What is the nervous system? How the human nervous system works.

There are several systems in the human body, including the digestive, cardiovascular, and muscular systems. The nervous one deserves special attention - it makes the human body move, respond to irritating factors, see and think.

The human nervous system is a set of structures that performs function of regulation of absolutely all parts of the body, responsible for movement and sensitivity.

In contact with

Types of the human nervous system

Before answering the question of interest to people: “how does the nervous system work”, it is necessary to understand what it actually consists of and what components it is usually divided into in medicine.

With the types of NS, not everything is so simple - it is classified according to several parameters:

• area of ​​localization;
• type of management;
• method of information transfer;
• functional affiliation.

Localization area

The human nervous system in the area of ​​localization is central and peripheral. The first is represented by the brain and bone marrow, and the second consists of nerves and the autonomic network.

The central nervous system performs the functions of regulation of all internal and external organs. She makes them interact with each other. Peripheral is the one that, due to anatomical features, is located outside the spinal cord and brain.

How does the nervous system work? The PNS responds to stimuli by sending signals to the spinal cord and then to the brain. After the organs of the central nervous system process them and again send signals to the PNS, which sets, for example, the leg muscles in motion.

Information transfer method

According to this principle, reflex and neurohumoral systems. The first is the spinal cord, which, without the participation of the brain, is able to respond to stimuli.

Interesting! A person does not control the reflex function, since the spinal cord itself makes decisions. For example, when you touch in a hot surface, your hand immediately withdraws, and at the same time you did not even think to make this movement - your reflexes worked.

Neurohumoral, to which the brain belongs, must initially process information, you can control this process. After that, the signals are sent to the PNS, which carries out the commands of your think tank.

Functional affiliation

Speaking about the parts of the nervous system, one cannot fail to mention the autonomic, which in turn is divided into sympathetic, somatic and parasympathetic.

The autonomic system (ANS) is the department responsible for regulation of the lymph nodes, blood vessels, organs and glands(external and internal secretion).

The somatic system is a collection of nerves found in bones, muscles, and skin. It is they who react to all environmental factors and send data to the think tank, and then follow its orders. Absolutely every muscle movement is controlled by somatic nerves.

Interesting! The right side of the nerves and muscles is controlled by the left hemisphere, and the left side by the right.

The sympathetic system is responsible for the release of adrenaline into the blood. controls the heart, lungs and supply of nutrients to all parts of the body. In addition, it regulates body saturation.

Parasympathetic is responsible for reducing the frequency of movements, also controls the functioning of the lungs, some glands, and the iris. An equally important task is the regulation of digestion.

Type of control

Another clue to the question "how does the nervous system work" can be given by a convenient classification by type of control. It is divided into higher and lower activities.

Higher activity controls behavior in the environment. All intellectual and creative activity also belongs to the highest.

The lower activity is the regulation of all functions within the human body. This type of activity makes all body systems a single whole.

The structure and functions of the National Assembly

We have already figured out that the entire NS should be divided into peripheral, central, vegetative and all of the above, but there is still a lot to be said about their structure and functions.

Spinal cord

This body is located in the spinal canal and in fact is a kind of "rope" of nerves. It is divided into gray and white matter, where the first is completely covered by the second.

Interesting! In the section, it is noticeable that the gray matter is woven from the nerves in such a way that it resembles a butterfly. That is why it is often called "butterfly wings".

Total the spinal cord is made up of 31 sections, each of which is responsible for a separate group of nerves that control certain muscles.

The spinal cord, as already mentioned, can work without the participation of the brain - we are talking about reflexes that are not amenable to regulation. At the same time, it is under the control of the organ of thought and performs a conductive function.

Brain

This body is the least studied, many of its functions still raise many questions in scientific circles. It is divided into five departments:

• cerebral hemispheres (forebrain);
• intermediate;
• oblong;
• rear;
• average.

The first department makes up 4/5 of the entire mass of the organ. He is responsible for vision, smell, movement, thinking, hearing, sensitivity. The medulla oblongata is an incredibly important center that regulates processes such as heartbeat, breathing, protective reflexes, secretion of gastric juice and others.

The middle department controls a function such as. Intermediate plays a role in shaping the emotional state. Also here are the centers responsible for thermoregulation and metabolism in the body.

The structure of the brain

The structure of the nerve

The NS is a collection of billions of specific cells. To understand how the nervous system works, you need to talk about its structure.

A nerve is a structure that consists of a certain number of fibers. Those, in turn, consist of axons - they are the conductors of all impulses.

The number of fibers in one nerve can vary significantly. Usually it is about one hundred, but there are more than 1.5 million fibers in the human eye.

The axons themselves are covered with a special sheath, which significantly increases the speed of the signal - this allows a person to respond to stimuli almost instantly.

The nerves themselves are also different, and therefore they are classified into the following types:

• motor (transmit information from the central nervous system to the muscular system);
• cranial (this includes visual, olfactory and other types of nerves);
• sensitive (transmit information from the PNS to the CNS);
• dorsal (located in and control parts of the body);
• mixed (capable of transmitting information in two directions).

