Nerves in the nervous system. The human nervous system: its structure and features

Very clear, concise and clear. Posted as a keepsake.

1. What is the nervous system

One of the components of a person is his nervous system. It is reliably known that diseases of the nervous system adversely affect the physical condition of the entire human body. With a disease of the nervous system, both the head and the heart (the “motor” of a person) begin to hurt.

Nervous system is a system that regulates the activity of all human organs and systems. This system causes:

1) the functional unity of all human organs and systems;

2) the connection of the whole organism with the environment.

The nervous system also has its own structural unit, which is called a neuron. Neurons are cells that have special processes. It is neurons that build neural circuits.

The entire nervous system is divided into:

1) central nervous system;

2) peripheral nervous system.

The central nervous system includes the brain and spinal cord, and the peripheral nervous system includes the cranial and spinal nerves and nerve nodes extending from the brain and spinal cord.

Also conditionally, the nervous system can be divided into two large sections:

1) somatic nervous system;

2) autonomic nervous system.

somatic nervous system associated with the human body. This system is responsible for the fact that a person can move independently, it also determines the connection of the body with the environment, as well as sensitivity. Sensitivity is provided with the help of human sense organs, as well as with the help of sensitive nerve endings.

The movement of a person is ensured by the fact that with the help of the nervous system, skeletal muscle mass is controlled. Scientists-biologists call the somatic nervous system in another way animal, because movement and sensitivity are peculiar only to animals.

Nerve cells can be divided into two large groups:

1) afferent (or receptor) cells;

2) efferent (or motor) cells.

Receptor nerve cells perceive light (using visual receptors), sound (using sound receptors), smells (using olfactory and taste receptors).

Motor nerve cells generate and transmit impulses to specific executing organs. The motor nerve cell has a body with a nucleus, numerous processes called dendrites. A nerve cell also has a nerve fiber called an axon. The length of these axons ranges from 1 to 1.5 mm. With their help, electrical impulses are transmitted to specific cells.

In the cell membranes that are responsible for the sensation of taste and smell, there are special biological compounds that react to a particular substance by changing their state.

In order for a person to be healthy, he must first of all monitor the state of his nervous system. Today, people sit a lot in front of the computer, stand in traffic jams, and also get into various stressful situations (for example, a student received a negative grade at school or an employee received a reprimand from his immediate superiors) - all this negatively affects our nervous system. Today, enterprises and organizations create rest rooms (or relaxation rooms). Arriving in such a room, the worker mentally disconnects from all problems and just sits and relaxes in a favorable environment.

Employees of law enforcement agencies (police, prosecutors, etc.) have created, one might say, their own system to protect their own nervous system. Victims often come to them and talk about the misfortune that happened to them. If a law enforcement officer, as they say, takes to heart what happened to the victims, then he will retire as an invalid, if at all his heart can withstand until retirement. Therefore, law enforcement officers put, as it were, a “protective screen” between themselves and the victim or the criminal, that is, the problems of the victim, the criminal are listened to, but an employee, for example, of the prosecutor’s office, does not express any human participation in them. Therefore, you can often hear that all law enforcement officers are heartless and very evil people. In fact, they are not like that - they just have such a method of protecting their own health.

2. Autonomic nervous system

autonomic nervous system is one of the parts of our nervous system. The autonomic nervous system is responsible for: the activity of the internal organs, the activity of the endocrine and external secretion glands, the activity of the blood and lymphatic vessels, and also, to some extent, the muscles.

The autonomic nervous system is divided into two sections:

1) sympathetic section;

2) parasympathetic section.

Sympathetic nervous system dilates the pupil, it also causes an increase in heart rate, an increase in blood pressure, expands the small bronchi, etc. This nervous system is carried out by sympathetic spinal centers. It is from these centers that peripheral sympathetic fibers begin, which are located in the lateral horns of the spinal cord.

parasympathetic nervous system is responsible for the activity of the bladder, genitals, rectum, and it also “irritates” a number of other nerves (for example, glossopharyngeal, oculomotor nerve). Such a "diverse" activity of the parasympathetic nervous system is explained by the fact that its nerve centers are located both in the sacral spinal cord and in the brain stem. Now it becomes clear that those nerve centers that are located in the sacral spinal cord control the activity of the organs located in the small pelvis; nerve centers located in the brain stem regulate the activity of other organs through a number of special nerves.

