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The sequence of structural links of the reflex arc. Structure and function of the reflex arc

Reflex(from Latin "reflexus" - reflection) - the reaction of the body to changes in the external or internal environment, carried out through the central nervous system in response to irritation of the receptors.

Reflexes are manifested in the occurrence or cessation of any activity of the body: in the contraction or relaxation of muscles, in the secretion or cessation of secretion of glands, in the narrowing or expansion of blood vessels, etc.

Thanks to reflex activity, the body is able to quickly respond to various changes in the external environment or its internal state and adapt to these changes. In vertebrates, the importance of the reflex function of the central nervous system is so great that even its partial loss (during the surgical removal of certain parts of the nervous system or in case of its diseases) often leads to profound disability and the inability to perform the necessary vital functions without constant careful care.

The significance of the reflex activity of the central nervous system was fully revealed by the classical works of I. M. Sechenov and I. P. Pavlov. As early as 1862, I. M. Sechenov, in his epoch-making work "Reflexes of the Brain," stated: "All acts of conscious and unconscious life are reflexes by their mode of origin."

Types of reflexes

All reflex acts of the whole organism are divided into unconditioned and conditioned reflexes.

Unconditioned reflexes are inherited, they are inherent in every biological species; their arcs are formed by the time of birth and normally persist throughout life. However, they can change under the influence of the disease.

Conditioned reflexes arise with individual development and accumulation of new skills. The development of new temporary connections depends on changing environmental conditions. Conditioned reflexes are formed on the basis of unconditioned and with the participation of higher parts of the brain.

Unconditioned and conditioned reflexes can be classified into various groups according to a number of features.

By biological significance
1. defensive
2. indicative
  postural-tonic (reflexes of body position in space)
  locomotor (reflexes of movement of the body in space)
According to the location of the receptors, the irritation of which causes this reflex act

According to the location of the neurons involved in the reflex

NB!(Nota bene - pay attention!)

In the reflex acts carried out with the participation of neurons located in the higher parts of the central nervous system, neurons located in the lower parts - in the intermediate, middle, medulla oblongata and spinal cord always participate. On the other hand, with reflexes that are carried out by the spinal or medulla oblongata, middle or diencephalon, nerve impulses reach the higher parts of the central nervous system. Thus, this classification of reflex acts is to some extent conditional.

A reflex is the response activity of the body to irritation of receptors, carried out through the central nervous system.

reflex activity is characteristic of the nervous systems.

The reflex activity of the central nervous system, in particular the spinal cord, can be observed especially clearly in an animal with a removed brain. For this purpose, a frog is usually used. In a frog, the brain, including the oblong, is cut off, and it remains only with the spinal cord. A similar operation for the purpose of studying reflexes is also carried out on warm-blooded animals.

In a cat, dog or other warm-blooded animal, the spinal cord is cut at the border of the cervical and thoracic vertebrae.

Rice. SCHEME OF THE DOUBLE-NEURAL REFLECTOR ARC of the spinal REFLEX, 1-end of the centripetal nerve, 2-cent (motor) nerve in the muscle.

Animals operated in this way are called sleep.natural animals.

The spinal frog is suspended from a tripod. If the fingers of the hind foot of such a frog are lowered into a glass with a 0.5% solution of sulfuric acid, the frog will pull out its foot (defensive). If you pinch the foot with tweezers, you can observe the bending of the foot in response to the pinch ( flexion). If you attach a piece of filter paper soaked in a solution of sulfuric acid to the skin of the thigh, the frog makes rubbing movements with its paws, trying to throw off the paper ( rubbing); in the spring, the male can observe the so-called "hugging" reflex, if you rub your finger or some hard object on the skin on the chest between the front legs. In response to such rubbing, the frog tightly grasps a finger or some other object with its front paws.

A number of reflexes can be observed in humans. So, for example, illuminating the eye with bright light causes constriction of the pupil - the pupillary reflex; tickling, stroking or pricking the sole causes flexion of the foot and fingers - a plantar reflex; when putting the nipple in the mouthbaby, he begins to make sucking movements - a sucking reflex, etc.

There are a lot of such examples, it is enough to recall the reflex separation of saliva, gastric juice, or reflex cardiac arrest when a frog is struck on the stomach.

In all these cases, both in lower and higher animals, we observe essentially a phenomenon having the same physiological mechanism, although the final results in the cases described differ sharply from each other.

Rice. 2 SCHEME OF THE THREE-NEURAL REFLECTOR ARC OF THE SPINAL REFLEX. 1-endings of the centripetal nerve; 2-centripetal (sensitive) neuron and spinal ganglion (ganglion); 3 - contact (intermediate) neuron; 4 - centrifugal (motor) neuron; 6-endings of the centrifugal (motor) neuron.