The structure of the nerve trunk

We have already covered such topics as "Types of the Human Nervous System" and "How the Nervous System Works", but a lot of interesting facts have been left aside that are worthy of mention:

1. The number in our body is greater than the number of people on the entire planet Earth.
2. There are about 90–100 billion neurons in the brain. If all of them are connected in one line, then it will reach about 1 thousand km.
3. The speed of movement of impulses reaches almost 300 km/h.
4. After the onset of puberty, the mass of the organ of thinking every year decreases by approximately one gram.
5. Men's brains are about 1/12 larger than women's.
6. The largest organ of thought was recorded in a mentally ill person.
7. The cells of the central nervous system are practically not subject to restoration, and severe stress and unrest can seriously reduce their number.
8. Until now, science has not determined how many percent we use our main thinking organ. Known are the myths that no more than 1%, and geniuses - no more than 10%.
9. Thinking organ size not at all does not affect mental activity. It was previously believed that men are smarter than the fair sex, but this statement was refuted at the end of the twentieth century.
10. Alcoholic drinks greatly suppress the function of synapses (the place of contacts between neurons), which significantly slows down mental and motor processes.

We learned what the human nervous system is - it is a complex collection of billions of cells that interact with each other at a speed equal to the movement of the fastest cars in the world.

NERVOUS SYSTEM
a complex network of structures that permeates the entire body and ensures self-regulation of its vital activity due to the ability to respond to external and internal influences (stimuli). The main functions of the nervous system are the receipt, storage and processing of information from the external and internal environment, the regulation and coordination of the activities of all organs and organ systems. In humans, as in all mammals, the nervous system includes three main components: 1) nerve cells (neurons); 2) glial cells associated with them, in particular neuroglial cells, as well as cells that form neurilemma; 3) connective tissue. Neurons provide the conduction of nerve impulses; neuroglia performs supporting, protective and trophic functions both in the brain and spinal cord, and neurilemma, which consists mainly of specialized, so-called. Schwann cells, participates in the formation of sheaths of peripheral nerve fibers; connective tissue supports and links together the various parts of the nervous system. The human nervous system is divided in different ways. Anatomically, it consists of the central nervous system (CNS) and the peripheral nervous system (PNS). The central nervous system includes the brain and spinal cord, and the PNS, which provides communication between the central nervous system and various parts of the body, includes cranial and spinal nerves, as well as nerve nodes (ganglia) and nerve plexuses that lie outside the spinal cord and brain.

Neuron. The structural and functional unit of the nervous system is a nerve cell - a neuron. It is estimated that there are more than 100 billion neurons in the human nervous system. A typical neuron consists of a body (i.e., a nuclear part) and processes, one usually non-branching process, an axon, and several branching ones, dendrites. The axon carries impulses from the cell body to the muscles, glands, or other neurons, while the dendrites carry them to the cell body. In a neuron, as in other cells, there is a nucleus and a number of tiny structures - organelles (see also CELL). These include the endoplasmic reticulum, ribosomes, Nissl bodies (tigroid), mitochondria, the Golgi complex, lysosomes, filaments (neurofilaments and microtubules).

