Nerve impulse, its transformation and transmission mechanism. Nervous system. General plan of the structure Nerve impulses from the organ to the brain

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

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

please help, i really need it!

#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) 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

The nervous system regulates the activity of all organs and systems, causing their functional unity and ensures the connection of the organism as a whole with the external environment. The structural unit is a nerve cell with processes - a neuron.

Neurons conduct an electrical impulse to each other through bubble formations (synapses) filled with chemical mediators. According to the structure, neurons are of 3 types:

sensitive (with many short processes)
intercalary
motor (with long single processes).

The nerve has two physiological properties - excitability and conductivity. The nerve impulse is conducted along separate fibers, isolated on both sides, taking into account the electrical potential difference between the excited area (negative charge) and the unexcited positive one. Under these conditions, the electric current will spread to neighboring areas in jumps without attenuation. The speed of the pulse depends on the diameter of the fiber: the thicker, the faster (up to 120 m/s). the most slowly conduct (0.5-15 m/s) sympathetic fibers to the internal organs. The transmission of excitation to the muscles is carried out through motor nerve fibers that enter the muscle, lose their myelin sheath and branch. They end in synapses with a large number (about 3 million) of vesicles filled with a chemical mediator - acetylcholine. There is a synoptic gap between the nerve fiber and the muscle. Nerve impulses arriving at the presynaptic membrane of the nerve fiber destroy the vesicles and pour acetylcholine into the synaptic cleft. The mediator enters the cholinergic receptors of the postsynaptic muscle membrane and excitation begins. This leads to an increase in the permeability of the postsynaptic membrane to K + and N a + ions, which rush into the muscle fiber, giving rise to a local current that propagates along the muscle fiber. Meanwhile, in the postsynaptic membrane, acetylcholine is destroyed by the enzyme cholinesterase secreted here and the postsynaptic membrane “calms down” and acquires its original charge.

The nervous system is conventionally divided into somatic (optional) and vegetative (automatic) nervous system. The somatic nervous system communicates with the outside world, and the autonomic nervous system supports life.

In the nervous system, secrete central- brain and spinal cord peripheral nervous system - nerves extending from them. Peripheral nerves are motor (with the bodies of motor neurons in the CNS), sensory (the bodies of neurons are outside the brain) and mixed.

The Central Nervous System can have 3 kinds of effects on organs:

Starting (acceleration, braking)

Vasomotor (change in the width of blood vessels)

Trophic (increase or decrease in metabolism)

The response to irritation from the external system or the internal environment is carried out with the participation of the nervous system and is called a reflex. The path along which a nerve impulse travels is called a reflex arc. It has 5 parts:

1. sensitive center

2. sensitive fiber conducting excitation to the centers

3. nerve center

4. motor fiber to the periphery

5. acting organ (muscle or gland)

In any reflex act, there are processes of excitation (causes the activity of an organ or enhances an existing one) and inhibition (weakens, stops activity or prevents its occurrence). An important factor in the coordination of reflexes in the centers of the nervous system is the subordination of all overlying centers over the underlying reflex centers (the cerebral cortex changes the activity of all body functions). In the central nervous system, under the influence of various causes, a focus of increased excitability arises, which has the property of increasing its activity and inhibiting other nerve centers. This phenomenon is called dominant and is influenced by various instincts (hunger, thirst, self-preservation and reproduction). Each reflex has its own localization of the nerve center in the central nervous system. You also need a connection to the central nervous system. When the nerve center is destroyed, the reflex is absent.

Receptor classification:

By biological significance: food, defensive, sexual and indicative (introductory).

Depending on the working organ of the response: motor, secretory, vascular.

According to the location of the main nerve center: spinal, (for example, urination); bulbar (medulla oblongata) - sneezing, coughing, vomiting; mesencephalic (midbrain) - straightening the body, walking; diencephalic (interbrain) - thermoregulation; cortical - conditioned (acquired) reflexes.

According to the duration of the reflex: tonic (upright) and phase.

By complexity: simple (dilation of the pupil) and complex (the act of digestion).

According to the principle of motor innervation (nervous regulation): somatic, vegetative.

According to the principle of formation: unconditional (congenital) and conditional (acquired).

The following reflexes are carried out through the brain:

1. Food reflexes: sucking, swallowing, digestive juice secretion

2. Cardiovascular reflexes

3. Protective reflexes: coughing, sneezing, vomiting, tearing, blinking

4. Automatic breathing reflex

5. The vestibular nuclei of muscle tone of the posture reflex are located

The structure of the nervous system.

Spinal cord.

The spinal cord lies in the spinal canal and is a cord 41-45 cm long, somewhat flattened from front to back. At the top, it passes into the brain, and below it is sharpened by the brain case at the level of the II lumbar vertebra, from which the atrophied caudal terminal thread departs.

