home Tests A nerve impulse is conducted from the central nervous system. Conduct impulses from the organ to the brain. Peripheral nervous system

A nerve impulse is conducted from the central nervous system. Conduct impulses from the organ to the brain. Peripheral nervous system

The nervous system is divided into central (brain) and peripheral (peripheral nerves and ganglia). The central nervous system (CNS) receives information from receptors, analyzes it and gives an adequate command to the executive organs. The functional unit of the nervous system is neuron. It distinguishes (Fig. 6.) the body ( som) with a large nucleus and processes ( dendrites and axon). The main function of the axon is to conduct nerve impulses away from the body. Dendrites conduct impulses to the soma. Through sensitive (sensory) neurons, impulses are transmitted from receptors, and through efferent neurons, from the central nervous system to effectors. Most neurons in the CNS are intercalary (they analyze and store information, and also form commands).

Rice. 6. Diagram of the structure of a neuron.

The activity of the central nervous system has a reflex nature. Reflex - This is the response of the body to irritation, carried out with the participation of the central nervous system.

Reflexes are classified according to biological significance (orienting, defensive, food, etc.), the location of receptors (exteroceptive - caused by irritation of the body surface, interoceptive - caused by irritation of internal organs and blood vessels; proprioceptive - arising from irritation of receptors located in muscles, tendons and ligaments), depending on the organs involved in the formation of the response (motor, secretory, vascular, etc.), depending on which parts of the brain are necessary for the implementation of this reflex (spinal, for which there are enough neurons of the spinal cord; bulbar - arise with the participation of the medulla oblongata; mesencephalic - midbrain; diencephalic - diencephalon; cortical - neurons of the cerebral cortex). However, almost all departments of the central nervous system participate in most reflex acts. Reflexes are also divided into unconditioned (congenital) and conditional (acquired). The material substrate of the reflex is a reflex arc - a neural circuit along which an impulse passes from receptive field(part of the body, the irritation of which causes a certain reflex) to the executive body. The composition of the classical reflex arc includes: 1) receptor; 2) sensitive fiber; 3) nerve center (combination of intercalary neurons, which ensures the regulation of a certain function); 4) efferent nerve fiber.

The nerve centers are characterized by the following properties :

Unilateral holding excitation (from a sensitive neuron to an efferent one).

More slow holding excitation in comparison with nerve fibers (most of the time is spent on conducting excitation in chemical synapses - each for 1.5-2 ms).

Summation afferent impulses (manifested by an increase in the reflex).

Convergence - several cells can transmit impulses to one neuron.

Irradiation - one neuron can influence many nerve cells.

Occlusion(blockage) and relief. With occlusion, the number of excited neurons with simultaneous stimulation of two nerve centers is less than the sum of excited neurons with stimulation of each center separately. Relief has the opposite effect.

Rhythm transformation. The frequency of impulses at the entrance to the nerve center and the exit from it usually does not coincide.

Paftereffect - excitation may persist after cessation of stimulation.

High sensitivity to lack of oxygen and poisons.

Low functional mobility and high fatigue.

Posttetanic potentiation- strengthening of the reflex response after prolonged stimulation of the center.

Tone- even in the absence of irritation, many centers generate impulses.

Plastic- are able to change their own functionality.

To the basic principles of coordination of the work of the nerve centers are :

Irradiation - strong and prolonged irritation of the receptor can cause excitation of a larger number of nerve centers (for example, if one limb is slightly irritated, then only it contracts, if the irritation is increased, then both limbs contract).

The principle of a common final path - impulses coming to the CNS through different fibers can converge to the same neurons (for example, the motor neurons of the respiratory muscles are involved in breathing, sneezing and coughing).

Dominant principle(discovered by A.A. Ukhtomsky) - one nerve center can subjugate the activity of the entire nervous system and determine the choice of an adaptive reaction.

Feedback principle - it allows you to correlate changes in system parameters with its operation.

The principle of reciprocity- reflects the relationship of centers opposite in function (for example, inhalation and exhalation) and lies in the fact that the excitation of one of them inhibits the other.

The principle of subordination(subordination) - regulation is concentrated in the higher parts of the central nervous system, and the main one is the cortex hemispheres.

Function compensation principle - the functions of the damaged centers can be performed by other brain structures.

In the nervous system, the processes of excitation and inhibition constantly interact. Excitation causes reflex reactions, and inhibition adapts their strength and speed to existing needs.

Inhibition in the CNS discovered by I.M. Sechenov. Somewhat later, Goltz showed that inhibition can also cause strong excitation.

There are the following types of central braking:

postsynaptic(the main type of inhibition) - lies in the fact that the released inhibitory mediator hyperpolarizes the postsynaptic membrane, which reduces the excitability of the neuron.

Presynaptic - localized in the processes of the excitatory neuron.

Translational - due to the fact that an inhibitory neuron occurs along the path of excitation.

Returnable - carried out by intercalary inhibitory cells.

Pessimal - associated with persistent depolarization of the postsynaptic membrane with frequent or prolonged stimulation.

