A person acts as a kind of coordinator in our body. It transmits commands from the brain to muscles, organs, tissues and processes signals coming from them. A nerve impulse is used as a kind of data carrier. What is he? At what speed does it work? These, as well as a number of other questions, can be answered in this article.
What is a nerve impulse?
This is the name for the excitation wave that spreads along 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 does this process represent at the physiological level? The mechanism of nerve impulse transmission is that neuron membranes can change their electrochemical potential. And the process that interests us occurs in the area of synapses. The speed of the nerve impulse can vary from 3 to 12 meters per second. We will talk about it in more detail, as well as about the factors that influence it.
Study of structure and work
The passage of a nerve impulse was first demonstrated by German scientists E. Hering and G. Helmholtz using the example of a frog. It was then established that the bioelectric signal propagates at the previously indicated speed. In general, this is possible thanks to a special construction. In some ways, they resemble an electric cable. So, if we draw parallels with it, then the conductors are the axons, and the insulators are their myelin sheaths (they are a Schwann cell membrane, 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 factor is the quality of electrical insulation. By the way, the body uses lipoprotein myelin as a material, which has dielectric properties. All other things being equal, the larger its layer, the faster nerve impulses will travel. Even at the moment it cannot be said that this system has been fully explored. Much that relates to nerves and impulses still remains a mystery and a subject of research.
Features of structure and functioning
If we talk about the path of the nerve impulse, 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 couplings that are tightly strung on the rod of an electrical cable (albeit in this case on an axon). As a result, there are small non-insulated electrical areas from which ionic current can easily 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 interception of Ranvier. The presence of such a mechanism allows the nerve impulse to spread much faster. Let's talk about this with examples. Thus, the speed of nerve impulse conduction in a thick myelinated fiber, the diameter of which varies between 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. A nerve impulse ensures rapid propagation of similar signals along axons over a long distance. Therefore, this is the body’s most important means for exchanging information within it. Data on irritation are transmitted by changing their frequency. A complex system of periodicals operates here, which can count hundreds of nerve impulses in one second. Computer electronics works on a somewhat similar principle, although much more complicated. So, when nerve impulses arise in neurons, they are encoded in a certain way, and only then are transmitted. In this case, information is grouped into special “packs”, which have different numbers and patterns. All this, put together, forms the basis for the rhythmic electrical activity of our brain, which can be recorded using an electroencephalogram.
Cell types
Speaking about the sequence of passage of a nerve impulse, we cannot ignore the neurons through which electrical signals are transmitted. 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 transform into nerve impulses all temperature, chemical, sound, mechanical and light stimuli.
- Insert (also called conductor or closure). They serve to process and switch impulses. The largest number 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 bright sunshine, 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 with the last one. There are two types of shoots:
- Dendrites. They are entrusted with the function of perceiving irritation from the receptors located on them.
- Axons. Thanks to them, nerve impulses are transmitted from cells to the working organ.
Speaking about the conduction of nerve impulses by cells, it is difficult not to talk about one interesting point. So, when they are at rest, then, let's say, the sodium-potassium pump is engaged in moving ions in such a way as to achieve the effect of fresh water inside and salty outside. Due to the resulting imbalance, potential differences across the membrane can be observed up to 70 millivolts. For comparison, this is 5% of the usual ones. But as soon as the state of the cell changes, the resulting equilibrium is disrupted, 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 an action potential. When it reaches a certain point, 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 amount to measly millimeters per second. Then signals from the hand to the brain would take minutes, which is clearly not good. This is where the previously discussed myelin sheath plays its role in enhancing 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 what transmission sequence of nerve impulses works in the most important parts of our central nervous system. Here, neurons are separated from their neighbors by small gaps called synapses. The action potential cannot pass through them, so it looks for another way to get to the next nerve cell. At the end of each process there are small sacs called presynaptic vesicles. Each of them contains 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 equilibrium is disturbed and, probably, a new action potential appears. This is not yet known for certain; neurophysiologists are still 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.
- Will undergo chemical breakdown.
- They will return back to their bubbles (this is called recapture).
At the end of the 20th century, an amazing discovery was made. Scientists have learned that drugs that affect neurotransmitters (as well as their release and reuptake) can radically change a person's mental state. 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. Well, for now we do not have an answer to such a fundamental question: what causes a neuron to create an action potential? For now, the mechanism for “launching” this cell is a secret to 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 sent by their neighbors. The 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, we have learned 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. In theory this is true, although in some cases it is necessary to take into account some features. So, if you go into detail, 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 name for a change in the charge of the membrane from positive to negative, and vice versa. Whereas a nerve impulse is understood as a complex structural-electrochemical process. It spreads across the neuron membrane as a traveling wave of change. The action potential is just the electrical component of a nerve impulse. It characterizes the changes that occur with the charge of a local area 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 has diligently studied the physiology of arousal. There are four options:
- Receptor end of the dendrite. If it exists (which is not a fact), then it is possible that there is an adequate stimulus, which will first create a generator potential, and then a nerve impulse. Pain receptors work in a similar way.
- Membrane of the excitatory synapse. As a rule, this is only possible in the presence of severe irritation or their summation.
- Dendritic trigger zone. In this case, local excitatory postsynaptic potentials are formed as a response to the stimulus. If the first node of Ranvier is myelinated, then they are summed up on it. Due to the presence of a section of membrane there that has increased sensitivity, a nerve impulse arises here.
- Axon hillock. This is the name given to the place where the axon begins. The mound is the most frequent one to 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 increased sensitivity, as well as decreased sensitivity. Therefore, when the summation of numerous excitatory postsynaptic potentials begins, the hillock reacts to them first.
Example of propagating excitation
Talking in medical terms may cause misunderstanding of certain points. To eliminate this, it is worth briefly going through the knowledge presented. Let's take a fire as an example.
Remember the news reports from last summer (you can also hear this again soon). The fire is spreading! At the same time, trees and bushes that burn remain in their places. But the fire front is moving further and further from the place where the fire was located. The nervous system works in a similar way.
It is often necessary to calm the excitation of the nervous system that has begun. But this is not so easy to do, as in the case of fire. To do this, artificial interference is made in the functioning of the neuron (for therapeutic purposes) or various physiological means are used. This can be compared to pouring water on a fire.
The nervous system regulates the activity of all organs and systems, determining their functional unity and ensuring the connection of the body 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)
- insertion
- motor (with long single processes).
The nerve has two physiological properties - excitability and conductivity. The nerve impulse is carried out along separate fibers, isolated on both sides, taking into account the electrical potential difference between the excited area (negative charge) and the non-excited positive one. Under these conditions, the electric current will spread to neighboring areas in jumps without attenuation. The speed of the impulse depends on the diameter of the fiber: the thicker, the faster (up to 120 m/s). Sympathetic fibers conduct the most slowly (0.5-15 m/s) to the internal organs. The transmission of excitation to 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 the 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 release acetylcholine into the synaptic cleft. The mediator reaches the cholinergic receptors of the postsynaptic membrane of the muscle 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 spreading 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 (arbitrary) and vegetative (automatic) nervous system. The somatic nervous system communicates with the outside world, and the autonomic nervous system maintains vital functions.
In the nervous system there are central– brain and spinal cord and peripheral nervous system - nerves extending from them. Peripheral nerves are motor (with the bodies of motor neurons in the central nervous system), sensory (the bodies of neurons are outside the brain) and mixed.
The Central Nervous System can have 3 types of effects on organs:
Starting (acceleration, braking)
Vasomotor (change in the width of blood vessels)
Trophic (increase or decrease in metabolism)
The response to stimulation from the external system or 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. There are 5 links in it:
1. sensitive center
2. sensitive fiber conducting excitation to the centers
3. nerve center
4. motor fiber to the periphery
5. active organ (muscle or gland)
In any reflex act there are processes of excitation (causes the activity of an organ or strengthens an existing one) and inhibition (weakens, stops the 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 reasons, 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. Communication in the central nervous system is also needed. When the nerve center is destroyed, the reflex is absent.
Classification of receptors:
According to biological significance: nutritional, defensive, sexual and orientational (familiarization).
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 (diencephalon) – thermoregulation; cortical – conditioned (acquired) reflexes.
According to the duration of the reflex: tonic (upright) and phasic.
By complexity: simple (pupil dilation) and complex (digestion).
According to the principle of motor innervation (nervous regulation): somatic, autonomic.
According to the principle of formation: unconditional (congenital) and conditional (acquired).
The following reflexes occur 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 posture reflex muscle tone 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 at the bottom it sharpens into the brain case at the level of the II lumbar vertebra, from which the atrophied caudal terminal filament extends.