With all reflexes, irritation of the receptors occurs, i.e., the endings of sensory or centripetal nerves. The excitation that has arisen in the receptors is transmitted along the centripetal nerve fiber to the central nervous system. Centripetal nerve fibers are long processes of nerve fibers located outside the spinal cord - in special nerve nodes that are placed in the intervertebral foramens. Another, shorter, process of these cells enters the spinal cord, where excitation is transferred to another neuron. Excitation covers the motor cells located in the spinal cord, and through the motor or centrifugal nerves it enters the muscles, causing them to contract or relax, or to one or another organs, bringing them into an active state.

The path along which excitation occurs during the implementation of reflexes is called a reflex arc. If we schematically represent the simplest reflex arc, then it should consist of at least two neurons - centripetal and centrifugal. A diagram of such a two-neuron reflex arc is shown in Fig. Many scientists believe that another intercalary (contact or intermediate) neuron is included between these two nerve cells in the central nervous system (Fig. 2).

Therefore, the reflex arc includes the following neurons: 1) centripetal, or afferent, 2) centrifugal, or efferent, and 3) intercalary.

Rice. 3 RECEPTIVE RECEPTIVE FIELD OF THE REFLEX.

The centripetal part of the reflex arc is formed by neurons associated with receptors. They transmit to the central nervous system the excitation that has arisen in the receptors. This part of the reflex arc also includes neurons of the ascending pathways of the central nervous system. Through these pathways, excitation is transmitted to the higher parts of the central nervous system.

The centrifugal part of the reflex arc is made up of descending pathways of the central nervous system. According to thesetyam excitation from the higher divisions is transmitted to the lower divisions - to neurons, which in turn conduct excitation to the organ. Thus, in this part of the reflex arc, in addition to descending pathways, terminal centrifugal neurons are also included. Terminal neurons are either motor neurons or neurons of the autonomic nervous system.

The central part of the reflex arc is formed by intercalary neurons. These neurons do not go beyond the central nervous system and have no direct connection with receptors and organs.

Centripetal fibers do not contact directly with centrifugal nerve cells, but terminate at interneurons, and only interneurons are in contact with centrifugal nerve cells.

To conduct excitation and implement a reflex, the integrity of the reflex arc is necessary. It is enough to remove or paralyze the receptors or cut off the centripetal pathway, as the reflex response will disappear due to the fact that the excitation will not be perceived or conducted. Reflexes also disappear if the spinal cord is destroyed or the centrifugal nerve is cut. Thus, all linksreflex arcs are equally important, and their integrity is mandatory for a reflex act.

Each of the reflexes occurs when certain parts of the body are irritated. Flexion of the frog's leg can be induced by irritating the skin of the foot, and the hugging reflex can only be induced by irritating the skin of the chest, etc. The areas of the skin where the receptors are located, upon irritation of which this reflex occurs, are called the perceiving field of the reflex (Fig. 3). The receptive fields of different reflexes are not strictly demarcated and often overlap each other.

The receptors in our body are divided into two large groups: extrareceptors and interoreceptors. 1. Receptors located on the surface of the body - extrareceptors. They perceive irritations that fall on our body from objects of the outside world. 2 Receptors located inside the body - interoreceptors. The latter, in turn, are divided into receptors of internal organs, vessels and various tissues. These receptors perceive changes in the internal state of the body.

Receptors of muscles, tendons and joints - proprioceptors, although they belong to interoreceptors, but due to their special importance can be separated into an independent group.

Proprioreceptors perceive changes in the position of individual parts of the body in space.

Irritation of any of the listed receptors causes a corresponding reflex.

We have already become acquainted with the reflexes that arise when skin receptors are stimulated when considering the flexion, rubbing, and other reflexes of the spinal frog.

We have repeatedly encountered reflexes arising from internal organs, mucous membranes and blood vessels when considering digestion, blood circulation, respiration, etc. An example of such a reflex is a slowdown in cardiac activity and vasodilation that occurs with an increase in pressure in the aortic arch. In this case, the receptors of the depressor nerve are irritated, through which excitation enters the medulla oblongata and then is transmitted to the center of the vagus nerve, which slows down the activity of the heart, and to the general vasomotor center, which causes vasodilation. Finally, reflexes from muscles, tendons or joints occur when they are stretched and are important in maintaining a certain posture of our body. Such reflexes include the so-called tendon reflexes, an example of which is widelya well-known knee reflex, when a blow to the tendon manages to cause a more or less strong contraction of the muscle and straightening of the leg.

