The autonomic division of the nervous system does not regulate activity. Autonomic division of the nervous system. Functions of the ANS in the human body

Lecture No. 5. Autonomic nervous system

The nervous system is divided into somatic (Slide 2) and autonomic (vegetative) (Slide 3).

The somatic nervous system controls the work of skeletal muscles, and the autonomic nervous system regulates the activity of internal organs.

The autonomic and somatic nervous systems act cooperatively in the body, but at the same time there are many differences between their systems.

Differences between the autonomic and somatic nervous systems

The autonomic nervous system (vegetative) is involuntary, it is not controlled by consciousness, the somatic system is subject to voluntary control.

The autonomic nervous system innervates internal organs, exocrine and internal secretion glands, blood and lymphatic vessels, and smooth muscles. Its main function is to maintain the constancy of the internal environment of the body. The somatic nervous system innervates skeletal muscles.

The reflex arc of both somatic and autonomic reflexes consists of three links: afferent (sensory, sensitive), intercalary and effector (executive) (Slide 4). However, in the autonomic nervous system, the effector neuron is located outside the central nervous system and is located in the ganglia (nodes). Neurons of the autonomic nervous system, which are located in the central nervous system, are called preganglionic neurons, and their processes - preganglionic fibers. Effector neurons that are located in nodes are called postganglionic neurons, and their processes - respectively postganglionic fibers. In the somatic nervous system, effector neurons are found in the CNS (gray matter of the spinal cord).

Fibers of the autonomic nervous system exit the central nervous system only in certain areas of the brain stem, as well as in the thoracolumbar and sacral parts of the spinal cord. In the intraorgan section, reflex arcs are completely located in the organ and do not have exits from the central nervous system. The fibers of the somatic nervous system emerge from the spinal cord segmentally along its entire length (Slide 5).

Structure and function of the autonomic nervous system

The autonomic nervous system contains sympathetic and parasympathetic departments (Slide 6). Each of them, in turn, has central and peripheral sections. The central sections are located in the brain stem and spinal cord, where the bodies of preganglionic neurons are located.

The peripheral section is represented by processes of neurons (pre- and postganglionic fibers), as well as ganglia, in which the bodies of postganglionic neurons are located. In the ganglia of the autonomic nervous system there are synaptic contacts between pre- and postganglionic neurons.

Many internal organs receive both sympathetic and parasympathetic innervation. As a rule (though not always), the parasympathetic and sympathetic systems have opposite effects on tissues and organs.

In the walls of many hollow internal organs (bronchi, heart, intestines) there are nerve nodes that provide regulation of functions at the local level, largely independent of the parasympathetic and sympathetic systems. These nodes are combined into a separate part of the autonomic nervous system - metasympathetic(enteral, intraorgan)

Sympathetic division of the autonomic nervous system (Slide 7)

The centers of the sympathetic nervous system are represented by nuclei located in the lateral horns of the gray matter of the spinal cord (from the VIII cervical to the I–II lumbar segments). The axons of the preganglionic neurons that make up these nuclei exit the spinal cord as part of its anterior roots and end in para - or prevertebral ganglia.Paravertebral ganglia are located near the spinal column, and prevertebral- in the abdominal cavity. The paravertebral and prevertebral ganglia contain postganglionic neurons, the processes of which form postganglionic fibers. These fibers are suitable for the actuators.

The endings of preganglionic fibers secrete the mediator acetylcholine, while the endings of postganglionic fibers secrete mainly norepinephrine. The exceptions are postganglionic fibers that innervate the sweat glands and sympathetic nerves that dilate the vessels of skeletal muscles. These fibers are called sympathetic cholinergic, because acetylcholine is secreted from their endings.

Functions of the sympathetic system.The sympathetic nervous system is activated under stress. In animals, stress implies motor activity (flight or fight response), so the functions of the sympathetic nervous system are aimed at ensuring muscle work.

When the sympathetic nerves are excited, the work of the heart increases, the vessels of the skin and abdominal cavity narrow, and in the skeletal muscles and heart they dilate. Due to such influences on the cardiovascular system, blood flow in working organs (skeletal muscles, heart, brain) increases. The muscles of the bronchi relax, and their lumen increases. An increase in the lumen of the bronchi occurs in response to increased pulmonary ventilation and an increase in the volume of air passing through

through the respiratory tract.

Digestive and urinary functions are inhibited during physical activity, so the motor and secretory activity of the gastrointestinal tract decreases, the sphincters of the urinary and gallbladder contract and their bodies relax. Under the influence of the sympathetic system, the pupil dilates.

The sympathetic nervous system not only regulates the functioning of internal organs, but also influences metabolic processes occurring in skeletal muscles and the nervous system. When the sympathetic system is activated, metabolic processes increase. In addition, when it is excited, the activity of the adrenal medulla increases and adrenaline is released.

The sympathetic department of the autonomic nervous system is a system of alarm, mobilization of the body's defenses and resources (Slide 8). Its stimulation leads to an increase in blood pressure, the release of blood from the depot, the breakdown of glycogen in the liver and the entry of glucose into the blood, an increase in tissue metabolism, and activation of the central nervous system. All these processes are associated with energy consumption in the body, i.e. the sympathetic nervous system performs ergotropic function.

