Ministry of Health of the Republic of Belarus

EE "Gomel State Medical University"

Department of Normal Physiology

Discussed at a department meeting

Protocol No.__________200__

in normal physiology for 2nd year students

Subject: Neuron physiology.

Time 90 minutes

Educational and educational goals:

Provide information about the importance of the nervous system in the body, the structure and function of the peripheral nerve and synapses.

LITERATURE

2. Fundamentals of human physiology. Edited by B.I. Tkachenko. - St. Petersburg, 1994. - T.1. - P. 43 - 53; 86 - 107.

3. Human physiology. Edited by R. Schmidt and G. Thews. - M., Mir. - 1996. - T.1. - P. 26 - 67.

5. General course of human and animal physiology. Edited by A.D. Nozdrachev. - M., Higher School. - 1991. - Book. 1. - pp. 36 - 91.

MATERIAL SUPPORT

1. Multimedia presentation 26 slides.

CALCULATION OF STUDY TIME

	List of educational questions	Amount of allocated time in minutes
	Structure and functions of the nerve.
	Peripheral nervous system: cranial and spinal nerves, nerve plexuses.
	Classification of nerve fibers.
	Laws of conduction of excitation along nerves.
	Parabiosis according to Vvedensky.
	Synapse: structure, classification.
	Mechanisms of excitation transmission in excitatory and inhibitory synapses.

Total 90 min

1. Structure and functions of the nerve.

The importance of nervous tissue in the body is associated with the basic properties of nerve cells (neurons, neurocytes) to perceive the action of a stimulus, enter an excited state, and propagate action potentials. The nervous system regulates the activity of tissues and organs, their relationship and the connection of the body with the environment. Nervous tissue consists of neurons that perform a specific function, and neuroglia, which play an auxiliary role, performing supporting, trophic, secretory, delimiting and protective functions.

Nerve fibers (nerve cell processes covered with membranes) perform a specialized function - conducting nerve impulses. Nerve fibers form a nerve or nerve trunk, consisting of nerve fibers enclosed in a common connective tissue sheath. Nerve fibers that conduct excitation from receptors to the central nervous system are called afferent, and fibers that conduct excitation from the central nervous system to the executive organs are called efferent. Nerves consist of afferent and efferent fibers.

All nerve fibers are morphologically divided into 2 main groups: myelinated and non-myelinated. They consist of a nerve cell process, which lies in the center of the fiber and is called the axial cylinder, and a sheath formed by Schwann cells. A cross section of a nerve shows sections of axial cylinders, nerve fibers and the glial sheaths covering them. Between the fibers in the trunk there are thin layers of connective tissue - endoneurium; bundles of nerve fibers are covered with perineurium, which consists of layers of cells and fibrils. The outer sheath of the nerve, the epineurium, is a connective fibrous tissue rich in fat cells, macrophages, and fibroblasts. The epineurium along the entire length of the nerve receives a large number of blood vessels that anastomose with each other.

General characteristics of nerve cells

A neuron is a structural unit of the nervous system. A neuron consists of a soma (body), dendrites, and an axon. The structural and functional unit of the nervous system is a neuron, a glial cell and feeding blood vessels.

Functions of a neuron

The neuron has irritability, excitability, conductivity, and lability. A neuron is capable of generating, transmitting, perceiving the action of a potential, and integrating influences with the formation of a response. Neurons have background(without stimulation) and caused by(after stimulus) activity.

Background activity can be:

Single - generation of single action potentials (AP) at different time intervals.

Burst - generation of series of 2-10 PDs every 2-5 ms with longer time intervals between bursts.

Group - series contain dozens of PDs.

Induced activity occurs:

At the moment the stimulus is turned on, the neuron is “ON”.

At the moment of switching off, "OF" is a neuron.

To turn on and off "ON - OF" - neurons.

Neurons can gradually change their resting potential under the influence of a stimulus.

Transfer function of a neuron. Physiology of nerves. Classification of nerves.

Based on their structure, nerves are divided into myelinated (pulp) and unmyelinated.

According to the direction of information transmission (center - periphery), nerves are divided into afferent and efferent.

Efferents according to their physiological effect are divided into:

Motor(innervates muscles).

Vasomotor(innervates blood vessels).

Secretory(innervate the glands). Neurons have a trophic function - they provide metabolism and maintain the structure of the innervated tissue. In turn, a neuron that has lost its innervation object also dies.

Based on the nature of their influence on the effector organ, neurons are divided into launchers(transfer tissue from a state of physiological rest to a state of activity) and corrective(change the activity of a functioning organ).

LECTURE ON THE TOPIC: HUMAN NERVOUS SYSTEM

Nervous system is a system that regulates the activities of all human organs and systems. This system determines: 1) the functional unity of all human organs and systems; 2) the connection of the whole organism with the environment.