The study of relatively constant reflexes in humans is of great importance in the clinic, as it makes it possible to establish the presence of certain lesions in the central nervous system. These relatively constant reflexes include some skin, tendon and eye reflexes (contraction of the abdominal wall at the site of irritation, constriction of the pupil, extension of the leg at the knee joint, etc.).

1 - receptor; 2 - sensitive (afferent) neuron; 3 - spinal node on the back root; 4 - gray matter of the spinal cord; 5 - white matter of the spinal cord; 6 - motor (efferent) neuron; 7- effector (working body); 8 - intercalary neuron 9 - the body of the motor neuron;.

For the implementation of the reflex, the integrity of all links of the reflex arc is necessary. Violation of at least one link leads to a violation of the reflex.

The reflex arc consists of 5 links:

1. receptor, perceiving external or internal influences; receptors convert the influencing energy into the energy of a nerve impulse; receptors have very high sensitivity and specificity (certain receptors perceive only a certain type of energy)

2. sensitive (centripetal, afferent)) a neuron formed by a sensitive neuron, through which a nerve impulse enters the central nervous system

3. intercalary neuron, lying in the CNS, through which a nerve impulse switches to a motor neuron

4. motor neuron (centrifugal, efferent) through which the nerve impulse is conducted to the working organ that responds to irritation

5. nerve endings - effectors transmitting a nerve impulse to the working organ (muscle, gland, etc.)

The reflex arcs of some reflexes do not have intercalary neurons, for example, the knee jerk.

Each reflex has:

Reflex time - the time from the application of irritation to the response to it

Receptive field - a certain reflex occurs only when a certain receptor zone is irritated

The nerve center is a specific localization of each reflex in the central nervous system.

Unconditioned reflexes are specific, permanent, hereditary, persist throughout life.

In the process of embryonic development, reflex arcs of all unconditioned reflexes are formed.

The totality of complex innate reflexes are instincts. Conditioned reflexes are individual, acquired during a person's life, not inherited.

A person has complex social behavior, thinking, consciousness, individual experience (higher nervous activity) - this is a combination of a huge number of various conditioned reflexes.

The material basis of conditioned reflexes is the cerebral cortex. The author of the doctrine of higher nervous activity is the outstanding Russian physiologist I.P. Pavlov, Nobel Prize winner (1904).

The coordination of all reflex reactions is carried out in the central nervous system due to the processes

Brain and spinal cord

Spinal cord

The spinal cord is a cylindrical nerve cord about 45 cm long in men and 40-42 cm in women, with a diameter of about 1 cm. It is located in the bony spinal canal. The spinal cord is covered with three membranes - solid, arachnoid and vascular, which perform protective and trophic functions. It has two thickenings - cervical and lumbar. At the bottom it ends at level 2 of the lumbar vertebra in the form of a cone-shaped narrowing, at the top it passes into the medulla oblongata at the level of the foramen magnum. Inside, along the spinal cord, a narrow spinal canal, filled cerebrospinal fluid. On the anterior surface along the spinal cord passes anterior median fissure, the posterior median passes along the posterior surface. The spinal cord is divided into segments: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal, in total 31 segments. A pair of mixed spinal nerves depart from each segment (one to the right and one to the left). Each spinal nerve in the immediate vicinity of the spinal cord is divided into two roots - anterior and posterior. The posterior root is composed of axons of sensory neurons, it has a thickening - the spinal ganglion, in which the bodies of sensory neurons are located. The anterior root extends from the anterior surface of the spinal cord segment and consists of the axons of motor neurons. There is no spinal ganglion on the anterior root. Both roots, merging, form a common mixed spinal nerve.

Brain

The brain is enclosed in the braincase of the skull. The mass of the brain of an adult is on average 1400 - 1600 g. The human brain develops very quickly: in a newborn, its mass is about 400 g, by the age of seven it is already close to the mass of an adult, by the age of fourteen it almost reaches a maximum. The relative size and mass of the brain in humans significantly predominate over animals: including great apes. The brain during embryonic development is formed as a result of the expansion of the anterior part of the neural tube: first three cerebral vesicles are formed, and then five. Subsequently, brain regions are formed from these cerebral vesicles.

6. The forebrain (cerebral hemispheres) is the largest and most developed part of the brain, its mass is about 80% of the mass of the brain. The forebrain is formed by two symmetrical halves - the cerebral hemispheres, which are separated from each other by a deep vertical fissure. In the depths of it lies a jumper of white medulla connecting the hemispheres - the corpus callosum.

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Reflex, reflex arc (structural components of the reflex arc)

The activity of the body is a natural reflex reaction to a stimulus. Reflex - the reaction of the body to irritation of receptors, which is carried out with the participation of the central nervous system.