How is the control over the activity of the sympathetic and parasympathetic nervous system carried out? Control over the activity of these sections of the nervous system is carried out by special autonomic apparatus, which are located in the brain.

Diseases of the autonomic nervous system. The causes of diseases of the autonomic nervous system are as follows: a person does not tolerate hot weather or, conversely, feels uncomfortable in winter. A symptom may be that a person, when excited, quickly begins to blush or turn pale, his pulse quickens, he begins to sweat a lot.

It should be noted that diseases of the autonomic nervous system occur in people from birth. Many believe that if a person gets excited and blushes, then he is simply too modest and shy. Few people would think that this person has some kind of autonomic nervous system disease.

Also, these diseases can be acquired. For example, due to a head injury, chronic poisoning with mercury, arsenic, due to a dangerous infectious disease. They can also occur when a person is overworked, with a lack of vitamins, with severe mental disorders and experiences. Also, diseases of the autonomic nervous system can be the result of non-compliance with safety regulations at work with dangerous working conditions.

The regulatory activity of the autonomic nervous system may be impaired. Diseases can "mask" as other diseases. For example, with a disease of the solar plexus, bloating, poor appetite can be observed; with a disease of the cervical or thoracic nodes of the sympathetic trunk, chest pains can be observed, which can radiate to the shoulder. These pains are very similar to heart disease.

To prevent diseases of the autonomic nervous system, a person should follow a number of simple rules:

1) avoid nervous fatigue, colds;

2) observe safety precautions in production with hazardous working conditions;

3) eat well;

4) go to the hospital in a timely manner, complete the entire prescribed course of treatment.

Moreover, the last point, timely admission to the hospital and complete completion of the prescribed course of treatment, is the most important. This follows from the fact that delaying your visit to the doctor for too long can lead to the most unfortunate consequences.

Good nutrition also plays an important role, because a person "charges" his body, gives him new strength. Having refreshed, the body begins to fight diseases several times more actively. In addition, fruits contain many beneficial vitamins that help the body fight disease. The most useful fruits are in their raw form, because when they are harvested, many useful properties can disappear. A number of fruits, in addition to containing vitamin C, also have a substance that enhances the action of vitamin C. This substance is called tannin and is found in quinces, pears, apples, and pomegranates.

3. Central nervous system

The human central nervous system consists of the brain and spinal cord.

The spinal cord looks like a cord, it is somewhat flattened from front to back. Its size in an adult is approximately 41 to 45 cm, and its weight is about 30 gm. It is "surrounded" by the meninges and is located in the brain canal. Throughout its length, the thickness of the spinal cord is the same. But it has only two thickenings:

1) cervical thickening;

2) lumbar thickening.

It is in these thickenings that the so-called innervation nerves of the upper and lower extremities are formed. Dorsal brain is divided into several departments:

1) cervical;

2) thoracic region;

3) lumbar;

4) sacral department.

The human brain is located in the cranial cavity. It has two large hemispheres: the right hemisphere and the left hemisphere. But, in addition to these hemispheres, the trunk and cerebellum are also isolated. Scientists have calculated that the brain of a man is heavier than the brain of a woman by an average of 100 gm. They explain this by the fact that most men are much larger than women in terms of their physical parameters, that is, all parts of a man's body are larger than parts of a woman's body. The brain actively begins to grow even when the child is still in the womb. The brain reaches its "real" size only when a person reaches the age of twenty. At the very end of a person's life, his brain becomes a little lighter.

There are five main divisions in the brain:

1) telencephalon;

2) diencephalon;

3) midbrain;

4) hindbrain;

5) medulla oblongata.

If a person has suffered a traumatic brain injury, then this always negatively affects both his central nervous system and his mental state.

When the psyche is disturbed, a person can hear voices inside the head that command him to do this or that. All attempts to drown out these voices are futile and in the end the person goes and does what the voices ordered him to do.

