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Organization of the nervous system

Neurons

The neurons are long (sometimes up to a meter), narrow and very sensitive. They cannot recover on their own, so disorders of the nervous system lead to paralysis and are often incurable.

Neurons transmit signals to and from the central nervous system (brain and spinal cord) in the form of impulses. They receive external and internal information through their senses: skin, ears, eyes, tongue and nose. This information is transformed into an electrical signal, which is transmitted in the form of an impulse from neuron to neuron.

Neurons consist of a body, which has a large nucleus, and bundles, or nerve fibers.

There are two types of fibers:

Dendrites, which carry impulses to the cells of the body.
Axons that carry impulses from cells.

The fatty substance myelin forms the white ending of the axons of some neurons, insulating them and increasing the speed of impulse transmission. The myelin sheath is formed in sections along the axon by the Schwann cell, which curls around the axon. The junctions of sections of myelinated fibers are called nodes of Ranvier. They also speed up the transmission of impulses, ensuring the fastest possible delivery of information.

Some axons do not have a myelin layer, so the speed of impulse transmission in unmyelinated cells is slower.

At the end of the axon there are small fibers - fibrils. They transmit impulses to the dendrites of the next neuron.

Neurons are connected to each other by synapses. Once an impulse reaches a synapse, a neurotransmitter chemical is released, which allows the impulse to travel from one neuron to another through the process of diffusion.

Neurons are supported by neuroglial cells, a type of connective tissue unique to the nervous system. These cells fill the space between neurons, providing a scaffold, and displace damaged cells and foreign particles through the process of phagocytosis.

Groups of neurons form nerves. There are five types of nerves and nervous tissue that make up the nervous system.

These include:

Sensitive or afferent nerves carrying impulses to the central nervous system, i.e. to the brain and spinal cord.
Motor, or efferent nerves, which carry impulses from the central nervous system throughout the body. Mixed nerves, consisting of both afferent and efferent nerves, which are found in the spinal cord and allow impulses to flow in both directions.

White matter is a bundle of nerve fibers containing myelin inside the brain and on the surface of the spinal cord that connect parts of the central nervous system.

Gray matter - cell bodies with dendrites and axons, without myelin fibers. Gray matter is located on the surface of the brain and inside the spinal cord and is responsible for the coordinated activity of the central nervous system.

Central nervous system (CNS)

The spinal cord and brain form the central nervous system. Both brains are protected by skin, muscles and bones.

Beneath these lie layers of tissue, collectively called soft medulla, which also protect the brain and spinal cord.

Sympathetic nervous system

The sympathetic nervous system is formed by a network of nerves that lie opposite the thoracic and lumbar vertebrae. They form plexuses that branch to provide nerves to the organs of the body.

The hypothalamus uses its connection with endocrine system to stimulate the release of the hormone adrenaline by the adrenal glands. This activates the plexuses of nerves responsible for the body’s behavior in stressful situations:

The heart rate increases and blood pressure increases, causing blood from the skin and digestive system to flow to the heart and skeletal muscles.
Increases oxygen supply and release carbon dioxide: The bronchi dilate, facilitating the entry and exit of air.
Energy production is accelerated by transforming glycogen in the liver.
Digestion slows down as blood flows to other organs.
Increases muscle tone urethral and anal sphincters, which delays urination and bowel movements.
The pupils dilate and the eyes open wider to provide better vision.
Sweating increases.
The muscles that lift the hair contract, causing goosebumps.

Parasympathetic nervous system

The parasympathetic nervous system is a network of nerves whose functions are opposite to those of the sympathetic nervous system. After a stressful situation, the hypothalamus stops the release of adrenaline from the adrenal glands, and the parasympathetic nervous system comes into action. It calms the body, softens the stimulating effect of the sympathetic nervous system and allows you to relax:

Heart rate and blood pressure decrease.
Breathing slows down as the need for oxygen decreases.
Digestion and absorption of food are restored, since the need for blood flow from the heart and muscles is reduced.
Control over urination and bowel movements returns, as the urethral and anal sphincters relax.
The pupils contract, the eyelids relax, which determines the sleepy appearance.

Functions of the nervous system

Touch function

Sensory neurons are found in the sense organs (eg ears). The endings of the dendrites form sensory receptors that detect changes sensed by the senses (for example, sounds). The received information in the form of impulses is carried to the cells of the body: the impulse travels along the axon to its end, and is transmitted through a chemical neurotransmitter to the dendrite of the next neuron. This process takes place in the peripheral nervous system, spinal cord and ultimately reaches the brain.

Sense organs

These include the nose, tongue, eyes, ears and skin.

Nose

The sense of smell - the perception of smells - is provided by the nose.

Chemicals that stimulate the sense of smell enter the nose with gases in the air. The mucous membrane of the tender humidifies the air, breaking gases into chemical particles. The cilia of the nose are nerve endings that can distinguish the smells of different chemicals.

Special olfactory cells located on back wall nose, send a signal about the smell to the olfactory bulb of the brain for analysis. Information travels along the olfactory nerves through the olfactory nerve pathway in the anterior part of the brain to the marginal center of the brain, where the interpretation of smell occurs.

Language

The surface of the tongue is covered with tiny taste buds. They have round shape and form bundles of cell bodies and nerve endings of the 7th, 9th and 10th cranial nerves. These cells have taste hairs that rise up to tiny pores on the surface of the tongue. The taste hairs are stimulated by the food we take in orally and send electrical impulses to the gustatory area of the brain to interpret taste. Different areas of the tongue sense different tastes.

The sweet taste is felt by the tip of the tongue.

Sour and salty are determined by the taste buds on the sides of the tongue.

The bitter taste is felt at the back of the tongue.

Eyes

Iridology is the determination of health status by the iris of the eye.

The eyes are located in the sockets, formed by bones skulls Both eyes are spherical in shape and contain: the cornea, iris, pupil and retina. The optic nerves (second cranial nerves) connect the eyes to the brain. Light enters the eye through the transparent cornea. The colored part of the eye, the iris, responds to the amount of incoming light by changing the size of the pupil. The retina, the inner layer of the eye, has light-sensitive cells that convert light into electrical impulses. These impulses are coming! to the brain via the optic nerve to interpret what was seen.

Ears

The outer part of the ear, or pinna, is called the outer ear, which also includes the ear canal and eardrum. Interior The ear consists of the middle and inner ear. Auricle consists of a lower lobe and an upper curl. The earlobe is formed by fibrous and fatty tissue and has an abundant blood supply. The helix consists of elastic cartilage with a poor blood supply.

The auditory canal is a winding passage leading from the outer ear to the eardrum, middle and inner ear.

The ears perform the functions of balance and hearing.

Balance: The ears sense changes in head position and send a corresponding signal through the 8th cranial nerve to the brain and cerebellum. The message is deciphered, and the skeletal muscles receive a command regarding posture and, accordingly, balance. Loss of balance occurs when we cannot cope with changes in head position, such as twisting, and we may fall.
Hearing: Sound waves in the ear are converted into electrical impulses and transmitted to the brain along the 8th cranial nerve where they are interpreted.

Leather

Sensitive nerve endings in the skin sense touch, pain, and temperature changes.

Linking function

The brain receives various impulses from the senses through sensory nerves. These impulses are combined, interpreted and stored. As a result, a course of action is consciously or subconsciously formed in the form of response impulses. The brain gets used to constant or frequent stimulation and sensory adaptation occurs. This means that the effect of stimulation decreases, for example, we get used to the actions of our hands during a massage, the smell of perfume, etc.

Motor function

Response impulses from the central nervous system diverge to the muscles and organs along the motor nerves, which run parallel to the peripheral nerves.

Impulses are transmitted from neuron to neuron using neurotransmitters until they reach a target - a muscle or organ that will carry out the impulse's instruction.

Some of these actions are voluntary, such as walking down stairs.

Others involve the autonomic nervous system; they are involuntary, that is, they are performed without conscious effort (for example, the movement of nutrients through the digestive tract).