Inhibition followed by excitation- if, after stimulation, hyperpolarization develops on the neuron, then a new impulse of normal strength does not cause excitation.

Reciprocal inhibition- ensures the coordinated work of antagonist structures, for example, flexor and extensor muscles.

PARTICULAR PHYSIOLOGY OF THE CENTRAL NERVOUS SYSTEM

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

Spinal cord located in the spinal canal and consists of segments. One segment innervates one of its own and two neighboring metameres of the body. Therefore, the defeat of one segment leads to a decrease in sensitivity in them, and its complete loss is observed only if at least two adjacent segments are damaged. Each of them has posterior roots, white matter, gray matter and anterior roots (Fig. 7.).

Sensitive centripetal nerve fibers from receptors pass in the posterior roots. The anterior roots are centrifugal (motor and vegetative). If the posterior roots are cut on the right, and the anterior roots are cut on the left, then the right limbs lose sensitivity, but are capable of movement, and the left ones remain sensitive, but do not move.

The gray matter of the spinal cord contains motoneurons or motor neurons(in front horns) interneurons or intermediate neurons(in the posterior horns) and autonomic neurons(in the lateral horns).

The white matter of the spinal cord along the ascending pathways transmits information from the receptors to the overlying parts of the central nervous system, and the descending pathways of the spinal cord come from the overlying nerve centers.

Own reflexes of the spinal cord are segmental. For example, the cervical and thoracic segments contain the centers of movement of the arms, while the sacral segments contain the centers of movement of the lower extremities. In the sacral segments is located the center of urine separation.

Complete transection of the spinal cord leads to spinal shock(temporary cessation of activity of the segments below the place of cutting). It is caused by a loss of communication with the overlying parts of the central nervous system. The shock lasts for a frog for several minutes, for monkeys - for weeks or months, for a person - for several months.

In the brain, there are (Fig. 8.) Three main sections: the trunk, diencephalon, and telencephalon. In its turn trunk consists of the medulla oblongata, pons, midbrain and cerebellum.

The border between dorsal and medulla oblongata is the exit point of the first cervical roots. There are no segments in the medulla oblongata, but there are clusters of neurons (nuclei). They form the centers of inhalation and exhalation, the vasomotor center (regulates vascular tone and blood pressure), the main center of cardiac activity, the center of salivation, and many others. Damage to the medulla oblongata ends in death. This is due to the presence in it of vital centers (respiratory and cardiovascular).

The medulla oblongata is responsible for protective reflexes such as vomiting, coughing, sneezing, tearing, closing the eyelids, as well as sucking, chewing and swallowing. It is also involved in maintaining posture, redistributing muscle tone during movement, and performing a primary analysis of skin, taste, auditory and vestibular stimuli.

Pons performs motor, sensory, integrative and conductive functions. motor nuclei the bridge is innervated by mimic and chewing muscles, muscles that abduct the eyeball outward and strain the eardrum. Sensitive cores receive signals from receptors of the skin of the face, nasal mucosa, teeth, periosteum of the bones of the skull, conjunctiva and are responsible for the primary analysis of vestibular and taste stimuli. Vegetative nuclei regulate the secretory activity of the salivary glands. The bridge also contains pneumotaxic center, alternately triggering the centers of exhalation and inhalation. The pontine reticular formation activates the cerebral cortex and causes awakening.

AT midbrain there are nuclei that provide raising of the upper eyelid, eye movements, changes in the lumen of the pupil and the curvature of the lens. Red cores inhibit the activity of Deiters nuclei in the medulla oblongata. Transection between the midbrain and medulla oblongata leads to decerebrate rigidity(the tone of the extensor muscles of the limbs, neck and back increases). This is due to the increase in the activity of the Deiters nucleus. black matter regulates the acts of chewing and swallowing, and also coordinates the precise movements of the fingers. The reticular formation of the midbrain regulates the development of sleep and its change to wakefulness.. Tubercles of the quadrigemina provide visual (turning the head and eyes towards the light stimulus, fixing the gaze and tracking moving objects) and auditory (turning the head towards the sound source) orienting reflexes. The midbrain is also involved in the reflex holding of body parts in place, and also corrects the orientation of the limbs when changing their position.

Cerebellum continuously receives information from the muscles, joints, organs of vision and hearing. Under the control of the cortex, it is responsible for programming complex movements, coordinating postures and proportionate purposeful movement. The cerebellum affects the excitability of the telencephalon, is involved in the vegetative support of the activity of the skeletal muscles and the cardiovascular system, as well as metabolism and hematopoiesis.

Cerebellar lesions are accompanied by: asthenia(decreased strength of muscle contractions and fatigue), ataxia(impaired coordination of movements - they are sweeping, sharp, limbs when walking are thrown behind middle line, tilting the head down or to the side causes a strong opposite movement), astasia(inability to maintain balance - the animal stands with its paws wide apart), atony(decreased muscle tone) , tremor(trembling of limbs and head at rest) and uneven movements.

main structures diencephalon are thalamus (optic tubercle) and hypothalamus (hypothalamus).

thalamus is the place of processing of all information sent from all (except olfactory) receptors to the cerebral cortex.