In the hemisphere, the olfactory brain and basal nuclei are distinguished. Also, everyone knows such a comic phrase: “Strain your brain”, that is, think. Indeed, the "drawing" of the brain is very complex. The complexity of this "pattern" is predetermined by the fact that furrows and ridges go along the hemispheres, which form a kind of "gyrus". Despite the fact that this "drawing" is strictly individual, there are several common furrows. Thanks to these common furrows, biologists and anatomists have identified 5 lobes of the hemispheres:

1) frontal lobe;

2) parietal lobe;

3) occipital lobe;

4) temporal lobe;

5) hidden share.

The brain and spinal cord are covered with membranes:

1) dura mater;

2) arachnoid;

3) soft shell.

Hard shell. The hard shell covers the outside of the spinal cord. In its shape, it most of all resembles a bag. It should be said that the outer hard shell of the brain is the periosteum of the bones of the skull.

Arachnoid. The arachnoid is a substance that is almost closely adjacent to the hard shell of the spinal cord. The arachnoid membrane of both the spinal cord and the brain does not contain any blood vessels.

Soft shell. The pia mater of the spinal cord and brain contains nerves and blood vessels, which, in fact, feed both brains.

Despite the fact that hundreds of works have been written on the study of the functions of the brain, its nature has not been fully elucidated. One of the most important mysteries that the brain “guesses” is vision. Rather, how and with what help we see. Many mistakenly assume that vision is the prerogative of the eyes. This is not true. Scientists are more inclined to believe that the eyes simply perceive the signals that our environment sends us. Eyes pass them on "by authority". The brain, having received this signal, builds a picture, i.e. we see what our brain “shows” to us. Similarly, the issue with hearing should be resolved: it is not the ears that hear. Rather, they also receive certain signals that the environment sends us.

In general, what the brain is, mankind will not find out to the end soon. It is constantly evolving and developing. It is believed that the brain is the "residence" of the human mind.

Nervous system consists of tortuous networks of nerve cells that make up various interconnected structures and control all the activities of the body, both desired and conscious actions, and reflexes and automatic actions; the nervous system allows us to interact with the outside world, and is also responsible for mental activity.

The nervous system consists of various interconnected structures that together make up an anatomical and physiological unit. consists of organs located inside the skull (brain, cerebellum, brain stem) and spine (spinal cord); is responsible for interpreting the state and various needs of the body based on the information received, in order to then generate commands designed to obtain appropriate responses.

consists of many nerves that go to the brain (brain pairs) and spinal cord (vertebral nerves); acts as a transmitter of sensory stimuli to the brain and commands from the brain to the organs responsible for their execution. The autonomic nervous system controls the functions of numerous organs and tissues through antagonistic effects: the sympathetic system is activated during anxiety, while the parasympathetic system is activated at rest.

central nervous system Includes the spinal cord and brain structures.

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 the saturation of the body.

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 much 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 the formation of 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:

The number in our body is greater than the number of people on the entire planet Earth.
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.
The speed of movement of impulses reaches almost 300 km/h.
After the onset of puberty, the mass of the organ of thinking every year decreases by approximately one gram.
Men's brains are about 1/12 larger than women's.
The largest organ of thought was recorded in a mentally ill person.
The cells of the central nervous system are practically not subject to restoration, and severe stress and unrest can seriously reduce their number.
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%.
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.
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.

Among many types of cells, these are the most difficult to recover, and some of their subspecies cannot be restored at all. That is why they are perfectly protected by the skull and vertebral bones.

It is also interesting that NS diseases are the least treatable. Modern medicine is basically only capable of slowing down cell death, but it is impossible to stop this process. Many other types of cells with the help of special preparations can be protected from destruction for many years - for example, liver cells. At this time, the cells of the epidermis (skin) are able to regenerate in a matter of days or weeks to their previous state.

Nervous system - spinal cord (grade 8) - biology, preparation for the exam and the OGE

The human nervous system. Structure and functions

Conclusion

Absolutely every movement, every thought, glance, sigh and heartbeat is all controlled by a network of nerves. It is responsible for the interaction of a person with the outside world and connects all other organs into a single whole - the body.