Nerve impulse. If the stimulation of a neuron exceeds a certain threshold value, then a series of chemical and electrical changes occur at the point of stimulation, which spread throughout the neuron. Transmitted electrical changes are called nerve impulses. Unlike a simple electric discharge, which, due to the resistance of the neuron, will gradually weaken and be able to overcome only a short distance, a much slower "running" nerve impulse in the process of propagation is constantly restored (regenerates). The concentrations of ions (electrically charged atoms) - mainly sodium and potassium, as well as organic substances - outside the neuron and inside it are not the same, so the nerve cell at rest is negatively charged from the inside, and positively from the outside; as a result, a potential difference appears on the cell membrane (the so-called "resting potential" is approximately -70 millivolts). Any change that reduces the negative charge inside the cell and thereby the potential difference across the membrane is called depolarization. The plasma membrane surrounding a neuron is a complex formation consisting of lipids (fats), proteins and carbohydrates. It is practically impermeable to ions. But some of the protein molecules in the membrane form channels through which certain ions can pass. However, these channels, called ionic channels, are not always open, but, like gates, they can open and close. When a neuron is stimulated, some of the sodium (Na +) channels open at the point of stimulation, due to which sodium ions enter the cell. The influx of these positively charged ions reduces the negative charge of the inner surface of the membrane in the region of the channel, which leads to depolarization, which is accompanied by a sharp change in voltage and a discharge - a so-called. "action potential", i.e. nerve impulse. The sodium channels then close. In many neurons, depolarization also causes potassium (K+) channels to open, causing potassium ions to flow out of the cell. The loss of these positively charged ions again increases the negative charge on the inner surface of the membrane. The potassium channels then close. Other membrane proteins also begin to work - the so-called. potassium-sodium pumps that ensure the movement of Na + from the cell, and K + into the cell, which, along with the activity of potassium channels, restores the initial electrochemical state (resting potential) at the point of stimulation. Electrochemical changes at the point of stimulation cause depolarization at the adjacent point of the membrane, triggering the same cycle of changes in it. This process is constantly repeated, and at each new point where depolarization occurs, an impulse of the same magnitude is born as at the previous point. Thus, together with the renewed electrochemical cycle, the nerve impulse propagates along the neuron from point to point. Nerves, nerve fibers and ganglia. A nerve is a bundle of fibers, each of which functions independently of the others. The fibers in a nerve are organized into clusters surrounded by specialized connective tissue, which contains vessels that supply the nerve fibers with nutrients and oxygen and remove carbon dioxide and waste products. Nerve fibers along which impulses propagate from peripheral receptors to the central nervous system (afferent) are called sensitive or sensory. Fibers that transmit impulses from the central nervous system to muscles or glands (efferent) are called motor or motor. Most nerves are mixed and consist of both sensory and motor fibers. A ganglion (ganglion) is a cluster of neuron bodies in the peripheral nervous system. Axon fibers in the PNS are surrounded by a neurilemma - a sheath of Schwann cells that are located along the axon, like beads on a thread. A significant number of these axons are covered with an additional sheath of myelin (a protein-lipid complex); they are called myelinated (meaty). Fibers that are surrounded by neurilemma cells, but not covered with a myelin sheath, are called unmyelinated (non-myelinated). Myelinated fibers are found only in vertebrates. The myelin sheath is formed from the plasma membrane of the Schwann cells, which winds around the axon like a roll of ribbon, forming layer upon layer. The area of ​​the axon where two adjacent Schwann cells touch each other is called the node of Ranvier. In the CNS, the myelin sheath of nerve fibers is formed by a special type of glial cells - oligodendroglia. Each of these cells forms the myelin sheath of several axons at once. Unmyelinated fibers in the CNS lack a sheath of any special cells. The myelin sheath accelerates the conduction of nerve impulses that "jump" from one node of Ranvier to another, using this sheath as a connecting electrical cable. The speed of impulse conduction increases with the thickening of the myelin sheath and ranges from 2 m/s (along unmyelinated fibers) to 120 m/s (along fibers, especially rich in myelin). For comparison: the speed of propagation of electric current through metal wires is from 300 to 3000 km / s.
Synapse. Each neuron has a specialized connection to muscles, glands, or other neurons. The zone of functional contact between two neurons is called a synapse. Interneuronal synapses are formed between different parts of two nerve cells: between an axon and a dendrite, between an axon and a cell body, between a dendrite and a dendrite, between an axon and an axon. A neuron that sends an impulse to a synapse is called presynaptic; the neuron receiving the impulse is postsynaptic. The synaptic space is slit-shaped. A nerve impulse propagating along the membrane of a presynaptic neuron reaches the synapse and stimulates the release of a special substance - a neurotransmitter - into a narrow synaptic cleft. Neurotransmitter molecules diffuse through the cleft and bind to receptors on the membrane of the postsynaptic neuron. If the neurotransmitter stimulates the postsynaptic neuron, its action is called excitatory; if it suppresses, it is called inhibitory. The result of the summation of hundreds and thousands of excitatory and inhibitory impulses simultaneously flowing to a neuron is the main factor determining whether this postsynaptic neuron will generate a nerve impulse at a given moment. In a number of animals (for example, in the spiny lobster), a particularly close connection is established between the neurons of certain nerves with the formation of either an unusually narrow synapse, the so-called. gap junction, or, if neurons are in direct contact with each other, tight junction. Nerve impulses pass through these connections not with the participation of a neurotransmitter, but directly, by electrical transmission. A few dense junctions of neurons are also found in mammals, including humans.
Regeneration. By the time a person is born, all his neurons and most of the interneuronal connections have already been formed, and in the future only single new neurons are formed. When a neuron dies, it is not replaced by a new one. However, the remaining ones can take over the functions of the lost cell, forming new processes that form synapses with those neurons, muscles or glands with which the lost neuron was connected. Cut or damaged PNS neuron fibers surrounded by neurilemma can regenerate if the cell body remains intact. Below the site of transection, the neurilemma is preserved as a tubular structure, and that part of the axon that remains connected with the cell body grows along this tube until it reaches the nerve ending. Thus, the function of the damaged neuron is restored. Axons in the CNS that are not surrounded by a neurilemma are apparently unable to grow back to the site of their former termination. However, many CNS neurons can give rise to new short processes - branches of axons and dendrites that form new synapses.
CENTRAL NERVOUS SYSTEM