The structural basis of the reflex is the reflex arc.

A reflex arc is a series-connected chain of nerve cells that ensures the implementation of a reaction, a response to irritation.

In the reflex arc, the following components are distinguished:

1. Receptors are highly specialized formations that are able to perceive the energy of the stimulus and transform it into nerve impulses.

All receptors can be divided into external or exteroreceptors (visual, auditory, gustatory, olfactory, tactile) and internal or interoreceptors (receptors of internal organs), among which it is useful to distinguish proprioceptors located in muscles, tendons and articular bags.

2. Sensory (afferent, centripetal) neurons that conduct nerve impulses from their dendrites to the central nervous system. In the spinal cord, sensory fibers are part of the posterior roots.

3. Interneurons (intercalary, contact) are located in the central nervous system, receive information from sensory neurons, process it and transmit it to efferent neurons. In the spinal cord, the bodies of intercalary neurons are located mainly in the posterior horns and the intermediate region.

4. Efferent (centrifugal) neurons receive information from interneurons (in exceptional cases from sensory neurons) and transmit it to working organs. The bodies of efferent neurons are located in the central nervous system, and their axons exit the spinal cord as part of the anterior roots and already belong to the peripheral nervous system: they go either to the muscles or to the exocrine glands. The motor neurons that control skeletal muscles of the spinal cord (motoneurons) are in the anterior horns, and the autonomic neurons are in the lateral horns. To provide somatic reflexes, one efferent neuron is sufficient, and for the implementation of vegetative reflexes, two are necessary: one of them is located in the central nervous system, and the body of the other is located in the autonomic ganglion.

5. The working organs or effectors are either muscles or glands, so reflex responses ultimately come down either to muscle contractions (skeletal muscles, smooth muscles of blood vessels and internal organs, cardiac muscle), or to the secretion of glands (digestive, sweat, bronchial, but not endocrine glands).

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The structure of the reflex arc and the functions of its links. Reflex arc and nerve centers.

The reflex arc consists of:

- receptors - perceiving irritation.

- sensitive (centripetal, afferent) nerve fiber that transmits excitation to the center

- the nerve center, where the switching of excitation from sensory neurons to motor neurons occurs

- motor (centrifugal, efferent) nerve fiber that carries excitation from the central nervous system to the working organ

- effector - a working organ that performs an effect, a reaction in response to receptor irritation.

Receptors and receptive fields

Receptor cells that perceive irritation.

receptive field- this is the anatomical region, when irritated, this reflex is caused.

The receptive fields of primary sensory receptors are organized in the most simple way. For example, the tactile or nociceptive receptive field of the skin surface is a branching of a single sensory fiber.

Receptors located in different parts of the receptive field have different sensitivity to adequate stimulation. A highly sensitive zone is usually located in the center of the receptive field, and sensitivity decreases closer to the periphery of the receptive field.

The receptive fields of secondary sensory receptors are organized in a similar way. The difference is that the branches of the afferent fiber do not end freely, but have synaptic contacts with sensitive receptor cells. Gustatory, vestibular, acoustic receptive fields are organized in this way.

overlapping receptive fields. One and the same area of the sensitive surface (for example, skin or retina) is innervated by several sensory nerve fibers, which, with their branchings, overlap the receptive fields of individual afferent nerves.

Due to the overlap of receptive fields, the total sensory surface of the body increases.

Classification of reflexes.

By type of education:

- conditional (acquired) - respond to the name, saliva from the dog into the light.

- unconditional (congenital) - blinking swallowing, knee.

By location receptors:

Exteroceptive (skin, visual, auditory, olfactory)

Interoceptive (from receptors of internal organs)

Proprioceptive (from receptors in muscles, tendons, joints)

For effectors:

Somatic, or motor, (skeletal muscle reflexes);

Vegetative internal organs - digestive, cardiovascular, excretory, secretory, etc.

By biological origin:

Defensive, or protective (response to tactile pain division)

Digestive (irritating receptors in the oral cavity.)

Sexual (hormones in the blood)

Approximate (turn of the head, body)

Motor

– posetonic (supporting body postures)

By the number of synapses:

Monosynaptic, the arcs of which consist of afferent and efferent neurons (for example, knee).

Polysynaptic, the arcs of which also contain 1 or more intermediate neurons and have 2 or more synaptic switches. (somatic and vegetative references).

Disynaptic (2 synapses, 3 neurons).

By the nature of the response:

- motor / motor (muscle contractions)

- secretory (secretory gland secretion)

- vasomotor (expansion and narrowing of blood vessels)

- cardiac (change. The work of the heart muscle.)