Backward brain. Anterior (A) and posterior (B) surfaces of the spinal cord:

1 - bridge, 2 - medulla oblongata, 3 - cervical thickening, 4 - anterior median fissure, 5 - lumbosacral thickening, 6 - posterior median sulcus, 7 - posterior lateral sulcus, 8 - cerebral cone, 9 - final (terminal) a thread

Cross section of the spinal cord:

1 - soft shell of the spinal cord, 2 - posterior median sulcus, 3 - posterior intermediate sulcus, 4 - posterior root (sensitive), 5 - posterior lateral sulcus, 6 - terminal zone, 7 - spongy zone, 8 - gelatinous substance, 9 - posterior horn, 10 - lateral horn, 11 - dentate ligament, 12 - anterior horn, 13 - anterior root (motor), 14 - anterior spinal artery, 15 - anterior median fissure

The spinal cord is divided vertically into the right and left sides by the anterior median fissure, and posteriorly by the posterior median sulcus with two slightly pronounced longitudinal grooves passing side by side. These furrows divide each side into three longitudinal cords: anterior, middle and lateral (sheaths here). In places where the nerves exit to the upper and lower extremities, the spinal cord has two thickenings. At the beginning of the prenatal period in the embryo, the spinal cord occupies the entire spinal canal, and then does not keep up with the growth rate of the spine. Due to this “ascent” of the spinal cord, the nerve roots departing from it take an oblique direction, and in the lumbar region they go inside the spinal canal parallel to the terminal thread and form a bundle - a ponytail.

Internal structure of the spinal cord. On a section of the brain, you can see that it consists of gray matter (an accumulation of nerve cells) and white matter (nerve fibers that are collected in pathways). In the center, longitudinally, passes the central canal with cerebrospinal fluid (CSF). Inside is a gray substance that looks like a butterfly and has anterior, lateral and posterior horns. The anterior horn has a short quadrangular shape and consists of cells of the motor roots of the spinal cord. The posterior horns are longer and narrower and contain cells to which the sensory fibers of the posterior roots approach. The lateral horn forms a small triangular protrusion and consists of cells of the autonomic part of the nervous system. The gray matter is surrounded by white matter, which is formed by the pathways of longitudinally running nerve fibers. Among them, there are 3 main types of paths:

Descending fibers from the brain, giving rise to the anterior motor roots.

Ascending fibers to the brain from the posterior sensory roots.

Fibers that connect different parts of the spinal cord.

The spinal cord performs a conductive function between the brain and various parts of the spinal cord due to ascending and descending paths, and is also a segmental reflex center with receptors and working organs. A certain segmental center in the spinal cord and two nearby lateral segments are involved in the implementation of the reflex.

In addition to the motor centers of skeletal muscles, there are a number of autonomic centers in the spinal cord. In the lateral horns of the thoracic and upper segments of the lumbar, there are centers of the sympathetic nervous system that innervate the heart, blood vessels, gastrointestinal tract, skeletal muscles, sweat glands, and pupil dilation. In the sacral region, there are parasympathetic centers innervating the pelvic organs (reflex centers for urination, defecation, erection, ejaculation).

The spinal cord is covered with three membranes: a hard membrane covers the outside of the spinal cord and between it and the periosteum of the vertebral valve is fatty tissue and the venous plexus. Deeper lies a thin sheet of the arachnoid membrane. The soft shell directly encircles the spinal cord and contains the vessels and nerves that feed it. The subarachnoid space between the pia mater and the arachnoid is filled with cerebrospinal fluid (CSF), which communicates with the cerebrospinal fluid. The dentate ligament secures the brain in its position on the sides. The spinal cord is supplied with blood by branches of the vertebral posterior costal and lumbar arteries.

Peripheral nervous system.

31 pairs of mixed nerves depart from the spinal cord, which are formed, which are formed by the fusion of the anterior and posterior roots: 8 pairs of cervical, 12 pairs of thoracic, 5 pairs of lumbar, 5 pairs of sacral and 1 pair of coccygeal nerves. They have certain segments, locations in the spinal cord. The spinal nerves depart from the segments with two roots on each side (anterior motor and posterior sensory) and unite into one mixed nerve, thereby forming a segmental pair. At the exit from the intervertebral foramen, each nerve divides into 4 branches:

Returns to the meninges;

To the node of the sympathetic trunk;

Back for the muscles and skin of the neck and back. These include the suboccipital and large occipital nerve emerging from the cervical region. Sensitive fibers of the lumbar and sacral nerves form the upper and middle nerves of the buttocks.

The anterior nerves are the most powerful and innervate the anterior surface of the trunk and limbs.

Schematic representation of the plexuses of the spinal nerves:

1 - brain in the cranial cavity, 2 - cervical plexus, 3 - phrenic nerve, 4 - spinal cord in the spinal canal, 5 - diaphragm. 6 - lumbar plexus, 7 - femoral nerve. 8 - sacral plexus, 9 - muscular branches of the sciatic nerve, 10 - common peroneal nerve, 11 - superficial peroneal nerve, 12 - saphenous nerve of the leg, 13 - deep peroneal nerve, 14 - tibial nerve, 15 - sciatic nerve, 16 - median nerve , 17 - ulnar nerve, 18 - radial nerve, 19 - musculocutaneous nerve, 20 - axillary nerve, 21 - brachial plexus

They form 4 plexuses:

cervical plexus begins with the cervical vertebrae and at the level of the sternocleidomastoid muscle are divided into sensory branches (skin, ear, neck and shoulder) and motor nerves that innervate the muscles of the neck; the mixed branch forms the phrenic nerve, which innervates the diaphragm (motor) and (sensory).

Brachial plexus formed by the lower cervical and first thoracic nerves. In the armpit below the clavicle, short nerves begin that innervate the muscles of the shoulder girdle, as well as long branches of the shoulder girdle under the clavicle innervate the arm.