Reflex function

The nervous system is capable of reacting to internal and external stimuli with great speed in the form of reflexes: you will automatically withdraw your hand from a hot plate as soon as you feel its temperature. The nervous system forms a simple pathway - a reflex arc: a nerve receptor on the surface of the skin reacts to irritation (a hot plate) and sends an impulse to the spinal cord. In this case, the impulse does not go to the brain, but is sent along the motor nerve to the performer, who automatically responds to the irritation. Reflex refers to involuntary reactions of the autonomic nervous system, as well as acts of swallowing, vomiting, coughing, sneezing, and the knee reflex.

Reflexes allow the body to avoid damage associated with irritation, and also to perform certain functions involuntarily.

Regulatory function

The nervous system uses all its parts to regulate processes in the body to ensure homeostasis:

The central nervous system regulates the actions of the entire nervous system, for example, the hypothalamus of the brain controls the ANS.
The PNS regulates sensory and motor activity of the body. This is how the sense organs react to irritation by sending impulses to the brain along the sensory nerves, and receive response impulses through the motor nerves.
The ANS regulates involuntary actions: breathing, digestion, etc.

Possible violations

Possible nervous system disorders from A to Z:

Harmony

The nervous system is very vulnerable and needs protection.

Liquid

Alcohol and caffeine weaken the nervous system. This effect is even stronger if taken together. This combination increases reaction time and can lead to intoxication and a subsequent hangover. The initial effect of caffeine and alcohol is stimulating: they give you energy. But since these substances are also diuretics, the body becomes dehydrated, which often causes headaches. The more caffeine/alcohol, the more pain! Drinking water will help combat dehydration and relieve headaches.

Nutrition

Power plays important role in the functioning of the nervous system. Toxins damage nerve tissue, and this affects all parts of the system, including mental performance, memory and concentration. Large amounts of sugar or soluble carbohydrates, which are rich in fast food products, have a negative effect on mental performance.

B vitamins are especially beneficial for mental performance. These include vitamins B 1, B 3, B 5, B 6 and B 12. They are contained:

Vitamins B 1, B 3 and B 6 - in watercress, cauliflower and cabbage.
Vitamins B 1, B 3 and B 5 are found in mushrooms.
Vitamin B 12 - in fatty fish, dairy products and poultry.

It is important to remember that the beneficial properties of these products are neutralized by caffeine and alcohol.

Rest

The nervous system needs sleep because this is the time when the brain sorts and “sorts out” the information received during the day. Like the rest of the body's systems, the nervous system gets tired and needs adequate rest to relieve the stress it has experienced during the day. The nervous system also benefits from short rest between periods of mental activity. Taking a break from work will help your brain restructure itself. During this time, you can flip through a magazine or, better yet, meditate for a few minutes.

Rest helps clear your brain and make room for new information. Relaxation is facilitated by procedures such as Indian hand massage, which prepare the parasympathetic nervous system for activity. They can be performed at any time of the day to relieve tension. Activity: Mental and muscular activity is important to promote a healthy nervous system. Boredom leads to lethargy and lack of interest in life. Activity, physical and mental, makes life fun.

Air

The nervous system needs an abundant supply of oxygen: without it, nerve cells quickly die. Since nerve cells are largely unregenerated, oxygen is vital to the nervous system.

The quality of the air we breathe is important. Both dirty air and smoking should be avoided: both impair mental alertness, concentration and memory. Practicing breathing techniques allows you to cleanse both the body and mind.

Age

With aging, there is a tendency for mental processes to deteriorate. The reaction often slows down, coordination deteriorates, and the senses lose some functions. Vision, hearing, smell, taste seriously deteriorate over time, and as the body ages, various difficulties arise:

It becomes difficult to focus vision on close objects.
Hearing gradually deteriorates.
The ability to sense certain odors disappears: gas, body odors, cooking food, etc.

The sense of taste weakens along with the sense of smell, since they are closely related.

Memory may be affected: then short-term memory is significantly worse than long-term memory.

Like most other parts of the body, the nervous system is dependent on overall health. The saying “what we have, we don’t keep; when we lose it, we cry” fits this situation perfectly and reminds us that we need to use all opportunities. This will not only improve the condition of the system, but will also allow it to function much longer.

Color

Associated with the nervous system are violet, blue and yellow colors. Violet corresponds to the seventh chakra, located in the brain area. Blue, the color of the sixth chakra, is directly associated with vision, smell, hearing, taste and balance. Yellow corresponds to the third chakra - the solar plexus - and is thus associated with the autonomic nervous system. You can use colors using your sense of sight and touch. You can also visualize them - imagine them with eyes closed. This opportunity is facilitated during relaxing procedures. Patients often report that during the procedure they “saw” some color (during Indian massage, facial treatments, reflexology sessions, etc.). As a therapist, you too may sometimes close your eyes during a session to reach another level of concentration and at such times are able to “see” colors. This vision is associated with certain part body, for example, with one that needs treatment, or can be a connection between the therapist and the patient, allowing the first to intuitively feel the needs of the second, to really feel its vibrations. For some people, such phenomena are absolutely natural and familiar. To others they seem strange and even supernatural. No matter how you feel about it, it is better to be open to new knowledge: many therapists and clients subsequently become interested in studying such techniques, and general idea It won't hurt to know about them, even if you don't intend to put them into practice yourself.

Knowledge

It is important to know how we can help bring balance to the body.

Avoid excessive exercise: this will prevent muscle strain and associated headaches.
Eat in a relaxed environment: Remember that digestion slows down when the sympathetic nervous system is working. Eating at a leisurely pace will prevent indigestion and more. serious problems, such as intestinal colic.

These factors determine the majority of stress-related problems, but they are easy to exclude.

Special care

Caring for the nervous system is associated with caring for the entire body, and one is impossible without the other. The nervous system performs so many functions, the knowledge of which is not yet complete, and medicine continues to gradually study the capabilities of the brain. A huge number of inexplicable processes occur in the brain, and it is possible to achieve things that would seem to be beyond our capabilities. As we develop our skills, we develop both mental abilities and intuition. The development of these abilities is facilitated by the penetration of more and more Eastern practices into Western culture.

As therapists, we need to develop both sides of the brain and especially to see the logic in a new idea or concept and find a way to apply it to the benefit of ourselves and our patients.

Divisions of the nervous system

All parts of the nervous system are interconnected. But for convenience of consideration, we will divide it into two main sections, each of which includes two subsections (Fig. 2.8).

The central nervous system includes all neurons of the brain and spinal cord. The peripheral nervous system includes all the nerves that connect the brain and spinal cord to other parts of the body. The peripheral nervous system is further divided into the somatic system and the autonomic system (the latter is also called the autonomic system).

The sensory nerves of the somatic system transmit information about external stimuli from the skin, muscles and joints to the central nervous system; from it we learn about pain, pressure, temperature fluctuations, etc. The motor nerves of the somatic system transmit impulses from the central nervous system to the muscles of the body, initiating movement. These nerves control all the muscles involved in voluntary movements, as well as involuntary regulation of posture and balance.

The nerves of the autonomic system run to and from the internal organs, regulating breathing, heart rate, digestion, etc. The autonomic system, which plays a leading role in emotions, will be discussed later in this chapter.

Most of the nerve fibers that connect different parts of the body to the brain come together in the spinal cord, where they are protected by the bones of the spine. The spinal cord is extremely compact and barely reaches the diameter of the little finger. Some of the simplest reactions to stimuli, or reflexes, are carried out at the level of the spinal cord. This, for example, is the knee-jerk reflex - straightening the leg in response to a light tap on the tendon on the kneecap. Doctors often use this test to determine the condition of spinal reflexes. The natural function of this reflex is to ensure that the leg straightens when the knee tends to bend under the influence of gravity, so that the body remains erect. When the patellar tendon is struck, the muscle attached to it is stretched and the signal from the sensory cells in it is transmitted along sensory neurons to the spinal cord. In it, sensory neurons synapse directly with motor neurons, which send impulses back to the same muscle, causing it to contract and the leg to straighten. Although this reaction can be carried out by the spinal cord alone without any intervention from the brain, it is modified by messages from higher nerve centers. If you clench your fists just before hitting your knee, the straightening motion will be exaggerated. If you warn the doctor and want to consciously slow down this reflex, then you may succeed. The main mechanism is built into the spinal cord, but its operation can be influenced by higher brain centers.