Nervous system is a system that regulates the activity of all human organs and systems. This system causes:

1) the functional unity of all human organs and systems;

2) the connection of the whole organism with the environment.

The nervous system also has its own structural unit, which is called a neuron. Neurons are cells that have special processes. It is neurons that build neural circuits.

The entire nervous system is divided into:

1) central nervous system;

2) peripheral nervous system.

The central nervous system includes the brain and spinal cord, and the peripheral nervous system includes the cranial and spinal nerves and nerve nodes extending from the brain and spinal cord.

Also conditionally, the nervous system can be divided into two large sections:

1) somatic nervous system;

2) autonomic nervous system.

Nerve cells can be divided into two large groups:

1) afferent (or receptor) cells;

2) efferent (or motor) cells.

Receptor nerve cells perceive light (using visual receptors), sound (using sound receptors), smells (using olfactory and taste receptors).

In the cell membranes that are responsible for the sensation of taste and smell, there are special biological compounds that react to a particular substance by changing their state.

2. Autonomic nervous system

The autonomic nervous system is divided into two sections:

1) sympathetic section;

2) parasympathetic section.

To prevent diseases of the autonomic nervous system, a person should follow a number of simple rules:

1) avoid nervous fatigue, colds;

2) observe safety precautions in production with hazardous working conditions;

3) eat well;

4) go to the hospital in a timely manner, complete the entire prescribed course of treatment.

3. Central nervous system

The human central nervous system consists of the brain and spinal cord.

1) cervical thickening;

2) lumbar thickening.

It is in these thickenings that the so-called innervation nerves of the upper and lower extremities are formed. Dorsal brain is divided into several departments:

1) cervical;

2) thoracic region;

3) lumbar;

4) sacral department.

There are five main divisions in the brain:

1) telencephalon;

2) diencephalon;

3) midbrain;

4) hindbrain;

5) medulla oblongata.

If a person has suffered a traumatic brain injury, then this always negatively affects both his central nervous system and his mental state.

1) frontal lobe;

2) parietal lobe;

3) occipital lobe;

4) temporal lobe;

5) hidden share.

The brain and spinal cord are covered with membranes:

1) dura mater;

2) arachnoid;

3) soft shell.

Soft shell. The pia mater of the spinal cord and brain contains nerves and blood vessels, which, in fact, feed both brains.

In general, what the brain is, mankind will not find out to the end soon. It is constantly evolving and developing. It is believed that the brain is the "residence" of the human mind.

The nervous system consists of the spinal cord, the brain, the sense organs, and all the nerve cells that connect these organs to the rest of the body. Together, these organs are responsible for the control of the body and the communication between its parts. The brain and spinal cord form a control center known as the central nervous system (CNS), where information is evaluated and decisions are made. The sensory nerves and sense organs of the peripheral nervous system (PNS) monitor … [Read below]

Head and neck
Chest and upper back
Pelvis and lower back
Arms and hands
Legs and feet

[Beginning at the top] … conditions inside and outside the body and send this information to the CNS. The efferent nerves in the PNS carry signals from the control center to the muscles, glands, and organs to regulate their functions.

nervous tissue

Most tissues of the nervous system are composed of two classes of cells: neurons and neuroglia.

Neurons, also known as nerve cells, communicate in the body by transmitting electrochemical signals. Neurons are quite different from other cells in the body due to the many complex cellular processes that take place in their central body. The cell body is the roughly circular part of the neuron that contains the nucleus, mitochondria, and most of the cell organelles. Small tree-like structures called dendrites extend from the cell body to receive stimuli from the environment, they are called receptors. Transmitting nerve cells are called axons, they extend from the cell body to send signals forward to other neurons or effector cells in the body.

There are 3 main classes of neurons: afferent neurons, efferent neurons, and interneurons.
afferent neurons. Also known as sensory neurons, they transmit afferent sensory signals to the central nervous system from receptors in the body.

efferent neurons. Also known as motor neurons, efferent neurons carry signals from the central nervous system to effectors in the body such as muscles and glands.