The CNS consists of the brain and spinal cord and their protective membranes. The outermost is the dura mater, under it is the arachnoid (arachnoid), and then the pia mater, fused with the surface of the brain. Between the soft and arachnoid membranes is the subarachnoid (subarachnoid) space containing the cerebrospinal (cerebrospinal) fluid, in which both the brain and the spinal cord literally float. The action of the buoyancy force of the fluid leads to the fact that, for example, the brain of an adult, having an average mass of 1500 g, actually weighs 50-100 g inside the skull. The meninges and cerebrospinal fluid also play the role of shock absorbers, softening all kinds of shocks and shocks that experiences the body and which could cause damage to the nervous system. The CNS is made up of gray and white matter. Gray matter is made up of cell bodies, dendrites, and unmyelinated axons, organized into complexes that include countless synapses and serve as information processing centers for many of the functions of the nervous system. White matter consists of myelinated and unmyelinated axons, which act as conductors that transmit impulses from one center to another. The composition of gray and white matter also includes glial cells. CNS neurons form many circuits that perform two main functions: they provide reflex activity, as well as complex information processing in higher brain centers. These higher centers, such as the visual cortex (visual cortex), receive incoming information, process it, and transmit a response signal along the axons. The result of the activity of the nervous system is one or another activity, which is based on the contraction or relaxation of muscles or the secretion or cessation of secretion of glands. It is with the work of muscles and glands that any way of our self-expression is connected. Incoming sensory information is processed by passing through a sequence of centers connected by long axons, which form specific pathways, such as pain, visual, auditory. Sensitive (ascending) pathways go in an ascending direction to the centers of the brain. Motor (descending) pathways connect the brain with the motor neurons of the cranial and spinal nerves. Pathways are usually organized in such a way that information (for example, pain or tactile) from the right side of the body goes to the left side of the brain and vice versa. This rule also applies to descending motor pathways: the right half of the brain controls the movements of the left half of the body, and the left half controls the right. There are a few exceptions to this general rule, however. The brain consists of three main structures: the cerebral hemispheres, the cerebellum, and the brainstem. The cerebral hemispheres - the largest part of the brain - contain higher nerve centers that form the basis of consciousness, intellect, personality, speech, and understanding. In each of the large hemispheres, the following formations are distinguished: isolated accumulations (nuclei) of gray matter lying in the depths, which contain many important centers; a large array of white matter located above them; covering the hemispheres from the outside, a thick layer of gray matter with numerous convolutions, constituting the cerebral cortex. The cerebellum also consists of a deep gray matter, an intermediate array of white matter, and an outer thick layer of gray matter that forms many convolutions. The cerebellum provides mainly coordination of movements. The brain stem is formed by a mass of gray and white matter, not divided into layers. The trunk is closely connected with the cerebral hemispheres, cerebellum and spinal cord and contains numerous centers of sensory and motor pathways. The first two pairs of cranial nerves depart from the cerebral hemispheres, the remaining ten pairs from the trunk. The trunk regulates such vital functions as breathing and blood circulation.
see also HUMAN BRAIN.
Spinal cord. Located inside the spinal column and protected by its bone tissue, the spinal cord has a cylindrical shape and is covered with three membranes. On a transverse section, the gray matter has the shape of the letter H or a butterfly. Gray matter is surrounded by white matter. The sensory fibers of the spinal nerves end in the dorsal (posterior) sections of the gray matter - the posterior horns (at the ends of H facing the back). The bodies of motor neurons of the spinal nerves are located in the ventral (anterior) sections of the gray matter - the anterior horns (at the ends of H, remote from the back). In the white matter, there are ascending sensory pathways ending in the gray matter of the spinal cord, and descending motor pathways coming from the gray matter. In addition, many fibers in the white matter connect the different parts of the gray matter of the spinal cord.
PERIPHERAL NERVOUS SYSTEM
The PNS provides a two-way connection between the central parts of the nervous system and the organs and systems of the body. Anatomically, the PNS is represented by cranial (cranial) and spinal nerves, as well as a relatively autonomous enteric nervous system localized in the intestinal wall. All cranial nerves (12 pairs) are divided into motor, sensory or mixed. The motor nerves originate in the motor nuclei of the trunk, formed by the bodies of the motor neurons themselves, and the sensory nerves are formed from the fibers of those neurons whose bodies lie in the ganglia outside the brain. 31 pairs of spinal nerves depart from the spinal cord: 8 pairs of cervical, 12 thoracic, 5 lumbar, 5 sacral and 1 coccygeal. They are designated according to the position of the vertebrae adjacent to the intervertebral foramen from which these nerves emerge. Each spinal nerve has an anterior and a posterior root that merges to form the nerve itself. The back root contains sensory fibers; it is closely related to the spinal ganglion (posterior root ganglion), which consists of the bodies of neurons whose axons form these fibers. The anterior root consists of motor fibers formed by neurons whose cell bodies lie in the spinal cord.
AUTONOMIC SYSTEM