Parasympathetic division of the autonomic nervous system

The centers of the parasympathetic division of the autonomic nervous system (Slide 9) are nuclei located in the midbrain (III pair of cranial nerves), medulla oblongata (VII, IX and X pairs of cranial nerves) and the sacral spinal cord. Preganglionic fibers of the parasympathetic nerves emerge from the midbrain, which are part of the oculomotor nerve (III). Preganglionic fibers emerge from the medulla oblongata, running as part of the facial (VII), glossopharyngeal (IX) and vagus (X) nerves. Preganglionic parasympathetic fibers depart from the sacral spinal cord and form part of the pelvic nerve.

The parasympathetic part of the III nerve is responsible for the constriction of the pupil, the VII and IX nerves innervate the salivary and lacrimal glands. The vagus nerve provides parasympathetic innervation to almost all organs of the thoracic and abdominal cavities, with the exception of the pelvis. The pelvic organs receive parasympathetic innervation from the sacral segments of the spinal cord.

The ganglia of the parasympathetic nervous system are located near or inside innervated organs, therefore, unlike the sympathetic department, preganglionic fibers of the parasympathetic department are long, and postganglionic fibers are short. Acetylcholine is released at the endings of parasympathetic fibers. Parasympathetic fibers innervate only certain parts of the body. Skeletal muscles, brain, smooth muscle of blood vessels, sensory organs and adrenal medulla do not have parasympathetic

innervation.

Functions of the parasympathetic nervous system.The parasympathetic division of the autonomic nervous system is active at rest, its action is aimed at restoration and maintenance constancy of the composition of the internal environment of the body ( Slide 10 ). Thus, the parasympathetic nervous system performs in the body trophotropic function.

When the parasympathetic nerves are excited, the work of the heart is inhibited, the tone of the smooth muscles of the bronchi increases, as a result of which their lumen decreases and the pupil narrows. The digestive processes (motility and secretion) are also stimulated, thereby ensuring the restoration of the level of nutrients in the body, and the gall bladder, bladder, and rectum are emptied. Acting on the pancreas, the vagus nerve promotes the production of insulin. This in turn leads to a decrease in blood glucose levels, stimulation of glycogen synthesis in the liver and the formation of fats.

Intraorgan department (enteric, metasympathetic)

This section includes the intramural (that is, located in the wall of the organ) nerve plexuses of all hollow internal organs that have their own automatic motor activity: heart, bronchi, bladder, digestive tract, uterus, gall bladder and bile ducts (Slides 11, 12) .

The intraorgan section has all the links of the reflex arc: afferent, intercalary and efferent neurons, which are entirely located in the nerve plexuses of the internal organs. This department is characterized by stricter autonomy, i.e. independence from the central nervous system. Sympathetic and parasympathetic nerves form synaptic contacts on intercalary and efferent neurons of the intraorgan nervous system. Some efferent neurons of the metasympathetic system can simultaneously be parasympathetic postganglionic neurons. All this ensures reliability in the activities of organs.

Preganglionic fibers of the metasympathetic system secrete

acetylcholine and norepinephrine, postganglionic - ATP adenosine, acetylcholine, norepinephrine, serotonin, dopamine, adrenaline, histamin

This section of the autonomic nervous system controls the functioning of smooth muscles, absorptive and secreting epithelium, local blood flow, local endocrine and immune mechanisms. Thus, the metasympathetic system is responsible for the implementation of the simplest motor and secretory functions, and the sympathetic and parasympathetic departments control and correct its work, performing more complex functions.

Mediators of the autonomic nervous system (Slide 13)

Preganglionic neurons of both parts of the autonomic nervous system

systems release the neurotransmitter acetylcholine. On the postynaptic membrane of all postganglionic neurons there are H-cholinergic receptors(they are sensitive to nicotine).

At the endings of postganglionic neurons of the parasympathetic

system secretes acetylcholine, which acts on M-cholinergic receptors in tissues. These receptors are sensitive to fly agaric venom

muscarine.

In the endings of sympathetic postganglionic neurons are released norepinephrine , which acts onα- and β-adrenergic receptors. The effect of the sympathetic nervous system on organs and tissues depends on the type of adrenergic receptors that are located there, and sometimes this effect can be the opposite. For example, vessels in which there are α-adrenergic receptors narrow under the influence of the sympathetic system, and vessels withβ-receptors - expand.

α-adrenergic receptors are mainly found in the smooth muscles of the vessels of the skin, mucous membranes and abdominal organs, as well as in the radial muscle of the eye, smooth muscles of the intestines, sphincters of the digestive tract and bladder, in the pancreas, fat cells, and platelets.

β- adrenergic receptors located mainly in the heart, smooth muscles of the intestines and bronchi, in adipose tissue, and in the vessels of the heart.

Centers for regulation of autonomous functions (Slide 14)

The centers of the autonomic nervous system described above (in the middle, medulla oblongata and spinal cord) are regulated by the overlying parts of the central nervous system. One of the highest centers for the regulation of autonomous functions is located in

hypothalamus. Stimulation of the nuclei of the posterior group of the hypothalamus accompanied by

It is caused by reactions similar to irritation of the sympathetic nervous system: dilation of the pupils and palpebral fissures, increased heart rate, constriction of blood vessels and increased blood pressure, inhibition of motor activity of the stomach and intestines, increased levels of adrenaline and norepinephrine in the blood, and glucose concentrations. Stimulation anterior nuclei of the hypothalamus leads to effects similar to irritation of the parasympathetic nervous system: constriction of the pupils and palpebral fissures, slowing the heart rate, lowering blood pressure, increasing the motor activity of the stomach and intestines, increasing the secretion of the gastric glands, stimulating insulin secretion and reducing blood glucose levels. Middle group of hypothalamic nuclei provides regulation of metabolism and water balance; the centers of hunger, thirst and satiety are located there. In addition, the hypothalamus is responsible for emotional behavior, the formation of sexual and aggressive defensive reactions.