The back of the 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 - conus medullaris, 9 - terminal (terminal) a thread
Cross section of the spinal cord:
1 - pia mater 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 at the back by the posterior median sulcus with two faint longitudinal grooves running side by side. These grooves divide each side into three longitudinal cords: anterior, middle and lateral (shells). At the points where the nerves exit to the upper and lower extremities, the spinal cord has two thickenings. At the beginning of the fetal period, the spinal cord occupies the entire spinal canal, and then does not keep up with the rate of growth of the spine. Thanks to this “ascent” of the spinal cord, the nerve roots extending from it take an oblique direction, and in the lumbar region they run inside the spinal canal parallel to the terminal filum and form a bundle - the cauda equina.
Internal structure of the spinal cord. A cross-section of the brain shows that it consists of gray matter (a collection of nerve cells) and white matter (nerve fibers that gather into pathways). In the center, longitudinally, runs the central canal with cerebrospinal fluid (CSF). Inside is gray matter, which 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 dorsal horns are longer and narrower and include cells to which the sensory fibers of the dorsal 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 that give rise to the anterior motor roots.
Ascending fibers to the brain from the posterior sensory roots.
Fibers connecting different parts of the spinal cord.
The spinal cord, through the ascending and descending tracts, carries out the conductor function between the brain and various parts of the spinal cord, 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, the spinal cord contains a number of autonomic centers. In the lateral horns of the thoracic and upper segments of the lumbar regions there are centers of the sympathetic nervous system that innervate the heart, blood vessels, gastrointestinal tract, skeletal muscles, sweat glands, and pupil dilation. The sacral region contains parasympathetic centers that innervate the pelvic organs (reflex centers for urination, defecation, erection, ejaculation).
The spinal cord is covered with three membranes: the dura mater covers the outside of the spinal cord and between it and the periosteum of the vertebral valve there is adipose tissue and a venous plexus. Deeper lies a thin sheet of arachnoid membrane. The soft membrane directly surrounds the spinal cord and contains the vessels and nerves that supply it. The subarachnoid space between the pia mater and the arachnoid membrane is filled with cerebrospinal fluid (CSF), which communicates with the cerebrospinal fluid of the brain. On the sides, the dentate ligament secures the brain in its position. The spinal cord is supplied with blood by branches of the vertebral posterior costal and lumbar arteries.
Peripheral nervous system.
From the spinal cord there are 31 pairs of mixed nerves that 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 specific segments located in the spinal cord. The spinal nerves arise 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 is divided into 4 branches:
Returns to the meninges;
To the node of the sympathetic trunk;
Posterior for the muscles and skin of the neck and back. These include the suboccipital and greater occipital nerves emerging from the cervical region. Sensory fibers of the lumbar and sacral nerves form the superior and middle nerves of the buttock.
The anterior nerves are the most powerful and innervate the anterior surface of the trunk and limbs.
Schematic representation of the spinal nerve plexuses:
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, is 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 axillary fossa below the collarbone, short nerves begin that innervate the muscles of the shoulder girdle, and long branches of the shoulder girdle under the collarbone 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 shoulder flexor muscles, as well as the sensory branch of the skin of the forearm.
The radial nerve innervates the skin and muscles of the posterior surface 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 of the forearm and thumb, and also innervates the skin of the fingers, except 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 flexor muscles 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 lumbar segments. Three short branches innervate the lower parts of the muscles and skin of the abdomen, external genitalia and upper thigh.
Long branches extend 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 thigh, and its cutaneous branch, the saphenous nerve, goes to the medial surface of the leg and dorsum of the foot.
Sacral plexus formed by the lower lumbar, sacral and coccygeal nerves. Coming from the sciatic foramen, it gives short branches to the muscles and skin of the perineum, pelvic muscles and 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 to form the motor nerves of the leg and foot, and also form the calf nerve from the plexus of cutaneous branches.
Brain.
The brain is located in the cranial cavity. Its upper part is convex and covered with convolutions of the 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 the 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 - lysopharyngeal nerve, 18 - vestibulocochlear nerve, 19 - facial nerve, 20 - abducens nerve, 21 - trigeminal nerve, 22 - trochlear nerve, 23 - oculomotor nerve, 24 - optic nerve, 25 - olfactory sulcus
The brain grows until the age of 20 and gains different weight, on average 1245g in women, 1375g in men. The brain is covered with the same membranes as the spinal cord: the dura mater forms the periosteum of the skull, in some places it splits into two layers and forms sinuses with venous blood. Dura shell forms many processes that extend between the processes of the brain: the falx cerebellum enters the longitudinal fissure between the hemispheres, the falx cerebellum separates the cerebellar hemispheres. The tent separates the cerebellum from the hemispheres, and the sella turcica of the sphenoid bone with the underlying pituitary gland is closed by the sella diaphragm.
Sinuses of the dura mater:
1 - cavernous sinus, 2 - inferior petrosal sinus, 3 - superior petrosal sinus, 4 - sigmoid sinus, 5 - transverse sinus. 6 - occipital sinus, 7 - superior sagittal sinus, 8 - straight sinus, 9 - inferior sagittal sinus
Arachnoid– transparent and thin lies on the brain. In the area of the recesses of the brain, expanded areas of the subarachnoid space - cisterns - are formed. The largest cisterns are located between the cerebellum and medulla oblongata, as well as at the base of the brain. Soft shell contains vessels and directly covers the brain, entering all the cracks and grooves. 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 onto the surface of the cerebrum:
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 brain is supplied with blood by the vertebral and carotid arteries, which form the anterior, middle and posterior cerebral arteries, 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 collect in the 3rd ventricle into the most powerful vein of the brain (Galen), 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 evolutionarily ancient structures: medulla oblongata, hindbrain, middle, intermediate, and also into an evolutionarily new structure: the telencephalon.
Medulla connects to the spinal cord at the point where the first spinal nerves exit. On its front surface two longitudinal pyramids and oblong olive trees 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 medulla oblongata contains the nuclei of the IX - XII pairs of cranial nerves. The medulla oblongata provides a conductive connection between the spinal cord and all parts of the brain. The white matter of the brain is formed by long systems of conducting fibers to and from the spinal cord, as well as short pathways to the brain stem.
The hindbrain is represented by the pons and cerebellum.
Bridge below it borders with the medulla oblongata, above it passes into the cerebral peduncles, and laterally into the middle peduncles of the cerebellum. In front are their own accumulations of gray matter, and behind them are the olivary nuclei and the reticular formation. The nuclei of nerves V - VIII also lie here. The white matter of the pons is represented in front by transverse fibers going to the cerebellum, and in the back by ascending and descending fiber systems.
Cerebellum is located opposite. It consists of two hemispheres with narrow convolutions of the cortex with gray matter and a central part - the vermis, in the depths of which the cerebellar nuclei are formed from accumulations of gray matter. From above, the cerebellum passes into the upper peduncles to the midbrain, the middle ones connect to the pons, and the lower ones 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 the cavity of the medulla oblongata and hindbrain, which communicates from below with the central spinal canal, and from above passes into the cerebral aqueduct of the midbrain.
Midbrain consists of the cerebral peduncles and the roof plate with two upper hills of the visual pathway and two lower hills of the auditory pathway. From them originates the motor pathway 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 of the III and IV pairs of the brain. nerves. Inside, the midbrain has three layers: a roof, a tegmentum with systems of ascending pathways and two large nuclei (red and nuclei of the reticular formation), as well as the cerebral peduncles (or base of the formation). The black substance lies on top of the base, and below the base is formed by fibers of the pyramidal tracts and tracts connecting the cerebral cortex with the pons and cerebellum. The midbrain plays an important role in regulating muscle tone and in standing and walking. Nerve fibers from the cerebellum, basal ganglia and cerebral cortex approach the red nuclei, and from them motor impulses are sent along the extrapyramidal tract originating here to the spinal cord. The sensory nuclei of the quadrigeminal region perform primary auditory and visual reflexes (accommodation).
Diencephalon fuses with the cerebral hemispheres and has four formations and the cavity of the third ventricle in the middle, which communicates in front with the 2 lateral ventricles, and in the back passes into the cerebral aqueduct. The thalamus is represented by paired clusters of gray matter with three groups of nuclei to integrate processing and switching of all sensory pathways (except olfactory). Plays a significant role in emotional behavior. The upper layer of the white matter of the thalamus is connected with all the motor nuclei of the subcortex - the basal nuclei of the cerebral cortex, the hypothalamus and the nuclei of the midbrain and medulla oblongata.
The thalamus and other parts of the brain in a midline longitudinal section of the brain:
1 - hypothalamus, 2 - cavity of the third ventricle, 3 - anterior (white) commissure, 4 - cerebral fornix, 5 - corpus callosum, 6 - interthalamic fusion. 7 - thalamus, 8 - epithalamus, 9 - midbrain, 10 - pons, 11 - cerebellum, 12 - medulla oblongata.