The autonomic, or autonomic, nervous system regulates the activity of the involuntary muscles, the heart muscle, and various glands. Its structures are located both in the central nervous system and in the peripheral. The activity of the autonomic nervous system is aimed at maintaining homeostasis, i.e. a relatively stable state of the internal environment of the body, such as a constant body temperature or blood pressure, corresponding to the needs of the body. Signals from the CNS arrive at the working (effector) organs through pairs of series-connected neurons. The bodies of neurons of the first level are located in the CNS, and their axons terminate in the autonomic ganglia lying outside the CNS, and here they form synapses with the bodies of neurons of the second level, the axons of which directly contact the effector organs. The first neurons are called preganglionic, the second - postganglionic. In that part of the autonomic nervous system, which is called the sympathetic, the bodies of preganglionic neurons are located in the gray matter of the thoracic (thoracic) and lumbar (lumbar) spinal cord. Therefore, the sympathetic system is also called the thoraco-lumbar system. The axons of its preganglionic neurons terminate and form synapses with postganglionic neurons in the ganglia located in a chain along the spine. Axons of postganglionic neurons are in contact with effector organs. The endings of postganglionic fibers secrete norepinephrine (a substance close to adrenaline) as a neurotransmitter, and therefore the sympathetic system is also defined as adrenergic. The sympathetic system is complemented by the parasympathetic nervous system. The bodies of its pregangliar neurons are located in the brainstem (intracranial, i.e. inside the skull) and the sacral (sacral) section of the spinal cord. Therefore, the parasympathetic system is also called the craniosacral system. Axons of preganglionic parasympathetic neurons terminate and form synapses with postganglionic neurons in the ganglia located near the working organs. The endings of postganglionic parasympathetic fibers release the neurotransmitter acetylcholine, on the basis of which the parasympathetic system is also called cholinergic. As a rule, the sympathetic system stimulates those processes that are aimed at mobilizing the body's forces in extreme situations or under stress. The parasympathetic system contributes to the accumulation or restoration of the body's energy resources. The reactions of the sympathetic system are accompanied by the consumption of energy resources, an increase in the frequency and strength of heart contractions, an increase in blood pressure and blood sugar, as well as an increase in blood flow to skeletal muscles due to a decrease in its flow to internal organs and skin. All of these changes are characteristic of the "fright, flight or fight" response. The parasympathetic system, on the contrary, reduces the frequency and strength of heart contractions, lowers blood pressure, and stimulates the digestive system. The sympathetic and parasympathetic systems act in a coordinated manner and cannot be regarded as antagonistic. Together they support the functioning of internal organs and tissues at a level corresponding to the intensity of stress and the emotional state of a person. Both systems function continuously, but their activity levels fluctuate depending on the situation.
REFLEXES
When an adequate stimulus acts on the receptor of a sensory neuron, a volley of impulses arises in it, triggering a response action called a reflex act (reflex). Reflexes underlie most of the manifestations of the vital activity of our body. The reflex act is carried out by the so-called. reflex arc; this term refers to the path of transmission of nerve impulses from the point of initial stimulation on the body to the organ that performs the response. The arc of the reflex that causes contraction of the skeletal muscle consists of at least two neurons: a sensory neuron, whose body is located in the ganglion, and the axon forms a synapse with the neurons of the spinal cord or brain stem, and the motor (lower, or peripheral, motor neuron), whose body is located in gray matter, and the axon terminates in a motor end plate on skeletal muscle fibers. The reflex arc between the sensory and motor neurons can also include a third, intermediate, neuron located in the gray matter. The arcs of many reflexes contain two or more intermediate neurons. Reflex actions are carried out involuntarily, many of them are not realized. The knee jerk, for example, is elicited by tapping the quadriceps tendon at the knee. This is a two-neuron reflex, its reflex arc consists of muscle spindles (muscle receptors), a sensory neuron, a peripheral motor neuron, and a muscle. Another example is the reflex withdrawal of a hand from a hot object: the arc of this reflex includes a sensory neuron, one or more intermediate neurons in the gray matter of the spinal cord, a peripheral motor neuron, and a muscle. Many reflex acts have a much more complex mechanism. The so-called intersegmental reflexes are made up of combinations of simpler reflexes, in the implementation of which many segments of the spinal cord take part. Thanks to such reflexes, for example, coordination of the movements of the arms and legs when walking is ensured. The complex reflexes that close in the brain include movements associated with maintaining balance. Visceral reflexes, i.e. reflex reactions of internal organs mediated by the autonomic nervous system; they provide emptying of the bladder and many processes in the digestive system.
see also REFLEX.
DISEASES OF THE NERVOUS SYSTEM
Damage to the nervous system occurs with organic diseases or injuries of the brain and spinal cord, meninges, peripheral nerves. Diagnosis and treatment of diseases and injuries of the nervous system is the subject of a special branch of medicine - neurology. Psychiatry and clinical psychology deal mainly with mental disorders. The areas of these medical disciplines often overlap. See individual diseases of the nervous system: ALZHEIMER'S DISEASE;
STROKE ;
MENINGITIS;
NEURITIS;
PARALYSIS;
PARKINSON'S DISEASE;
POLIO;
MULTIPLE SCLEROSIS ;
TENETIS;
CEREBRAL PALSY ;
CHOREA;
ENCEPHALITIS;
EPILEPSY.
see also
ANATOMY COMPARATIVE;
HUMAN ANATOMY .
LITERATURE
Bloom F., Leizerson A., Hofstadter L. Brain, mind and behavior. M., 1988 Human Physiology, ed. R. Schmidt, G. Tevsa, vol. 1. M., 1996