Brain organization

There are various ways to theoretically describe the brain. One of these methods is shown in Fig. 2.9.

Rice. 2.9.

The posterior region of the brain includes all structures located at the back of the brain. The middle region is located in the middle part of the brain, and the frontal region includes structures located in the front of the brain.

According to this approach, the brain is divided into three zones, according to their localization: 1) posterior section, including all structures located in the posterior, or occipital, part of the brain closest to the spinal cord; 2) the middle (middle section), located in the central part of the brain and 3) the anterior (frontal) section, localized in the front, or frontal, part of the brain. Canadian researcher Paul McLean proposed a different model of brain organization, based on the functions of brain structures, rather than on their location. According to MacLean, the brain consists of three concentric layers: a) the central brainstem, b) the limbic system, and c) the cerebral hemispheres (collectively called big brain). The relative position of these layers is shown in Fig. 2.10; For comparison, the cross-sectional components of the brain are shown in more detail in Fig. 2.11.

Rice. 2.10.

The central trunk and limbic system are shown in their entirety, and only the right hemisphere is shown. The cerebellum controls balance and muscle coordination; the thalamus serves as a switchboard for messages coming from the senses; The hypothalamus (not shown in the picture, but located under the thalamus) regulates endocrine functions and vital processes such as metabolism and body temperature. The limbic system deals with emotions and actions aimed at satisfying basic needs. The cerebral cortex (the outer layer of cells covering the cerebrum) is the center of higher mental functions; here sensations are registered, voluntary actions are initiated, decisions are made and plans are developed.

Rice. 2.11.

The main structures of the central nervous system are schematically shown (only the upper part of the spinal cord is shown).

Central brainstem

The central trunk, also known as the brainstem, controls involuntary behaviors such as coughing, sneezing, and burping, as well as “primitive” behaviors under voluntary control such as breathing, vomiting, sleeping, eating and drinking, and temperature regulation. and sexual behavior. The brainstem includes all the structures of the posterior and middle parts of the brain and two structures of the anterior part, the hypothalamus and thalamus. This means that the central trunk extends from the back to the front of the brain. In this chapter, we will limit our discussion to five brainstem structures—the medulla oblongata, the cerebellum, the thalamus, the hypothalamus, and the reticular formation—responsible for regulating the most important primitive behaviors necessary for survival. Table 2.1 lists the functions of these five structures, as well as the functions of the cerebral cortex, corpus callosum, and hippocampus.

Table 2.1.

The first small thickening of the spinal cord where it enters the skull is the medulla oblongata: it controls breathing and some reflexes that help the body maintain an upright position. It is also where the major nerve pathways coming out of the spinal cord cross, causing the right side of the brain to be connected to the left side of the body and the left side of the brain to the right side of the body.

Cerebellum. The convoluted structure adjacent to the back of the brain stem just above the medulla oblongata is called the cerebellum. It is primarily responsible for coordinating movements. Certain movements may take longer to initiate high levels, but their fine coordination depends on the cerebellum. Damage to the cerebellum leads to jerky, uncoordinated movements.

Until recently, most scientists believed that the cerebellum was exclusively concerned with the precise control and coordination of body movements. However, some intriguing new evidence suggests direct neural connections between the cerebellum and the anterior regions of the brain involved in speech, planning, and thinking (Middleton & Strick, 1994). Such neural connections in humans it is much more extensive than in monkeys and other animals. These and other data suggest that the cerebellum may be as involved in the control and coordination of higher mental functions as it is in providing dexterity in body movements.

Thalamus. Directly above the medulla oblongata and below the cerebral hemispheres are two egg-shaped groups of nerve cell nuclei that form the thalamus. One area of the thalamus acts as a relay station; it sends information to the brain from visual, auditory, tactile and taste receptors. Another area of the thalamus plays an important role in the control of sleep and wakefulness.

The hypothalamus is much smaller than the thalamus and is located exactly below it. Hypothalamic centers mediate eating, drinking and sexual behavior. The hypothalamus regulates endocrine functions and maintains homeostasis. Homeostasis is the normal level of functional characteristics healthy body such as body temperature, heart rate and blood pressure. During stress, homeostasis is disrupted, and then processes are launched aimed at restoring balance. For example, when we are hot, we sweat, when it is cold, we shiver. Both of these processes restore normal temperature and are controlled by the hypothalamus.

The hypothalamus also plays an important role in human emotions and reactions to stressful situation. Moderate electrical stimulation of certain areas of the hypothalamus causes pleasant sensations, and stimulation of adjacent areas causes unpleasant sensations. By influencing the pituitary gland, located just below it (Fig. 2.11), the hypothalamus controls the endocrine system and, accordingly, the production of hormones. This control is especially important when the body must mobilize a complex set of physiological processes (the “fight or flight” response) to cope with the unexpected. For its special role in mobilizing the body to action, the hypothalamus was called the “stress center.”

Reticular formation. The neural network that extends from the lower part of the brain stem to the thalamus and passes through some other formations of the central brainstem is called the reticular formation. It plays an important role in controlling the state of excitability. When a certain voltage is applied through electrodes implanted into the reticular formation of a cat or dog, the animal falls asleep; when stimulated by tension with a more rapidly changing wave pattern, the animal wakes up.

The ability to concentrate attention on certain stimuli also depends on the reticular formation. Nerve fibers from all sensory receptors pass through the reticular system. This system appears to work as a filter, allowing some sensory messages to pass into the cerebral cortex (become accessible to consciousness) and blocking others. Thus, at any moment the state of consciousness is influenced by the filtration process occurring in the reticular formation.

Limbic system

Around the central brain stem are several structures that are collectively called the limbic system. This system has close connections with the hypothalamus and appears to exercise additional control over some forms of instinctive behavior controlled by the hypothalamus and medulla oblongata (refer back to Figure 2.10). Animals that have only an undeveloped limbic system (for example, fish and reptiles) are capable of various types of activity - feeding, attack, flight from danger and mating - realized through behavioral stereotypes. In mammals, the limbic system appears to inhibit some instinctive behavior patterns, allowing the organism to be more flexible and adaptive to a changing environment.

The hippocampus, part of the limbic system, plays a special role in memory processes. Cases of damage to the hippocampus or surgical removal of it show that this structure is crucial for remembering new events and storing them in long-term memory, but not necessary for retrieving old memories. After surgery to remove the hippocampus, the patient easily recognizes old friends and remembers his past, he can read and use previously acquired skills. However, he will be able to remember very little (if anything) about what happened in the year or so before the surgery. He will not remember events or people he met after the operation at all. Such a patient will not be able, for example, to recognize a new person with whom he spent many hours earlier in the day. He will complete the same cut-out puzzle week after week and will never remember that he has completed it before, and will read the same newspaper over and over again without remembering its contents (Squire & Zola, 1996).

The limbic system is also involved in emotional behavior. Monkeys with lesions in certain areas of the limbic system react violently to even the slightest provocation, which suggests that the damaged area had an inhibitory effect. Monkeys with damage to other parts of the limbic system no longer exhibit aggressive behavior and do not show hostility, even when they are attacked. They simply ignore the attacker and act as if nothing happened.

Viewing the brain as consisting of three concentric structures - the central brainstem, the limbic system and the cerebrum (discussed in the next section) - should not give reason to think that they are independent of each other. An analogy can be made with a network of interconnected computers: each performs its own special functions, but we must work together to get the most effective result. Similarly, analyzing information from the senses requires one type of calculation and decision making (the large brain is well adapted to this); it is different from the one that controls the sequence of reflex acts (the limbic system). For more precise muscle adjustment (when writing, for example, or playing a musical instrument), another control system is required, mediated in this case by the cerebellum. All these types of activities are combined into a single system that preserves the integrity of the body.

Big brain

In humans, the large brain, consisting of two cerebral hemispheres, is more developed than in any other creature. Its outer layer is called the cerebral cortex; in Latin cortex means “tree bark”. On a brain specimen, the cortex appears gray because it consists primarily of nerve cell bodies and nerve fibers that are not covered with myelin—hence the term “gray matter.” The interior of the cerebrum, underneath the cortex, consists mostly of myelin-covered axons and appears white.