Medial cutaneous nerve of the shoulder

The medial cutaneous nerve of the forearm innervates the skin of the corresponding areas of the arm.

The musculocutaneous nerve innervates the flexor muscles of the shoulder, as well as the sensitive branch of the skin of the forearm.

The radial nerve innervates the skin and muscles of the back of the shoulder and forearm, as well as the skin of the thumb, index and middle fingers.

The median nerve gives branches to almost all flexors on the forearm and thumb, and also innervates the skin of the fingers, except for the little finger.

The ulnar nerve innervates part of the muscles of the inner surface of the forearm, as well as the skin of the palm, ring and middle fingers, and the flexors of the thumb.

Anterior branches of the thoracic spinal nerves do not form plexuses, but independently form intercostal nerves and innervate the muscles and skin of the chest and anterior abdominal wall.

Lumbar plexus formed by the lumbar segments. Three short branches innervate the lower parts of the muscles and skin of the abdomen, vulva and upper thigh.

Long branches pass to the lower limb.

The lateral cutaneous nerve of the thigh innervates its outer surface.

The obturator nerve at the hip joint gives branches to the adductor muscles of the thigh and the skin of the inner surface of the thigh.

The femoral nerve innervates the muscles and skin of the anterior surface of the thigh, and its cutaneous branch - the saphenous nerve - goes to the medial surface of the lower leg and the rear of the foot.

sacral plexus formed by the lower lumbar, sacral and coccygeal nerves. Coming out of the sciatic foramen, it gives short branches to the muscles and skin of the perineum, the muscles of the pelvis and the long branches of the leg.

Posterior femoral cutaneous nerve for the gluteal region and posterior thigh.

* The sciatic nerve in the popliteal fossa is divided into the tibial and peroneal nerves, which branch out to form the motor nerves of the lower leg and foot, and also form the calf nerve from the plexus of the skin branches.

Brain.

The brain is located in the cranial cavity. Its upper part is convex and covered with convolutions of two cerebral hemispheres separated by a longitudinal fissure. The base of the brain is flattened and connects to the brainstem and cerebellum, as well as outgoing 12 pairs of cranial nerves.

Base of the brain and exit points of the cranial nerve roots:

1 - olfactory bulb, 2 - olfactory tract, 3 - anterior perforated substance, 4 - gray tubercle, 5 - optic tract, 6 - mastoid bodies, 7 - trigeminal ganglion, 8 - posterior perforated space, 9 - pons, 10 - cerebellum, 11 - pyramid, 12 - olive, 13 - spinal nerve, 14 - hypoglossal nerve, 15 - accessory nerve, 16 - vagus nerve, 17 - pharyngeal nerve, 18 - vestibulocochlear nerve, 19 - facial nerve, 20 - abducens nerve, 21 - trigeminal nerve, 22 - trochlear nerve, 23 - oculomotor nerve, 24 - optic nerve, 25 - olfactory groove

The brain grows up to 20 years and gains different mass, on average 1245g in women, 1375g in men. The brain is covered with the same membranes as the spinal cord: a hard shell forms the periosteum of the skull, in some places it splits into two sheets and forms sinuses with venous blood. hard shell forms many processes that go between the processes of the brain: so the sickle of the brain enters the longitudinal gap between the hemispheres, the sickle of the cerebellum separates the hemispheres of the cerebellum. The tent separates the cerebellum from the hemispheres, and the Turkish saddle of the sphenoid bone with the lying pituitary gland is closed by the diaphragm of the saddle.

Sinuses of the dura mater:

1 - cavernous sinus, 2 - inferior stony sinus, 3 - superior stony sinus, 4 - sigmoid sinus, 5 - transverse sinus. 6 - occipital sinus, 7 - superior sagittal sinus, 8 - direct sinus, 9 - inferior sagittal sinus

Arachnoid- transparent and thin lies on the brain. In the area of the recesses of the brain, expanded sections of the subarachnoid space are formed - tanks. The largest cisterns are located between the cerebellum and the medulla oblongata, as well as at the base of the brain. soft shell contains blood vessels and directly covers the brain, going into all the cracks and furrows. Cerebrospinal fluid (CSF) is formed in the choroid plexuses of the ventricles (intracerebral cavities). It circulates inside the brain through the ventricles, outside in the subarachnoid space and descends into the central canal of the spinal cord, providing constant intracranial pressure, protection and metabolism in the central nervous system.

Projection of the ventricles on the surface of the brain:

1 - frontal lobe, 2 - central sulcus, 3 - lateral ventricle, 4 - occipital lobe, 5 - posterior horn of the lateral ventricle, 6 - IV ventricle, 7 - cerebral aqueduct, 8 - III ventricle, 9 - central part of the lateral ventricle, 10 - lower horn of the lateral ventricle, 11 - anterior horn of the lateral ventricle.

The vertebral and carotid arteries supply the brain with blood, which form the anterior, middle and posterior cerebral arteries, which are connected at the base by the arterial (Vesilian) circle. The superficial veins of the brain directly flow into the venous sinuses of the dura mater, and the deep veins gather in the 3rd ventricle into the most powerful vein of the brain (Galena), which flows into the direct sinus of the dura mater.