The main function of the thalamus is to evaluate the biological significance of all the information received, and then combine it and transfer it to the cortex.

In humans, the visual tubercle is also necessary for the manifestation of emotions with a kind of facial expressions, gestures and vegetative reactions.

Hypothalamus is the main subcortical vegetative center. Irritation of some of its nuclei mimics the effects of the parasympathetic nervous system. Stimulation of others - accompanied by sympathetic effects. The nuclei of the hypothalamus also regulate the change in the cycle of the sleep-wake cycle, metabolism and energy, food (there are: the center of saturation, the center of hunger and the center of thirst) and sexual behavior, urination, and the formation of emotions.

The regulation of many functions of the hypothalamus is carried out through the endocrine glands and, first of all, through the hypothalamus.

Mainly in the brain stem located reticular formation (RF). Only a small number of formations related to it are located in the thalamus and in the upper segments of the spinal cord. Reticular formationhas a generalized activating effect on the anterior parts of the brain and the entire cortex(ascending activating system), as well as descending (facilitating and inhibitory) effect on the spinal cord. The main RF structures that control motor activity are the nucleus of Deiters (medulla oblongata) and the red nucleus (midbrain).

RF of the midbrain reflexively changes the functioning of the oculomotor apparatus (especially with the sudden appearance of moving objects, changes in the position of the head and eyes) and regulates autonomic functions (for example, blood circulation). The RF of the medulla oblongata contains the centers of inhalation and exhalation (their activity is controlled by the pneumotaxic center of the pons), as well as the vasomotor center.

RF irritation causes an “awakening reaction” and an orienting reflex, affects hearing acuity, vision, smell and pain sensitivity. Transection of the brain below the RF causes wakefulness, above - sleep.

limbic system - functional unification of the CNS structures, which provides (in interaction with the cerebral cortex departments) emotional and motivational components of behavior and the integration of body functions aimed at its adaptation to the conditions of existence. It responds to afferent information from the surface of the body and internal organs organization of behavioral acts (sexual, defensive, food), formation of motivations and emotions, learning, storage of information, as well as a change in the phases of sleep and wakefulness.

The departments of the limbic system include (Fig. 9.): the olfactory bulb and the olfactory tubercle (weakly developed in humans), the mastoid bodies, the hippocampus, the thalamus, the amygdala, the cingulate and happocampal gyrus. Often referred to as the limbic system more structures (eg, parts of the frontal and temporal cortex, hypothalamus, and midbrain RF).

Many of the signals in the limbic system go in circles. In the "circle of Peipes" impulses from the hippocampus pass into the mastoid bodies, from them into the nuclei of the thalamus, then through the cingulate and hippocampal gyrus return to the hippocampus. The described circulation ensures the formation of emotions, memory and learning. Another circle (almond → hypothalamus → mesencephalic structures → amygdala) regulates food, sexual and aggressive-defensive forms of behavior.

Stimulation of certain areas of the limbic system causes pleasant sensations ("pleasure centers"). Next to them are structures that lead to avoidance reactions (“displeasure centers”).

Damage to the limbic system leads to a pronounced violation of social behavior (they behave aloof, anxious and unsure of themselves) and the comparison of new information with the stored in memory (they do not distinguish edible objects from inedible ones and therefore take everything in their mouths), it becomes impossible to concentrate.

The cerebral hemispheres and the region connecting them (the corpus callosum and fornix) belong to telencephalon. Each hemisphere is divided into frontal, parietal, occipital, temporal and hidden (island) lobes. Their surface is covered with bark. The telencephalon in humans also includes accumulations of gray matter inside the hemispheres ( basal nuclei). The hippocampus separates the hemisphere from the brainstem. Between the basal ganglia and the cortex is white matter . It consists of many nerve fibers connecting different parts of the hemispheres with each other and other parts of the brain.

Basal ganglia provide a transition from the idea of movement to action, control the strength, amplitude and direction of movements of the face, mouth and eyes, inhibit unconditioned reflexes and the development conditioned reflexes, participate in the formation of memory and perception of information, are responsible for the organization of eating behavior and orienting reactions.

After the destruction of the basal ganglia, there are: a mask-like face, hypodynamia, emotional dullness, twitching of the head and limbs during movement, monotonous speech, and a violation of the coordination of movement of the limbs when walking.

The cerebral cortex (KBP) of the brain consists of many neurons and is a layer of gray matter.

Based on the evolutionary approach, ancient, old and new bark are distinguished. To the ancient olfactory structures that are poorly developed in humans. old bark make up the main parts of the limbic system: cingulate gyrus, hippocampus, amygdala. The close relationship between ancient and old cortex provides the emotional component of olfactory perception.