Centers of the limbic system. These centers are responsible for the formation of the autonomous component of emotional reactions (that is, changes in the functioning of internal organs during emotional states), eating, sexual, defensive behavior, as well as the regulation of systems that provide sleep

and wakefulness, attention.

Cerebellar centers. Due to the presence of activating and inhibitory mechanisms, the cerebellum can have a stabilizing effect on the activity of internal organs, correcting autonomic reflexes.

Centers of the reticular formation. The reticular formation tones and increases the activity of other autonomous nerve centers.

Centers of the cerebral cortex. The cerebral cortex exercises higher integrative (general) control of autonomic functions, exerting descending inhibitory and activating influences on the reticular formation and other subcortical centers.

In general, the higher-lying parts of the central nervous system, without interfering with the activity of lower-lying centers, adjust their work based on the specific situation and state of the body. Thus, the autonomic nervous system has a hierarchical (subordinate) structure; the lowest elements of this system are the intraorgan nodes, which ensure the performance of simple functions (for example, nerve plexuses in the intestinal walls regulate peristaltic contractions), and the highest element is the cerebral cortex.

The nervous system is divided into 2 parts:

• central - spinal cord and brain;
• peripheral - nerves and nerve ganglia.

Nerves are bundles of nerve fibers surrounded by a connective tissue sheath.
Glands are collections of neuron cell bodies outside the central nervous system, such as the solar plexus.

The nervous system is divided into 2 parts according to its functions:

• somatic - controls skeletal muscles, obeys consciousness;
• vegetative (autonomous) - controls internal organs, does not obey consciousness. It consists of two parts - sympathetic and parasympathetic.

The brain and spinal cord are covered with three membranes - hard, arachnoid and soft. Between the bars of connective tissue in the arachnoid membrane there is a space filled with cerebrospinal fluid. It is also contained in the spinal canal of the spinal cord and in the four ventricles of the brain. Its total volume is about 120 ml, it performs nutritional, excretory and support functions.

Tests

1. The somatic nervous system regulates activity
A) heart, stomach
B) endocrine glands
B) skeletal muscles
D) smooth muscles

2. The human peripheral nervous system is formed
A) interneurons
B) spinal cord
B) nerves and ganglia
D) brain pathways

3. The somatic nervous system, unlike the autonomic nervous system, controls the work
A) skeletal muscles
B) heart and blood vessels
B) intestines
D) kidney

4) What nerves carry impulses that increase the pulse?
A) sympathetic
B) spinal
B) parasympathetic
D) cranial sensory

5. The autonomic nervous system regulates muscle function
A) chest
B) limbs
B) abdominals
D) internal organs

6. The autonomic part of the human nervous system regulates muscle function
A) backs
B) chewable
B) stomach
D) limbs

7. The autonomic (autonomic) nervous system controls activity
A) internal organs
B) analyzers
B) skeletal muscles
D) brain and spinal cord

8) Which part of the nervous system does NOT contain cerebrospinal fluid?
A) ventricles of the brain
B) soft shell
B) arachnoid membrane
D) spinal canal

The autonomic nervous system (ANS) regulates the activity of vital internal organs and systems of the body. Nerve fibers of the autonomic nervous system are located throughout the human body.

The ANS centers are located in the midbrain, diencephalon, and spinal cord. The nerves emerging from all these centers belong to two subgroups of the autonomic nervous system: sympathetic and parasympathetic.

Due to the fact that in the abdominal cavity there are many different organs, the activity of which is regulated by the autonomic nervous system, there are also many nerves and nerve plexuses located here, for example, along the aorta there is the so-called solar plexus. Nerve plexuses in the chest regulate the functions of the heart and lungs.

Functions of the ANS

The autonomic nervous system controls the activity of the most important human organs and systems. It regulates all functions of the heart and blood vessels, for example, when playing sports, individual muscles need more blood, therefore, when exposed to nerve impulses, the number of heart contractions increases and the blood vessels dilate. At the same time, the nervous system also increases breathing so that the blood can carry more oxygen to the muscles that bear a greater load. In a similar way, the ANS regulates body temperature. Excess heat is removed by intense blood circulation in the skin.

By regulating the blood circulation of the pelvic organs, the ANS also regulates human sexual functions. Thus, if the blood circulation of the pelvic organs is impaired, impotence may occur in men. The ANS regulates urinary function. Its centers are located in the lumbar and sacrum segments and the spinal cord.

The nerves of the ANS regulate the movement of the muscles of the digestive system from the esophagus, stomach, and intestines towards the anus.

If food needs to be digested, they stimulate the liver and pancreas to produce digestive juices. At the same time, blood circulation in the stomach and intestines becomes more intense, and the nutrients of eaten and digested food are immediately absorbed and distributed throughout the human body.