Collier Encyclopedia. - Open society. 2000 .

The nervous system controls the activity of all systems and organs and ensures the connection of the body with the external environment.

The structure of the nervous system

The structural unit of the nervous system is the neuron - a nerve cell with processes. In general, the structure of the nervous system is a collection of neurons that are constantly in contact with each other using special mechanisms - synapses. The following types of neurons differ in function and structure:

• Sensitive or receptor;
• Effector - motor neurons that send an impulse to the executive organs (effectors);
• Closing or plug-in (conductor).

Conventionally, the structure of the nervous system can be divided into two large sections - somatic (or animal) and vegetative (or autonomous). The somatic system is primarily responsible for the connection of the body with the external environment, providing movement, sensitivity and contraction of skeletal muscles. The vegetative system affects the growth processes (respiration, metabolism, excretion, etc.). Both systems have a very close relationship, only the autonomic nervous system is more independent and does not depend on the will of a person. That is why it is also called autonomous. The autonomous system is divided into sympathetic and parasympathetic.

The entire nervous system consists of the central and peripheral. The central part includes the spinal cord and brain, and the peripheral system represents the outgoing nerve fibers from the brain and spinal cord. If you look at the brain in section, you can see that it consists of white and gray matter.

Gray matter is an accumulation of nerve cells (with the initial sections of processes extending from their bodies). Separate groups of gray matter are also called nuclei.

White matter consists of nerve fibers covered with myelin sheath (processes of nerve cells from which gray matter is formed). In the spinal cord and brain, nerve fibers form pathways.

Peripheral nerves are divided into motor, sensory and mixed, depending on what fibers they consist of (motor or sensory). The bodies of neurons, whose processes are made up of sensory nerves, are located in ganglions outside the brain. The bodies of motor neurons are located in the motor nuclei of the brain and the anterior horns of the spinal cord.

Functions of the nervous system

The nervous system has different effects on the organs. The three main functions of the nervous system are:

• Starting, causing or stopping the function of an organ (secretion of the gland, muscle contraction, etc.);
• Vasomotor, which allows you to change the width of the lumen of the vessels, thereby regulating the flow of blood to the organ;
• Trophic, lowering or increasing metabolism, and, consequently, the consumption of oxygen and nutrients. This allows you to constantly coordinate the functional state of the body and its need for oxygen and nutrients. When impulses are sent along the motor fibers to the working skeletal muscle, causing its contraction, then impulses are simultaneously received that increase metabolism and dilate blood vessels, which makes it possible to provide the energy for performing muscle work.

Diseases of the nervous system

Together with the endocrine glands, the nervous system plays a crucial role in the functioning of the body. It is responsible for the coordinated work of all systems and organs of the human body and unites the spinal cord, brain and peripheral system. Motor activity and sensitivity of the body is supported by nerve endings. And thanks to the autonomic system, the cardiovascular system and other organs are inverted.

Therefore, a violation of the functions of the nervous system affects the work of all systems and organs.

All diseases of the nervous system can be divided into infectious, hereditary, vascular, traumatic and chronically progressive.

Hereditary diseases are genomic and chromosomal. The most famous and common chromosomal disease is Down's disease. This disease is characterized by the following symptoms: a violation of the musculoskeletal system, the endocrine system, lack of mental abilities.

Traumatic lesions of the nervous system occur due to bruises and injuries, or when squeezing the brain or spinal cord. Such diseases are usually accompanied by vomiting, nausea, memory loss, disorders of consciousness, loss of sensitivity.

Vascular diseases mainly develop against the background of atherosclerosis or hypertension. This category includes chronic cerebrovascular insufficiency, cerebrovascular accident. Characterized by the following symptoms: attacks of vomiting and nausea, headache, impaired motor activity, decreased sensitivity.

Chronically progressive diseases, as a rule, develop as a result of metabolic disorders, exposure to infection, intoxication of the body, or due to anomalies in the structure of the nervous system. Such diseases include sclerosis, myasthenia, etc. These diseases usually progress gradually, reducing the efficiency of some systems and organs.

Causes of diseases of the nervous system:

The placental route of transmission of diseases of the nervous system during pregnancy (cytomegalovirus, rubella), as well as through the peripheral system (poliomyelitis, rabies, herpes, meningoencephalitis) is also possible.

In addition, the nervous system is negatively affected by endocrine, heart, kidney diseases, malnutrition, chemicals and drugs, heavy metals.

The human nervous system is a stimulator of the muscular system, which we talked about in. As we already know, muscles are needed to move parts of the body in space, and we even studied specifically which muscles are designed for which work. But what powers the muscles? What and how makes them work? This will be discussed in this article, from which you will draw the necessary theoretical minimum for mastering the topic indicated in the title of the article.

First of all, it is worth saying that the nervous system is designed to transmit information and commands to our body. The main functions of the human nervous system are the perception of changes within the body and the space surrounding it, the interpretation of these changes and the response to them in the form of a certain form (including muscle contraction).

Nervous system- many different, interacting nervous structures, which, along with the endocrine system, provide coordinated regulation of the work of most of the body's systems, as well as a response to changing conditions of the external and internal environment. This system combines sensitization, motor activity and the correct functioning of such systems as endocrine, immune and not only.

The structure of the nervous system

Excitability, irritability and conductivity are characterized as functions of time, that is, it is a process that occurs from irritation to the appearance of an organ response. The propagation of a nerve impulse in the nerve fiber occurs due to the transition of local foci of excitation to neighboring inactive areas of the nerve fiber. The human nervous system has the property of transforming and generating the energies of the external and internal environment and transforming them into a nervous process.

The structure of the human nervous system: 1- brachial plexus; 2- musculocutaneous nerve; 3- radial nerve; 4- median nerve; 5- ilio-hypogastric nerve; 6- femoral-genital nerve; 7- locking nerve; 8- ulnar nerve; 9- common peroneal nerve; 10 - deep peroneal nerve; 11- superficial nerve; 12- brain; 13- cerebellum; 14- spinal cord; 15- intercostal nerves; 16 - hypochondrium nerve; 17- lumbar plexus; 18 - sacral plexus; 19- femoral nerve; 20 - genital nerve; 21- sciatic nerve; 22 - muscular branches of the femoral nerves; 23 - saphenous nerve; 24- tibial nerve

The nervous system functions as a whole with the sense organs and is controlled by the brain. The largest part of the latter is called the cerebral hemispheres (in the occipital region of the skull there are two smaller hemispheres of the cerebellum). The brain is connected to the spinal cord. The right and left cerebral hemispheres are interconnected by a compact bundle of nerve fibers called the corpus callosum.