According to duration:

phasic (fast) hand withdrawal

tonic (slow) posture maintenance

According to the location of the nerve center:

- spinal (neurons of the SM participate) - pulling the Hand away from the hot segments 2-4, knee jerk.

- reflexes in the brain

- bulbar (medulla oblongata) - closing of the eyelids when touching. to the cornea.

- Mesencephalic (middle m) - vision is a landmark.

- diencephalic (midbrain) - sense of smell

- cortical (bark BP GM) - conditional. ref.

Properties of nerve centers.

1. Unilateral propagation of excitation.

Excitation is transmitted from the afferent to the efferent neuron (reason: the structure of the synapse).

Slowing down the transfer of excitation.

Conditioner The presence of many synapses also depends on the strength of the irritant (summation) and on the physical state. CNS (fatigue).

3.Summation summation of effects, below threshold stimuli.

Temporary: ref. From prev. Imp-sa has not yet passed, but a trace. Already arrived.

Spatial: mixing several.

Backwater They are owl conditioned. Images. Ref.

Facilitation and occlusion center.

The center of relief - occurs under the action of the optimal stimulus (max response) - appeared. Relief Center.

Under the action of min irr. (reduced otv. Rektsiya) there was an occlusion.

Assimilation and transformation of the rhythm of excitation.

Transformation - a change in the frequency of a nerve impulse when passing through the nerve center. The frequency can be increased or decreased.

Assimilation (dance, daily routine)

Consequence

The delay in the end of the response after the cessation of the stimulus. Associated with the circulatory nerve. Imp. Closed Circuits of neurons.

short term (fractions of a second)

long (seconds)

Rhythmic activity of nerve centers.

An increase or decrease in the frequency of nerve impulses associated with the properties of the synapse and the integrative duration of neurons.

8. Plasticity of nerve centers.

The ability to rebuild the functionality of a property for more effective regulation of functions, the implementation of new reflexes that were not previously characteristic of this center, or the restoration of func. At the heart of the layer of synps is a change in the mall-th str-ry.

Changes in excitability under the influence of chemicals.

High sensitivity to real difference.

Fatigue of the nerve centers.

Associated with high synapse fatigue. Reduce feelings. Receptors.

General principles of the coordination activity of the central nervous system.

Braking- special ner. percent manifested in the reduction or complete disappearance of resp. reactions.

Convergence principle

Convergence is the convergence of impulses coming through different afferent pathways in any one central neuron or nerve center.

2 . The principle of convergence is closely related to the principle common final path open Sherrinkton. Many different stimuli can excite the same motor neuron and the same motor response. This principle is due to the unequal number of afferent and efferent pathways.

Principle of divergence

This is the contact of one neuron with many others.

Irradiation and concentration of excitation.

The spread of the excitation process to other nerve centers is called irradiation (electoral- in one direction , generalized- extensive).

After some time, irradiation is replaced by the phenomenon of excitation concentration in the same initial point of the CNS.

The process of irradiation plays a positive (formation of new conditioned reflexes) and negative (violation of the subtle relationships that have developed between the processes of excitation and inhibition, which leads to a disorder of motor activity) roles.

The principle of reciprocity (slows down)

Excitation of some cells causes inhibition of others through the intercalary neuron.

Dominant principle

Ukhtomsky formulated the principle of dominance as a working principle of the activity of nerve centers. term dominant denotes the dominant focus of excitation of the central nervous system, which determines the current activity of the body.

Principles of the dominant focus :

- increased excitability of nerve centers;

- resistance of excitation of excitation in time;

- the ability to summation of extraneous stimuli;

- inertia (the ability to maintain arousal for a long time after the end of the action of irritation); the ability to cause conjugate inhibitions.

The efferent part of the reflex arc.

Afferent part of the reflex arc represented by a sensory neuron.

Some receptor cells are secreted into separate formations - sense organs.

The efferent part of the reflex arc represented by neurons in either the somatic nervous system or the autonomic nervous system.

The central part of the reflex arc, it is made up of intercalary neurons, which within the CNS unite into nerve centers.

There is an anatomical and physiological concept nerve center.

anatomical concept nerve center- spatial association of individual neurons into a single whole.

physiological concept nerve center- neurons united by responsibility for performing the same function. Separate parts of the nerve centers can be located on different floors of the CNS.

Neurons in nerve centers unite into nerve circuits chains create nerve networks.

Exist two types of neural networks:

1. local nerve networks;

2. hierarchical neural networks.

local nerve networks- they combine neurons with a short axon, i.e. neurons located at the same level of CNS organization.