Arteries of the brain. Bottom view (from R. D. Sinelnikov):

1 - anterior communicating artery. 2 - anterior cerebral arteries, 3 - internal carotid artery, 4 - middle cerebral artery, 5 - posterior communicating artery, 6 - posterior cerebral artery, 7 - basilar artery, 8 - vertebral artery, 9 - posterior inferior cerebellar artery. 10 - anterior inferior cerebellar artery, 11 - superior cerebellar artery.

The brain consists of 5 parts, which are divided into the main evolutionary ancient structures: oblong, posterior, middle, intermediate, as well as an evolutionary new structure: the telencephalon.

Medulla connects to the spinal cord at the exit of the first spinal nerves. On its front surface, two longitudinal pyramids and oblong olives lying on top outside of them are visible. Behind these formations, the structure of the spinal cord continues, which passes to the lower cerebellar peduncles. The nuclei of the IX-XII pairs of cranial nerves are located in the medulla oblongata. The medulla oblongata carries out the conductive connection of the spinal cord with all parts of the brain. The white matter of the brain is formed by long systems of conductive fibers from and to the spinal cord, as well as short paths to the brainstem.

The hindbrain is represented by the pons and the cerebellum.

Bridge from below it borders on oblong, from above it passes into the legs of the brain, and from the side into the middle legs of the cerebellum. In front are their own accumulations of gray matter, and behind the nucleus of the olive and the reticular formation. The nuclei of the V - VIII PM nerves also lie here. The white matter of the bridge is represented in front by transverse fibers leading to the cerebellum, and ascending and descending fiber systems pass behind.

Cerebellum is located opposite. Two hemispheres are distinguished in it with narrow convolutions of the cortex with gray matter and the central part - the worm, in the depths of which the cerebellar nuclei are formed from accumulations of gray matter. From above, the cerebellum passes into the upper legs to the midbrain, the middle connects to the bridge, and the lower to the medulla oblongata. The cerebellum is involved in the regulation of movements, making them smooth, precise, and is an assistant to the cerebral cortex in controlling skeletal muscles and the activity of autonomic organs.

fourth ventricle is a cavity of the medulla oblongata and hindbrain, which communicates with the central spinal canal from below, and from above passes into the cerebral aqueduct of the midbrain.

midbrain consists of the legs of the brain and the roof plate with two upper hills of the visual pathway and two lower ones - the auditory pathway. From them originates the motor path going to the anterior horns of the spinal cord. The cavity of the midbrain is the cerebral aqueduct, which is surrounded by gray matter with nuclei III and IV pairs of ch.m. nerves. Inside, the midbrain has three layers: a roof, a tire with ascending tract systems and two large nuclei (red and nuclei of the reticular formation), as well as brain legs (or the base of the formation). Above the base lies the black substance, and below the base is formed by the fibers of the pyramidal pathways and the pathways connecting the cortex of the cerebral hemispheres with the bridge and the cerebellum. The midbrain plays an important role in the regulation of muscle tone and in the implementation of standing and walking. Nerve fibers from the cerebellum, basal nuclei and cerebral cortex approach the red nuclei, and motor impulses are sent from them along the extrapyramidal tract originating here to the spinal cord. The sensitive nuclei of the quadrigemina perform primary auditory and visual reflexes (accommodation).

diencephalon fuses with the cerebral hemispheres and has four formations and a cavity of the third ventricle in the middle, which communicates in front with 2 lateral ventricles, and behind passes into the cerebral aqueduct. The thalamus is represented by paired aggregations of gray matter with three groups of nuclei to combine processing and switch all sensory pathways (except olfactory). It plays a significant role in emotional behavior. The upper layer of the white matter of the thalamus is associated with all the motor nuclei of the subcortex - the basal nuclei of the cerebral cortex, the hypothalamus and the nuclei of the middle and medulla oblongata.

Thalamus and other parts of the brain on the median longitudinal section of the brain:

1 - hypothalamus, 2 - cavity of the third ventricle, 3 - anterior (white) commissure, 4 - fornix of the brain, 5 - corpus callosum, 6 - interthalamic fusion. 7 - thalamus, 8 - epithalamus, 9 - midbrain, 10 - bridge, 11 - cerebellum, 12 - medulla oblongata.

In the epithalamus lies the upper appendage of the brain, the pineal gland (pineal gland) on two leashes. The metathalamus is connected by bundles of fibers to the roof plate of the midbrain, in which the nuclei are located, which are the reflex centers of vision and hearing. The hypothalamus includes the tuberous region itself and a number of formations with neurons capable of secreting neurosecretion, which then enters the lower appendage of the brain - the pituitary gland. The hypothalamus regulates all autonomic functions, as well as metabolism. In the anterior sections are parasympathetic centers, and in the posterior sympathetic. The hypothalamus has centers that regulate body temperature, thirst and hunger, fear, pleasure and not pleasure. From the anterior hypothalamus, along long processes of neurons (axons), the hormones vagopressin and oxytocin flow into the storage system of the posterior anterior pituitary gland for entry into the blood. And from the posterior section through the blood vessels, substances releasing factors enter the pituitary gland, stimulating the formation of hormones in its anterior lobe.

reticular formation.