Each of the sensory systems (for example, visual, auditory, tactile) supplies information to specific areas of the cortex. Movements of body parts (motor reactions) are controlled by their own area of the cortex. The rest of it, which is neither sensory nor motor, consists of associative zones. These zones are associated with other aspects of behavior - memory, thinking, speech - and occupy most of the cerebral cortex.

Before looking at some of these areas, let us introduce some landmarks to describe the main areas of the cerebral hemispheres of the brain. The hemispheres are generally symmetrical and deeply separated from each other from front to back. Therefore, the first point of our classification will be the division of the brain into the right and left hemispheres. Each hemisphere is divided into four lobes: frontal, parietal, occipital and temporal. The boundaries of the lobes are shown in Fig. 2.12. The frontal lobe is separated from the parietal lobe by a central groove running almost from the top of the head to the sides towards the ears. The boundary between the parietal and occipital lobes is less clear; For our purposes, it will suffice to say that the parietal lobe is at the top of the brain behind the central sulcus, and the occipital lobe is at the back of the brain. The temporal lobe is separated by a deep groove on the side of the brain called the lateral groove.

Rice. 2.12.

Each hemisphere has several large lobes separated by sulci. In addition to these externally visible lobes, the cortex has a large internal fold called the “island” located deep in the lateral sulcus, a) lateral view; b) top view; c) cross section of the cerebral cortex; note the difference between the gray matter lying on the surface (shown as darker) and the deeper lying white matter; d) photograph of a human brain.

Primary motor area. The primary motor area controls voluntary body movements; it is located just in front of the central sulcus (Fig. 2.13). Electrical stimulation of certain areas of the motor cortex causes movements of the corresponding parts of the body; if these same areas of the motor cortex are damaged, movements are impaired. The body is represented in the motor cortex in an approximately inverted form. For example, the movements of the toes are controlled by the area located above, and the movements of the tongue and mouth are controlled by the lower part of the motor area. The movements of the right side of the body are controlled by the motor cortex of the left hemisphere; movements of the left side - the motor cortex of the right hemisphere.

Rice. 2.13.

Most of the cortex is responsible for generating movements and analyzing sensory signals. Corresponding areas (including motor, somatosensory, visual, auditory and olfactory) are present on both hemispheres. Some functions are represented on only one side of the brain. For example, Broca's area and Wernicke's area, which are involved in the production and understanding of speech, as well as the angular gyrus, which correlates the visual and auditory forms of a word, are present only on the left side human brain.

Primary somatosensory area. In the parietal zone, separated from the motor zone by the central sulcus, there is an area whose electrical stimulation causes sensory sensations somewhere on the opposite side of the body. They look as if some part of the body is moving or being touched. This area is called the primary somatosensory area (the area of bodily sensations). These include sensations of cold, touch, pain, and sensations of body movement.

Most of the nerve fibers in the pathways leading to and from the somatosensory and motor areas pass to the opposite side of the body. Therefore, sensory impulses from the right side of the body go to the left somatosensory cortex, and muscles right leg and the right hand is controlled by the left motor cortex.

Apparently, it can be considered a general rule that the volume of the somatosensory or motor area associated with a certain part of the body is directly determined by its sensitivity and the frequency of use of the latter. For example, among four-legged mammals, the dog's front paws are represented in only a very small area of the cortex, but the raccoon, which makes extensive use of its front paws to explore and manipulate its environment, has a much wider area, with areas for each toe. The rat, which receives a lot of information about its environment through its sensory antennae, has a separate area of cortex for each antennae.

Primary visual area. At the back of each occipital lobe there is a region of cortex called the primary visual area. In Fig. 2.14 fibers are shown optic nerve and neural pathways from each eye to the visual cortex. Please note that some optic fibers go from the right eye to the right hemisphere, and some cross the brain in the so-called visual chiasm and go to the opposite hemisphere; the same thing happens with the fibers of the left eye. Fibers from the right sides of both eyes go to right hemisphere brain, and fibers from the left sides of both eyes go to left hemisphere. Therefore, damage to the visual area in one hemisphere (say, the left) will result in blind areas on the left side of both eyes, causing a loss of visibility of the right side of the surroundings. This fact sometimes helps determine the location of a brain tumor and other abnormalities.

Rice. 2.14.

Nerve fibers from the inner, or nasal, halves of the retina intersect at the optic chiasm and go to opposite sides of the brain. Therefore, the stimuli that fall on right side each retina are transmitted to the right hemisphere, and stimuli falling on left side each retina are transmitted to the left hemisphere.

Primary auditory zone. The primary auditory zone is located on the surface of the temporal lobes of both hemispheres and is involved in the analysis of complex auditory signals. It plays a special role in the temporal structuring of sounds such as human speech. Both ears are represented in the auditory areas of both hemispheres, but the connections with the opposite side are stronger.

Association zones. The cerebral cortex contains many large areas that are not directly associated with sensory or motor processes. These are called association zones. The anterior association areas (parts of the frontal lobes located in front of the motor area) play an important role in the thinking processes that occur when solving problems. In monkeys, for example, damage to the frontal lobes impairs their ability to solve delayed-response tasks. In such tasks, in front of the monkey, food is placed in one of two cups and covered with identical objects. Then an opaque screen is placed between the monkey and the cups, after a certain time it is removed and the monkey is allowed to choose one of these cups. Usually a monkey remembers the correct cup after a delay of several minutes, but monkeys with damaged frontal lobes cannot solve this problem if the delay exceeds a few seconds (French & Harlow, 1962). Normal monkeys have neurons in the frontal lobe that fire action potentials during the delay, thereby mediating their memory for events (Goldman-Rakie, 1996).

Posterior association zones are located next to the primary sensory zones and are divided into subzones, each of which serves a specific type of sensation. For example, Bottom part The temporal lobe is associated with visual perception. Damage to this area impairs the ability to recognize and distinguish the shapes of objects. Moreover, it does not impair visual acuity, as would be the case with damage to the primary visual cortex in the occipital lobe; a person “sees” shapes and can trace their outline, but cannot determine what shape it is or distinguish it from another (Goodglass & Butters, 1988).

Live brain images

To obtain images of the living brain without causing harm or suffering to the patient, several techniques have been developed. When they were still imperfect, accurate localization and identification of most types of brain injuries could only be done through neurosurgical examination and complex neurological diagnostics or by autopsy - after the death of the patient. New methods are based on complex computer technology, which became a reality quite recently.

One of these methods is computed axial tomography (abbreviated CAT or simply CT). A narrow beam of X-rays is passed through the patient's head and the intensity of the radiation passed through is measured. What was fundamentally new in this method was the measurement of intensity at hundreds of thousands of different orientations (or axes) of the X-ray beam relative to the head. The measurement results are sent to a computer, where, through appropriate calculations, a cross-sectional picture of the brain is recreated, which can be photographed or shown on a television screen. The section layer can be selected at any depth and at any angle. The name “computed axial tomography” comes from the critical role of the computer, the multiple axes along which measurements are taken, and the resulting image showing a cross-sectional layer of the brain (tomo means “slice” or “section” in Greek).

A newer and more advanced method creates images using magnetic resonance. This type of scanner uses strong magnetic fields, pulses in the radio frequency range and computers that form the image itself. The patient is placed in a donut-shaped tunnel that is surrounded by a large magnet that creates a strong magnetic field. When an anatomical organ of interest is placed in a strong magnetic field and exposed to a radiofrequency pulse, the tissue of that organ begins to emit a signal that can be measured. Like CAT, hundreds of thousands of measurements are taken here, which are then converted by a computer into a two-dimensional image of the given anatomical organ. Experts usually call this technique nuclear magnetic resonance (NMR) because it measures changes in the energy level of the nuclei of hydrogen atoms caused by radio frequency pulses. However, many doctors prefer to omit the word "nuclear" and simply say "magnetic resonance imaging", fearing that the public will mistake the reference to atomic nuclei for atomic radiation.