Local networks are characterized by the phenomenon reverb ( excitation circulation with gradual decay ).

Hierarchical neural networks- they predominantly combine neurons that have long axons, which allow you to combine neurons that are located on different levels of the CNS. These networks are used to build subordinate relationship different levels of the CNS.

Hierarchical neural networks organize their activities according to two principles. : divergences, convergences.

Divergence. Available one input of information into the nervous network, and exit from the network multichannel.

Convergence. Inputs online information lot, a exit is one.

Properties of nerve centers:

1. Summation. The sum is: temporal and spatial.

2. Irradiation. Spread of excitation to adjacent nerve centers.

3. Concentration. Contraction of excitation from a large area of the nervous structure to one or more neurons.

4. Induction. Guidance of the opposite process to adjacent nerve centers.

Induction happens:

- positive(when the excitation process is induced);

- negative(when the braking process is initiated).

Induction is divided into:

- simultaneous;

- sequential.

Simultaneous induction. Primarily arising excitation or inhibition in one center, for the second time induces the opposite process to the neighboring center.

Sequential induction. Develops in one center, i.e. one process in the center induces in it the opposite process.

5. Transformation- the ability of the nerve centers to convert the frequency and strength of the incoming excitation.

6. Occlusion(blockage) of the output channel of information. Occurs when information is redundant.

7. Animation. Nerve centers are able to multiply the effect.

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Chemistry Reflex arc, its components, types, functions

transmitting part.

integrative part.

The receiving part.

Neuron. Features of the structure, meaning, types

The structural and functional unit of the nervous tissue is the nerve cell. neuron.

A neuron is a specialized cell that is able to receive, encode, transmit and store information, establish contacts with other neurons, and organize the body's response to irritation.

Functionally in a neuron, there are:

1) the receptive part (the dendrites and the membrane of the soma of the neuron);

2) integrative part (soma with axon hillock);

3) the transmitting part (axon hillock with axon).

Dendrites- the main perceiving field of the neuron. The dendrite membrane is able to respond to neurotransmitters. The neuron has several branching dendrites. This is explained by the fact that a neuron as an information formation must have a large number of inputs. Through specialized contacts, information flows from one neuron to another. These contacts are called spikes.

The soma membrane of a neuron is 6 nm thick and consists of two layers of lipid molecules. The hydrophilic ends of these molecules are turned towards the aqueous phase: one layer of molecules is turned inward, the other is turned outward. The hydrophilic ends are turned towards each other - inside the membrane. Proteins are embedded in the lipid bilayer of the membrane, which perform several functions:

1) pump proteins - move ions and molecules in the cell against the concentration gradient;

2) proteins built into the channels provide selective membrane permeability;

3) receptor proteins recognize the desired molecules and fix them on the membrane;

4) enzymes facilitate the flow of a chemical reaction on the surface of the neuron.

In some cases, the same protein can act as both a receptor, an enzyme, and a pump.

axon hillock the exit point of an axon from a neuron.

The soma of a neuron (the body of a neuron) performs, along with an informational and trophic function, regarding its processes and synapses. The soma provides the growth of dendrites and axons. The soma of the neuron is enclosed in a multilayer membrane, which ensures the formation and distribution of the electrotonic potential to the axon hillock.

axon- an outgrowth of the cytoplasm adapted to carry information that is collected by dendrites and processed in a neuron. The axon of a dendritic cell has a constant diameter and is covered with a myelin sheath, which is formed from glia; the axon has branched endings that contain mitochondria and secretory formations.

Functions of neurons:

1) generalization of the nerve impulse;

2) receipt, storage and transmission of information;

3) the ability to summarize excitatory and inhibitory signals (integrative function).

Types of neurons:

1) by localization:

a) central (brain and spinal cord);

b) peripheral (cerebral ganglia, cranial nerves);

2) depending on the function:

a) afferent (sensitive), carrying information from receptors in the central nervous system;

b) intercalary (connector), in the elementary case, providing a connection between the afferent and efferent neurons;

c) efferent:

- motor - anterior horns of the spinal cord;

- secretory - lateral horns of the spinal cord;

3) depending on the functions:

a) exciting;

b) inhibitory;

4) depending on the biochemical characteristics, on the nature of the mediator;

5) depending on the quality of the stimulus that is perceived by the neuron:

a) monomodal;

b) polymodal.

The activity of the body is a natural reflex reaction to a stimulus.

Reflex- the reaction of the body to irritation of receptors, which is carried out with the participation of the central nervous system. The structural basis of the reflex is the reflex arc.

reflex arc- a series-connected chain of nerve cells that ensures the implementation of a reaction, a response to irritation.