The mesh (reticular) formation consists of nerve cells of the brain itself and their fibers, with an accumulation of neurons in the nucleus of the reticular formation. This is a dense network of branching processes of neurons of specific nuclei of the brainstem (medulla oblongata, middle and intermediate) of the brain, conducting certain types of sensitivity from receptors from the periphery to the brainstem and further to the cerebral cortex. In addition, non-specific pathways to the cerebral cortex, subcortical nuclei and spinal cord begin from the neurons of the reticular formation. Without its own territory, the reticular formation is a regulator of muscle tone, as well as a functional corrector of the brain and spinal cord, providing an activating effect with a supporting state of alertness and concentration. It can be compared with the role of a regulator on a TV: without giving an image, it can change the lighting and sound volume.

Terminal brain.

It consists of two separated hemispheres, which are connected by a plate of white matter of the corpus callosum, below which are two communicating with each other lateral ventricles. The surface of the hemispheres completely repeats the inner surface of the skull, has a complex pattern due to the convolutions and hemispheres between them. The furrows of each hemisphere are divided into 5 lobes: frontal, parietal, temporal, occipital and latent lobes. The cerebral cortex is covered with gray matter. Thickness up to 4 mm. moreover, on top there are sections of an evolutionarily newer cortex of 6 layers, and under it lies a new cortex with fewer layers and a simpler device. The oldest part of the cortex is a rudimentary formation of animals - the olfactory brain. At the point of transition to the lower (basal) surface is the hippocampal ridge, which is involved in the formation of the walls of the lateral ventricles. Inside the hemispheres there are accumulations of gray matter in the form of basal nuclei. They are subcortical motor centers. White matter occupies the space between the cortex and the basal ganglia. It consists of a large number of fibers, which are divided into 3 categories:

1. Associative (associative), connecting different parts of one hemisphere.

2. Adhesions (commissural), connecting the right and left hemispheres.

3. Projection fibers of the pathways from the hemispheres to the low of the brain and spinal cord.

Pathways of the brain and spinal cord.

The system of nerve fibers that conduct impulses from various parts of the body to parts of the central nervous system are called ascending (sensitive) pathways, which usually consist of 3 neurons: the first is always outside the brain, being in the spinal nodes or sensory nodes of the cranial nerves. The systems of the first fibers from the cortex and underlying nuclei of the brain through the spinal cord to the working organ are called motor (descending) pathways. They are formed from two neurons, the latter is always represented by cells of the anterior horns of the spinal cord or cells of the motor nuclei of the cranial nerves.

Sensitive paths (ascending) . The spinal cord conducts 4 types of sensitivity: tactile (touch and pressure), temperature, pain and proprioceptive (joint-muscular sense of position and movement of the body). The bulk of the ascending pathways conducts proprioceptive sensitivity to the cortex of the hemispheres and to the cerebellum.

Ecteroceptive pathways:

The lateral spinothalamic pathway is the path of pain and temperature sensitivity. The first neurons are located in the spinal nodes, giving peripheral processes to the spinal nerves and central processes and central processes that go to the posterior horns of the spinal cord (2nd neuron). At this site, a cross occurs and further the processes rise along the lateral funiculus of the spinal cord and further towards the thalamus. The processes of the 3rd neuron in the thalamus form a bundle going to the postcentral gyrus of the cerebral hemispheres. As a result of the fact that the fibers cross along the way, impulses from the left side of the body are transmitted to the right hemisphere and vice versa.

The anterior spinothalamic pathway is the pathway of touch and pressure. It consists of fibers that conduct tactile sensitivity, which run in the anterior funiculus of the spinal cord.

proprioceptive pathways:

The posterior spinal tract (Flexiga) starts from the neuron of the spinal ganglion (1 neuron) with a peripheral process leading to the muscular-articular apparatus, and the central process goes as part of the posterior root to the dorsal horn of the spinal cord (2nd neuron). The processes of the second neurons rise along the lateral funiculus of the same side to the cells of the cerebellar vermis.

The fibers of the anterior spinal tract (Govers) form a decussation twice in the spinal cord and before entering the cerebellar vermis in the midbrain region.

The proprioceptive path to the cerebral cortex is represented by two bundles: a gentle bundle from the proprioceptors of the lower extremities and the lower half of the body and lies in the posterior funiculus of the spinal cord. The wedge-shaped bundle adjoins it and carries the impulses of the upper half of the body and arms. The second neuron lies in the same-named nuclei of the medulla oblongata, where they cross and gather into a bundle and reach the thalamus (3rd neuron). The processes of the third neurons are sent to the sensory and partially motor cortex.

Motor ways (descending).

Pyramid Paths:

Cortical-nuclear pathway- control of conscious head movements. It starts from the precentral gyrus and passes to the motor roots of the cranial nerves from the opposite side.

Lateral and anterior corticospinal tracts- begin in the precentral gyrus and, after crossing, go to the opposite side to the motor roots of the spinal nerves. They control the conscious movements of the muscles of the trunk and limbs.

Reflex (extrapyramidal) path. It includes the red nuclear spinal cord, which begins and crosses in the midbrain and goes to the motor roots of the anterior horns of the spinal cord; they form the maintenance of skeletal muscle tone and control automatic habitual movements.

Tectospinal pathway also begins in the midbrain and is associated with auditory and visual perception. It establishes a connection between the quadrigemina and the spinal cord; it transmits the influence of the subcortical centers of vision and hearing on the tone of skeletal muscles, and also forms protective reflexes

Vestibulo-spinal path- from the rhomboid fossa of the wall of the fourth ventricle of the medulla oblongata, is associated with maintaining the balance of the body and head in space.