When diagnosing diseases of the brain and spinal cord, NMR provides greater accuracy than a CAT scanner. For example, cross-sectional MRI images of the brain show symptoms of multiple sclerosis that are undetectable by CAT scanners; Previously, diagnosis of this disease required hospitalization and testing with the injection of a special dye into the spinal cord canal. NMR is also useful for detecting disorders in the spinal cord and base of the brain, such as slipped discs, tumors, and birth defects.

CAT and NMR allow us to see anatomical details of the brain, but it is often desirable to have data on the degree of neural activity in different areas of the brain. This information can be obtained by a computer scanning method called positron emission tomography (abbreviated PET). This method is based on the fact that metabolic processes in every cell of the body require energy. Neurons in the brain use glucose as their main source of energy, taking it from the bloodstream. If you add a little radioactive dye to glucose, each molecule becomes slightly radioactive (in other words, labeled). This composition is harmless, and 5 minutes after injecting it into the blood, radiation-labeled glucose begins to be consumed by brain cells in the same way as regular glucose. A PET scanner is first and foremost a highly sensitive radioactivity detector (it works not like an X-ray machine, which emits X-rays, but like a Geiger counter, which measures radioactivity). The most active neurons in the brain require more glucose and will therefore become more radioactive. A PET scanner measures the amount of radioactivity and sends the information to a computer, which creates a color cross-sectional image of the brain, with different colors representing different levels of neural activity. The radioactivity measured by this method is created by the flow (emission) of positively charged particles called positrons - hence the name "positron emission tomography".

A comparison of the results of PET scanning of normal individuals and patients with neurological disorders shows that this method can detect many brain diseases (epilepsy, blood clots, brain tumors, etc.). In psychological research, the PET scanner has been used to compare brain states in schizophrenics and has revealed differences in the metabolic rates of certain cortical areas (Andreasen, 1988). PET has also been used to study areas of the brain activated during various activities - listening to music, solving math problems and having a conversation; the goal was to establish which brain structures are involved in the corresponding higher mental functions(Posner, 1993).

The PET image shows three areas in the left hemisphere that are active during a speech task.

Areas with the highest activity are shown in red, areas with the least activity in blue.

Scanners using CAT, NMR and PET have proven invaluable tools for studying the connection between the brain and behavior. These tools are an example of how technological advances in one scientific field enable another field to also make leaps forward (Raichle, 1994; Pechura & Martin, 1991). For example, PET scans can be used to study differences in neural activity between the two hemispheres of the brain. These differences in hemispheric activity are called brain asymmetries.

Brain asymmetries

At first glance, the two halves of the human brain appear to be mirror images of each other. But a closer look reveals their asymmetry. When the brain is measured after an autopsy, the left hemisphere is almost always larger than the right. In addition, the right hemisphere contains many long nerve fibers that connect widely separated areas of the brain, while the left hemisphere contains many short fibers that form a large number of connections in a limited area (Hillige, 1993).

Back in 1861, French physician Paul Broca examined the brain of a patient suffering from speech loss and discovered damage in the left hemisphere in the frontal lobe just above the lateral sulcus. This area, known as Broca's area (Figure 2.13), is involved in speech production. Destruction of the corresponding area in the right hemisphere usually does not lead to speech impairment. Areas involved in speech understanding and the ability to write and understand what is written are usually also located in the left hemisphere. Thus, a person who has suffered damage to the left hemisphere as a result of a stroke is more likely to develop speech impairments than someone who has received damage localized in the right hemisphere. For very few left-handers, the speech centers are located in the right hemisphere, but for the vast majority they are located in the same place as for right-handers - in the left hemisphere.

Although the role of the left hemisphere in speech functions has become known in the relatively recent past, only recently has it become possible to learn what each hemisphere can do on its own. Normally, the brain works as a single unit; information from one hemisphere is immediately transmitted to the other along a wide bundle of nerve fibers connecting them, which is called the corpus callosum. In some forms of epilepsy, this connecting bridge can cause problems due to the fact that the initiation of a seizure from one hemisphere passes into the other and causes a massive discharge of neurons in it. In an effort to prevent such generalization of seizures in some seriously ill epileptics, neurosurgeons began to use surgical dissection of the corpus callosum. For some patients, this operation is successful and reduces seizures. At the same time, there are no undesirable consequences: in everyday life, such patients act no worse than people with connected hemispheres. Special tests were needed to find out how the separation of the two hemispheres affected mental performance. Before describing the following experiments, let's give some additional information.

Split-brain subjects. As we have seen, motor nerves switch sides when they leave the brain, so that the left hemisphere of the brain controls the right side of the body, and the right hemisphere controls the left. We also noted that the speech production area (Broca's area) is located in the left hemisphere. When the gaze is directed straight ahead, objects located to the left of the fixation point are projected onto both eyes and information from them goes to the right side of the brain, and information about objects to the right of the fixation point goes to the left side of the brain (Fig. 2.15). As a result, each hemisphere “sees” the half of the visual field in which “its” hand usually operates; for example, the left hemisphere sees the right hand in the right side of the visual field. Normally, information about stimuli received in one hemisphere of the brain is immediately transmitted through the corpus callosum to the other, so that the brain acts as a single whole. Let's now see what happens in a person with a split brain, that is, when his corpus callosum is cut and the hemispheres cannot communicate with each other.

Rice. 2.15.

If you look straight ahead, then stimuli located to the left of your gaze fixation point go to the right hemisphere, and stimuli to the right of it go to the left hemisphere. The left hemisphere controls the movements of the right hand, and the right hemisphere controls the movements of the left. Most of the input auditory signals go to the opposite hemisphere, but some of them also fall on the same side as the ear that heard them. The left hemisphere controls spoken and written language and mathematical calculations. The right hemisphere provides understanding only of simple language; its main function is related to spatial design and a sense of structure.

Roger Sperry pioneered work in this area and was awarded the Nobel Prize for research in the field of neuroscience. In one of his experiments, a subject (who had undergone surgery to dissect the brain) was in front of a screen that covered his hands (Fig. 2.16a). The subject fixed his gaze on a spot in the center of the screen, and on the left side of the screen on a very a short time(0.1 s) the word “nut” was presented. Recall that this visual signal goes to the right side of the brain, which controls the left side of the body. With his left hand, the subject could easily select a nut from a pile of objects that were inaccessible to observation. But he could not tell the experimenter which word was appearing on the screen, since speech is controlled by the left hemisphere, and visual image the word “nut” was not transmitted to this hemisphere. The split-brain patient was apparently unaware of what his left arm was doing when asked about it. Because the sensory input from the left hand goes to the right hemisphere, the left hemisphere did not receive any information about what the left hand was feeling or doing. All information went to the right hemisphere, which received the initial visual signal of the word “nut.”

Rice. 2.16.

A) A split-brain subject correctly finds an object by touching objects with the left hand when the name of the object is presented to the right hemisphere, but cannot name the object or describe what it does.

B) The word “hatband” appears on the screen so that “hat” goes to the right hemisphere, and “band” to the left. The subject replies that he sees the word “tape”, but has no idea which one it is.

C) First, both hemispheres are presented with a list of names of familiar objects (including the words “book” and “cup”). Then a word from this list (“book”) is presented to the right hemisphere. On command, the patient writes the word “book” with his left hand, but cannot answer what his left hand wrote, and says at random: “cup”.

It is important that the word appears on the screen for no more than 0.1 s. If this continues longer, the patient has time to shift his gaze and then this word enters the left hemisphere. If a split-brain subject can move his gaze freely, information is sent to both hemispheres, which is one reason why cutting the corpus callosum has little impact on the patient's daily activities.

Further experiments showed that the split-brain patient could give a verbal report only of what was happening in the left hemisphere. In Fig. Figure 2.16b shows another experimental situation. The word “hatband” is projected so that “hatband” falls on the right hemisphere, and “ribbon” on the left. When asked what word he sees, the patient answers “tape.” When asked what kind of tape he is, he begins to make all sorts of guesses: “adhesive tape”, “variegated tape”, “highway tape”, etc. - and only by chance guesses that it is “hat tape”. Experiments with other word combinations showed similar results. What is perceived by the right hemisphere is not transmitted to the left hemisphere for awareness. When the corpus callosum is dissected, each hemisphere is indifferent to the experience of the other.