The sympathetic nervous system is connected to the spinal cord, where the bodies of the first neurons are located, the processes of which end in the nerve nodes (ganglia) of two sympathetic chains located on either side of the front of the spine. Due to the connection of the ganglia with other organs, in some internal diseases certain areas of the skin begin to hurt, which makes diagnosis easier.

Automated activities

It is almost impossible to influence the functions of the autonomic nervous system, because it acts automatically, it regulates all functions of the body that should also operate during sleep. The mechanism of regulation of the ANS can be influenced by hypnosis or by mastering autogenic training exercises. Therefore, these methods are used to treat various NS disorders.

How are the functions regulated?

Autonomic nervous system is widespread throughout the body. It regulates vital processes and every “mistake” it makes can be costly. The activity of the ANS is mainly automatic, involuntary and only to a small extent controlled by consciousness.

Where are the regulatory centers located?

The parasympathetic system causes the pupil to constrict, and the sympathetic system causes the pupil to dilate.

The ANS centers are located in the spinal cord and brain. The regulatory function is carried out through nerve plexuses and nodes. They independently regulate some processes that constantly occur in the human body, but only until the load requires the “intervention” of the brain. For example, the function of the muscles of the stomach and intestines is regulated in this way. The task to activate the activity of certain glands, muscles or tissues is transmitted to the nerves of the ANS in different ways, for example, the body can release the corresponding hormones, or the nerves can respond to a stimulus. An example of such a reaction is contraction of the muscles of the walls of blood vessels in order to stop bleeding (this is important, for example, when donating blood - excitement, causing spasm of the muscles of the blood vessel, complicates this process).

Do not try to influence your body's natural functions (such as your heartbeat) through autogenic training or yoga, as this may cause serious heart rhythm disturbances.

Sympathetic and parasympathetic nervous system

The autonomic nervous system is represented by two divisions - sympathetic and parasympathetic. In a number of cases, the sympathetic nervous system enhances the same function of an organ, and the parasympathetic system inhibits it; in relation to other functions and organs, it is the other way around. For example, the sympathetic nervous system increases heart rate, speeds up metabolism, and decreases the peristalsis of the stomach and intestines, causing blood vessels to contract and slow blood flow. The parasympathetic nervous system does the opposite: it stimulates digestion, blood circulation in the skin, and slows down the heart rate and metabolism.

Various nerve conductors have opposite effects on internal organs - some weaken their functions, while others strengthen them. For example, to speed up the heartbeat during physical activity and slow it down after it, the action of nerves is necessary, both stimulating the activity of the heart and slowing it down. Thus, the regulation of autonomic functions is carried out due to the coordinated action of sympathetic and parasympathetic nerves.

Consequences of disturbances in the functioning of the ANS

The consequences of disruption of the interaction of parts of the ANS are deterioration of well-being and the development of serious diseases. Insomnia, headache, stomach pain, internal anxiety and tension, a feeling of “pressure” on the heart, fainting - all these symptoms may indicate autonomic dystonia. Sometimes autonomic disorders contribute to disorders of the menstrual cycle, as well as sexual and urinary functions. During treatment, in addition to taking sedatives, psychotherapy or autogenic training, yoga are recommended.

Insomnia

A common cause of insomnia is a dysfunction of the ANS regulation function. For example, if you ate food that is difficult to digest or overeat before going to bed, then the VNS stimulates not only the stomach and intestines, but also the heart and the blood vessel system.

Alcohol is very dangerous

People who are under stress often suffer from a functional disorder of the autonomic nervous system. Drinking alcohol usually helps them cope with stress. However, in the future, alcohol abuse leads to the development

The nervous system regulates muscle function; muscle contraction is initiated by the nervous system, which, together with the endocrine system, controls the human body.

They are responsible for the constancy of the internal environment and the coordination of all body functions.

The nerve cell neuron is the basic unit of the nervous system (Fig. 1). The cells present in muscles are called motor neurons. A neuron consists of a body and projections.

The short ones are called dendrites, and the long ones are called axons. Through dendrites, a neuron can receive information from other neurons.

The axon carries the processed information to other cells (for example, muscle cells).

Further propagation of information along the neuron occurs by changing the voltage in the cell membrane, the so-called action potential.

The transmission of information between individual nerve cells is then fixed using chemical agents.

When the action potential reaches the axon terminal, transmitter is released.

The nervous system regulates muscle function.

Figure 1. Neuron organization.

The neuromuscular junction is where the last motor neuron is converted into muscle movement. The binding of a transmitter (acetylcholine) to the receptor results in another action potential that propagates along the muscle cell membrane.

Central and peripheral nervous system.

The nervous system consists of the central and peripheral nervous systems (Fig. 2).

Rice. 2. Organization of the nervous system.

The central nervous system (CNS) consists of the brain and spinal cord. The brain consists of different parts, which are indicated in (Figure 3).

Different parts of the central nervous system are interconnected through ascending and descending pathways creating functional integrity.

Rice. 3. Brain structure.

The peripheral nervous system consists of 12 pairs of head nerves connected to the brain and 31 pairs of spinal nerves attached to the spinal cord.

Sensory nerves transmit information from the body's receptors to the central nervous system. Motor nerves transport information from the central nervous system to muscle fibers.

How does the autonomic nervous system regulate muscle function?