In the epithalamus lies the upper appendage of the brain, the epiphysis (pineal body) on two leashes. The metathalamus is connected by bundles of fibers to the plate of the roof of the midbrain, which contain nuclei that are reflex centers of vision and hearing. The hypothalamus includes the subtubercular 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. The parasympathetic centers are located in the anterior sections, and the sympathetic centers in the posterior sections. The hypothalamus has centers that regulate body temperature, thirst and hunger, fear, pleasure and non-pleasure. From the anterior hypothalamus, the hormones vagopressin and oxytocin flow down the long processes of neurons (axons) into the storage system of the posterior anterior lobe of the pituitary gland to enter the blood. And from the posterior section, releasing factor substances enter the pituitary lobe through the blood vessels, stimulating the formation of hormones in its anterior lobe.
Reticular formation.
The reticular (reticular) formation consists of nerve cells of the brain itself and their fibers, with an accumulation of neurons in the core of the reticular formation. This is a dense network of branching processes of neurons of specific nuclei of the brain stem (medulla oblongata, midbrain and diencephalon), conducting certain types of sensitivity from receptors from the periphery to the brain stem and further to the cerebral cortex. In addition, nonspecific 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 that maintains alertness and concentration. It can be compared to the role of a regulator on a TV: without giving an image, it can change the illumination and sound volume.
Finite brain.
It consists of two separated hemispheres, which are connected by a plate of white matter of the corpus callosum, below which there are two lateral ventricles communicating with each other. 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 sulci of each hemisphere are divided into 5 lobes: frontal, parietal, temporal, occipital and hidden lobe. The cerebral cortex is covered with gray matter. Up to 4 mm thick. Moreover, on top there are sections of an evolutionarily newer crust of 6 layers, and below it lies a new crust with fewer layers and a simpler structure. The oldest part of the cortex is the rudimentary formation of animals - the olfactory brain. At the point of transition to the lower (basal) surface there is a hippocampal ridge, which participates in the formation of the walls of the lateral ventricles. Inside the hemispheres there are accumulations of gray matter in the form of the basal ganglia. 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. Combinative (associative), connecting different parts of one hemisphere.
2. Commissural (commissural), connecting the right and left hemispheres.
3. Projection fibers of the pathways from the hemispheres to the low brain and spinal cord.
Conducting 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 located outside the brain, located in the spinal ganglia or sensory ganglia 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.
Sensory pathways (ascending) . The spinal cord conducts 4 types of sensitivity: tactile (touch and pressure), temperature, pain and proprioceptive (articular-muscular sense of body position and movement). The bulk of the ascending pathways conduct proprioceptive sensitivity to the cerebral cortex and the cerebellum.
Ecteroceptive pathways:
The lateral spinothalamic tract is the path of pain and temperature sensitivity. The first neurons are located in the spinal ganglia, giving peripheral processes to the spinal nerves and central processes and central processes that go to the dorsal horn of the spinal cord (2nd neuron). At this site, a crossover occurs and then the processes rise along the lateral cord 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 fibers crossing along the way, impulses from the left side of the body are transmitted to the right hemisphere and vice versa.
The anterior spinothalamic tract is the pathway of touch and pressure. It consists of fibers that conduct tactile sensitivity, which pass in the anterior cord of the spinal cord.
Proprioceptive pathways:
The posterior spinocerebellar tract (Flexiga) starts from the neuron of the spinal ganglion (1 neuron) with a peripheral process going to the musculo-articular apparatus, and the central process goes as part of the dorsal root to the dorsal horn of the spinal cord (2nd neuron). The processes of the second neurons rise along the lateral cord of the same side to the cells of the cerebellar vermis.
The fibers of the anterior spinocerebellar tract (Govers) form a decussation twice in the spinal cord and before entering the cerebellar vermis in the midbrain region.
The proprioceptive pathway 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 cord of the spinal cord. The wedge-shaped bundle is adjacent to it and carries impulses from the upper half of the body and arms. The second neuron lies in the nuclei of the same name in the medulla oblongata, where they intersect and gather into a bundle and reaches the thalamus (3rd neuron). The processes of the third neurons are directed to the sensitive and partial motor zone of the cortex.
Motor tracts (descending).
Pyramid paths:
Cortical-nuclear pathway- control of conscious head movements. It starts from the precentral gyrus and moves to the motor roots of the cranial nerves on the opposite side.
Lateral and anterior corticospinal tracts- begin in the precentral gyrus and, after decussation, go to the opposite side to the motor roots of the spinal nerves. They control conscious movements of the muscles of the trunk and limbs.
Reflex (extrapyramidal) pathway. It includes the red nuclear spinal cord, which begins and decussates 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 tract also begins in the midbrain and is associated with auditory and visual perception. It establishes a connection between the quadrigeminal cord 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
Vestibulospinal 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.
Reticulum-spinal tract begins from the nuclei of the reticular formation, which then diverges both along its own and on the opposite side of the spinal nerves. It transmits impulses from the brain stem to the spinal cord to maintain skeletal muscle tone. Regulates the state of the spinal-brain autonomic 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 a body part, but to its accuracy of movements. The area for controlling movements of the hand, tongue and facial muscles 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 pathway.
Sensitive areas are located in different parts of the cortex: the occipital zone is associated with vision, and the temporal zone with hearing; skin sensitivity is projected in the postcentral zone. The size of individual areas 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 gyri. 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 ganglia) and has extensive connections with all areas of the brain, reticular formation, and hypothalamus. It provides supreme control of all autonomic functions (cardiovascular, respiratory, digestive, metabolism and energy), and also forms emotions and motivation.
Association zones occupy the remaining surface and communicate between different areas of the cortex, combining all impulses flowing into the cortex into integral acts of learning (reading, writing, speech, logical thinking, memory) and providing the possibility of an adequate response of behavior.
Cranial nerves:
12 pairs of cranial nerves arise from the brain. Unlike the spinal nerves, some of the cranial nerves are motor (III, IV, VI, VI, XI, XII pairs), some are sensory (I, II, VIII pairs), and 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 along the olfactory tract to the cerebral cortex.
II. Pair (optic nerve) formed by the processes of nerve cells of the retina, then in front of the sella turcica of the sphenoid bone it forms an incomplete chiasm of the optic nerves and passes into two visual 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 through the orbit and innervates five of the six muscles of the eyeball, and also parasympathetically innervates the muscle that constricts 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. Motor nerves innervate the masticatory and oral muscles. The nuclei of the trigeminal nerve are located in the bridge, from where two roots emerge (motor and sensory), 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 sensory, and the third also includes motor fibers.
VI. Pair (abducens nerve) motor, starts from the bridge and innervates the external, rectus muscle of the eye.
VII. Pair (facial nerve) motor, innervates the facial muscles of the face and neck. It begins in the tegmentum of the bridge along with the intermediate nerve, which innervates the papillae of the tongue and salivary glands. They unite in the internal auditory canal, where the facial nerve gives off the greater petrosal nerve and the chorda tympani.
VIII Pair (vestibular-cochlear nerve) consists of the cochlear part, which conducts the auditory sensations of the inner ear, and the vestibular part of the labyrinth of the ear. Connecting, they enter the pons nuclei at the border with the medulla oblongata.
IX. Pair (glossopharyngeal) contains motor, sensory and parasympathetic fibers. Its nuclei lie in the medulla oblongata. In the area of the jugular foramen, the occipital bone forms two nodes of sensory 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. Pair (wandering) the longest cranial nerve, mixed, begins in the medulla oblongata and with its branches innervates the respiratory organs, passes through the diaphragm and forms the celiac plexus with branches to the liver, pancreas, kidneys, reaching the descending colon. Parasympathetic fibers innervate the smooth muscles of the internal organs, the heart and glands. Motor fibers innervate the skeletal muscles of the pharynx, soft palate, and larynx.
XI. Pair (additional) begins in the medulla oblongata, innervates the sternocleidomastoid muscle of the neck and trapezius muscle with motor fibers
XII. Pair (sublingual) from the medulla oblongata controls the movement of the tongue muscles.
Autonomic nervous system.
The unified nervous system is conventionally divided into two parts: somatic, innervating only skeletal muscles, and autonomic, innervating the entire body as a whole. Coordination of the motor and autonomic functions of the body is carried out by the limbic system and the frontal lobes of the cerebral cortex. Autonomic nerve fibers emerge from only a few areas of the brain and spinal cord, go as part of somatic nerves and necessarily form autonomic nodes, from which post-nodal sections of the reflex arc extend to the periphery. The autonomic nervous system has three types 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 (autonomic) nervous system. Parasympathetic (A) and sympathetic (B) part:
1 - superior cervical ganglion of the sympathetic nerve, 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 (included in organ plexuses), 16 - vagus nerve, 17 - auricular (parasympathetic) node, 18 - submandibular (parasympathetic) node, 19 - ala palatine (parasympathetic) node, 20 - ciliary (parasympathetic) node, 21 - dorsal nucleus of the vagus nerve, 22 - inferior salivary nucleus, 23 - superior salivary nucleus, 24 - accessory nucleus of the oculomotor nerve. Arrows show the paths of nerve impulses to organs
Sympathetic nervous system . The central section is formed by cells of the lateral horns of the spinal cord at the level of all 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). Then each nerve, through the white connecting branch, connects to the corresponding node (ganglion). The nerve ganglia are divided into two groups: on the sides of the spine, the paravertebral ganglia with the right and left sympathetic trunk, and the prevertebral ganglia, which lie in the thoracic and abdominal cavities. After the nodes, the postganglionic gray connecting branches go to the spinal nerves, the sympathetic fibers of which form plexuses along the arteries supplying the organ.