New bark performs the most complex functions. To her sensory area all sensitive paths converge. The projection area of each sensation formed in the cortex is directly proportional to its importance (projections from the skin of the hands are larger than from the entire body). The cortical part of the visual (informs about the properties of the light signal) analyzer is located in the occipital lobe. Its removal leads to blindness. The cortical part of the auditory analyzer is localized in the temporal lobe (perceives and analyzes sound signals, organizes auditory control of speech). Its removal causes deafness. Tactile, pain, temperature and other types of skin sensitivity are projected into the parietal lobe.

Motor(motor) areas are in the frontal lobes. In them, each group of neurons is responsible for the voluntary activity of individual muscles (their contraction is caused by irritation of certain areas of the cortex). Moreover, the size of the cortical motor zone is proportional not to the mass of the controlled muscles, but to the accuracy of movements (the largest zones control the movements of the hand, tongue, mimic muscles). The left hemisphere is directly related to the motor mechanisms of speech. With his defeat, the patient understands speech, but cannot speak.

Motor areas receive the information necessary for decision making and execution from association areas(occupies about 80% of the entire surface of the hemispheres) , which unite the signals coming into it from all receptors into integral acts of learning, thinking and long-term memory, and also form programs of purposeful behavior. If the parietal associative cortex forms ideas about the surrounding space and the body, then the temporal cortex is involved in the auditory control of speech, and the frontal cortex forms complex behavior. When the associative zones are damaged, the sensations are preserved, but their evaluation is impaired. It manifests itself apraxia(inability to perform learned movements: fastening buttons, writing text, etc.) and agnosia(disorders of recognition). With motor agnosia, he understands speech, but cannot speak, with sensory agnosia, he speaks, but does not understand speech.

Thus, the telencephalon plays the role of an organ of consciousness, memory and mental activity, which is manifested in behavior and is necessary for a person to adapt to changing environmental conditions.

AUTONOMIC SYSTEM

The nervous system is divided into somatic and autonomic. All effector neurons of the somatic nervous system are motor neurons. They begin in the CNS and end in the skeletal muscles. The autonomic nervous system innervates all internal organs, glands (secretory neurons), smooth muscles (motor neurons) of blood vessels, the digestive tract and urinary tract, and also regulates metabolism (trophic neurons) in various tissues.

The afferent link of the somatic and autonomic reflex arcs is common. The axons of the central autonomic neurons leave the CNS and switch in the ganglia to the peripheral neuron, which innervates the corresponding cells.

The autonomic nervous system is divided into sympathetic and parasympathetic.

Sympathetic nervous system innervates all organs and tissues of the body. Its centers are represented in the lateral horns of the gray matter of the spinal cord (from I thoracic to II-IV lumbar segments). When excited, they increase the work of the heart, dilate the bronchi and pupils, reduce the activity of digestion, cause contraction of the sphincters of the urinary and gall bladders. Sympathetic influences quickly mobilize energy-related metabolism, respiration and blood circulation in the body, which allows it to quickly respond to adverse factors. This also explains the increase in the efficiency of skeletal muscles during stimulation of the sympathetic nerve (the Orbeli-Ginetsinsky phenomenon).

Parasympathetic centers are nuclei in the brainstem and sacral spinal cord. The parasympathetic nervous system does not innervate skeletal muscles, many blood vessels, and sensory organs. When it is excited, the work of the heart is inhibited, the bronchi and pupil are narrowed, digestion is stimulated, the gall and urinary bladders are emptied, as well as the rectum. Changes in metabolism caused by the parasympathetic nervous system ensure the restoration and maintenance of the constancy of the composition of the internal environment of the body, disturbed by the excitation of the sympathetic nervous system.

Autonomic functions are not subject to consciousness, but are regulated by almost all departments of the central nervous system. Stimulation of the spinal centers dilates the pupil, increases sweating, cardiac activity and expands the bronchi. Here are the centers of defecation, urination, sexual reflexes. Stem centers regulate the pupillary reflex and accommodation of the eyes, inhibit the activity of the heart, stimulate lacrimation, increase the secretion of the salivary, gastric and pancreatic glands, as well as bile secretion, contractions of the stomach and intestines. The vasomotor center is responsible for the reflex change in the lumen of the vessels. The hypothalamus is the main subcortical level of autonomic functions. It is responsible for the appearance of emotions, aggressive-defensive and sexual reactions. The limbic system is responsible for the formation of the autonomic component of emotional reactions. The cortex exercises the highest control of vegetative functions, influencing all subcortical vegetative centers, as well as coordinating vegetative and somatic functions during a behavioral act.