If a split-brain subject is blindfolded and left hand put an object familiar to him (a comb, toothbrush, keychain), he will be able to recognize it; he will be able, for example, to demonstrate its use with appropriate gestures. But what the subject knows, he cannot express in speech. If, while manipulating this object, you ask him what is happening, he will not say anything. This will happen as long as all sensory signals from this object to the left (speech) hemisphere are blocked. But if the subject accidentally touches this object with his right hand or the object makes a characteristic sound (for example, the jingling of a key fob), the speech hemisphere will work and the correct answer will be given.

Although the right hemisphere is not involved in the act of speaking, it does have some language capabilities. It is able to learn the meaning of the word "nut", which we saw in the first example, and it "can" write a little.

In the experiment illustrated in Fig. 2.16c, the split-brain subject is first shown a list of common objects, such as a cup, a knife, a book, and a mirror. Show long enough for the words to be projected into both hemispheres. The list is then removed and one of these words (eg, “book”) is briefly presented on the left side of the screen so that it enters the right hemisphere. Now, if the subject is asked to write what he saw, his left hand writes the word "book". When asked what he wrote, he does not know and names a word at random from the original list. He knows that he has written something because he feels the movements of his body while writing. But because there is no connection between the right hemisphere, which saw and wrote the word, and the left hemisphere, which controls speech, the subject cannot say what he wrote (Sperry, 1970, 1968; see also Hellige, 1990 , Gazzaniga, 1995).

Hemisphere specialization. Studies conducted on split-brain subjects show that the hemispheres work differently. The left hemisphere controls our ability to express ourselves through speech. It can perform complex logical operations and has mathematical calculation skills. The right hemisphere understands only the most simple speech. It can, for example, respond to simple nouns, choosing from a set of objects, say, a nut or a comb, but does not understand more abstract linguistic forms. It usually does not respond to simple commands such as “blink”, “nod your head”, “shake your head” or “smile”.

However, the right hemisphere has a highly developed sense of space and structure. It is superior to the left in creating geometric and perspective designs. It can assemble colored blocks according to a complex drawing much better than the left one. When split-brain subjects are asked to assemble blocks according to a picture with their right hand, they make a lot of mistakes. Sometimes they find it difficult to keep their left hand from automatically correcting mistakes made by their right hand.

Studies of normal subjects seem to confirm the existence of differences in the specialization of the hemispheres. For example, if verbal information (words or nonsense syllables) is presented in short bursts to the left hemisphere (i.e., in the right part of the visual field), then it is recognized faster and more accurately than when presented to the right. On the contrary, recognition of faces, emotional facial expressions, the slope of lines, or the location of dots occurs more quickly when presented to the right hemisphere (Hellige, 1990). Electroencephalograms (EEG) show that electrical activity the left hemisphere increases when solving verbal problems, and the activity of the right increases when solving spatial problems (Springer & Deutsch, 1989; Kosslyn, 1988).

We should not conclude from our discussion that the hemispheres operate independently of each other. Just the opposite. The specialization of the hemispheres is different, but they always work together. It is thanks to their interaction that it becomes possible mental processes, much more complex and more different from those that make up the special contribution of each hemisphere separately. As Levy noted:

“These differences are clear from a comparison of the contributions made by each hemisphere to all types of cognitive activity. When a person reads a story, the right hemisphere may play a special role in decoding visual information, forming a coherent story structure, appreciating humor and emotional content, extracting meaning from past associations, and understanding metaphors. At the same time, the left hemisphere plays a special role in understanding syntax, translating written words into their phonetic representations, and extracting meaning from complex relationships between verbal concepts and syntactic forms. But there is no activity to which only one hemisphere performs or contributes” (Levy, 1985, p. 44).

Speech and the brain

Much has been learned about the brain mechanisms of speech through observations of brain-damaged patients. The damage may result from a tumor, penetrating head injury, or rupture of blood vessels. Speech disorders resulting from brain damage are called aphasia.

As mentioned, in 1860 Broca noticed that damage to a specific area of the left frontal lobe was associated with a speech disorder called expressive aphasia. [The most complete classification of various forms of aphasia was developed by A. R. Luria (see: Psychological Dictionary / Edited by V. P. Zinchenko, B. G. Meshcheryakov. M.: Pedagogika-Press, 1996). - Approx. ed.] Patients with damaged Broca's area had difficulty with correct pronunciation words, their speech was slow and labored. Their speech is often meaningful, but contains only keywords. As a rule, nouns have a singular form, and adjectives, adverbs, articles and connectives are omitted. However, such people do not have difficulties understanding spoken and written language.

In 1874, German researcher Carl Wernicke reported that damage to another part of the cortex (also in the left hemisphere, but in the temporal lobe) was associated with a speech disorder called receptive aphasia. People with damage to this area - Wernicke's area - cannot understand words; they hear the words but do not know their meaning.

They easily compose sequences of words, articulate them correctly, but use the words incorrectly, and their speech, as a rule, is meaningless.

After analyzing these disorders, Wernicke proposed a model for the generation and understanding of speech. Although the model is 100 years old, it is still generally correct. Using this as a basis, Norman Geschwind developed a theory that is known as the Wernicke-Geschwind model (Geschwind, 1979). According to this model, Broca's area stores articulation codes that determine the sequence of muscle operations necessary to pronounce a word. When these codes are transmitted to the motor area, they activate the muscles of the lips, tongue, and larynx in the sequence necessary to pronounce the word.

On the other hand, Wernicke's area stores auditory codes and word meanings. To pronounce a word, it is necessary to activate its auditory code in Wernicke's area and transmit it along a bundle of fibers to Broca's area, where it activates the corresponding articulation code. In turn, the articulation code is transmitted to the motor area to pronounce the word.

To understand a word spoken by someone, it must be transmitted from the auditory area to Wernicke's area, where for the spoken word there is its equivalent - the auditory code, which in turn activates the meaning of the word. When a written word is presented, it is first registered by the visual area and then transmitted to the angular gyrus, through which the visual form of the word is associated with its auditory code in Wernicke's area; When the auditory code of a word is found, its meaning is also found. Thus, the meanings of words are stored along with their acoustic codes in Wernicke's area. Broca's area stores articulation codes, and through the angular gyrus, the written word is matched to its auditory code; however, neither of these two zones contains information only about the meaning of the word. [The value is stored along with the acoustic code. - Approx. ed.] The meaning of a word is reproduced only when its acoustic code is activated in Wernicke’s area.

This model explains many speech disorders in aphasia. Damage limited to Broca's area causes impairment in speech production but has less impact on comprehension of written and spoken language. Damage to Wernicke's area leads to disruption of all components of speech understanding, but does not prevent a person from pronouncing words clearly (since Broca's area is not affected), although speech will be meaningless. According to the model, individuals with damage to the angular gyrus will not be able to read, but will be able to understand oral speech and speak for yourself. Finally, if only the auditory area is damaged, the person will be able to speak and read normally, but will not be able to understand spoken language.

The Wernicke-Geschwind model does not apply to all available data. For example, when the speech areas of the brain are electrically stimulated during neurosurgery, speech perception and production functions may be interrupted when only one area of the area is affected. It follows that in some areas of the brain there may be mechanisms involved in both the production and understanding of speech. We are still far from a perfect model of human speech, but at least We know that some language functions have a clear brain localization (Hellige, 1994; Geschwind & Galaburda, 1987).

The human nervous system is a stimulator of work muscular system, which we talked about in. As we already know, muscles are needed to move body parts in space, and we have even studied specifically which muscles are intended 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 learn the necessary theoretical minimum for mastering the topic indicated in the title of the article.

First of all, it is worth informing 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 nervous structures interacting with each other, providing, along with the endocrine system, 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 systems such as endocrine, immune and more.

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 a nerve fiber occurs due to the transition of local foci of excitation to adjacent inactive areas of the nerve fiber. The human nervous system has the property of transforming and generating energies from the external and internal environment and converting them into a nervous process.