The sympathetic trunk has different sections:
Cervical region consists of three nodes with outgoing branches innervating the organs of the head, neck and heart.
Thoracic region consists of 10-12 nodes lying in front of the necks of the ribs and outgoing branches to the aorta, heart, lungs and esophagus, forming organ plexuses. The largest large and small splanchnic nerves pass through the diaphragm into the abdominal cavity to the solar (celiac) plexus with preganglionic fibers of the celiac ganglia.
Lumbar consists of 3-5 nodes with branches forming the plexuses of the abdominal cavity and pelvis.
Sacral section consists of 4 nodes on the anterior surface of the sacrum. Below, the chains of nodes of the right and left sympathetic trunks are connected in one coccygeal node. All these formations are united under the name of the pelvic section of the sympathetic trunks and participate in the formation of the pelvic plexuses.
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 Yakubovich nucleus, the processes enter the oculomotor nerve, which switches at the ciliary ganglion border and innervates the ciliary muscle that constricts the pupil. The superior salivary nucleus lies in the rhomboid fossa; its processes enter the trigeminal and then the facial nerve. They form two nodes on the periphery: the pterygopalatine node, which innervates with its trunks the lacrimal glands and glands of the nasal and oral cavity, and the submandibular node, the submandibular and sublingual and sublingual glands. The inferior salivary nucleus penetrates with its processes into the glossopharyngeal nerve and switches in the ear ganglion and gives rise to the “secretory” fibers of the parotid gland. The largest number of parasympathetic fibers passes 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 pelvic organs, is carried out by the pelvic nerves of the sacral spinal cord. They participate in the formation of the autonomic nerve plexuses and switch in the plexus nodes of the pelvic organs.
The fibers form plexuses with the sympathetic processes, which enter the internal organs. The fibers of the vagus nerves are switched in nodes located in the walls of 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 which the postgantlionar branches form plexuses on the vessels to the organs. Another powerful autonomic plexus descends along the abdominal aorta: the superior hypogastric plexus, which descends into the pelvis to form the right and left hypogastric plexus. Sensitive fibers from internal organs also pass through these plexuses.
Well, aren't your brains swollen? - Yan asked and turned into a teapot with a rattling lid from the steam escaping.
Well, yes, you gave me a hard time - said Yai and scratched the back of his head - although, basically, everything is clear.
Well done!!! “You deserve a medal,” Yan said and hung a shiny circle around Ya’s neck.
Wow! How brilliant and clearly written “To the greatest smart guy of all time.” Well, thank you? And what should I do with her?
And you smell it.
Why does it smell like chocolate? Ah-ah-ah, this is such a candy! Yai said and unfolded the foil.
Eat for now, sweets are good for brain function, and I’ll tell you another interesting thing: you saw this medal, touched it with your hands, smelled it, and now you hear it crunching in your mouth with what parts of the body?
Well, many different things.
So, all of them are called sense organs, which help the body navigate the environment and use it for its needs.
A) Interaction of the autonomic nervous system and immunity. The bone marrow, like the lymphatic tissue of the thymus, lymph nodes and spleen, is abundantly innervated by adrenergic nerve fibers. Adrenergic receptors are found on the surface of T-lymphocytes, B-lymphocytes and macrophages.
Under conditions of acute psychological stress, the content of norepinephrine in the human body increases, activating the lymphatic system: there is an increase in the number of NK cells (natural killer cells) and cytotoxic T lymphocytes. The subsequent weakening of the immune response leads to greater susceptibility to infectious diseases.
b) Visceral afferents of the autonomic nervous system in the central nervous system. Afferent nerve fibers conduct excitation from the organs of the chest and abdominal cavity, innervated by the ANS, to the central nervous system. In addition, they take part in important reflexes that control blood circulation, breathing, digestion, urination and sexual intercourse. Typically, the central nervous system does not control the activity of internal organs, however, in a number of pathological conditions, a signal about a change in their activity reaches consciousness. The presence of visceral pain is of great importance for making a clinical diagnosis.
1. Visceral pain. There are three main types of visceral pain:
1) True visceral pain, felt directly in the affected organ.
2) Referred visceral pain, subjectively felt in the area of the corresponding somatic nerves.
3) Viscerosomatic pain caused by the spread of the disease to somatic structures.
2. True visceral pain. True visceral pain is characterized by a deep and subtle diffuse distribution; in most cases it is accompanied by nausea and increased sweating. This type of pain occurs under conditions such as inflammation and/or ulceration of the wall of the gastrointestinal tract, intestinal obstruction, obstruction of the biliary tract or ureter, as well as when the capsule of parenchymal organs (liver, kidneys, pancreas) is stretched as a result of any disease. At the same time, the internal organs remain insensitive to mechanical or thermal damage.
3. Referred visceral pain. As visceral pain in the organ intensifies, it begins to be subjectively felt in the projection area of the adjacent organ innervated by the same segment of the spinal cord. Examples of such referred pain are pain in the chest (angina) during myocardial ischemia, pain in the anterior abdominal wall during diseases of the gallbladder and intestines, pain in the sacral spine during labor pains.
According to the theory of projection convergence (a generally accepted theory of the development of referred pain), the brain erroneously determines the source of pain impulses due to the fact that excitation from both somatic and visceral nociceptive receptors is carried out along common spinothalamic pathways. Before this theory emerged, it was believed that these neurons were responsible for transmitting the signal about somatic pain.
4. Viscerosomatic pain. The parietal layers of the serous membranes (pleura and peritoneum), abundantly innervated by the overlying intercostal nerves, are very sensitive to the exudate of acute inflammation. The transition of the inflammatory process to the surface of the stomach, intestines, appendix and gall bladder causes persistent, sharp pain in the anterior abdominal wall in the projection of the inflamed organ. With the development of acute peritonitis, tension in the muscles of the abdominal wall occurs (protective reflex).
5. Soreness. Tenderness (pain on palpation) of the abdomen can be detected when pressing with fingers or the palm of the hand on the abdominal wall. In fact, the doctor plunges his fingertips to the level of the parietal peritoneum and looks for the inflamed organ. If the organ has great mobility (for example, the appendix), reducing its “mobile” pain can be achieved by asking the patient to turn on the other side.
6. Physical pain and the human psyche. Despite the well-established mechanisms leading to visceral pain (inflammation, smooth muscle spasm, ischemia and stretching), in some cases chest or abdominal pain may occur in the absence of any diseases of the internal organs. Recurrent or constant pain over a long period of time (several months), the cause of which cannot be determined after standard diagnostic tests, has a psychological rather than a physical explanation. This fact does not deny the presence of pain, but indicates its central origin.
An example of such a situation is children who have been subjected to violence: their complaints of abdominal pain are a “cry of despair.” In adults, recurring and difficult-to-diagnose pain may be a symptom of major depression.
Irritable bowel syndrome (IBS) is a very common disease, usually occurring in people aged 20-40 years. With this syndrome, disturbances develop in the intestinal cell wall, but the cause of changes in intestinal motility appears to be a disorder of the nervous regulation of the digestive tract.
The process of activation of nociceptive neurons of the intestinal wall:(1) Serotonin released by enterochromaffin cells activates a nociceptive neuron that travels to the dorsal horn of the spinal cord.
(2) The opposite current of impulses causes the release of substance P, which in turn is responsible for the release of histamine from mast cells.
(3) Histamine enhances the action of serotonin.
V) Afferent nerve fibers of blood vessels. In the anatomy of the visceral afferent, two networks of unipolar neurons innervating the vessels are described. One of them is represented by mechanoreceptors in the carotid sinus and aortic arch, their function is the regulation of systemic blood pressure; another neural network is represented by chemoreceptors of the carotid body, the function of which is to regulate breathing. There is a strong tendency to consider all vascular afferents as visceral, since the afferent fibers of the peripheral vessels are neither morphologically nor functionally different from the afferent fibers of the heart. All of them contain substance P, do not affect human health, and in case of illness or damage they participate in the development of pain syndrome (for example, nagging pain in the legs with varicose veins or sharp acute pain when the wall of the brachial artery is damaged by a needle during an injection into the ulnar hole).
The mechanism of transmission of nerve impulses to the dorsal roots of the spinal cord is not fully understood. However, it has been previously established that the nerve impulse from the perivascular fibers located above the elbow or knee goes along the course of the sympathetic nerves (but in the opposite direction), and the impulses from most peripheral perivascular fibers go together with the impulses from the cutaneous nerves (and in the same direction) . The arrangement of visceral afferent fibers within cutaneous nerves is similar to that of nerve fibers terminating in the Golgi tendon organs of the wrist and ankle.