#1
properties such as excitability and contractility are characteristic of tissue:
a) epithelial
b) connecting
c) nervous
d) muscular
#2
smooth muscle tissue forms
a) body covering
b) skin
c) blood vessel walls
d) bone marrow
#3
sensory neurons are involved in impulse transmission
a) neuron to neuron
b) sensory organs to the spinal cord and brain
c) spinal cord and brain to organs
d) one internal organ to another
#4
are the following statements true?
a) white matter is formed by axons covered with a myelin sheath.
b) motor neurons transmit impulses from the sense organs in the back and brain
1) only A is true
2) only B is true
3) both statements are true
4) both options are wrong
#5

What element of the somatic reflex arc is completely located in the spinal cord? 1) motor neuron 2) intercalary neuron

3) receptor

4) working body

A fern growing in the shady thickets of a forest is the generation on which

1) sprouts

2) sex cells

4) pregrowths

In the event of a lung injury, the first step is to

1) hold artificial respiration

2) tightly bandage the wound, fixing chest on exhalation

3) conduct an indirect heart massage

4) put the victim on a flat surface and bend his knees

With which of the following organisms can an oak develop symbiotic relationship?

2) white mushroom

3) oak weevil

4) butterfly oak silkworm

Are the following judgments about the structure of the human nervous system correct?

A. Nerve nodes are an accumulation of nerve cell bodies outside the central nervous system

B. Motor neurons transmit nerve impulses from the sense organs to the spinal cord.

1) only A is true

2) only B is true

3) both statements are correct

4) both judgments are wrong

During the germination of a rye seed, the seedling receives nutrients for the first time.
substances from
1) cotyledons
2) germinal root
3) endosperm
4) soil

What tissue lined the head and articular fossa of the joints?
1) cartilaginous
2) nervous
3) smooth muscle
4) striated muscle

What happens in the human body if the air has increased
concentration of carbon dioxide?
1) depression of the respiratory center
2) excitation of the respiratory center
3) irritation of the respiratory tract
4) narrowing of the capillaries of the pulmonary vesicles

Are the following judgments about agrotechnical methods of cultivation correct?
cultivated plants?
A. Nitrogen fertilizers are applied to the soil in the form of top dressing to enhance growth.
leaves and stems of plants.
B. Root pinching is carried out for the development of lateral and adventitious roots
in the upper layers of the soil.
1) only A is true
2) only B is true
3) both statements are correct
4) both judgments are wrong

Put the organisms in the correct order in the food chain. In response
write down the corresponding sequence of numbers.
1) spider
2) owl
3) flowering plant
4) fly
5) toad

Which of the following is NOT a function of the spinal cord? 1) conduction of impulses from the brain to the skeletal muscles 2) exercise

the simplest motor reflexes 3) conduction of impulses from the skeletal muscles to the brain 4) control of voluntary movements of the skeletal muscles

Help, please) Set the match. The essence of the function A) Transmission of a nerve impulse from

feelings. neuron to intercalary neuron

B) Transmission of a nerve impulse from the receptors of the skin, muscles through the white matter of the spinal cord to the brain

C) Transmission of a nerve impulse from an intercalary neuron to an executive neuron

D) Transmission of a nerve impulse from the brain to the executive neurons of the spinal cord.

spinal cord function

1) reflex

2) conductive

What element of the somatic reflex arc is completely located in the spinal cord? 1) motor neuron 2) intercalary neuron

3) receptor

4) working body

A fern growing in the shady thickets of a forest is the generation on which

1) sprouts

2) sex cells

4) pregrowths

In the event of a lung injury, the first step is to

1) perform artificial respiration

2) bandage the wound tightly, fixing the chest on exhalation

3) conduct an indirect heart massage

4) put the victim on a flat surface and bend his knees

With which of the following organisms can an oak form a symbiotic relationship?

2) white mushroom

3) oak weevil

4) butterfly oak silkworm

Are the following judgments about the structure of the human nervous system correct?

A. Nerve nodes are an accumulation of nerve cell bodies outside the central nervous system

B. Motor neurons transmit nerve impulses from the sense organs to the spinal cord.

1) only A is true

2) only B is true

3) both statements are correct

4) both judgments are wrong

During the germination of a rye seed, the seedling receives nutrients for the first time.
substances from
1) cotyledons
2) germinal root
3) endosperm
4) soil

What tissue lined the head and articular fossa of the joints?
1) cartilaginous
2) nervous
3) smooth muscle
4) striated muscle

Put the organisms in the correct order in the food chain. In response
write down the corresponding sequence of numbers.
1) spider
2) owl
3) flowering plant
4) fly
5) toad

please help, i really need it!

Neuro-humoral regulation of vital processes of the body. Nervous system. Reflex. Reflex arc.

It is important to understand that the body is a single system, one of the main functions of which is to maintain homeostasis- constancy of the internal environment.

Depending on changes in the external environment, the body reacts:

perceives changes in environmental parameters (light, temperature, pressure, etc.);

· processes them;

produces a physiological response.

This coordinated work is provided by two mechanisms - nervous regulation and humoral regulation.

Nervous regulation- regulation of the vital activity of the body with the help of the nervous system.

Humoral regulationcarried out through chemical substances through liquid media body (blood, lymph, intercellular fluid).

The first kind - fast reaction literally in seconds. Second - slow, within minutes.

However, they cannot be separated. These are interrelated processes - the functioning of the nervous system is influenced by the biochemical substances of the body and vice versa, not a single substance is excreted by the body without a corresponding nerve impulse. Therefore, these two processes are often combined under the term Neuro-humoral regulation.