Spinal cord- the main nerve trunk of the body - passes through the canal formed by the openings of the vertebrae, and stretches from the brain to the sacral spine. From each side of the spinal cord, nerves depart symmetrically to different parts of the body. Touch in general terms is provided by certain nerve fibers, the innumerable endings of which are located in the skin.

Classification of the nervous system

The so-called types of the human nervous system can be represented as follows. The whole integral system is conditionally formed: the central nervous system - CNS, which includes the brain and spinal cord, and the peripheral nervous system - PNS, which includes numerous nerves extending from the brain and spinal cord. The skin, joints, ligaments, muscles, internal organs and sensory organs send input signals to the CNS via PNS neurons. At the same time, outgoing signals from the central NS, the peripheral NS sends to the muscles. As a visual material, below, in a logically structured way, the entire human nervous system (diagram) is presented.

central nervous system- the basis of the human nervous system, which consists of neurons and their processes. The main and characteristic function of the central nervous system is the implementation of reflective reactions of various degrees of complexity, which are called reflexes. The lower and middle sections of the central nervous system - the spinal cord, medulla oblongata, midbrain, diencephalon and cerebellum - control the activity of individual organs and systems of the body, implement communication and interaction between them, ensure the integrity of the body and its correct functioning. The highest department of the central nervous system - the cerebral cortex and the nearest subcortical formations - for the most part controls the communication and interaction of the body as an integral structure with the outside world.

peripheral nervous system- is a conditionally allocated part of the nervous system, which is located outside the brain and spinal cord. Includes nerves and plexuses of the autonomic nervous system, connecting the central nervous system with the organs of the body. Unlike the CNS, the PNS is not protected by bones and can be subject to mechanical damage. In turn, the peripheral nervous system itself is divided into somatic and autonomic.

• somatic nervous system- part of the human nervous system, which is a complex of sensory and motor nerve fibers responsible for the excitation of muscles, including skin and joints. She also manages the coordination of body movements, and the receipt and transmission of external stimuli. This system performs actions that a person controls consciously.
• autonomic nervous system divided into sympathetic and parasympathetic. The sympathetic nervous system governs the response to danger or stress, and can cause an increase in heart rate, blood pressure, and sensory stimulation, among other things, by increasing the level of adrenaline in the blood. The parasympathetic nervous system, in turn, controls the state of rest, and regulates pupillary contraction, slowing of the heart rate, dilation of blood vessels, and stimulation of the digestive and genitourinary systems.

Above you can see a logically structured diagram, which shows the parts of the human nervous system, in the order corresponding to the above material.

The structure and functions of neurons

All movements and exercises are controlled by the nervous system. The main structural and functional unit of the nervous system (both central and peripheral) is the neuron. Neurons are excitable cells that are capable of generating and transmitting electrical impulses (action potentials).

The structure of the nerve cell: 1 - cell body; 2- dendrites; 3- cell nucleus; 4- myelin sheath; 5- axon; 6 - the end of the axon; 7- synaptic thickening

The functional unit of the neuromuscular system is the motor unit, which consists of a motor neuron and the muscle fibers innervated by it. Actually, the work of the human nervous system on the example of the process of muscle innervation occurs as follows.

The cell membrane of the nerve and muscle fiber is polarized, that is, there is a potential difference across it. Inside the cell contains a high concentration of potassium ions (K), and outside - sodium ions (Na). At rest, the potential difference between the inner and outer side of the cell membrane does not lead to the appearance of an electric charge. This defined value is the resting potential. Due to changes in the external environment of the cell, the potential on its membrane constantly fluctuates, and if it rises, and the cell reaches its electrical threshold of excitation, there is a sharp change in the electrical charge of the membrane, and it begins to conduct an action potential along the axon to the innervated muscle. By the way, in large muscle groups, one motor nerve can innervate up to 2-3 thousand muscle fibers.

In the diagram below, you can see an example of what path a nerve impulse takes from the moment a stimulus occurs to receiving a response to it in each individual system.

Nerves are connected to each other through synapses, and to muscles through neuromuscular junctions. Synapse- this is the place of contact between two nerve cells, and - the process of transmitting an electrical impulse from a nerve to a muscle.

synaptic connection: 1- neural impulse; 2- receiving neuron; 3- axon branch; 4- synaptic plaque; 5- synaptic cleft; 6 - neurotransmitter molecules; 7- cell receptors; 8 - dendrite of the receiving neuron; 9- synaptic vesicles

Neuromuscular contact: 1- neuron; 2- nerve fiber; 3- neuromuscular contact; 4- motor neuron; 5- muscle; 6- myofibrils

Thus, as we have already said, the process of physical activity in general and muscle contraction in particular is completely controlled by the nervous system.

Conclusion

Today we learned about the purpose, structure and classification of the human nervous system, as well as how it is related to its motor activity and how it affects the work of the whole organism as a whole. Since the nervous system is involved in the regulation of the activity of all organs and systems of the human body, including, and possibly, first of all, the cardiovascular system, in the next article from the series on the systems of the human body, we will move on to its consideration.

a set of nerve formations in vertebrates and humans, through which the perception of stimuli acting on the body is realized, the processing of the resulting excitation impulses, the formation of responses. Thanks to it, the functioning of the body as a whole is ensured:

1) contacts with the outside world;

2) implementation of goals;

3) coordination of the work of internal organs;

4) holistic adaptation of the body.