G) Summary. The ANS contains three chains of effector neurons: hypothalamic neurons, brainstem neurons, and preganglionic spinal neurons. The axons of the latter form synapses with cells of the autonomic ganglia, from which postganglionic fibers extend to target tissues.
Sympathetic preganglionic fibers going to the ganglia as part of the sympathetic trunk are located at the thoracic and lumbar levels. Some fibers form synapses with underlying ganglia. Others move upward and form synapses with the superior cervical, middle cervical and stellate ganglia. Postganglionic fibers emanating from these ganglia innervate the head, neck, upper limbs and heart. The other part of the fibers goes down and forms synapses with the lumbar or sacral ganglia, the postganglionic fibers of which pass as part of the lumbosacral plexus and are responsible for the innervation of the vessels of the lower extremities. In addition, fibers are secreted that pass through the sympathetic trunk without switching; they form synapses with the adrenal medulla and with the ganglia of the ventral nerve cord. Fibers extending from these ganglia innervate the gastrointestinal tract and genitourinary system.
Parasympathetic preganglionic fibers come from nuclei located in the brain (cranial fibers) and the sacral spinal cord (sacral fibers). Cranial parasympathetic innervation is carried out through the oculomotor nerve (synapse with the ciliary ganglion, innervation of the sphincter of the pupil and ciliary muscle); facial nerve (forms a synapse with the pterygopalatine ganglion - innervation of the lacrimal and nasal glands, as well as with the submandibular ganglion - innervation of the submandibular and sublingual salivary glands); glossopharyngeal nerve (synapse with the ear ganglion, innervation of the parotid salivary gland); vagus nerve (synapses with ganglia on or in the walls of the heart, bronchi and gastrointestinal tract, innervation of muscle tissue and glands of these organs). Sacral parasympathetic innervation is carried out through preganglionic fibers from the sacral segments S2-S4 of the spinal cord (they form synapses with the intramural ganglia of the distal colon and rectum, as well as with the pelvic ganglia, which are responsible for the innervation of the bladder and internal pudendal arteries).
All preganglionic fibers are cholinergic, activating ganglionic nicotinic receptors. All postganglionic fibers end in neuroeffector connections. As a rule, these synapses in the sympathetic nervous system are adrenergic, releasing norepinephrine, which activates postsynaptic α 1 -adrenergic receptors of smooth muscles, presynaptic α 2 -adrenergic receptors of local nerve endings, postsynaptic β 1 -adrenergic receptors of the cardiac muscle or postsynaptic β 2 -adrenergic receptors ( more sensitive to adrenaline). Adrenaline is secreted by chromaffin cells and, as a result of connection with β 2 -adrenergic receptors, causes relaxation of smooth muscles.
Postganglionic fibers of the parasympathetic nervous system are cholinergic; cholinergic receptors of the heart muscle, smooth muscles and glands are muscarinic.
Visceral afferents. Nociceptive afferent fibers from blood vessels and organs of the chest and abdominal cavity are sent to the central nervous system as part of the autonomic nerve pathways. True visceral pain is deep and vague. Referred visceral pain is subjectively felt in the area of somatic structures, the innervation of which comes from the corresponding segments of the spinal cord. Viscerosomatic pain is caused by chemical or thermal damage to the serous membranes: it is very strong and persistent, accompanied by protective tension of the superficial muscles.
1) central- dorsal and
2) peripheral- nerves and ganglia.
- Nerves are bundles of nerve fibers surrounded by a connective tissue sheath.
- Glands are collections of neuron cell bodies outside the central nervous system, such as the solar plexus.
The nervous system is divided into 2 parts according to its functions.
1) somatic- controls skeletal muscles, obeys consciousness.
2) vegetative (autonomous)- controls internal organs, does not obey consciousness. Consists of two parts:
- sympathetic: governs organs during stress and physical activity
- increases pulse, blood pressure and blood glucose concentrations
- activates the nervous system and sensory organs
- dilates the bronchi and pupil
- slows down the digestive system.
- parasympathetic the system works in a state of rest, bringing the functioning of organs back to normal (opposite functions).
Reflex arc
This is the path along which the nerve impulse passes during exercise. Consists of 5 parts
1) Receptor- sensitive formation capable of responding to a certain type of stimulus; converts irritation into a nerve impulse.
2) By sensory neuron the nerve impulse goes from the receptor to the central nervous system (spinal cord or brain).
3) Interneuron located in the brain, transmits a signal from a sensitive neuron to an executive one.
4) By executive (motor) neuron the nerve impulse goes from the brain to the working organ.
5) Working (executive) body- muscle (contracts), gland (secretes), etc.
Analyzer
This is a system of neurons that perceive irritation, conduct nerve impulses and process information. Consists of 3 departments:
1) peripheral– these are receptors, for example, cones and rods in the retina of the eye
2) conductive- these are the nerves and pathways of the brain
3) central, located in the cortex - this is where the final analysis of information takes place.
Choose one, the most correct option. The section of the auditory analyzer, which transmits nerve impulses to the human brain, is formed
1) auditory nerves
2) receptors located in the cochlea
3) eardrum
4) auditory ossicles
Answer
Choose three correct answers out of six and write down the numbers under which they are indicated. What examples illustrate arousal of the sympathetic nervous system?
1) increased heart rate
2) increased intestinal motility
3) lowering blood pressure
4) dilation of the pupils of the eyes
5) increase in blood sugar
6) narrowing of the bronchi and bronchioles
Answer
1. Choose three correct answers out of six and write down the numbers under which they are indicated. What effect does the parasympathetic nervous system have on the human body?
1) increases heart rate
2) activates salivation
3) stimulates the production of adrenaline
4) enhances the formation of bile
5) increases intestinal motility
6) mobilizes organ functions under stress
Answer
2. Select three correct answers out of six and write down the numbers under which they are indicated in the table. Under the influence of the parasympathetic nervous system occurs
1) increased intestinal motility
2) decrease in blood pressure in the vessels
3) increased heart rate
4) slowing down the formation of gastric juice
5) reduction in pupil diameter
6) increased sweating
Answer
3. Select three options. How does the parasympathetic nervous system affect the functioning of human organs?
1) pupils constrict
2) breathing movements become more frequent
3) heart contractions increase
4) heart contractions slow down
5) blood sugar increases
6) wave-like bowel movements become more frequent
Answer
Choose one, the most correct option. Nerve impulses from receptors to the central nervous system are carried out
1) sensory neurons
2) motor neurons
3) sensory and motor neurons
4) intercalary and motor neurons
Answer
Choose three correct answers out of six and write down the numbers under which they are indicated. Receptors are nerve endings in the human body that
1) perceive information from the external environment
2) perceive impulses from the internal environment
3) perceive excitation transmitted to them via motor neurons
4) are located in the executive body
5) convert perceived stimuli into nerve impulses
6) implement the body’s response to irritation from the external and internal environment
Answer
Choose one, the most correct option. Peripheral part of the visual analyzer
1) optic nerve
2) visual receptors
3) pupil and lens
4) visual cortex
Answer
Choose one, the most correct option. Reflexes that cannot be strengthened or inhibited at the will of a person are carried out through the nervous system
1) central
2) vegetative
3) somatic
4) peripheral
Answer
1. Establish a correspondence between the feature of regulation and the part of the nervous system that carries it out: 1) somatic, 2) autonomic
A) regulates the functioning of skeletal muscles
B) regulates metabolic processes
B) provides voluntary movements
D) is carried out autonomously regardless of the person’s wishes
D) controls the activity of smooth muscles
Answer
2. Establish a correspondence between the function of the human peripheral nervous system and the department that performs this function: 1) somatic, 2) autonomic
A) sends commands to skeletal muscles
B) innervates the smooth muscles of internal organs
B) provides movement of the body in space
D) regulates the functioning of the heart
D) enhances the functioning of the digestive glands
Answer
3. Establish a correspondence between the characteristic and the department of the human nervous system: 1) somatic, 2) autonomic. Write numbers 1 and 2 in the order corresponding to the letters.
A) sends commands to skeletal muscles
B) changes the activity of various glands
B) forms only a three-neuron reflex arc
D) changes heart rate
D) causes voluntary body movements
E) regulates the contraction of smooth muscles
Answer
4. Establish a correspondence between the properties of the nervous system and its types: 1) somatic, 2) autonomic. Write numbers 1 and 2 in the correct order.
A) innervates the skin and skeletal muscles
B) innervates all internal organs
C) actions are not subject to consciousness (autonomous)
D) actions are controlled by consciousness (voluntary)
D) helps maintain the body’s connection with the external environment
E) regulates metabolic processes and body growth
Answer
5. Establish a correspondence between the types of nervous system and their characteristics: 1) autonomic, 2) somatic. Write numbers 1 and 2 in the order corresponding to the letters.
