascular or arachnoid.

The characteristics of shell 1 are as follows: soft, penetrated by vessels and nerves. It is enveloped by the avascular part. There is some space here called “subarachnoid”. The cerebrospinal fluid generated in one of the systems flows into this niche. The last shell is made up of connective tissue; it is strong and flexible. The membranes of the spinal cord and brain are identical and form a single structure.

Segmental structure

A segment of the spinal cord is a piece of a tourniquet along with associated nerves. There is no morphological separation of one segment of the spinal cord from another. It is extremely functional. Each of the segments innervates a certain region. The designation of spinal cord segments is represented by alphanumeric indices, oriented to a part of the spinal cord and containing segment numbers.

The spinal cord consists of about 33 segments. The spinal cord segments have 4 roots, a pair of anterior and posterior. The spinal column is significantly longer than the cord, so it should be remembered that the segments are not numbered in the same way as the vertebrae. Any nerve consists of motor-sensitive roots. They come out in bunches from this bundle to the openings between the vertebrae.

The nerve ending located behind forms a ganglion and merges with the nerve ending in front. In this case, a mixed nerve is formed, which is divided into branches:

1. The meningeal branch innervates in accordance with the nature of the spinal cord membrane and the canal wall.
2. Dorsal - the skin in the corresponding areas, as well as deep muscle tissue.
3. The connective tissue branch is the connecting link between the tourniquet and the ganglia.
4. The abdominal branch is responsible for innervation of the limbs, lateral surfaces of the body and tissue of the abdominal part of the body.

Blood supply

The tourniquet is supplied with blood through the adjacent arteries. Through the fusion of the branches of the vertebral arteries, the anterior artery is formed. It is designed to be located along the front slit of the tourniquet. The blood supply to the spinal cord is also provided by the arteries located there. They are located behind the tourniquet.

They connect to the neck and arteries, which are called the “posterior intercostal, lumbar and lateral sacral arteries.” Between them there is a network of anastomoses, due to which the tourniquet is literally entangled in the branches of the arteries. To supply blood to the spinal cord, in addition to arteries, veins are needed, which also provide blood outflow.

Functions and role in the body

The human spinal cord has two main functions: one normalizes the brain-body connection. It is reflexive, it puts everything into action not without the participation of the will. The second conducts impulses to the main brain in an ascending manner and transmits them back from it. The descending or efferent pathways of the spinal cord are responsible for this activity.

The ascending tracts of the spinal cord are represented by the following tracts:

• spinothalamic;
• spinocerebellar;
• wedge-shaped and thin beams.

The pyramidal tracts, vestibulospinal, tectospinal and red nuclear spinal tracts are classified as special efferent pathways.

The reflex function is aimed at maintaining posture (position reflexes) and the ability to consistently alternate actions (motor programs), for example, walking. This function also provides a reflex defense mechanism (quickly moving the limbs away from hot objects).

Autonomic reflexes of the spinal cord are control signals that ensure the smooth functioning of internal organs. Myomatic reflexes are designed to provide contractile activity of muscles in response to their inflammation.

Anatomy and physiology of the spinal cord is a whole field of knowledge that describes its structure and features of functioning. It helps to understand how important the organ is and how the spinal cord and brain are connected. Thanks to this description, people receive the necessary ideas about an important organ.

Video “Human Anatomy and Physiology”

From this video you will learn about the biological structure of the organ.

The spinal cord is the most ancient formation of the central nervous system. A characteristic feature of the structure is segmentarity.

Neurons of the spinal cord form it Gray matter in the form of anterior and posterior horns. They perform the 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 dorsal horns contain afferent neurons that respond to pain, temperature, tactile, vibration, and proprioceptive stimuli.

The anterior horns contain neurons (motoneurons) that give axons to muscles; they are efferent. All descending pathways of the central nervous system of motor reactions end in the anterior horns.

The neurons of the sympathetic division of the autonomic nervous system are located in the lateral horns of the cervical and two lumbar segments, and the parasympathetic ones are located in the second to fourth segments.

The spinal cord contains many interneurons that provide communication with the segments and with the overlying parts of the central nervous system; 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 plays a conductive role.

Short fibers connect neurons of the same 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 conductive functions.

The reflex function allows for the implementation of all 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 impulse transmission through the fibers, and the influence of the brain.

Reflexes are divided into:

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

2) interoceptive (occurs when irritation of 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 the formations associated with it. They have a monosynaptic reflex arc. Proprioceptive reflexes regulate motor activity due to tendon and postural reflexes. Tendon reflexes (knee, Achilles, triceps brachii, etc.) occur when muscles are stretched and cause relaxation or contraction of the muscle, occurring with every muscle movement;

4) postural reflexes (occur when vestibular receptors are excited when the speed of movement and position of the head relative to the body changes, which leads to a redistribution of muscle tone (increased tone of extensors and decreased flexors) and ensures body balance).

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

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

The spinal cord performs conductor and reflex functions.

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

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

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

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

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

Rice. 11.4.

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

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

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