The neuron acts as the main structural and functional element of the nervous system. Stand out:

1) the central nervous system - which consists of the brain and spinal cord;

2) peripheral nervous system - which consists of nerves extending from the brain and spinal cord, from intervertebral nerve nodes, as well as from the peripheral part of the autonomic nervous system;

3) vegetative nervous system - structures of the nervous system that provide control of the vegetative functions of the body.

NERVOUS SYSTEM

English nervous system) - a set of nerve formations in the human body and vertebrates. Its main functions are: 1) ensuring contacts with the outside world (perception of information, organization of body reactions - from simple responses to stimuli to complex behavioral acts); 2) realization of the goals and intentions of a person; 3) integration of internal organs into systems, coordination and regulation of their activities (see Homeostasis); 4) organization of integral functioning and development of the organism.

Structural and functional element of N. with. is a neuron - a nerve cell consisting of a body, dendrites (the receptor and integrating apparatus of the neuron) and an axon (its efferent part). On the terminal branches of the axon there are special formations that are in contact with the body and dendrites of other neurons - synapses. Synapses are of 2 types - excitatory and inhibitory, with their help, respectively, the transmission or blockade of the impulse message passing through the fiber to the destination neuron occurs.

The interaction of postsynaptic excitatory and inhibitory effects on one neuron creates a multi-conditioning response of the cell, which is the simplest element of integration. Neurons, differentiated in structure and function, are combined into neural modules (neural ensembles) - next. a stage of integration that ensures high plasticity in the organization of brain functions (see Plasticity n. s).

N. s. divided into central and peripheral. C. n. With. It consists of the brain, which is located in the cranial cavity, and the spinal cord, located in the spine. The brain, especially its cortex, is the most important organ of mental activity. The spinal cord carries out g. inborn behaviors. Peripheral N. with. consists of nerves extending from the brain and spinal cord (the so-called cranial and spinal nerves), intervertebral ganglions, and also from the peripheral part of the autonomic N. with. - accumulations of nerve cells (ganglia) with nerves approaching them (preganglionic) and departing from them (postganglionic) nerves.

The vegetative functions of the body (digestion, blood circulation, respiration, metabolism, etc.) are controlled by vegetative nervous system, which is divided into sympathetic and parasympathetic sections: the 1st section mobilizes the functions of the body in a state of increased mental stress, the 2nd - ensures the functioning of internal organs under normal conditions. Si. Blocks of the brain, Deep structures of the brain, Cortex, Neuron-detector, Properties n. With. (N. V. Dubrovinskaya, D. A. Farber.)

NERVOUS SYSTEM

nervous system) - a set of anatomical structures formed by nervous tissue. The nervous system consists of many neurons that transmit information in the form of nerve impulses to various parts of the body and receive it from them to maintain the active life of the body. The nervous system is divided into central and peripheral. The brain and spinal cord form the central nervous system; peripheral nerves include paired spinal and cranial nerves with their roots, their branches, nerve endings and ganglia. There is another classification, according to which the unified nervous system is also conventionally divided into two parts: somatic (animal) and autonomic (autonomous). The somatic nervous system innervates mainly the organs of the soma (body, striated, or skeletal, muscles, skin) and some internal organs (tongue, larynx, pharynx), provides a connection between the body and the external environment. The autonomic (autonomous) nervous system innervates all the viscera, glands, including endocrine, smooth muscles of organs and skin, blood vessels and the heart, regulates metabolic processes in all organs and tissues. The autonomic nervous system, in turn, is divided into two parts: parasympathetic and sympathetic. In each of them, as in the somatic nervous system, the central and peripheral sections are distinguished (ed.). The main structural and functional unit of the nervous system is the neuron (nerve cell).

Nervous system

Word formation. Comes from the Greek. neuron - vein, nerve and systema - connection.

Specificity. Her work provides:

Contacts with the outside world;

Realization of goals;

Coordination of the work of internal organs;

Whole body adaptation.

The neuron is the main structural and functional element of the nervous system.

The central nervous system, which consists of the brain and spinal cord,

Peripheral nervous system, consisting of nerves extending from the brain and spinal cord, intervertebral ganglions;

Peripheral division of the autonomic nervous system.

NERVOUS SYSTEM

Collective designation of a complete system of structures and organs, consisting of nervous tissue. Depending on what is in the center of attention, various schemes for isolating parts of the nervous system are used. The most common is the anatomical division into the central nervous system (the brain and spinal cord) and the peripheral nervous system (everything else). Another taxonomy is based on functions, dividing the nervous system into the somatic nervous system and the autonomic nervous system, the former for voluntary, conscious sensory and motor functions, and the latter for visceral, automatic, involuntary ones.

Source: Nervous system

A system that ensures the integration of the functions of all organs and tissues, their trophism, communication with the outside world, sensitivity, movement, consciousness, alternation of wakefulness and sleep, the state of emotional and mental processes, including manifestations of higher nervous activity, the development of which determines the characteristics of a person's personality. S.n. It is divided primarily into central, represented by the brain tissue (brain and spinal cord), and peripheral, which includes all other structures of the nervous system.