The reflex arc consists of six components: receptors, afferent (sensory) pathway, reflex center, efferent (motor, secretory) pathway, effector (working organ), feedback.

Reflex arcs are of two types:

1) simple - monosynaptic reflex arcs (reflex arc of the tendon reflex), consisting of 2 neurons (receptor (afferent) and effector), there is 1 synapse between them;

2) complex - polysynaptic reflex arcs. They include 3 neurons (there may be more) - receptor, one or more intercalary and effector.

The idea of a reflex arc as an expedient response of the body dictates the extreme importance of supplementing the reflex arc with one more link - a feedback loop. This component establishes a connection between the realized result of the reflex reaction and the nerve center that issues executive commands. With the help of this component, the open reflex arc is transformed into a closed one.

Features of a simple monosynaptic reflex arc:

1) geographically close receptor and effector;

2) the reflex arc is two-neuron, monosynaptic;

3) nerve fibers of group A? (70-120 m/s);

4) short reflex time;

5) muscles that contract as a single muscle contraction.

Features of a complex monosynaptic reflex arc:

1) territorially separated receptor and effector;

2) the receptor arc is three-neuronal (maybe more neurons);

3) the presence of nerve fibers of groups C and B;

4) muscle contraction by the type of tetanus.

Features of the autonomic reflex:

1) the intercalary neuron is located in the lateral horns;

2) from the lateral horns begins the preganglionic nerve path, after the ganglion - postganglionic;

3) the efferent path of the reflex of the autonomic neural arch is interrupted by the autonomic ganglion, in which the efferent neuron lies.

The difference between the sympathetic neural arch and the parasympathetic one: in the sympathetic neural arch, the preganglionic path is short, since the autonomic ganglion lies closer to the spinal cord, and the postganglionic path is long.

In the parasympathetic arc, the opposite is true: the preganglionic path is long, since the ganglion lies close to the organ or in the organ itself, and the postganglionic path is short.

RECEPTORS. education, capable perceive irritation energy, transform it into a nerve impulse and hand over information to the central nervous system.

The structure of receptors is diverse. First of all, these are free nerve endings, neuron dendrites, enclosed either in the thickness of an organ or in smooth muscles. It can also be encapsulated nerve endings, in which the dendrites are surrounded by special capsules of their connective tissue. Such capsules also perform the function of protecting nerve endings, and amplify the signal acting on them. Finally, these are a variety of highly specialized cells that perceive only a strictly defined type of stimulus energy (light, sound wave vibrations, a certain chemical substance) and transmit information to nerve cells, for example, cones and rods of the retina, etc. Figure 3 shows two types of receptors: encapsulated nerve endings and specialized cells.

Due to the diversity of the structure, the receptors can perceive a wide variety of stimuli. In accordance with what kind of energy the receptors perceive, they are usually classified by modality.

Figure 3. Types of receptors

Classification of receptors by modality

1. Tactile

2. Painful (nociceptors).

3. Chemoreceptors (pH, gas tension, electrolyte concentration)

4. Osmoreceptors

5. Thermoreceptors

6. Mechanoreceptors (baroreceptors: pressure, stretch)

7. Highly specialized receptor cells: receptors of the organs of taste, smell (chemoreceptors), vision (photoreceptors), hearing, vestibular apparatus (mechanoreceptors).

Receptors perceive a certain type of irritation (heat, cold, pressure, light, vibrations, stretching, etc.) and transform into a nerve impulse, which is transmitted to the central nervous system. The task of receptors is to translate various stimuli into the language of the nervous system: nerve impulses transmitted at different frequencies.

The accumulation of receptors, the irritation of which causes strictly defined reflexes, is called RECEPTION FIELDS or REFLEXOGENIC ZONES.

The location of the receptors it is possible to distinguish extero-, interoceptive and proprioceptive, reflexes - reflexes that occur when receptors located on the surface of the body, in internal organs or skeletal muscles are irritated. For example, pulling back a hand during a burn is an exteroceptive reflex, a knee-jerk reflex, which we observe in a neurologist's office in response to a blow with a hammer, is proprioceptive.

AFFERENT LINK OF THE REFLECTOR ARC It is represented by neurons, the processes of which connect receptors with nerve centers. This link provides centripetal conduction of excitation from receptors to the structures of the CNS. Most afferent nerve fibers that carry information from tactile, temperature, pain and mechanoreceptors belong to group A and conduct excitation from receptive fields to nerve centers at a speed of 80 - 120 m / s .

NERVE CENTERS- a set of nerve cells, an "ensemble" of neurons that are involved in the regulation of a specific function or in the implementation of a specific reflex act.