From the point of view of maintaining homeostasis, the nervous system ensures: maintaining the parameters of the internal environment at a given level; inclusion of behavioral responses; adaptation to new conditions if they persist for a long time.

Neuron(nerve cell) - the main structural and functional element of the nervous system; Humans have more than one hundred billion neurons. A neuron consists of a body and processes, usually one long process - an axon and several short branched processes - dendrites. Along dendrites, impulses follow to the cell body, along an axon - from the cell body to other neurons, muscles or glands. Thanks to the processes, neurons contact each other and form neural networks and circles through which nerve impulses circulate.

A neuron is a functional unit of the nervous system. Neurons are susceptible to stimulation, that is, they are capable of being excited and transmitting electrical impulses from receptors to effectors. Based on the direction of impulse transmission, afferent neurons (sensory neurons), efferent neurons (motor neurons) and interneurons are distinguished.

Nervous tissue is called excitable tissue. In response to some impact, a process of excitation arises and spreads in it - rapid recharging of cell membranes. The emergence and propagation of excitation (nerve impulse) is the main way the nervous system carries out its control function.

The main prerequisites for the occurrence of excitation in cells: the existence of an electrical signal on the membrane in a resting state - the resting membrane potential (RMP);

the ability to change the potential by changing the permeability of the membrane for certain ions.

The cell membrane is a semi-permeable biological membrane, it has channels that allow potassium ions to pass through, but there are no channels for intracellular anions, which are retained at the inner surface of the membrane, creating a negative charge of the membrane from the inside, this is the resting membrane potential, which averages - – 70 millivolts (mV). There are 20-50 times more potassium ions in the cell than outside, this is maintained throughout life with the help of membrane pumps (large protein molecules capable of transporting potassium ions from the extracellular environment to the inside). The MPP value is determined by the transfer of potassium ions in two directions:

1. from the outside into the cell under the action of pumps (with a large expenditure of energy);

2. from the cell to the outside by diffusion through membrane channels (without energy consumption).

In the process of excitation, the main role is played by sodium ions, which are always 8-10 times more abundant outside the cell than inside. Sodium channels are closed when the cell is at rest; in order to open them, it is necessary to act on the cell with an adequate stimulus. If the stimulation threshold is reached, the sodium channels open and sodium enters the cell. In thousandths of a second, the membrane charge will first disappear and then change to the opposite - this is the first phase of the action potential (AP) - depolarization. The channels close - the peak of the curve, then the charge is restored on both sides of the membrane (due to potassium channels) - the repolarization stage. The excitation stops and while the cell is at rest, the pumps exchange the sodium that entered the cell for potassium, which left the cell.

An PD evoked at any point in a nerve fiber itself becomes an irritant for neighboring sections of the membrane, causing AP in them, which in turn excite more and more sections of the membrane, thus spreading throughout the entire cell. In fibers covered with myelin, APs will occur only in areas free of myelin. Therefore, the speed of signal propagation increases.

The transfer of excitation from cell to another occurs through a chemical synapse, which is represented by the point of contact of two cells. The synapse is formed by presynaptic and postsynaptic membranes and the synaptic cleft between them. Excitation in the cell resulting from AP reaches the area of ​​the presynaptic membrane where synaptic vesicles are located, from which a special substance, the transmitter, is released. The transmitter entering the gap moves to the postsynaptic membrane and binds to it. Pores open in the membrane for ions, they move into the cell and the process of excitation occurs

Thus, in the cell, the electrical signal is converted into a chemical one, and the chemical signal again into an electrical one. Signal transmission in a synapse occurs more slowly than in a nerve cell, and is also one-sided, since the transmitter is released only through the presynaptic membrane, and can only bind to receptors of the postsynaptic membrane, and not vice versa.

Mediators can cause not only excitation but also inhibition in cells. In this case, pores open on the membrane for ions that strengthen the negative charge that existed on the membrane at rest. One cell can have many synaptic contacts. An example of a mediator between a neuron and a skeletal muscle fiber is acetylcholine.

The nervous system is divided into central nervous system and peripheral nervous system.

In the central nervous system, a distinction is made between the brain, where the main nerve centers and the spinal cord are concentrated, and here there are lower-level centers and pathways to peripheral organs.

Peripheral section - nerves, nerve ganglia, ganglia and plexuses.