Sechato (reticulo)-spinal tract begins from the nuclei of the reticular formation, which then diverges both along its own and along the opposite side of the spinal nerves. It transmits impulses from the brainstem to the spinal cord to maintain skeletal muscle tone. Regulates the state of the cerebrospinal vegetative centers.

Motor zones cerebral cortex are located in the precentral gyrus, where the size of the zone is proportional not to the mass of the muscles of the body part, but to its accuracy of movements. The zone of control of movements of the hand, tongue and mimic muscles of the face is especially large. The path of impulses of derivative movements from the cortex to the motor neurons of the opposite side of the body is called the pyramidal path.

sensitive areas are located in different parts of the cortex: the occipital zone is associated with vision, and the temporal with hearing, skin sensitivity is projected in the post-central zone. The size of individual sections is not the same: the projection of the skin of the hand occupies a larger area in the cortex than the projection of the surface of the body. Articular-muscular sensitivity is projected into the postcentral and precentral gyrus. The olfactory zone is located at the base of the brain, and the projection of the taste analyzer is located in the lower part of the postcentral gyrus.

limbic system consists of formations of the telencephalon (cingulate gyrus, hippocampus, basal nuclei) and has broad connections with all areas of the brain, the reticular formation, and the hypothalamus. It provides the highest control of all autonomic functions (cardiovascular, respiratory, digestive, metabolism and energy), as well as forms emotions and motivation.

Association zones occupy the rest of the surface and carry out a connection between different areas of the cortex, combining all the impulses flowing into the cortex into integral acts of learning (reading, writing, speech, logical thinking, memory) and providing the possibility of an adequate reaction of behavior.

cranial nerves:

12 pairs of cranial nerves leave the brain. Unlike the spinal nerves, some of the cranial nerves are motor (III, IV, VI, VI, XI, XII pairs), some are sensitive (I, II, VIII pairs), the rest are mixed (V, VII, IX, X). The cranial nerves also contain parasympathetic fibers for smooth muscles and glands (III, VII, IX, X pairs).

I. Pair (olfactory nerve) - represented by processes of olfactory cells, the upper nasal passage, which form the olfactory bulb in the ethmoid bone. From this second neuron, impulses travel through the olfactory tract to the cerebral cortex.

II. Para (optic nerve) formed by processes of the nerve cells of the retina, then in front of the Turkish saddle of the sphenoid bone forms an incomplete intersection of the optic nerves and passes into two optic tracts heading to the subcortical visual centers of the thalamus and midbrain.

III. Pair (oculomotor) motor with an admixture of parasympathetic fibers, starts from the midbrain, passes the orbit and innervates five of the six muscles of the eyeball, and also parasympathetically innervates the muscle that narrows the pupil and the ciliary muscle.

IV. Pair (block-shaped) motor, starts from the midbrain and innervates the superior oblique muscle of the eye.

V. Pair (trigeminal nerve) mixed: innervates the skin of the face and mucous membranes, is the main sensory nerve of the head. The motor nerves innervate the masticatory and mouth muscles. The nuclei of the trigeminal nerve are located in the bridge, from where two roots (motor and sensory) emerge, forming the trigeminal ganglion. The peripheral processes form three branches: the ophthalmic nerve, the maxillary nerve, and the mandibular nerve. The first two branches are purely sensitive, and the third also includes motor fibers.

VI. Pair (abducens nerve) motor, starts from the bridge and innervates the external, rectus eye muscle.

VII. Pair (facial nerve) motor, innervates the mimic muscles of the face and neck. It begins in the tire of the bridge along with the intermediate nerve, which innervates the papillae of the tongue and salivary glands. In the internal auditory meatus, they join, where the facial nerve gives off a large stony nerve and a tympanic string.

VIII Pair (vestibulocochlear nerve) consists of the cochlear part, which conducts the auditory sensations of the inner ear, and the vestibular part of the ear labyrinth. Connecting, they enter the nuclei of the bridge on the border with the medulla oblongata.

IX. Pair (glossopharyngeal) contains motor, sensory and parasympathetic fibers. Its nuclei lie in the medulla oblongata. In the region of the jugular foramen of the occipital bone, it forms two nodes of sensitive branches to the back of the tongue and pharynx. Parasympathetic fibers are secretory fibers of the parotid gland, and motor fibers are involved in the innervation of the muscles of the pharynx.

X. Couple (wandering) the longest cranial nerve, mixed, begins in the medulla oblongata and innervates the respiratory organs with its branches, passes through the diaphragm and forms a celiac plexus with branches to the liver, pancreas, kidneys, reaching the descending colon. Parasympathetic fibers innervate the smooth muscles of the internal organs of the heart and glands. Motor fibers innervate the skeletal muscles of the pharynx, soft palate, and larynx.

XI. Pair (additional) originates in the medulla oblongata, innervates the sternocleidomastoid muscle of the neck and the trapezius muscle with motor fibers

XII. Pair (sublingual) from the medulla oblongata controls the movement of the muscles of the tongue.

autonomic nervous system.