Structure of the human nervous system: 1-brachial plexus; 2- musculocutaneous nerve; 3rd radial nerve; 4- median nerve; 5- iliohypogastric nerve; 6-femoral-genital nerve; 7- locking nerve; 8- ulnar nerve; 9- general 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 senses 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 connects to the spinal cord. The right and left cerebral hemispheres are connected to each other 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 foramina of the vertebrae and stretches from the brain to sacral region spine. On each side of the spinal cord, nerves extend symmetrically to different parts of the body. The sense of touch is, in general terms, provided by certain nerve fibers, countless 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 entire integral system is conditionally formed by: 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 central nervous system via PNS neurons. At the same time, outgoing signals from the central nervous system are sent by the peripheral nervous system to the muscles. As visual material, below, the complete human nervous system (diagram) is presented in a logically structured manner.

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 varying degrees of complexity, called reflexes. The lower and middle parts of the central nervous system - the spinal cord, medulla oblongata, midbrain, diencephalon and cerebellum - control the activities of individual organs and systems of the body, realize communication and interaction between them, ensure the integrity of the body and its correct functioning. Higher department The central nervous system - the cerebral cortex and the nearest subcortical formations - for the most part controls the connection 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 the nerves and plexuses of the autonomic nervous system, connecting the central nervous system to the organs of the body. Unlike the central nervous system, the PNS is not protected by bones and can be susceptible 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 excitation of muscles, including skin and joints. It also guides the coordination of body movements and the reception 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 controls the response to danger or stress, and can, among other things, cause an increase in heart rate, increased blood pressure and stimulation of the senses by increasing the level of adrenaline in the blood. The parasympathetic nervous system, in turn, controls the state of rest, and regulates the contraction of the pupils, slowing heart rate, dilation of blood vessels and stimulation of the digestive and genitourinary systems.

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

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– these are excitable cells that are capable of generating and transmitting electrical impulses (action potentials).

Structure nerve cell: 1- cell body; 2- dendrites; 3- cell nucleus; 4- myelin sheath; 5- axon; 6- axon ending; 7- synaptic thickening

The functional unit of the neuromuscular system is the motor unit, which consists of a motor neuron and its innervated muscle fibers. Actually, the work of the human nervous system, using the process of muscle innervation as an example, 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 high concentration potassium ions (K), and outside – sodium ions (Na). At rest, the potential difference between the internal and outside cell membrane does not give rise to an electrical charge. This specific 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 increases and the cell reaches its electrical threshold for 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 the path a nerve impulse takes from the moment a stimulus occurs to the receipt of a response to it in each individual system.

Nerves connect to each other through synapses, and to muscles through neuromuscular junctions. Synapse- this is the point 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 his motor activity and how it affects the functioning of the whole organism as a whole. Since the nervous system is involved in regulating the activity of all organs and systems of the human body, including, and perhaps primarily, the cardiovascular system, then in the next article in the series about the systems of the human body, we will move on to its consideration.

The nervous system is one, but it is conventionally divided into parts. According to topographical principles, the nervous system is divided into central and peripheral. The central nervous system includes the brain and spinal cord, and the peripheral nervous system includes the nerves extending from the brain (12 pairs of cranial nerves), and the nerves extending from the spinal cord (31 pairs of spinal nerves), as well as nerve ganglia. The central nervous system is built from cells and fibers that developed from the dorsally located neural tube (Table 11.3). Peripheral nervous system - nerve fibers connecting the central nervous system and the body, as well as groups of cells that lie outside the central nervous system and are called ganglia (Table 11.4).

According to the functional principle, the nervous system is divided into somatic (animal) and autonomous (vegetative) parts. The first innervates the striated muscles of the skeleton and some organs - the tongue, pharynx, larynx, etc., and also provides sensitive innervation of the entire body. Through the somatic nervous system, a person can control movements, voluntarily induce or stop them. The autonomic, or autonomic, nervous system innervates all the smooth muscles of the body, providing motor and secretory innervation of internal organs, motor innervation of the cardiovascular system and trophic innervation of striated muscles. The work of the autonomic nervous system is not subject to human will. It is impossible, for example, to stop the heart at will, speed up the digestion process, or delay sweating.

The autonomic nervous system, in turn, is divided into two divisions: sympathetic and parasympathetic. As a rule, they have opposite effects on organs. For example, the sympathetic nerve strengthens and speeds up the work of the heart, and the parasympathetic nerve slows down and weakens it. The autonomic nervous system influences processes common to animals and plants (metabolism, respiration, excretion, etc.), which is where its name comes from (vegetative - plant).

Table 11.3. General plan of the structure of the central nervous system

Nervous system	Brain	Spinal cord
Large hemispheres	Cerebellum	Trunk
Composition and structure	Shares: frontal, parietal, occipital, two temporal. Bark formed by gray matter - the bodies of nerve cells. The thickness of the cortex is 1.5-3 mm. The area of the cortex is 2-2.5 thousand cm 2, it consists of 14 billion neuron bodies. White matter is formed by nerve processes	Gray matter forms the cortex and nuclei within the cerebellum. Consists of two hemispheres connected by a bridge	Formed by the diencephalon, midbrain, pons, medulla oblongata. Consists of white matter, in the thickness there are nuclei of gray matter. The trunk passes into the spinal cord	A cylindrical cord is 42-45 cm long and about 1 cm in diameter. It runs in the spinal canal. Inside it is the spinal canal filled with fluid. Gray matter is located inside, white matter is located outside. Passes into the brain stem, forming a single system
Functions	Carries out higher nervous activity (thinking, speech. second signaling system. memory, imagination, ability to write, read) Communication with the external environment occurs with the help of analyzers located in the occipital lobe (visual zone), in the temporal lobe (auditory zone), along the central sulcus (musculocutaneous zone) and on inner surface cortex (gustatory and olfactory areas). Regulates the functioning of the entire body through the peripheral nervous system	Regulates and coordinates body movements, muscle tone Carries out unconditioned reflex activity (centers of innate reflexes)	Connects the brain with the spinal cord into a single central nervous system. The medulla oblongata contains the respiratory and digestive centers. cardiovascular. The pons connects both halves of the cerebellum. The midbrain controls reactions to external stimuli, muscle tone (tension). The diencephalon regulates metabolism, body temperature, connects body receptors with the cerebral cortex	Functions under the control of the brain. Arcs of unconditioned (innate) reflexes pass through it, excitation and inhibition during movement. Pathways are white matter that connects the brain to the spinal cord; is a conductor of nerve impulses. Regulates the functioning of internal organs through the peripheral nervous system. Voluntary movements of the body are controlled through the spinal nerves.

Table 11.4. General plan of the structure of the central nervous system

somatic (nerve fibers are not interrupted; impulse conduction speed is 30-120 m/s)	vegetative (nerve fibers are interrupted by nodes; impulse conduction speed is 1-3 m/s)
		cranial nerves (12 pairs)	spinal nerves (31 pairs)
Composition and structure
	They depart from various parts of the brain in the form of nerve fibers. They are divided into centripetal and centrifugal. Innervates sensory organs, internal organs, skeletal muscles	They depart from various parts of the brain in the form of nerve fibers. They are divided into centripetal and centrifugal. Innervates sensory organs, internal organs, skeletal muscles	They depart from various parts of the brain in the form of nerve fibers. They are divided into centripetal and centrifugal. Innervates sensory organs, internal organs, skeletal muscles
Functions
	Provide a connection between the body and the external environment, quick reactions on its change, orientation in space, body movements (purposeful), sensitivity, vision, hearing, smell, touch, taste, facial expressions, speech. Activities are carried out under the control of the brain	They ensure the body’s connection with the external environment, quick reactions to its changes, orientation in space, body movements (purposeful), sensitivity, vision, hearing, smell, touch, taste, facial expressions, speech. Activities are carried out under the control of the brain	They ensure the body’s connection with the external environment, quick reactions to its changes, orientation in space, body movements (purposeful), sensitivity, vision, hearing, smell, touch, taste, facial expressions, speech. The activity is carried out under the control of the brain. The activity of the autonomic nervous system regulates the work of all internal organs, adapting them to the needs of the whole organism.