The autonomic nervous system controls the activity of internal organs (heart, glands, smooth muscles). This happens against the will.

It consists of the sympathetic and parasympathetic systems, which both try to maintain the functional balance of the human body, which becomes prevalent in certain situations.

In athletes, the sympathetic system becomes dominant during motor activity, and the parasympathetic system dominates during rest.

The sympathetic nervous system increases the activity of organs, and the parasympathetic nervous system produces the opposite effect, that is, it reduces the activity of organs.

In the human body, the work of all its organs is closely interconnected, and therefore the body functions as a single whole. The coordination of the functions of internal organs is ensured by the nervous system. In addition, the nervous system communicates between the external environment and the regulatory organ, responding to external stimuli with appropriate reactions.

The perception of changes occurring in the external and internal environment occurs through nerve endings - receptors.

Any stimulation (mechanical, light, sound, chemical, electrical, temperature) perceived by the receptor is converted (transformed) into the process of excitation. Excitation is transmitted along sensitive - centripetal nerve fibers to the central nervous system, where an urgent process of processing nerve impulses occurs. From here, impulses are sent along the fibers of centrifugal neurons (motor) to the executive organs that implement the response - the corresponding adaptive act.

This is how a reflex occurs (from the Latin “reflexus” - reflection) - a natural reaction of the body to changes in the external or internal environment, carried out through the central nervous system in response to irritation of receptors.

Reflex reactions are varied: constriction of the pupil in bright light, salivation when food enters the oral cavity, etc.

The path along which nerve impulses (excitation) pass from the receptors to the executive organ during the implementation of any reflex is called reflex arc.

The reflex arcs are closed in the segmental apparatus of the spinal cord and brain stem, but they can also be closed higher, for example, in the subcortical ganglia or in the cortex.

Taking into account the above, there are:

• central nervous system (brain and spinal cord) and
• the peripheral nervous system, represented by nerves extending from the brain and spinal cord and other elements lying outside the spinal cord and brain.

The peripheral nervous system is divided into somatic (animal) and autonomic (or autonomic).

• The somatic nervous system primarily communicates the body with the external environment: perception of irritations, regulation of movements of the striated muscles of the skeleton, etc.
• vegetative - regulates metabolism and the functioning of internal organs: heartbeat, peristaltic contractions of the intestines, secretion of various glands, etc.

The autonomic nervous system, in turn, based on the segmental principle of structure, is divided into two levels:

• segmental - includes the sympathetic, anatomically connected to the spinal cord, and the parasympathetic, formed by clusters of nerve cells in the midbrain and medulla oblongata, nervous systems
• suprasegmental level - includes the reticular formation of the brain stem, hypothalamus, thalamus, amygdala and hippocampus - limbic-reticular complex

The somatic and autonomic nervous systems function in close cooperation, but the autonomic nervous system has some independence (autonomy), controlling many involuntary functions.

CENTRAL NERVOUS SYSTEM

Represented by the brain and spinal cord. The brain consists of gray and white matter.

Gray matter is a collection of neurons and their short processes. In the spinal cord it is located in the center, surrounding the spinal canal. In the brain, on the contrary, gray matter is located along its surface, forming a cortex (cloak) and separate clusters, called nuclei, concentrated in the white matter.

The white matter is located under the gray matter and is composed of nerve fibers covered with membranes. Nerve fibers, when connected, form nerve bundles, and several such bundles form individual nerves.

The nerves through which excitation is transmitted from the central nervous system to the organs are called centrifugal, and the nerves that conduct excitation from the periphery to the central nervous system are called centripetal.

The brain and spinal cord are surrounded by three membranes: dura mater, arachnoid membrane and vascular membrane.

• Hard - external, connective tissue, lining the internal cavity of the skull and spinal canal.
• The arachnoid is located under the dura mater - it is a thin shell with a small number of nerves and vessels.
• The choroid is fused with the brain, extends into the grooves and contains many blood vessels.

Between the choroid and arachnoid membranes, cavities filled with brain fluid are formed.

Spinal cord is located in the spinal canal and has the appearance of a white cord stretching from the occipital foramen to the lower back. There are longitudinal grooves along the anterior and posterior surfaces of the spinal cord; the spinal canal runs in the center, around which the gray matter is concentrated - an accumulation of a huge number of nerve cells that form a butterfly outline. Along the outer surface of the spinal cord there is white matter - a cluster of bundles of long processes of nerve cells.

In the gray matter, anterior, posterior and lateral horns are distinguished. The anterior horns contain motor neurons, and the posterior horns contain intercalary neurons, which communicate between sensory and motor neurons. Sensory neurons lie outside the cord, in the spinal ganglia along the course of the sensory nerves.

Long processes extend from the motor neurons of the anterior horns - the anterior roots, which form motor nerve fibers. The axons of sensory neurons approach the dorsal horns, forming the dorsal roots, which enter the spinal cord and transmit excitation from the periphery to the spinal cord. Here the excitation is switched to the interneuron, and from it to the short processes of the motor neuron, from which it is then communicated to the working organ along the axon.

In the intervertebral foramina, the motor and sensory roots unite, forming mixed nerves, which then split into anterior and posterior branches. Each of them consists of sensory and motor nerve fibers. Thus, at the level of each vertebra, a total of 31 pairs of mixed-type spinal nerves extend from the spinal cord in both directions.