Interneurons. Interneurons form complex networks in the central nervous system to integrate information received from afferent neurons and direct bodily function through efferent neurons.
Neuroglia. Neuroglia, also known as glial cells, acts as a "messenger" for cells in the nervous system. Every neuron in the body is surrounded by anywhere from 6 to 60 neuroglia that protect, nourish, and insulate the neuron. Because neurons are extremely specialized cells that are essential to the functioning of the body and almost never multiply, neuroglia are vital to maintaining a functional nervous system.

Brain

The brain, a soft, wrinkled organ that weighs about 1.2 kg, is located inside the cranial cavity, where the bones of the skull surround and protect it. Approximately 100 billion neurons in the brain form the main control center of the body. The brain and spinal cord together form the central nervous system (CNS), where information is processed and responses are formed. The brain is the seat of higher mental functions such as consciousness, memory, planning, and voluntary action, and controls lower bodily functions such as breathing, heart rate, blood pressure, and digestion.
Spinal cord
It is a long, thin mass of clustered neurons that carry information, located in the spinal cavity. Starting in the medulla oblongata at its upper end and continuing downward in the lumbar region of the spine. In the lumbar region, the spinal cord divides into a bundle of individual nerves called the cauda equina (because of its resemblance to a horse's tail), which continues down to the sacrum and coccyx. The white matter of the spinal cord acts as the main channel - a conductor of nerve signals to the body from the brain. The gray matter of the spinal cord integrates reflexes to stimuli.

Nerves

Nerves are bundles of axons in the peripheral nervous system (PNS) that act as information channels for transmitting signals between the brain, spinal cord, and the rest of the body. Each axon wrapped in a sheath of connective tissue is called an endoneuritis. Individual axons, grouped into groups of axons, the so-called bundles, are wrapped in a sheath of connective tissue and are called the perineurium. Finally, many bundles are packed together in another layer of connective tissue called the epineurium to form the entire nerve. The sheathing of nerves with connective tissue helps protect axons and increase their rate of transmission within the body.

Afferent, efferent and mixed nerves.
Some of the nerves in the body are specialized to carry information in only one direction, like a one-way street. Nerves that carry information from sensory receptors only to the central nervous system are called afferent neurons. Other neurons, known as efferent neurons, carry signals only from the central nervous system to effectors such as muscles and glands. Finally, some nerves are of mixed type, containing both afferent and efferent axons. Mixed nerve functions like 2 one way streets where afferent axons act as a streak towards the central nervous system and efferent axons act as a streak away from the central nervous system.

Cranio-cerebral nerves.
12 pairs of cranial nerves extend from the underside of the brain. Each pair of cranial nerves is identified by a Roman numeral from 1 to 12, based on its location along the anterior-posterior axis of the brain. Each nerve also has a descriptive name (eg, olfactory, optic, etc.) that identifies its function or location. The cranial nerves provide direct connections to the brain for special sense organs, the muscles of the head, neck and shoulders, the heart, and the gastrointestinal tract.

Spinal nerves.
There are 31 pairs of spinal nerves on the left and right sides of the spinal cord. Spinal nerves are mixed nerves that carry both sensory and motor signals between the spinal cord and specific areas of the body. The 31 pairs of nerves in the spinal cord are divided into 5 groups, named after the 5 regions of the spinal column. Thus, there are 8 pairs of cervical nerves, 12 pairs of thoracic nerves, 5 pairs of lumbar nerves, 5 pairs of sacral nerves, and 1 pair of coccygeal nerves. A separate spinal nerve exits the spinal cord through the intervertebral foramina between a pair of vertebrae or between the C1 vertebra and the occipital bone of the skull.

meninges

The meninges are the protective covering of the central nervous system (CNS). It consists of three layers: the dura mater, the arachnoid mater and the pia mater.

Hard shell.
This is the thickest, toughest and most superficial layer of the shell. Made of dense irregular connective tissue, it contains many tough collagen fibers and blood vessels. The dura mater protects the central nervous system from external damage, contains cerebrospinal fluid that surrounds the central nervous system and provides blood to the nervous tissue of the central nervous system.