Control questions

1. What classifications of the nervous system do you know?

2. How does an axon differ from a dendrite (in structure and function)?

3. What are the types of nerve cells (by structure and function)?

4. Name the types of synapses known to you.

5. Explain the structure of the synapse and the mechanism of the generation of a nerve impulse (postsynaptic potential).

6. What types of neuroglia exist?

7. How is the sheath of myelinated and unmyelinated nerve fibers built?

8. Explain the structure and significance of the blood-brain barrier.

9. Define and describe the structure of the reflex arc.

10. Describe the features of the phylo- and ontogenetic development of the nervous system.

GENERAL PHYSIOLOGY OF THE NERVOUS SYSTEM

Functions of the nervous system

Centers of the nervous system

Inhibition processes in the central nervous system

Reflex and reflex arc. Types of reflex

Functions and parts of the nervous system

The body is a complex, highly organized system consisting of functionally interconnected cells, tissues, organs and their systems. Management of their functions, as well as their integration (interconnection), ensures nervous system. The NS also communicates the body with the external environment by analyzing and synthesizing various information received from receptors. It provides movement and functions as a regulator of behavior necessary in specific conditions of existence. This ensures adequate adaptation to the surrounding world. In addition, the processes underlying mental activity person (attention, memory, emotions, thinking, etc.).

Thus, nervous system functions:

Regulates all processes occurring in the body;

Carries out the relationship (integration) of cells, tissues, organs and systems;

Performs analysis and synthesis of information entering the body;

Regulates behavior;

Provides processes underlying human mental activity.

According to morphological principle central(brain and spinal cord) and peripheral(paired spinal and cranial nerves, their roots, branches, nerve endings, plexuses and ganglia located in all parts of the human body).

By functional principle the nervous system is divided into somatic And vegetative. The somatic nervous system provides innervation mainly to the organs of the body (soma) - skeletal muscles, skin, etc. This part of the nervous system connects the body with the external environment through the senses and provides movement. The autonomic nervous system innervates internal organs, blood vessels, glands, including endocrine glands, smooth muscles, regulates metabolic processes in all organs and tissues. The autonomic nervous system includes sympathetic, parasympathetic And metasympathetic departments.

2. Structural and functional elements of the NS

The main structural and functional unit of the NS is neuron with its branches. Their functions are to perceive information from the periphery or from other neurons, process it and transmit it to neighboring neurons or executive organs. In a neuron there are body (soma) And shoots (dendrites And axon). Dendrites are numerous highly branched protoplasmic projections near the soma, through which excitation is conducted to the body of the neuron. Their initial segments have a larger diameter and lack spines (cytoplasmic outgrowths). An axon is the only axial-cylindrical process of a neuron, having a length from several microns to 1 m, the diameter of which is relatively constant throughout its entire length. The terminal sections of the axon are divided into terminal branches, through which excitation is transmitted from the neuron body to another neuron or working organ.

The integration of neurons into the nervous system occurs through interneuronal synapses.

Neuron functions:

1. Perception of information (dendrites and neuron body).

2. Integration, storage and reproduction of information (neuron body). Integrative activity of a neuron consists in the intracellular transformation of many heterogeneous excitations coming to the neuron and the formation of a single response.

3. Synthesis of biologically active substances (neuron body and synaptic endings).

4. Generation of electrical impulses (axon hillock - axon base).

5. Axonal transport and conduction of excitation (axon).

6. Transmission of excitations (synaptic endings).

There are several neuron classifications. According to morphological classification neurons are distinguished by the shape of the soma. There are granular neurons, pyramidal neurons, stellate neurons, etc. Based on the number of neurons extending from the body, processes are divided into unipolar neurons (one process), pseudounipolar neurons (T-shaped branching process), bipolar neurons (two processes), multipolar neurons (one axon and many dendrites).

Functional classification neurons is based on the nature of the function they perform. Highlight afferent (sensitive, receptor) neurons (pseudounipolar), efferent (motor neurons, motor) neurons (multipolar) and associative (insertion, interneurons) neurons (mostly multipolar). Biochemical classification of neurons is carried out taking into account the nature of the produced mediator. Based on this, they distinguish cholinergic(mediator acetylcholine), monoaminergic(adrenaline, norepinephrine, serotonin, dopamine), GABAergic (gamma-aminobutyric acid), peptidergic(substance P, enkephalins, endorphins, other neuropeptides), etc.

One of the components of the central nervous system is neuroglia (glial cells). It makes up almost 90% of NS cells and consists of two types: macroglia, represented by astrocytes, oligodendrocytes and ependymocytes, and microglia. Astrocytes– large stellate cells perform supporting and trophic (nutritional) functions. Astrocytes ensure the constancy of the ionic composition of the environment. Oligodendrocytes form the myelin sheath of the axons of the central nervous system. Oligodendrocytes outside the central nervous system are called Schwann cells, they take part in axon regeneration. Ependymocytes line the ventricles of the brain and the spinal canal (these are cavities filled with brain fluid, which is secreted by epidemiocytes). Cells microglia can transform into mobile forms, migrate throughout the central nervous system to the site of damage to nervous tissue and phagocytose decay products. Unlike neurons, Glial cells do not generate action potentials, but can influence excitation processes.

According to the histological principle in the structures of the NS it is possible to distinguish white And Gray matter. Gray matter– these are the cerebral cortex and cerebellum, various nuclei of the brain and spinal cord, peripheral (i.e. located outside the central nervous system) ganglia. Gray matter is formed by clusters of neuron cell bodies and their dendrites. It follows that it is responsible for reflex functions: perception and processing of incoming signals, as well as the formation of a response. The remaining structures of the nervous system are formed by white matter. White matter formed by myelinated axons (hence the color and name), the function of which is carrying out nerve impulses.

3. Features of the spread of excitation in the central nervous system

Excitation in the central nervous system is not only transmitted from one nerve cell to another, but is also characterized by a number of features. These are the convergence and divergence of neural pathways, the phenomena of irradiation, spatial and temporal facilitation and occlusion.

Divergence pathways are the contact of one neuron with many neurons of higher orders.

Thus, in vertebrates, there is a division of the axon of a sensitive neuron entering the spinal cord into many branches (collaterals), which are directed to different segments of the spinal cord and to various departments brain. Signal divergence is also observed in the output nerve cells. Thus, in humans, one motor neuron excites dozens of muscle fibers (in the eye muscles) and even thousands of them (in the muscles of the limbs).

Numerous synaptic contacts of one axon of a nerve cell with a large number dendrites of several neurons are the structural basis of the phenomenon irradiation excitation (expanding the scope of the signal). Irradiation happens directed, when excitation covers a certain group of neurons, and diffuse. An example of the latter is an increase in the excitability of one receptor site (for example, the right leg of a frog) upon irritation of another (painful effect on the left leg).

Convergence- this is the convergence of many nerve pathways to the same neurons. The most common in the central nervous system is multisensory convergence, which is characterized by the interaction on individual neurons of several afferent excitations of different sensory modalities (visual, auditory, tactile, temperature, etc.).

The convergence of many neural pathways to a single neuron makes that neuron integrator of the corresponding signals. If we are talking about motor neuron, i.e. the final link of the nervous path to the muscles, they speak of common final path. The presence of convergence of multiple paths, i.e. nerve circuits, on one group of motor neurons underlies the phenomena of spatial facilitation and occlusion.

Spatial and temporal relief– this is the excess of the effect of the simultaneous action of several relatively weak (subthreshold) excitations over the sum of their separate effects. The phenomenon is explained by spatial and temporal summation.

Occlusion– this is the opposite phenomenon of spatial relief. Here, two strong (suprathreshold) excitations together cause an excitation of such strength that is less than the arithmetic sum of these excitations separately.

The reason for the occlusion is that these afferent inputs, due to convergence, partly excite the same structures and therefore each can create in them almost the same suprathreshold excitation as together.

Centers of the nervous system

A functionally connected set of neurons located in one or more structures of the central nervous system and providing the regulation of a particular function or the implementation of an integral reaction of the body is called center of the nervous system. Physiological concept of the nerve center differs from the anatomical concept of the nucleus, where closely located neurons are united by common morphological features.