We will analyze the properties of the nerve centers in detail later, but for now we will note only the functional significance of the centers. Integration occurs in the nerve center all information coming through the afferent pathways, and a command for action comes from the center.

Reflex centers can be located in any part of the CNS . Depending on the location of the nerve centers There are SPINAL reflexes - nerve centers are located in segments of the spinal cord, BULBAR - in the medulla oblongata, MESENCEPHAL - in the structures of the midbrain, CORTICAL - in various areas of the cerebral cortex. For example, pulling a hand when burned is a spinal reflex.

reflex arc- this is a chain of neurons along which a nerve impulse passes from the receptor (perceiving part) to the organ that responds to irritation.

The reflex arc consists of 5 links:

1) Receptor - a link that perceives irritation

2) sensitive (afferent) link - centripetal nerve fiber - processes of receptor neurons that transmit impulses from sensory nerve endings to the central nervous system

3) central link - nerve center (optional element)

4) motor neuron (centrifugal, efferent) - a link that transmits from the nerve center to the effector

5) effector - an executive organ, the activity of which changes as a result of a reflex (muscle, gland, etc.)

CLASSIFICATION OF REFLECTOR ARCHES

According to the components of the reflex arc, they distinguish

A) monosynaptic arcs (two neurons)

B) polysynaptic arcs (three or more neurons)

According to the location of the main neurons of the arc, without which the reflex is not realized, they distinguish:

1) Spinal arches

2) Zulbar arcs (medulla oblongata)

3) Mesencephalic arches (midbrain)

4) Cortical arches (cerebral cortex)

By the nature of the receptors, the irritation of which causes a certain reflex, there are:

1) Interoreceptive arches

2) Extrareceptive arches

According to biological significance, they distinguish:

1) Sexual

2) Defensive

3) Food

According to the departments of the central nervous system, there are:

1) Vegetative arcs

2) Somatic arches

Reflex - a complex formation consisting of nerve endings, dendrites, sensitive neurons, glia, special tissue cells, which together ensure the transformation of the influence of external or internal environmental factors into a nerve impulse.

receptive reflex field- a surface with receptors, the irritation of which causes a reflex reaction.

Types of reflexes:

Location in the body

Exteroreceptors - located on the surface or near the surface of the body and perceive nerve stimuli

Interoreceptors - located in the internal organs and perceive internal stimuli

Proprioreceptors - receptors of the musculoskeletal system

2) According to the ability to perceive different stimuli:

Monomodal - responds to one type of stimulus

Polymodal - responds to several types of stimuli

3) According to the biological correspondence of the stimulus:

- adequate - stimuli that correspond to a given tissue. For example, for the retina of the eye, light - all other stimuli do not correspond to the retina, for muscle tissue - a nerve impulse, etc.;

Inappropriate - irritants that do not correspond to this tissue. For the retina, all stimuli except light will be inadequate, and for muscle tissue, all stimuli, except for a nerve impulse

Methods for studying the functions of the central nervous system.

There are the following methods for studying the functions of the central nervous system:

1. The method of transections of the brain stem at various levels. For example, between the medulla oblongata and the spinal cord.

2. The method of extirpation (removal) or destruction of parts of the brain.

3. Method of irritation of various departments and centers of the brain.

4. Anatomical and clinical method. Clinical observations of changes in the functions of the central nervous system in case of damage to any of its departments, followed by a pathoanatomical study.

5. Electrophysiological methods:

a. electroencephalography - registration of brain biopotentials from the surface of the skin of the skull. The technique was developed and implemented in the clinic by G. Berger.

b. registration of biopotentials of various nerve centers; used in conjunction with stereotaxic technique, in which electrodes are inserted into a strictly defined nucleus with the help of micromanipulators.

in. the method of evoked potentials, registration of the electrical activity of brain regions during electrical stimulation of peripheral receptors or other regions;

6. method of intracerebral administration of substances using microinophoresis;

7. chronoreflexometry - determination of the time of reflexes.

Spinal cord. Functions of the anterior and posterior roots of the spinal cord. Classification of nerve fibers. Interaction of neurons in the spinal cord. Major pathways of the spinal cord.

Spinal cord- an organ of the central nervous system located in the spinal canal.

Front roots are axons of nerve cells. The anterior roots are motor, they contain centrifugal efferent fibers that conduct motor impulses to the periphery of the body: to striated and smooth muscles, glands, etc.

back roots

consist of processes of cells that lie in the spinal ganglion. The posterior roots contain afferent (centripetal) nerve fibers that conduct sensory impulses from the periphery, that is, from all tissues and organs of the body, to the central nervous system.

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