Nervous system

The nervous system is responsible for the coordinated activity of various organs and systems, as well as for the regulation of body functions. It also connects the organism with the external environment, thanks to which we feel various changes in the environment and react to them.

nervous tissue

nervous tissue is a specialized tissue of the body from which the entire nervous system is built. This tissue is capable of perceiving stimuli from the external and internal environment, being excited under their influence, producing, conducting and transmitting nerve impulses. So the properties nervous tissue are excitability and conduction.

Neurons, or neurocytes, are functional and structural units of the nervous tissue, cells of the nervous system. Each neuron has body and processes (axons and dendrites) . The body has one nucleus, usually located in the center of the cell, and the cytoplasm, which contains a well-developed apparatus for protein synthesis (ribosomes and granular endoplasmic reticulum). Neurons differ from each other in shape, size, number of processes, and function.

Neurons conduct nerve impulses:

from receptors to the central nervous system ( sensory neurons);

from the central nervous system to the executive organs ( motor, or executive neurons).

Interneurons connect sensory and motor neurons.

Dendrites and axon are the names of the various processes of a neuron.

dendrites there may be a different amount, along which nerve impulses propagate to the cell body. Dendrites are usually strongly branched and contain all the organelles that are in the cell body.

axon, an elongated process of a neuron, through which excitation (nerve impulse) propagates from the body of the neuron. The axon, unlike dendrites, usually does not branch, it does not have an apparatus for protein synthesis.

Neuroglia cells- these are cells that fill all the spaces between neurons, their processes and blood vessels. These cells provide support for neurons, nourish them, protect them, regulate the metabolism in the nervous tissue and create barriers between the nervous and other types of tissues, forming sheaths around the bodies and processes of nerve cells.

nerve impulse is a form of transmission of excitation (information) from one cell to other cells. Under the influence of various stimuli, the nerve cell enters a state of excitation, i.e., a state of performance of functions. At the same time, the permeability cell membrane for sodium ions increases and it is recharged: the inner side of the membrane is charged positively, and the outer side is negatively charged (in a calm state, vice versa). As a result, circular currents arise between the excited and neighboring sections of the membrane. These currents irritate neighboring areas, in which the membrane is also recharged. So the nerve impulse moves from one part of the membrane to another, from cell to cell. The speed of propagation of a nerve impulse in skeletal muscles - 12 - 15 m / s, in smooth - 1 - 18 m / s, in nerve fibers (processes of nerve cells) that do not have a sheath - 0.5 - 3 m / s, in nerve sheathed fibers - 30 - 120 m/s.

The main processes occurring in the nervous system , - excitation and inhibition. The nervous system is highly excitable and conductive, based on its regulatory and coordination activities lie reflexes- the body's response to irritation. The path along which nerve impulses are conducted during the implementation of reflexes is called reflex arc.

First, the body receives information - excitation, which goes through the nerve pathways - sensitive pathways to the "analytical center" - the spinal cord and brain, which issues a "decision" - a response excitation that goes to the working organ along the motor path - a reaction occurs (for example, release required hormone).

Contacts between neurons and cells of the working organs are carried out through synapses. Depending on the composition of the fluid that the target cell receives, both excitation and inhibition can occur in it. A reflex occurs when all links of the reflex arc are excited. If at least one link develops inhibition and there are no detours, the reflex will not appear.

In reflex activity, there are direct connections that go from the brain to the organs and cause them to work, and feedback that informs the brain about the results achieved. If the reflex includes several stages, then the next stage will not begin until information comes to the central nervous system via feedback that the first stage is completed.

Together with the sense organs, the nervous system is involved in the recognition of objects and phenomena. outside world, in the perception, processing and storage of information, as well as in the use of the information received to meet the needs of the body.

The nervous system is made up of two parts : central and peripheral. To central part relate brain and spinal cord. Their nerve cells (neurons) form nerve centers, perceiving and processing incoming information, as well as regulating the work of bodies. The bodies of neurons are in clusters gray matter: either on the surface of the brain (in the cortex), or in its thickness (in the form of nuclei).

CENTRAL NERVOUS SYSTEM

Nervous system	central nervous system
brain	spinal cord
large hemispheres	cerebellum	trunk
Composition and structure	Lobes: frontal, parietal, occipital, two temporal. The cortex is formed by gray matter - the bodies of nerve cells. The thickness of the bark is 1.5-3 mm. The area of the cortex is 2-2.5 thousand cm 2, it consists of 14 billion bodies of neurons. White matter is made up of nerve fibers	The gray matter forms the cortex and nuclei within the cerebellum. Consists of two hemispheres connected by a bridge	Educated: diencephalon midbrain bridge medulla oblongata It consists of white matter, in the thickness are the nuclei of gray matter. The trunk passes into the spinal cord	Cylindrical cord 42-45 cm long and about 1 cm in diameter. Passes in the spinal canal. Inside it is the spinal canal filled with fluid. Gray matter is located inside, white - outside. Passes into the brain stem, forming a single system
Functions	Carries out the highest 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 (musculoskeletal zone) and on inner surface cortex (gustatory and olfactory zones). Regulates the work of the whole organism 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. In the medulla oblongata there are centers: respiratory, digestive, cardiovascular. The bridge 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	Operates under the control of the brain. Arcs of unconditioned (innate) reflexes pass through it, excitation and inhibition during movement. Pathways - white matter connecting the brain to the spinal cord; is a conductor of nerve impulses. Regulates the work of internal organs through the peripheral nervous system Through the spinal nerves, voluntary movements of the body are controlled