Spider matter.
Much thinner than the dura mater. It lines the inside of the dura mater and contains many thin fibers that connect it to the underlying pia mater. These fibers traverse a fluid-filled space called the subarachnoid space between the arachnoid and pia mater.

The proper functioning of the nervous system is affected by both physical and psychological stress, so it is important to periodically relieve tension arising from stressful situations. One way to unload is to change from bad to good mood, for example, when browsing entertainment sites.

Pia matter.
The pia mater is a thin to very thin layer of tissue that lies on the outside of the brain and spinal cord. Contains many blood vessels that feed the nervous tissue of the central nervous system. The pia mater penetrates into the valleys of the sulci and fissures of the brain, as it covers the entire surface of the central nervous system.
cerebrospinal fluid
The space surrounding the organs of the central nervous system is filled with a clear fluid known as cerebrospinal fluid (CSF). It is formed from blood plasma by special structures called the choroid plexus. The choroid plexus contains many capillaries lined with epithelial tissue that filters the blood plasma and allows the filtered fluid to enter the space around the brain.

The newly created CSF flows through the inside of the brain in hollow spaces called the ventricles and through a small cavity in the middle of the spinal cord called the central canal. It also flows through the subarachnoid space around the outside of the brain and spinal cord. CSF is continuously produced in the choroid plexus and reabsorbed into the blood in structures called arachnoid villi.

The cerebrospinal fluid provides several vital functions of the central nervous system:
It absorbs shock between the brain and skull, and between the spinal cord and vertebrae. This impact absorption protects the central nervous system from impacts or sudden changes in speed, such as during a car accident.

CSF reduces the mass of the brain and spinal cord due to buoyancy. The brain is a very large but soft organ that requires a large volume of blood to function effectively. The reduced weight in the cerebrospinal fluid allows the brain's blood vessels to remain open and helps protect nerve tissue from being crushed by its own weight.

It also helps maintain chemical homeostasis in the central nervous system. Since it contains ions, nutrients, oxygen and albumins, which maintain the chemical and osmotic balance of the nervous tissue. CSF also removes waste products that are formed as by-products of cellular metabolism within the nervous tissue.

sense organs

All sense organs are components of the nervous system. Special sense organs, taste, smell, hearing and balance are known, specialized organs such as eyes, taste buds and olfactory epithelium have been found. Sensitive receptors for general senses like touch, temperature and pain are found throughout much of the body. All sensory receptors in the body are connected to afferent neurons, which carry their sensory information to the CNS to be processed and integrated.

Functions of the nervous system

It has three main functions: sensory, connective (conductive) and motor.

Touch.
The sensory function of the nervous system involves the collection of information from sensory receptors that control the body's internal and external conditions. These signals are then transmitted to the central nervous system (CNS) for further processing by afferent neurons (and nerves).

Integration.
Integration is the processing of multiple sensory signals that are transmitted to the central nervous system at any given time. These signals are processed, compared, used for decision making, discarded or stored in memory as deemed appropriate. Integration occurs in the gray matter of the brain and spinal cord and is carried out by interneurons. Many interneurons work together to form complex networks that provide this processing power.

motor function. After networks of interneurons in the CNS evaluate sensory information and decide on an action, they stimulate efferent neurons. Efferent neurons (also called motor neurons) carry signals from the gray matter of the CNS through the nerves of the peripheral nervous system to effector cells. The effector may be smooth cardiac or skeletal muscle tissue or glandular tissue. The effector then releases a hormone or moves a body part to respond to the stimulus.

Departments of the nervous system

CNS - central
The spinal cord and brain together form the central nervous system or CNS. The CNS acts as the body's control center, providing its processing, memory, and regulation systems. The central nervous system is involved in all conscious and subconscious gathering of sensory information from the body's sensory receptors in order to stay aware of the body's internal and external conditions. With the help of this sensory information, she makes decisions about what conscious and subconscious actions to take to maintain the body's homeostasis and ensure its survival. The CNS is also responsible for the higher functions of the nervous system, such as language, creativity, expression, emotion, and personality. The brain is the seat of consciousness and determines who we are as humans.