A) regulates the functioning of internal organs
B) regulates the functioning of skeletal muscles
C) reflexes are carried out quickly and are subject to human consciousness
D) reflexes are slow and do not obey human consciousness
D) the highest organ of this system is the hypothalamus
E) the highest center of this system is the cerebral cortex
Answer
6n. Establish a correspondence between the characteristic and the department of the human nervous system to which it belongs: 1) somatic, 2) autonomic. Write numbers 1 and 2 in the order corresponding to the letters.
A) regulates the diameter of blood vessels
B) has a reflex arc motor pathway consisting of two neurons
C) provides a variety of body movements
D) works arbitrarily
D) supports the activity of internal organs
Answer
Choose three correct answers out of six and write down the numbers under which they are indicated. The somatic nervous system in the human body regulates
1) heart rate
2) blood supply to muscles and skin
3) the work of facial muscles
4) flexion and extension of fingers
5) contraction and relaxation of skeletal muscles
6) activity of the exocrine glands
Answer
Establish a correspondence between the organs and types of the nervous system that control their activity: 1) somatic, 2) autonomic. Write numbers 1 and 2 in the correct order.
A) bladder
B) liver
B) biceps
D) intercostal muscles
D) intestines
E) extraocular muscles
Answer
Choose three options. The hearing analyzer includes
1) auditory ossicles
2) receptor cells
3) auditory tube
4) sensory nerve
5) semicircular canals
6) temporal lobe cortex
Answer
Choose one, the most correct option. Nerve impulses are transmitted to the brain through neurons
1) motor
2) insertion
3) sensitive
4) executive
Answer
Select three consequences of irritation of the sympathetic division of the central nervous system:
1) increased frequency and strengthening of heart contractions
2) slowing down and weakening of heart contractions
3) slowing down the formation of gastric juice
4) increased intensity of activity of the gastric glands
5) weakening of wave-like contractions of the intestinal walls
6) increased wave-like contractions of the intestinal walls
Answer
1. Establish a correspondence between the function of the organs and the department of the autonomic nervous system that carries it out: 1) sympathetic, 2) parasympathetic
A) increased secretion of digestive juices
B) slowing down the heart rate
B) increased ventilation of the lungs
D) pupil dilation
D) increased wave-like bowel movements
Answer
2. Establish a correspondence between the function of the organs and the department of the autonomic nervous system that carries it out: 1) sympathetic, 2) parasympathetic
A) increases heart rate
B) decreases breathing rate
C) stimulates the secretion of digestive juices
D) stimulates the release of adrenaline into the blood
D) increases ventilation of the lungs
Answer
3. Establish a correspondence between the function of the autonomic nervous system and its department: 1) sympathetic, 2) parasympathetic
A) increases blood pressure
B) enhances the separation of digestive juices
B) lowers heart rate
D) weakens intestinal motility
D) increases blood flow in muscles
Answer
4. Establish a correspondence between the functions and departments of the autonomic nervous system: 1) sympathetic, 2) parasympathetic. Write numbers 1 and 2 in the order corresponding to the letters.
A) expands the lumens of the arteries
B) increases heart rate
C) enhances intestinal motility and stimulates the functioning of the digestive glands
D) narrows the bronchi and bronchioles, reduces ventilation of the lungs
D) dilates the pupils
Answer
Choose one, the most correct option. What are nerves made of?
1) a collection of nerve cells in the brain
2) clusters of nerve cells outside the central nervous system
3) nerve fibers with a connective tissue sheath
4) white matter located in the central nervous system
Answer
Select three anatomical structures that are the initial link of human analyzers
1) eyelids with eyelashes
2) rods and cones of the retina
3) auricle
4) cells of the vestibular apparatus
5) lens of the eye
6) taste buds of the tongue
Answer
Choose one, the most correct option. A system of neurons that perceive stimuli, conduct nerve impulses and process information is called
1) nerve fiber
3) nerve
4) analyzer
Answer
Choose one, the most correct option. What is the name given to the system of neurons that perceive stimuli, conduct nerve impulses, and process information?
1) nerve fiber
2) central nervous system
3) nerve
4) analyzer
Answer
Choose three options. Visual analyzer includes
1) the white membrane of the eye
2) retinal receptors
3) vitreous body
4) sensory nerve
5) occipital cortex
6) lens
Answer
Choose one, the most correct option. The peripheral part of the human auditory analyzer is formed by
1) ear canal and eardrum
2) middle ear bones
3) auditory nerves
4) sensitive cells of the cochlea
Answer
When the sympathetic nervous system is excited, as opposed to when the parasympathetic nervous system is excited
1) arteries dilate
2) blood pressure increases
3) intestinal motility increases
4) the pupil narrows
5) the amount of sugar in the blood increases
6) heart contractions become more frequent
Answer
1. Establish the sequence of parts of the reflex arc when a nerve impulse passes through it. Write down the corresponding sequence of numbers.
1) sensitive neuron
2) working body
3) interneuron
4) department of the cerebral cortex
5) receptor
6) motor neuron
Answer
2. Establish the sequence of links in the reflex arc of the sweating reflex. Write down the corresponding sequence of numbers.
1) the occurrence of nerve impulses in receptors
2) sweating
3) excitation of motor neurons
4) irritation of skin receptors that perceive heat
5) transmission of nerve impulses to the sweat glands
6) transmission of nerve impulses along sensory neurons to the central nervous system
Answer
3. Establish the sequence of nerve impulse conduction in the reflex arc, which provides one of the mechanisms of thermoregulation in the human body. Write down the corresponding sequence of numbers.
1) transmission of a nerve impulse along a sensitive neuron to the central nervous system
2) transmission of nerve impulses to motor neurons
3) excitation of skin thermoreceptors when the temperature drops
4) transmission of nerve impulses to interneurons
5) reduction of the lumen of skin blood vessels
Choose three options. In the human nervous system, interneurons transmit nerve impulses
1) from the motor neuron to the brain
2) from the working organ to the spinal cord
3) from the spinal cord to the brain
4) from sensory neurons to working organs
5) from sensory neurons to motor neurons
6) from the brain to motor neurons
Answer
Arrange the elements of the human knee-jerk reflex arc in the correct order. Write the numbers in your answer in the order corresponding to the letters.
1) Motor neuron
2) Sensitive neuron
3) Spinal cord
4) Tendon receptors
5) Quadriceps femoris muscle
Answer
Select three functions of the sympathetic nervous system. Write down the numbers under which they are indicated.
1) enhances lung ventilation
2) reduces heart rate
3) lowers blood pressure
4) inhibits the secretion of digestive juices
5) enhances intestinal motility
6) dilates the pupils
Answer
Choose one, the most correct option. Sensory neurons in the three-neuron reflex arc are connected to
1) processes of interneurons
2) bodies of interneurons
3) motor neurons
4) executive neurons
Answer
Establish a correspondence between the functions and types of neurons: 1) sensitive, 2) intercalary, 3) motor. Write the numbers 1, 2, 3 in the order corresponding to the letters.
A) transmission of nerve impulses from the sense organs to the brain
B) transmission of nerve impulses from internal organs to the brain
B) transmission of nerve impulses to muscles
D) transmission of nerve impulses to the glands
D) transmission of nerve impulses from one neuron to another
Answer
Choose three correct answers out of six and write down the numbers under which they are indicated. What organs are controlled by the autonomic nervous system?
1) organs of the digestive tract
2) gonads
3) muscles of the limbs
4) heart and blood vessels
5) intercostal muscles
6) chewing muscles
Answer
Choose three correct answers out of six and write down the numbers under which they are indicated. The central nervous system includes
1) sensory nerves
2) spinal cord
3) motor nerves
4) cerebellum
5) bridge
6) nerve nodes
Answer
Analyze the “Neurons” table. For each cell indicated by a letter, select the appropriate term from the list provided. © D.V. Pozdnyakov, 2009-2019
The nervous system is divided into central (brain) and peripheral (peripheral nerves and ganglia). The central nervous system (CNS) receives information from receptors, analyzes it and gives an appropriate command to the executive organs. The functional unit of the nervous system is neuron. It is distinguished (Fig. 6.) body ( soma) with a large core and processes ( dendrites and axon). The main function of the axon is to conduct nerve impulses from the body. Dendrites conduct impulses to the soma. Sensitive (sensory) neurons transmit impulses from receptors, and efferent neurons transmit impulses from the central nervous system to effectors. Most neurons in the central nervous system are interneurons (they analyze and store information, and also form commands).
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Rice. 6. Diagram of the structure of a neuron. |
The activity of the central nervous system is of a reflex nature. Reflex - This is the body’s response to irritation, carried out with the participation of the central nervous system.