The white matter of the spinal cord forms pathways that stretch along the spinal cord, connecting both its individual segments with each other and the spinal cord with the brain. Some pathways are called ascending or sensory, transmitting excitation to the brain, others are called descending or motor, which conduct impulses from the brain to certain segments of the spinal cord.

Function of the spinal cord. The spinal cord performs two functions:

1. reflex [show] .

   Each reflex is carried out by a strictly defined part of the central nervous system - the nerve center. A nerve center is a collection of nerve cells located in one of the parts of the brain and regulating the activity of an organ or system. For example, the center of the knee reflex is located in the lumbar spinal cord, the center of urination is in the sacral, and the center of pupil dilation is in the upper thoracic segment of the spinal cord. The vital motor center of the diaphragm is localized in the III-IV cervical segments. Other centers - respiratory, vasomotor - are located in the medulla oblongata.

   The nerve center consists of many interneurons. It processes the information that comes from the corresponding receptors, and generates impulses that are transmitted to the executive organs - the heart, blood vessels, skeletal muscles, glands, etc. As a result, their functional state changes. To regulate the reflex and its accuracy, the participation of the higher parts of the central nervous system, including the cerebral cortex, is necessary.

   The nerve centers of the spinal cord are directly connected to the receptors and executive organs of the body. Motor neurons of the spinal cord provide contraction of the muscles of the trunk and limbs, as well as the respiratory muscles - the diaphragm and intercostal muscles. In addition to the motor centers of skeletal muscles, the spinal cord contains a number of autonomic centers.

2. conductor [show] .

Bundles of nerve fibers that form white matter connect various parts of the spinal cord to each other and the brain to the spinal cord. There are ascending pathways that carry impulses to the brain, and descending pathways that carry impulses from the brain to the spinal cord. According to the first, excitation arising in the receptors of the skin, muscles, and internal organs is carried along the spinal nerves to the dorsal roots of the spinal cord, perceived by sensitive neurons of the spinal nodes and from here sent either to the dorsal horns of the spinal cord, or as part of the white matter reaches the trunk, and then the cerebral cortex.

Descending pathways carry excitation from the brain to the motor neurons of the spinal cord. From here, excitation is transmitted along the spinal nerves to the executive organs. The activity of the spinal cord is controlled by the brain, which regulates spinal reflexes.

Brain located in the brain part of the skull. Its average weight is 1300 - 1400 g. After a person is born, brain growth continues up to 20 years. It consists of five sections: the forebrain (cerebral hemispheres), diencephalon, midbrain, hindbrain and medulla oblongata. Inside the brain there are four interconnected cavities - the cerebral ventricles. They are filled with cerebrospinal fluid. The first and second ventricles are located in the cerebral hemispheres, the third - in the diencephalon, and the fourth - in the medulla oblongata.

The hemispheres (the newest part in evolutionary terms) reach a high level of development in humans, making up 80% of the mass of the brain. The phylogenetically more ancient part is the brain stem. The trunk includes the medulla oblongata, pons, midbrain and diencephalon.

The white matter of the trunk contains numerous nuclei of gray matter. The nuclei of 12 pairs of cranial nerves also lie in the brain stem. The brainstem is covered by the cerebral hemispheres.

Medulla- continuation of the dorsal one and repeats its structure: grooves also lie here on the front and back surfaces. It consists of white matter (conducting bundles), where clusters of gray matter are scattered - the nuclei from which cranial nerves originate - from the IX to the XII pairs, including the glossopharyngeal (IX pair), vagus (X pair), innervating the organs respiration, blood circulation, digestion and other systems, sublingual (XII pair). At the top, the medulla oblongata continues into a thickening - the pons, and the lower cerebellar peduncles extend from the sides of it. From above and from the sides, almost the entire medulla oblongata is covered by the cerebral hemispheres and the cerebellum.

The gray matter of the medulla oblongata contains vital centers that regulate cardiac activity, breathing, swallowing, carrying out protective reflexes (sneezing, coughing, vomiting, lacrimation), secretion of saliva, gastric and pancreatic juice, etc. Damage to the medulla oblongata can cause death due to the cessation of cardiac activity and respiration.

hindbrain includes the pons and cerebellum. The pons is bounded below by the medulla oblongata, passes into the cerebral peduncles above, and its lateral sections form the middle cerebellar peduncles. The substance of the pons contains the nuclei of the V to VIII pairs of cranial nerves (trigeminal, abducens, facial, auditory).

The cerebellum is located posterior to the pons and medulla oblongata. Its surface consists of gray matter (cortex). Under the cerebellar cortex there is white matter, in which there are accumulations of gray matter - the nuclei. The entire cerebellum is represented by two hemispheres, the middle part - the vermis and three pairs of legs formed by nerve fibers, through which it is connected to other parts of the brain. The main function of the cerebellum is unconditional reflex coordination of movements, determining their clarity, smoothness and maintaining body balance, as well as maintaining muscle tone. Through the spinal cord, along the pathways, impulses from the cerebellum enter the muscles. The cerebral cortex controls the activity of the cerebellum.