Peripheral nervous system
She (PNS), includes all parts of the nervous system outside the brain and spinal cord. These parts include all cranial and spinal nerves, ganglia, and sensory receptors.

somatic nervous system
The SNS is a division of the PNS that includes all free efferent neurons. The SNS is the only consciously controlled part of the PNS and is responsible for stimulating the skeletal muscles in the body.

autonomic nervous system
The ANS is a division of the PNS that includes all involuntary efferent neurons. It controls subconscious effectors such as visceral muscle tissue, cardiac muscle tissue and glandular tissue.

There are 2 divisions of the autonomic nervous system in the body: sympathetic and parasympathetic divisions.

Sympathetic.
The sympathetic division forms the body's "fight or flight" response to stress, danger, excitement, exercise, emotions, and embarrassment. The sympathetic division increases breathing and heart rate, releases adrenaline and other stress hormones, and decreases digestion to deal with these situations.

Parasympathetic.
The parasympathetic division forms the response to rest when the body is relaxed or at rest. The parasympathetic department works to cancel the work of the sympathetic department after a stressful situation. Other functions of the parasympathetic division include decreasing breathing and heart rate, increasing digestion, and allowing waste to be eliminated.
Enteral nervous system
The ENS is a division of the ANS that is responsible for regulating digestion and the functions of the digestive organs.
The ENS receives signals from the central nervous system through the sympathetic and parasympathetic divisions of the ANS system to help regulate its functions. However, for the most part, the ENS operates independently of the central nervous system and continues to function without any external influence. For this reason, the ENS is often referred to as the "second brain." The ENS is a huge system, there are almost as many neurons in the ENS as there are in the spinal cord.

Action potentials

Neurons function through the generation and propagation of electrochemical signals known as action potentials (APs). The access point is created by the movement of sodium and potassium ions across the membrane of neurons.

Resting potential.
At rest, neurons maintain a concentration of sodium ions, regardless of the concentration of potassium ions inside the cell. This concentration is maintained by the cell membrane's sodium-potassium pump, which pumps 3 sodium ions out of the cell for every 2 potassium ions entering the chamber. The ion concentration results in a residual electrical potential of 70 mV (mV), which means that there is a negative charge inside the cell compared to the environment.

threshold potential.
If the signal allows enough positive ions to accumulate to enter the cell area and cause it to reach -55 mV, then the cell area will allow sodium ions to diffuse into the cell. - 55 MV threshold potential for neurons, since this is the "trigger" voltage that they must reach in order to cross the threshold in the formation of an action potential.

Depolarization.
Sodium carries a positive charge that causes the cell to depolarize from its normal negative charge. Voltage for depolarization of all neurons +30 mV. Cell depolarization is an access point that is transmitted along the neuron as a nerve signal. Positive ions propagate to neighboring regions of the cell, initiating a new access point in those regions where they reach -55 mV. The impulse continues to propagate down the cell membrane of the neuron until it reaches the end of the axon.

Repolarization.
After a depolarization voltage of +30 mV is reached, the voltage-gated potassium ion channels become open, allowing positive potassium ions to diffuse out of the cell. The loss of potassium along with the pumping of sodium ions back out of the chamber via the sodium-potassium pump restores the cell to a resting potential of -55 mV. At this point, the neuron is ready to start a new action potential.

Synapse

A synapse is a node between a neuron and another cell. Synapses can form between 2 neurons or between a neuron and an effector cell. There are two types of synapses found in the body: chemical synapses and electrical synapses.

chemical synapses.
At the end of the neuron is a region known as the axon. The axon is separated from the next cell by a small gap known as the synaptic cleft. When the signal reaches the axon, it opens voltage-gated calcium ion channels. Calcium ions cause vesicles containing chemicals known as neurotransmitters to release their contents by exocytosis into the synaptic cleft. NT molecules cross the synaptic cleft and bind to receptor molecules on the cell, forming synapses with the neuron. These receptor molecules open ion channels that can either stimulate the cellular receptor to generate a new action potential or can inhibit cells from generating an action potential when stimulated by another neuron.

electrical synapses.
Electrical synapses are formed when 2 neurons are connected by small holes called gap junctions. The gap in the junction allows electrical current to pass from one neuron to another, so that the signal from one chamber is transmitted directly to another cell through the synapse.
myelination
The axons of many neurons are coated with a coating known as myelin to increase the speed of nerve conduction throughout the body. Myelin is formed by 2 types in glial cells: Schwann cells in the PNS and oligodendrocytes in the central nervous system. In both cases, the glial cells wrap their plasma membrane around the axon many times to form a thick lipid coating. The development of these myelin sheaths is known as myelination.