Reflexes are classified according to biological significance (indicative, defensive, food, etc.), location of receptors (exteroceptive - caused by irritation of the body surface, interoceptive - caused by irritation of internal organs and blood vessels; proprioceptive - arising from irritation of receptors located in muscles, tendons and ligaments), depending on the organs involved in the formation of the response (motor, secretory, vascular, etc.), depending on which parts of the brain are necessary for the implementation of this reflex (spinal, for which there are enough spinal cord neurons; bulbar - arise with the participation of the medulla oblongata; mesencephalic - midbrain; diencephalic - diencephalon; cortical - neurons of the cerebral cortex). However, almost all parts of the central nervous system participate in most reflex acts. Reflexes are also divided into unconditioned (innate) and conditioned (acquired). The material substrate of the reflex is the reflex arc - a neural circuit along which an impulse from receptive field(a part of the body whose irritation causes a certain reflex) to the executive organ. The classical reflex arc includes: 1) receptor; 2) sensitive fiber; 3) nerve center (a union of interneurons that provides regulation of a certain function); 4) efferent nerve fiber.
The nerve centers are characterized by the following properties :
Unilateral conduction excitation (from the sensitive neuron to the efferent one).
More slow holding excitation compared to nerve fibers (most of the time is spent on excitation in chemical synapses - 1.5-2 ms in each).
Summation afferent impulses (manifested by increased reflex).
Convergence - several cells can transmit impulses to one neuron.
Irradiation - one neuron can influence many nerve cells.
Occlusion(blockage) and relief. During occlusion, the number of excited neurons during simultaneous stimulation of two nerve centers is less than the sum of excited neurons during stimulation of each center separately. Relief is characterized by the opposite effect.
Rhythm transformation. The frequency of impulses at the entrance to and exit from the nerve center usually does not coincide.
Pinvestigation - arousal may persist after cessation of stimulation.
High sensitivity to lack of oxygen and poisons.
Low functional mobility and high fatigue.
Post-tetanic potentiation- strengthening of the reflex response after prolonged stimulation of the center.
Tone– even in the absence of stimulation, many centers generate impulses.
Plastic- are able to change their own functional purpose.
TO the basic principles of coordination of the work of nerve centers include :
Irradiation - strong and prolonged irritation of the receptor can cause excitation of a larger number of nerve centers (for example, if you weakly irritate one limb, then only it contracts, but if the irritation is increased, then both limbs contract).
The principle of a common final path - impulses arriving in the central nervous system through different fibers can converge on the same neurons (for example, motor neurons of the respiratory muscles are involved in breathing, sneezing and coughing).
The principle of dominance(discovered by A.A. Ukhtomsky) - one nerve center can subordinate the activity of the entire nervous system and determine the choice of adaptive reaction.
Feedback principle - it allows you to correlate changes in system parameters with its operation.
The principle of reciprocity- reflects the relationship between centers that are opposite in function (for example, inhalation and exhalation) and lies in the fact that the excitation of one of them inhibits the other.
The principle of subordination(subordination) - regulation is concentrated in the higher parts of the central nervous system, and the main one is the cerebral cortex.
The principle of compensation of functions - the functions of damaged centers can be performed by other brain structures.
The processes of excitation and inhibition constantly interact in the nervous system. Excitation causes reflex reactions, and inhibition adapts their strength and speed to existing needs.
Inhibition in the central nervous system discovered by I.M. Sechenov. Somewhat later, Goltz showed that inhibition can also cause strong excitation.
The following types of central braking are distinguished:
Postsynaptic(the main type of inhibition) - is that the released inhibitory transmitter hyperpolarizes the postsynaptic membrane, which reduces the excitability of the neuron.
Presynaptic - localized in the processes of the excitatory neuron.
Progressive - due to the fact that an inhibitory neuron is encountered along the path of excitation.
Returnable - carried out by intercalary inhibitory cells.
Pessimal - associated with persistent depolarization of the postsynaptic membrane with frequent or prolonged stimulation.
Inhibition following excitation- if after stimulation hyperpolarization develops on the neuron, then a new impulse of normal strength does not cause excitation.
Reciprocal inhibition- ensures coordinated work of antagonistic structures, for example, flexor and extensor muscles.
PARTICULAR PHYSIOLOGY OF THE CENTRAL NERVOUS SYSTEM
The central nervous system consists of the brain and spinal cord.
Spinal cord located in the spinal canal and consists of segments. One segment innervates one of its own and two neighboring metameres of the body. Therefore, damage to one segment leads to a decrease in sensitivity in them, and its complete loss is observed only when at least two adjacent segments are damaged. Each of them has dorsal roots, white matter, gray matter and anterior roots (Fig. 7.).
Sensitive centripetal nerve fibers from receptors pass through the dorsal roots. The anterior roots are centrifugal (motor and vegetative). If the posterior roots are cut on the right, and the anterior ones on the left, then the right limbs lose sensitivity, but are capable of movement, and the left ones retain sensitivity, but do not make movements.
The gray matter of the spinal cord contains bodies motor neurons or motor neurons(in the front horns), interneurons or intermediate neurons(in the hind horns) and autonomic neurons(in the lateral horns).
The white matter of the spinal cord transmits information from receptors to the overlying parts of the central nervous system along the ascending pathways, and the descending pathways of the spinal cord come from the overlying nerve centers.
The spinal cord's own reflexes are segmental. For example, the cervical and thoracic segments contain the centers of movement of the arms, and the sacral segments contain the centers of movement of the lower extremities. The center of urine separation is located in the sacral segments.
Complete transection of the spinal cord results in spinal shock(temporary cessation of activity of segments located below the site of transection). It is caused by a loss of communication with the overlying parts of the central nervous system. Shock lasts several minutes in a frog, weeks or months in monkeys, and several months in humans.
The brain is divided into (Fig. 8.) three main sections: the brainstem, diencephalon and telencephalon. In its turn trunk consists of the medulla oblongata, pons, midbrain and cerebellum.
The border between the dorsal and medulla oblongata is the site of exit of the first cervical roots. There are no segments in the medulla oblongata, but there are clusters of neurons (nuclei). They form the centers of inhalation and exhalation, the vasomotor center (regulates vascular tone and blood pressure levels), the main center of cardiac activity, the center of salivation and many others. Damage to the medulla oblongata results in death. This is explained by the presence of vital centers (respiratory and cardiovascular) in it.
The medulla oblongata is responsible for such protective reflexes as vomiting, coughing, sneezing, lacrimation, closing the eyelids, as well as sucking, chewing and swallowing. It is also involved in maintaining posture, redistributing muscle tone during movement, and performing the primary analysis of skin, gustatory, auditory and vestibular stimulation.
Pons Performs motor, sensory, integrative and conductive functions. Motor nuclei The bridge is innervated by facial and masticatory muscles, muscles that abduct the eyeball outward and strain the eardrum. Sensitive nuclei receive signals from receptors on the skin of the face, nasal mucosa, teeth, periosteum of the skull bones, conjunctiva and are responsible for the primary analysis of vestibular and taste stimulation. Vegetative nuclei regulate the secretory activity of the salivary glands. The bridge also houses pneumotaxic center, alternately triggering the centers of exhalation and inhalation. The pontine reticular formation activates the cerebral cortex and causes awakening.
IN midbrain there are nuclei that provide elevation of the upper eyelid, eye movements, changes in the lumen of the pupil and the curvature of the lens. Red kernels inhibit the activity of Deiters nuclei in the medulla oblongata. The transection between the midbrain and medulla oblongata leads to decerebrate rigidity(the tone of the extensor muscles of the limbs, neck and back increases). This is due to an increase in the activity of the Deiters nucleus. Black matter regulates the acts of chewing and swallowing, and also coordinates the precise movements of the fingers. The reticular formation of the midbrain regulates the development of sleep and its change from wakefulness. Quadrigeminal tubercles provide visual (turning the head and eyes towards the light stimulus, fixing the gaze and tracking moving objects) and auditory (turning the head towards the sound source) orienting reflexes. The midbrain is also involved in reflexively holding body parts in place, and also corrects the orientation of the limbs when their position changes.
Cerebellum continuously receives information from muscles, joints, organs of vision and hearing. Under the control of the cortex, it is responsible for programming complex movements, postural coordination and proportionate, purposeful movement. The cerebellum influences the excitability of parts of the telencephalon, participates in the autonomic support of the activity of skeletal muscles and the cardiovascular system, as well as metabolism and hematopoiesis.
Cerebellar lesions are accompanied by: asthenia(decreased strength of muscle contractions and rapid fatigue), ataxia(impaired coordination of movements - they are sweeping, cutting, limbs are thrown behind the midline when walking, tilting the head down or to the side causes a strong opposite movement), astasia(inability to maintain balance - the animal stands with its paws widely spaced), atony(decreased muscle tone) , tremor(trembling of the limbs and head at rest) and uneven movements.
Main structures diencephalon are thalamus (visual thalamus) and hypothalamus (subthalamus).
Thalamus is the site of processing of all information sent from all (except olfactory) receptors to the cerebral cortex.
The main function of the thalamus is to evaluate the biological significance of all received information, and then combine it and transmit it to the cortex.
In humans, the visual thalamus is also necessary for the manifestation of emotions through peculiar facial expressions, gestures and autonomic reactions.