Midbrain located in front of the pons, it is represented by the quadrigeminal and cerebral peduncles. In its center there is a narrow canal (brain aqueduct) that connects the third and fourth ventricles. The cerebral aqueduct is surrounded by gray matter, in which the nuclei of the III and IV pairs of cranial nerves lie. The cerebral peduncles continue the pathways from the medulla oblongata and the pons to the cerebral hemispheres. The midbrain plays an important role in the regulation of tone and in the implementation of reflexes that make standing and walking possible. The sensitive nuclei of the midbrain are located in the quadrigeminal tubercles: the upper ones contain nuclei associated with the organs of vision, and the lower ones contain nuclei associated with the organs of hearing. With their participation, orienting reflexes to light and sound are carried out.

Diencephalon occupies the highest position in the trunk and lies anterior to the cerebral legs. Consists of two visual tuberosities, supracubertal, subtubercular region and geniculate bodies. Along the periphery of the diencephalon there is white matter, and in its thickness there are nuclei of gray matter. The visual hillocks are the main subcortical centers of sensitivity: impulses from all the receptors of the body arrive here along the ascending pathways, and from here to the cerebral cortex. In the subcutaneous part (hypothalamus) there are centers, the totality of which represents the highest subcortical center of the autonomic nervous system, regulating metabolism in the body, heat transfer, and the constancy of the internal environment. The parasympathetic centers are located in the anterior parts of the hypothalamus, and the sympathetic centers in the posterior parts. The subcortical visual and auditory centers are concentrated in the nuclei of the geniculate bodies.

The second pair of cranial nerves, the optic ones, goes to the geniculate bodies. The brain stem is connected to the environment and to the organs of the body by cranial nerves. By their nature they can be sensitive (I, II, VIII pairs), motor (III, IV, VI, XI, XII pairs) and mixed (V, VII, IX, X pairs).

Forebrain consists of highly developed hemispheres and the middle part connecting them. The right and left hemispheres are separated from each other by a deep fissure, at the bottom of which lies the corpus callosum. The corpus callosum connects both hemispheres through long processes of neurons that form pathways.

The cavities of the hemispheres are represented by the lateral ventricles (I and II). The surface of the hemispheres is formed by gray matter or the cerebral cortex, represented by neurons and their processes; under the cortex lies white matter - pathways. Pathways connect individual centers within one hemisphere, or the right and left halves of the brain and spinal cord, or different floors of the central nervous system. The white matter also contains clusters of nerve cells that form the subcortical nuclei of the gray matter. Part of the cerebral hemispheres is the olfactory brain with a pair of olfactory nerves extending from it (I pair).

The total surface of the cerebral cortex is 2000-2500 cm 2, its thickness is 1.5-4 mm. Despite its small thickness, the cerebral cortex has a very complex structure.

The cortex includes more than 14 billion nerve cells, arranged in six layers, which differ in shape, neuron size and connections. The microscopic structure of the cortex was first studied by V. A. Bets. He discovered pyramidal neurons, which were later given his name (Betz cells).

In a three-month embryo, the surface of the hemispheres is smooth, but the cortex grows faster than the braincase, so the cortex forms folds - convolutions limited by grooves; they contain about 70% of the surface of the cortex. The grooves divide the surface of the hemispheres into lobes.

Each hemisphere has four lobes:

• frontal
• parietal
• temporal
• occipital

The deepest grooves are the central one, which runs across both hemispheres, and the temporal one, separating the temporal lobe of the brain from the rest; The parieto-occipital sulcus separates the parietal lobe from the occipital lobe.

In front of the central sulcus (Rolandic sulcus) in the frontal lobe is the anterior central gyrus, behind it is the posterior central gyrus. The lower surface of the hemispheres and the brain stem is called the base of the brain.

Based on experiments with partial removal of different sections of the cortex in animals and observations of people with damaged cortex, it was possible to establish the functions of different parts of the cortex. Thus, the visual center is located in the cortex of the occipital lobe of the hemispheres, and the auditory center is located in the upper part of the temporal lobe. The musculocutaneous zone, which perceives irritations from the skin of all parts of the body and controls voluntary movements of skeletal muscles, occupies a section of the cortex on both sides of the central sulcus.

Each part of the body has its own section of the cortex, and the representation of the palms and fingers, lips and tongue, as the most mobile and sensitive parts of the body, occupies almost the same area of ​​the cortex in humans as the representation of all other parts of the body combined.

The cortex contains the centers of all sensory (receptor) systems, representatives of all organs and parts of the body. In this regard, centripetal nerve impulses from all internal organs or parts of the body approach the corresponding sensitive zones of the cerebral cortex, where analysis is carried out and a specific sensation is formed - visual, olfactory, etc., and it can control their work.

The functional system, consisting of a receptor, a sensitive pathway and a zone of the cortex where this type of sensitivity is projected, I. P. Pavlov called an analyzer.

Analysis and synthesis of the received information is carried out in a strictly defined area - the zone of the cerebral cortex. The most important areas of the cortex are motor, sensitive, visual, auditory, and olfactory. The motor zone is located in the anterior central gyrus in front of the central sulcus of the frontal lobe, the zone of musculocutaneous sensitivity is behind the central sulcus, in the posterior central gyrus of the parietal lobe. The visual zone is concentrated in the occipital lobe, the auditory zone is in the superior temporal gyrus of the temporal lobe, and the olfactory and gustatory zones are in the anterior temporal lobe.