Myelination speeds up the movement of impulses in axons. The process of myelination begins with an acceleration of nerve conduction during fetal development and continues into early adulthood. Myelinated axons turn white due to the presence of lipids. They form the white matter of the brain, inner and outer spinal cord. White matter is specialized to carry information quickly through the brain and spinal cord. The gray matter of the brain and spinal cord are unmyelinated integration centers where information is processed.

reflexes

Reflexes are quick, involuntary responses to stimuli. The best-known reflex is the patellar reflex, which is tested when a doctor taps a patient's knee during a physical examination. Reflexes are integrated in the gray matter of the spinal cord or in the brain stem. Reflexes allow the body to respond very quickly to stimuli by sending responses to effectors before nerve signals reach the conscious part of the brain. This explains why people often pull their hands away from a hot object before they realize they are in danger.

Functions of the cranial nerves
Each of the 12 cranial nerves has a specific function within the nervous system.
The olfactory nerve (I) carries odor information to the brain from the olfactory epithelium in the roof of the nasal cavity.
The optic nerve (II) transmits visual information from the eyes to the brain.
The oculomotor, trochlear, and abducens nerves (III, IV, and VI) all work together to allow the brain to control eye movement and focus. The trigeminal nerve (V) carries sensation from the face and innervates the muscles of mastication.
The facial nerve (VII) innervates the muscles of the face to make facial expressions and carries taste information from the anterior 2/3 of the tongue.
The vestibulocochlear nerve (VIII) conducts auditory information from the ears to the brain.

The glossopharyngeal nerve (IX) carries taste information from the posterior 1/3 of the tongue and aids in swallowing.

The vagus nerve (X), which is called the vagus nerve because it innervates many different areas, travels through the head, neck, and trunk. It carries information about the state of vital organs in the brain, provides motor signals for speech control, and provides parasympathetic signals to many organs.

The accessory nerve (XI) controls the movements of the shoulders and neck.

The hypoglossal nerve (XII) moves the tongue for speech and swallowing.

Sensory Physiology

All sensory receptors can be classified according to their structure and the type of stimulus they detect. Structurally, there are 3 classes of sensory receptors: free, encapsulated nerve endings, and specialized cells.
Free nerve endings are simply free dendrites at the end of a neuron that extend into tissue. Pain, heat and cold are all felt through free nerve endings. Encapsulated are free nerve endings wrapped in round capsules of connective tissue. When the capsule is deformed by touch or pressure, the neuron fires to send signals to the CNS. Specialized cells detect stimuli from the 5 special senses: sight, hearing, balance, smell and taste. Each of the special senses has its own unique sensory cells, such as rods and cones in the retina to detect light in the organs of vision.

Functionally, there are 6 main classes of receptors: mechanoreceptors, nociceptors, photoreceptors, chemoreceptors, osmoreceptors, and thermoreceptors.

Mechanoreceptors.
Mechanoreceptors are sensitive to mechanical stimuli like touch, pressure, vibration, and blood pressure.

Nociceptors.
Nociceptors respond to stimuli such as intense heat, cold, or tissue damage by sending pain signals to the CNS.

Photoreceptors.
The photoreceptors in the retina are designed to detect light in order to provide the sense of vision.

Chemoreceptors.
Chemoreceptors are receptors for detecting chemicals in the blood, they provide the senses of taste and smell.

Osmoreceptors.
Osmoreceptors are able to control the osmolarity of the blood to determine the level of hydration in the body.

Thermoreceptors.
Thermoreceptors are receptors for detecting temperature within the body and in its surroundings.