Hypothalamus is the main subcortical autonomic center. Irritation of its nuclei alone imitates the effects of the parasympathetic nervous system. Stimulation of others - accompanied by sympathetic effects. The nuclei of the hypothalamus also regulate the change in the sleep-wake cycle, metabolism and energy, food (here are the satiety center, the hunger center and the thirst center) and sexual behavior, urination, and the formation of emotions.
The hypothalamus regulates many functions through the endocrine glands and, first of all, through the hypothalamus.
Mainly in the brain stem located reticular formation (RF). Only a small number of related formations are located in the thalamus and in the upper segments of the spinal cord. Reticular formationhas a generalized activating effect on the anterior parts of the brain and the entire cortex(ascending activating system), and descending (facilitatory and inhibitory) effect on the spinal cord. The main structures of the Russian Federation that control motor activity are the Deiters nucleus (medulla oblongata) and the red nucleus (midbrain).
The midbrain RF reflexively changes the functioning of the oculomotor system (especially with the sudden appearance of moving objects, changes in the position of the head and eyes) and regulates autonomic functions (for example, blood circulation). In the RF of the medulla oblongata there are centers of inhalation and exhalation (their activity is controlled by the pneumotaxic center of the pons), as well as the vasomotor center.
Irritation of the Russian Federation causes the “awakening reaction” and the orientation reflex, affects the acuity of hearing, vision, smell and pain sensitivity. Transection of the brain below the RF causes wakefulness, above - sleep.
Limbic system - a functional unification of the structures of the central nervous system, providing (in interaction with the parts of the cerebral cortex) emotional and motivational components of behavior and the integration of body functions aimed at its adaptation to the conditions of existence. It responds to afferent information from the surface of the body and internal organs by organizing behavioral acts (sexual, defensive, eating), the formation of motivations and emotions, learning, storing information, as well as changing the phases of sleep and wakefulness.
The parts of the limbic system include (Fig. 9.): the olfactory bulb and the olfactory tubercle (poorly developed in humans), mammillary bodies, hippocampus, thalamus, amygdala, cingulate and hippocampal gyri. Often, a larger number of structures are included in the limbic system (for example, parts of the frontal and temporal cortex, the hypothalamus and the midbrain RF).
Many signals in the limbic system travel in circles. In the “Papes circle,” impulses from the hippocampus pass to the mammillary bodies, from them to the nuclei of the thalamus, then through the cingulate and hippocampal gyri they return to the hippocampus. The described circulation ensures the formation of emotions, memory and learning. Another circle (amygdala → hypothalamus → mesencephalic structures → amygdala) regulates eating, sexual and aggressive-defensive forms of behavior.
Stimulation of certain areas of the limbic system causes pleasant sensations (“pleasure centers”). Next to them are structures that lead to avoidance reactions (“displeasure centers”).
Damage to the limbic system leads to a pronounced impairment of social behavior (they behave aloof, anxious and unsure of themselves) and the comparison of new information with that stored in memory (they do not distinguish edible objects from inedible ones and therefore take everything into their mouth), concentration of attention becomes impossible.
The cerebral hemispheres and the area connecting them (corpus callosum and fornix) belong to telencephalon. Each hemisphere is divided into frontal, parietal, occipital, temporal and hidden (insula) lobes. Their surface is covered with bark. The telencephalon in humans also includes accumulations of gray matter inside the hemispheres ( basal ganglia). The hippocampus separates the hemisphere from the brain stem. Between the basal ganglia and the cortex is white matter . It consists of many nerve fibers that connect different parts of the hemispheres with each other and other parts of the brain.
Basal ganglia ensure the transition from the intention of movement to action, control the strength, amplitude and direction of movements of the face, mouth and eyes, inhibit unconditioned reflexes and the development of conditioned reflexes, participate in the formation of memory and perception of information, and are responsible for the organization of eating behavior and indicative reactions.
After the destruction of the basal ganglia, the following appear: a mask-like face, physical inactivity, emotional dullness, twitching of the head and limbs when moving, monotonous speech, impaired coordination of the movement of limbs when walking.
Cerebral cortex (CBD) of the brain consists of many neurons and is a layer of gray matter.
Based on the evolutionary approach, ancient, old and new bark are distinguished. To the ancient include poorly developed olfactory structures in humans. old bark make up the main parts of the limbic system: cingulate gyrus, hippocampus, amygdala. The close connection of the ancient and old cortex provides the emotional component of olfactory perception.
New crust performs the most complex functions. To her sensory area all sensory pathways converge. The projection area of each sensation formed in the cortex is directly proportional to its importance (projections from the skin of the hands are greater than from the entire body). The cortical part of the visual (informs about the properties of the light signal) analyzer is located in the occipital lobe. Its removal leads to blindness. The cortical part of the auditory analyzer is localized in the temporal lobe (perceives and analyzes sound signals, organizes auditory control of speech). Its removal causes deafness. Tactile, pain, temperature and other types of skin sensitivity are projected to the parietal lobe.
Motor(motor) areas are found in the frontal lobes. In them, each group of neurons is responsible for the voluntary activity of individual muscles (their contraction is caused by irritation of certain areas of the cortex). Moreover, the size of the cortical motor zone is proportional not to the mass of the muscles being controlled, but to the accuracy of the movements (the largest zones control the movements of the hand, tongue, and facial muscles). The left hemisphere is directly related to the motor mechanisms of speech. When it is affected, the patient understands speech, but cannot speak.
Motor areas receive information necessary for decision making and execution from associative areas(occupies about 80% of the entire surface of the hemispheres) , which combine signals received from all receptors into integral acts of learning, thinking and long-term memory, and also form programs of targeted behavior. If the parietal associative cortex forms ideas about the surrounding space and body, then the temporal cortex is involved in the auditory control of speech, and the frontal cortex forms complex behavior. If the associative zones are damaged, sensations are preserved, but their assessment is impaired. It shows up apraxia(inability to perform learned movements: fastening buttons, writing text, etc.) and agnosia(recognition disorders). With motor agnosia, he understands speech, but cannot speak; with sensory agnosia, he speaks, but cannot understand speech.
Thus, the telencephalon plays the role of an organ of consciousness, memory and mental activity, which manifests itself in behavior and is necessary for a person’s adaptation to changing environmental conditions.
AUTONOMIC NERVOUS SYSTEM
The nervous system is divided into somatic and autonomic. All effector neurons of the somatic nervous system are motor neurons. They begin in the central nervous system and end in the skeletal muscles. The autonomic nervous system innervates all internal organs, glands (secretory neurons), smooth muscles (motoneurons) of blood vessels, the digestive tract and urinary tract, and also regulates metabolism (trophic neurons) in various tissues.
The afferent link of the somatic and autonomic reflex arcs is common. The axons of the central autonomic neurons leave the central nervous system and switch in the ganglia to the peripheral neuron, which innervates the corresponding cells.
The autonomic nervous system is divided into sympathetic and parasympathetic.
Sympathetic nervous system innervates all organs and tissues of the body. Its centers are represented in the lateral horns of the gray matter of the spinal cord (from the I thoracic to the II-IV lumbar segments). When excited, they increase the work of the heart, dilate the bronchi and pupil, reduce the activity of digestion, and cause contraction of the sphincters of the urinary and gall bladders. Sympathetic influences quickly mobilize energy-related metabolism, respiration and blood circulation in the body, which allows it to quickly respond to unfavorable factors. This also explains the increase in the performance of skeletal muscles when the sympathetic nerve is irritated (Orbeli-Ginetzinsky phenomenon).
Parasympathetic centers are nuclei in the brain stem and sacral spinal cord. The parasympathetic nervous system does not innervate skeletal muscles, many blood vessels, and sensory organs. When it is excited, the heart slows down, the bronchi and pupil constrict, digestion is stimulated, the gall and bladder bladders, and the rectum are emptied. Changes in metabolism caused by the parasympathetic nervous system ensure the restoration and maintenance of the constancy of the composition of the internal environment of the body, disturbed when the sympathetic nervous system is excited.
Autonomic functions are not subject to consciousness, but are regulated by almost all parts of the central nervous system. Stimulation of the spinal centers dilates the pupil, increases sweating, cardiac activity and dilates the bronchi. The centers of defecation, urination, and sexual reflexes are also located here. The stem centers regulate the pupillary reflex and accommodation of the eyes, inhibit the activity of the heart, stimulate lacrimation, increase the secretion of the salivary, gastric and pancreatic glands, as well as bile secretion, contractions of the stomach and intestines. The vasomotor center is responsible for reflex changes in the lumen of blood vessels. The hypothalamus is the main subcortical level of autonomic functions. It is responsible for the appearance of emotions, aggressive-defensive and sexual reactions. The limbic system is responsible for the formation of the autonomic component of emotional reactions. The cortex exercises the highest control of autonomic functions, influencing all subcortical autonomic centers, as well as coordinating autonomic and somatic functions during a behavioral act.
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