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A person acts as a kind of coordinator in our body. It transmits commands from the brain to muscles, organs, tissues and processes the signals coming from them. A nerve impulse is used as a kind of data carrier. What does he represent? At what speed does it work? These and a number of other questions can be answered in this article.

What is a nerve impulse?

This is the name of the wave of excitation that propagates through the fibers as a response to irritation of neurons. Thanks to this mechanism, information is transmitted from various receptors to the central nervous system. And from it, in turn, to different organs (muscles and glands). But what is this process at the physiological level? The mechanism of transmission of a nerve impulse is that the membranes of neurons can change their electrochemical potential. And the process of interest to us takes place in the area of synapses. The speed of a nerve impulse can vary from 3 to 12 meters per second. In more detail about it, as well as about the factors that influence it, we will talk later.

Study of the structure and work

For the first time, the passage of a nerve impulse was demonstrated by the German scientists E. Goering and G. Helmholtz using a frog as an example. At the same time, it was found that the bioelectric signal propagates at the previously indicated speed. In general, this is possible due to the special construction. In some ways, they resemble an electrical cable. So, if we draw parallels with it, then the conductors are the axons, and the insulators are their myelin sheaths (they are the membrane of the Schwann cell, which is wound in several layers). Moreover, the speed of the nerve impulse depends primarily on the diameter of the fibers. The second most important is the quality of electrical insulation. By the way, the body uses myelin lipoprotein, which has the properties of a dielectric, as a material. Ceteris paribus, the larger its layer, the faster the nerve impulses will pass. Even on this moment It cannot be said that this system has been fully investigated. Much that relates to nerves and impulses still remains a mystery and a subject of research.

Features of the structure and functioning

If we talk about the path of a nerve impulse, then it should be noted that the fiber is not covered along its entire length. The design features are such that the current situation can best be compared with the creation of insulating ceramic sleeves that are tightly strung on the rod of an electrical cable (although in this case on the axon). As a result, there are small non-isolated electrical sections from which the ion current can safely flow from the axon into environment(or vice versa). This irritates the membrane. As a result, generation is caused in areas that are not isolated. This process is called the intercept of Ranvier. The presence of such a mechanism makes it possible to make the nerve impulse propagate much faster. Let's talk about this with examples. Thus, the speed of nerve impulse conduction in a thick myelinated fiber, the diameter of which fluctuates within 10-20 microns, is 70-120 meters per second. Whereas for those who have a suboptimal structure, this figure is 60 times less!

Where are they created?

Nerve impulses originate in neurons. The ability to create such "messages" is one of their main properties. The nerve impulse ensures the rapid propagation of the same type of signals along the axons over a long distance. Therefore, it is the most important means of the body for the exchange of information in it. Data on irritation are transmitted by changing the frequency of their repetition. A complex system of periodicals works here, which can count hundreds of nerve impulses in one second. According to a somewhat similar principle, although much more complicated, computer electronics work. So, when nerve impulses arise in neurons, they are encoded in a certain way, and only then are they transmitted. In this case, the information is grouped into special "packs", which have a different number and nature of the sequence. All this, put together, is the basis for the rhythmic electrical activity of our brain, which can be registered thanks to the electroencephalogram.

Cell types

Speaking about the sequence of passage of a nerve impulse, one cannot ignore (neurons), through which the transmission of electrical signals occurs. So, thanks to them, different parts of our body exchange information. Depending on their structure and functionality, three types are distinguished:

Receptor (sensitive). They encode and turn into nerve impulses all temperature, chemical, sound, mechanical and light stimuli.
Plug-in (also called conductor or closing). They serve to process and switch impulses. Most of them are in the head and spinal cord person.
Effector (motor). They receive commands from the central nervous system to perform certain actions (in the bright sun, close your eyes with your hand, and so on).

Each neuron has a cell body and a process. The path of a nerve impulse through the body begins precisely with the latter. Branches are of two types:

Dendrites. They are entrusted with the function of perceiving irritation of the receptors located on them.
Axons. Thanks to them, nerve impulses are transmitted from cells to the working organ.