The unified nervous system is conventionally divided into two parts: the somatic, which innervates only the skeletal muscles, and the vegetative, which innervates the entire body as a whole. The motor and autonomic functions of the body are coordinated by the limbic system and the frontal lobes of the cerebral cortex. Autonomic nerve fibers come out of only a few sections of the brain and spinal cord, go as part of the somatic nerves and necessarily form autonomic nodes, from which the post-nodal sections of the reflex arc depart to the periphery. The autonomic nervous system has three kinds of effects on all organs: functional (acceleration or deceleration), trophic (metabolism) and vasomotor (humoral regulation and homeostasis)

The autonomic nervous system consists of two divisions: sympathetic and parasympathetic.

Scheme of the structure of the autonomic (autonomous) nervous system. Parasympathetic (A) and sympathetic (B) part:

1 - superior cervical node of the sympathetic cost, 2 - lateral horn of the spinal cord, 3 - superior cervical cardiac nerve, 4 - thoracic cardiac and pulmonary nerves, 5 - great splanchnic nerve, 6 - celiac plexus, 7 - inferior mesenteric plexus, 8 - superior and lower hypogastric plexuses, 9 - small splanchnic nerve, 10 - lumbar splanchnic nerves, 11 - sacral splanchnic nerves, 12 - sacral parasympathetic nuclei, 13 - pelvic splanchnic nerves, 14 - pelvic (parasympathetic) nodes, 15 - parasympathetic nodes (composed of organ plexuses), 16 - vagus nerve, 17 - ear (parasympathetic) node, 18 - submandibular (parasympathetic) node, 19 - wing palatine (parasympathetic) node, 20 - ciliary (parasympathetic) node, 21 - dorsal nucleus of the vagus nerve, 22 - lower salivary nucleus, 23 - superior salivary nucleus, 24 - accessory nucleus of the oculomotor nerve. The arrows show the paths of nerve impulses to the organs.

Sympathetic nervous system . The central section is formed by cells of the lateral horns of the spinal cord at the level of all the thoracic and upper three lumbar segments. Sympathetic nerve fibers leave the spinal cord as part of the anterior roots of the spinal nerves and form sympathetic trunks (right and left). Further, each nerve through the white connecting branch is connected to the corresponding node (ganglion). Nerve nodes are divided into two groups: on the sides of the spine, paravertebral with the right and left sympathetic trunk and prevertebral, which lie in the chest and abdominal cavity. After the nodes, the postganglionic gray connecting branches go to the spinal nerves, the sympathetic fibers of which form plexuses along the arteries that feed the organ.

In the sympathetic trunk, various departments are distinguished:

cervical consists of three nodes with outgoing branches that innervate the organs of the head, neck and heart.

Thoracic consists of 10-12 nodes of the necks of the ribs lying in front and outgoing branches to the aorta, heart, lungs, esophagus, forming organ plexuses. The largest large and small celiac nerves pass through the diaphragm into the abdominal cavity to the solar (celiac) plexus by preganglionic fibers of the celiac nodes.

Lumbar consists of 3-5 nodes with branches forming plexuses of the abdominal cavity and pelvis.

sacral department consists of 4 nodes on the anterior surface of the sacrum. At the bottom, the chains of nodes of the right and left sympathetic trunks are connected in one coccygeal node. All these formations are combined under the name of the pelvic section of the sympathetic trunks, participate in the formation of the pelvic plexus.

Parasympathetic nervous system. The central sections are located in the brain, of particular importance are the hypothalamic region and the cerebral cortex, as well as in the sacral segments of the spinal cord. In the midbrain lies the nucleus of Yakubovich, the processes enter the oculomotor nerve, which switches in the ciliary border node and innervates the ciliary muscle that constricts the pupil. In the rhomboid fossa lies the superior salivary nucleus, the processes enter the trigeminal, and then into the facial nerve. They form two nodes on the periphery: the pterygopalatine node, which innervates the lacrimal glands and glands of the nasal and oral cavity with its trunks, and the submandibular node, the submandibular and sublingual and sublingual glands. The lower salivary nucleus penetrates the processes into the glossopharyngeal nerve and switches in the ear node and gives rise to the "secretory" fibers of the parotid gland. The largest number of parasympathetic fibers pass through the vagus nerve, starting from the dorsal nucleus and innervating all organs of the neck, chest and abdominal cavity up to and including the transverse colon. Parasympathetic innervation of the descending and colon, as well as all the organs of the small pelvis, is carried out by the pelvic nerves of the sacral spinal cord. They participate in the formation of autonomic nerve plexuses and switch in the nodes of the plexuses of the pelvic organs.

The fibers form plexuses with sympathetic processes that enter the internal organs. The fibers of the vagus nerves switch in the nodes located in the walls of the organs. In addition, parasympathetic and sympathetic fibers form large mixed plexuses, which consist of many clusters of nodes. The largest plexus of the abdominal cavity is the celiac (solar) plexus, from where the postgantlionic branches form plexuses on the vessels to the organs. Another powerful vegetative plexus descends along the abdominal aorta: the superior hypogastric plexus, which, descending into the small pelvis, forms the right and left hypogastric plexus. As part of these plexuses, sensitive fibers from the internal organs also pass.

Well Che, brains are not swollen? Yan asked and turned into a teapot with a rattling lid from the steam coming out.

Well, yes, you put me to sleep - said Yai and scratched his head - although, basically everything is clear.

Well done!!! You deserve a medal, said Yan, and hung a shiny circle around Yay's neck.

Wow! What a brilliant and clearly written "To the greatest clever man of all times and peoples." Well, thank you? And what should I do with it.

And you smell it.