Many neural processes take place in the cerebral cortex. Their purpose is twofold: interaction of the body with the external environment (behavioral reactions) and the unification of body functions, nervous regulation of all organs. The activity of the cerebral cortex of humans and higher animals was defined by I. P. Pavlov as higher nervous activity, which is a conditioned reflex function of the cerebral cortex.

PERIPHERAL NERVOUS SYSTEM

The peripheral nervous system is formed by nerves emerging from the central nervous system and ganglia and plexuses located mainly near the brain and spinal cord, as well as near various internal organs or in the walls of these organs. The peripheral nervous system is divided into somatic and autonomic divisions.

Somatic nervous system

This system is formed by sensory nerve fibers going to the central nervous system from various receptors and motor nerve fibers innervating skeletal muscles. The characteristic features of the fibers of the somatic nervous system are that they are not interrupted anywhere along the entire length from the central nervous system to the receptor or skeletal muscle, have a relatively large diameter and a high speed of excitation. These fibers make up most of the nerves that exit the central nervous system and form the peripheral nervous system.

There are 12 pairs of cranial nerves leaving the brain. The characteristics of these nerves are given in Table 1. [show] .

Table 1. Cranial nerves

Each segment of the spinal cord gives off one pair of nerves containing sensory and motor fibers. All sensory, or centripetal, fibers enter the spinal cord through the dorsal roots, on which there are thickenings - nerve ganglia. These nodes contain the bodies of centripetal neurons.

Fibers of motor, or centrifugal, neurons exit the spinal cord through the anterior roots. Each segment of the spinal cord corresponds to a specific part of the body - a metamer. However, the innervation of metameres occurs in such a way that each pair of spinal nerves innervates three adjacent metameres, and each metamer is innervated by three adjacent segments of the spinal cord. Therefore, in order to completely denervate any metamer of the body, it is necessary to cut the nerves of three adjacent segments of the spinal cord.

The autonomic nervous system is a section of the peripheral nervous system that innervates internal organs: heart, stomach, intestines, kidneys, liver, etc. It does not have its own special sensitive pathways. Sensitive impulses from organs are transmitted along sensory fibers, which also pass as part of the peripheral nerves; they are common to the somatic and autonomic nervous systems, but make up a smaller part of them.

Unlike the somatic nervous system, autonomic nerve fibers are thinner and conduct excitation much more slowly. On the way from the central nervous system to the innervated organ, they are necessarily interrupted with the formation of a synapse.

Thus, the centrifugal pathway in the autonomic nervous system includes two neurons - preganglionic and postganglionic. The body of the first neuron is located in the central nervous system, and the body of the second is outside it, in the nerve nodes (ganglia). There are many more postganglionic neurons than preganglionic neurons. As a result of this, each preganglionic fiber in the ganglion approaches and transmits its excitation to many (10 or more) postganglionic neurons. This phenomenon is called animation.

According to a number of signs, the autonomic nervous system is divided into sympathetic and parasympathetic divisions.

Sympathetic department The autonomic nervous system is formed by two sympathetic chains of nerve nodes (paired border trunk - vertebral ganglia), located on either side of the spine, and nerve branches that extend from these nodes and go to all organs and tissues as part of mixed nerves. The nuclei of the sympathetic nervous system are located in the lateral horns of the spinal cord, from the 1st thoracic to the 3rd lumbar segments.

Impulses entering the organs through sympathetic fibers provide reflex regulation of their activity. In addition to internal organs, sympathetic fibers innervate blood vessels in them, as well as in the skin and skeletal muscles. They strengthen and increase heart rate, cause rapid redistribution of blood by narrowing some vessels and dilating others.

Parasympathetic Division It is represented by a number of nerves, among which the largest is the vagus nerve. It innervates almost all organs of the thoracic and abdominal cavity.

The nuclei of the parasympathetic nerves lie in the middle, medulla oblongata and sacral parts of the spinal cord. Unlike the sympathetic nervous system, all parasympathetic nerves reach peripheral nerve nodes located in the internal organs or on the approaches to them. The impulses conducted by these nerves cause a weakening and slowing of cardiac activity, a narrowing of the coronary vessels of the heart and brain vessels, dilation of the vessels of the salivary and other digestive glands, which stimulates the secretion of these glands, and increases the contraction of the muscles of the stomach and intestines.

The main differences between the sympathetic and parasympathetic divisions of the autonomic nervous system are given in table. 2. [show] .

Table 2. Autonomic nervous system

Most internal organs receive dual autonomic innervation, that is, they are approached by both sympathetic and parasympathetic nerve fibers, which function in close interaction, exerting the opposite effect on the organs. This is of great importance in adapting the body to constantly changing environmental conditions.

L. A. Orbeli made a significant contribution to the study of the autonomic nervous system [show] .

Orbeli Leon Abgarovich (1882-1958) - Soviet physiologist, student of I. P. Pavlov. Academician Academy of Sciences of the USSR, Academy of Sciences of the Armenian SSR and Academy of Medical Sciences of the USSR. Head of the Military Medical Academy, Institute of Physiology named after. I, P. Pavlova of the USSR Academy of Sciences, Institute of Evolutionary Physiology, vice-president of the USSR Academy of Sciences.

The main direction of research is the physiology of the autonomic nervous system.

L. A. Orbeli created and developed the doctrine of the adaptive-trophic function of the sympathetic nervous system. He also conducted research on the coordination of the activity of the spinal cord, the physiology of the cerebellum, and higher nervous activity.