Speaking about the conduction of a nerve impulse by cells, it is difficult not to talk about one interesting point. So when they are at rest, let's say the sodium-potassium pump is busy moving the ions in such a way as to achieve the effect fresh water inside and salty outside. Due to the resulting imbalance of the potential difference across the membrane, up to 70 millivolts can be observed. For comparison, this is 5% of the usual ones. But as soon as the state of the cell changes, the resulting balance is disturbed, and the ions begin to change places. This happens when the path of a nerve impulse passes through it. Due to the active action of ions, this action is also called the action potential. When it reaches a certain value, then reverse processes begin, and the cell reaches a state of rest.

About the action potential

Speaking about the transformation of a nerve impulse and its propagation, it should be noted that it could be miserable millimeters per second. Then the signals from the hand to the brain would reach in minutes, which is clearly not good. This is where the previously discussed myelin sheath plays its role in strengthening the action potential. And all its "passes" are placed in such a way that they only have a positive effect on the speed of signal transmission. So, when an impulse reaches the end of the main part of one axon body, it is transmitted either to the next cell, or (if we talk about the brain) to numerous branches of neurons. In the latter cases, a slightly different principle works.

How does everything work in the brain?

Let's talk about which nerve impulse transmission sequence works in the most important parts of our central nervous system. Here, neurons are separated from their neighbors by small gaps, which are called synapses. The action potential cannot cross them, so it looks for another way to get to the next nerve cell. At the end of each process are small sacs called presynaptic vesicles. Each of them has special compounds - neurotransmitters. When an action potential arrives at them, molecules are released from the sacs. They cross the synapse and attach to special molecular receptors that are located on the membrane. In this case, the balance is disturbed and, probably, a new action potential appears. This is not yet known for certain, neurophysiologists are studying the issue to this day.

The work of neurotransmitters

When they transmit nerve impulses, there are several options for what will happen to them:

They will diffuse.
subjected to chemical degradation.
Return back to their bubbles (this is called recapture).

At the end of the 20th century, a startling discovery was made. Scientists have learned that drugs that affect neurotransmitters (as well as their release and reuptake) can change a person's mental state in a fundamental way. So, for example, a number of antidepressants like Prozac block the reuptake of serotonin. There are some reasons to believe that a deficiency in the brain neurotransmitter dopamine is to blame for Parkinson's disease.

Now researchers who study the borderline states of the human psyche are trying to figure out how all this affects the human mind. In the meantime, we do not have an answer to such a fundamental question: what causes a neuron to create an action potential? So far, the mechanism of "launching" this cell is a secret for us. Particularly interesting from the point of view of this riddle is the work of neurons in the main brain.

In short, they can work with thousands of neurotransmitters that are sent by their neighbors. Details regarding the processing and integration of this type of impulses are almost unknown to us. Although a lot of work is being done research groups. At the moment, it turned out to find out that all received impulses are integrated, and the neuron makes a decision - whether it is necessary to maintain the action potential and transmit them further. The functioning of the human brain is based on this fundamental process. Well, then it is not surprising that we do not know the answer to this riddle.

Some theoretical features

In the article, "nerve impulse" and "action potential" were used as synonyms. Theoretically, this is true, although in some cases it is necessary to take into account some features. So, if you go into details, then the action potential is only part of the nerve impulse. With a detailed examination of scientific books, you can find out that this is only the change in the charge of the membrane from positive to negative, and vice versa. Whereas a nerve impulse is understood as a complex structural and electrochemical process. It spreads across the neuron membrane like a traveling wave of changes. An action potential is just an electrical component in a nerve impulse. It characterizes the changes that occur with the charge of a local section of the membrane.

Where are nerve impulses created?

Where do they start their journey? The answer to this question can be given by any student who diligently studied the physiology of arousal. There are four options:

Receptor ending of a dendrite. If it exists (which is not a fact), then the presence of an adequate stimulus is possible, which will first create a generator potential, and then a nerve impulse. Pain receptors work in a similar way.
The membrane of the excitatory synapse. As a rule, this is possible only in the presence of strong irritation or their summation.
Trigger zone of the dentrid. In this case, local excitatory postsynaptic potentials are formed as a response to a stimulus. If the first node of Ranvier is myelinated, then they are summed up on it. Due to the presence of a section of the membrane there, which has increased sensitivity, a nerve impulse occurs here.
Axon hillock. This is the name of the place where the axon begins. The mound is the most frequent create impulses on a neuron. In all other places that were considered earlier, their occurrence is much less likely. This is due to the fact that here the membrane has an increased sensitivity, as well as a reduced one. Therefore, when the summation of numerous excitatory postsynaptic potentials begins, the hillock reacts to them first of all.

An example of a spreading excitation

The story in medical terms can cause misunderstanding of certain points. To eliminate this, it is worth briefly going through the stated knowledge. Let's take a fire as an example.

Think back to last summer's news bulletins (you might hear it again soon too). The fire is spreading! At the same time, trees and shrubs that burn remain in their places. But the front of the fire goes further and further from the place where the fire was. The nervous system works the same way.

It is often necessary to calm the excitation of the nervous system that has begun. But this is not so easy to do, as in the case of fire. To do this, artificial interference is made in the work of the neuron (in medicinal purposes) or use various physiological means. This can be compared to pouring water on a fire.