Why does it smell like chocolate? Ahh, this is candy! Yai said and unwrapped the foil.

Eat for now, sweets are good for the brain, and I’ll tell you another interesting thing: you saw this medal, touched it with your hands, sniffed it, and now you hear how it crunches in your mouth with what parts of the body?

Well, many of them.

So all of them are called sense organs, which help the body to navigate in the environment and use it for its needs.

The main terms and concepts tested in the examination paper:v autonomic nervous system, brain, hormones, humoral regulation, motor zone, glands, endocrine, glands, mixed secretion, cerebral cortex, parasympathetic nervous system, peripheral nervous system, reflex, reflex arcs, sympathetic nervous system, synapse, somatic nervous system system, spinal cord, central nervous system.

The structural and functional unit of the nervous system is the nerve cell - neuron . Its main properties are excitability and conductivity. Neurons consist of a body and processes. A long single process that transmits a nerve impulse from the body of a neuron to other nerve cells is called axon . The short processes along which the impulse is conducted to the body of the neuron are called dendrites. There may be one or more. Axons, uniting in bundles, form nerves.

neurons are interconnected synapses- the space between neighboring cells, in which the chemical transmission of a nerve impulse from one neuron to another takes place. Synapses can occur between the axon of one neuron and the body of another, between the axons and dendrites of neighboring neurons, between the processes of neurons of the same name.

Synaptic impulses are transmitted by neurotransmitters- biologically active substances - norepinephrine, acetylcholine and others. Molecules of mediators as a result of interaction with the cell membrane change its permeability for Ca ions + , TO + and Cl - . This leads to excitation of the neuron. The spread of excitation is associated with such a property of the nervous tissue as conductivity. There are synapses that inhibit the transmission of nerve impulses.

Depending on the function they perform, the following types are distinguished neurons:

– sensitive, or receptor whose bodies lie outside the CNS. They transmit an impulse from receptors to the central nervous system;

– intercalary that carry out the transfer of excitation from the sensitive to the executive neuron. These neurons lie within the CNS;

– executive, or motor, whose bodies are located in the central nervous system or in the sympathetic and parasympathetic nodes. They provide the transmission of impulses from the central nervous system to the working organs.

Nervous regulation carried out reflexively. A reflex is a response of the body to irritation that occurs with the participation of the nervous system. The nerve impulse that arose during irritation passes a certain path, called reflex arc. The simplest reflex arc consists of two neurons - sensitive and motor. Most reflex arcs are made up of several neurons.

reflex arc most often consists of the following units: receptor- a nerve ending that perceives irritation. Found in organs, muscles, skin, etc. Sensory neuron that transmits impulses to the CNS. An intercalary neuron lying in the central nervous system (brain or spinal cord), an executive (motor) neuron that transmits an impulse to an executive organ or gland.

Somatic reflex arcs carry out motor reflexes. Autonomic reflex arcs coordinate the work of internal organs.

The reflex reaction consists not only in excitation, but also in braking, i.e. in the delay or weakening of the resulting excitation. The relationship of excitation and inhibition ensures the coordinated work of the body.

EXAMPLES OF TASKS

Part A

A1. Nervous regulation is based on

1) electrochemical signal transmission

2) chemical signaling

3) mechanical signal propagation

4) chemical and mechanical signal transmission

A2. The central nervous system is made up of

1) brain

2) spinal cord

3) brain, spinal cord and nerves

4) brain and spinal cord

A3. The basic unit of nervous tissue is

1) nephron 2) axon 3) neuron 4) dendrite

A4. The site of transmission of a nerve impulse from neuron to neuron is called

1) neuron body 3) nerve ganglion

2) nerve synapse 4) intercalary neuron

A5. When the taste buds are stimulated, saliva begins to flow. This reaction is called

1) instinct 3) reflex

2) habit 4) skill

A6. The autonomic nervous system regulates activity

1) respiratory muscles 3) cardiac muscle

2) face muscles 4) limb muscles

A7. Which part of the reflex arc transmits a signal to the intercalary neuron

1) sensitive neuron 3) receptor

2) motor neuron 4) working organ

A8. The receptor is stimulated by a signal received from

1) sensitive neuron

2) intercalary neuron

3) motor neuron

4) external or internal stimulus

A9. Long processes of neurons unite in

1) nerve fibers 3) gray matter of the brain

2) reflex arcs 4) glial cells

A10. The mediator provides the transfer of excitation in the form

1) electrical signal

2) mechanical irritation

3) chemical signal

4) beep

A11. During lunch, the car alarm went off. Which of the following can happen at this moment in the cerebral cortex of this person

1) excitation in the visual center

2) inhibition in the digestive center

3) excitation in the digestive center

4) inhibition in the auditory center

A12. When burned, arousal occurs

1) in the bodies of executive neurons

2) in receptors

3) in any part of the nervous tissue

4) in intercalary neurons

A13. The function of the interneurons of the spinal cord is to

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 at the 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 uninsulated electrical sections from which the ion current can safely flow out of the axon into the 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. So, 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 found in the human brain and spinal cord.
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're at rest, let's say the sodium-potassium pump is busy moving the ions around in such a way as to achieve the effect of fresh water on the inside and salty on the 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 many research groups are working on this. 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, they make an artificial intervention in the work of a neuron (for medicinal purposes) or use various physiological means. This can be compared to pouring water on a fire.