The main mechanism of activity of the nervous system is reflex. A reflex is any response of the body to a change in the external or internal environment, which is carried out with the participation of the central nervous system in response to irritation of receptors. The structural basis of the reflex is the reflex arc. It includes five consecutive links:

1 - Receptor - a signaling device that perceives influence;

2 - Afferent neuron – brings a signal from the receptor to the nerve center;

3 - Interneuron – central part of the arc;

4 - Efferent neuron - the signal comes from the central nervous system to the executive structure;

5 - Effector - a muscle or gland performing a certain type of activity

Brain consists of clusters of nerve cell bodies, nerve tracts and blood vessels. Nerve tracts form the white matter of the brain and consist of bundles of nerve fibers that conduct impulses to or from various parts of the gray matter of the brain - nuclei or centers. Pathways connect various nuclei, as well as the brain and spinal cord.

Functionally, the brain can be divided into several sections: the forebrain (consisting of the telencephalon and diencephalon), the midbrain, the hindbrain (consisting of the cerebellum and the pons) and the medulla oblongata. The medulla oblongata, pons, and midbrain are collectively called the brainstem.

Spinal cord located in the spinal canal, reliably protecting it from mechanical damage.

The spinal cord has a segmental structure. Two pairs of anterior and posterior roots extend from each segment, which corresponds to one vertebra. There are 31 pairs of nerves in total.

The dorsal roots are formed by sensory (afferent) neurons, their bodies are located in the ganglia, and the axons enter the spinal cord.

The anterior roots are formed by the axons of efferent (motor) neurons, the bodies of which lie in the spinal cord.

The spinal cord is conventionally divided into four sections - cervical, thoracic, lumbar and sacral. It closes a huge number of reflex arcs, which ensures the regulation of many body functions.

The gray central substance is nerve cells, the white one is nerve fibers.

The nervous system is divided into somatic and autonomic.

TO somatic nervous system (from the Latin word “soma” - body) refers to part of the nervous system (both cell bodies and their processes), which controls the activity of skeletal muscles (body) and sensory organs. This part of the nervous system is largely controlled by our consciousness. That is, we are able to bend or straighten an arm, leg, etc. at will. However, we are unable to consciously stop perceiving, for example, sound signals.

Autonomic nervous system (translated from Latin “vegetative” - plant) is part of the nervous system (both cell bodies and their processes), which controls the processes of metabolism, growth and reproduction of cells, that is, functions common to both animals and plants organisms. The autonomic nervous system is responsible, for example, for the activity of internal organs and blood vessels.

The autonomic nervous system is practically not controlled by consciousness, that is, we are not able to relieve a spasm of the gallbladder at will, stop cell division, stop intestinal activity, dilate or constrict blood vessels

NERVES NERVES

(Latin unit nervus, from Greek neuron - vein, nerve), strands of nervous tissue connecting the brain and nerve nodes with other tissues and organs of the body. N. are formed by bundles of nerve fibers. Each bundle is surrounded by a connective tissue membrane (perineurium), from which thin layers (endonearium) extend into the bundle. The entire N. is covered with a common membrane (epineurium). Usually the nerve consists of 103-104 fibers, but in humans there are over 1 million of them in the visual nerve. In invertebrates, nerves are known that consist of several fibers. The impulse propagates along each fiber in isolation, without passing to other fibers. There are sensory (afferent, centripetal), motor (efferent, centrifugal) and mixed nerves. In vertebrates, cranial nerves depart from the brain, and spinal nerves depart from the spinal cord. Several neighboring N. can form nerve plexuses. Based on the nature of the innervated organs, N. is classified into vegetative and somatic, the combination of which forms a peripheral organ. nervous system.

.(Source: “Biological Encyclopedic Dictionary.” Editor-in-chief M. S. Gilyarov; Editorial Board: A. A. Babaev, G. G. Vinberg, G. A. Zavarzin and others - 2nd ed., corrected . - M.: Sov. Encyclopedia, 1986.)

Synonyms:

See what “NERVES” is in other dictionaries:

NERVES- NERVES, the peripheral part of the nervous system, conducting impulses from the central nervous system to the periphery and back; They are located outside the cranial spinal canal and in the form of cords disperse throughout all parts of the head, torso and limbs.... ... Great Medical Encyclopedia

You need to have nerves of steel or none at all. M. St. Domansky Do not waste your nerves on what you can spend money on. Leonid Leonidov The conviction that your work is extremely important is a sure sign of an approaching nervous breakdown. Bertrand... ... Consolidated encyclopedia of aphorisms

- (Latin nervus, Greek neuron). Grayish fibers running throughout the body of humans and animals, controlling its movements and perceiving external impressions, transmitting them to the brain. Dictionary of foreign words included in the Russian language. Chudinov... Dictionary of foreign words of the Russian language

- (Latin nervus, from the Greek neuron vein, nerve), strands of nervous tissue formed mainly by nerve fibers (neuron processes). Nerves connect the brain and ganglia with other organs and tissues of the body. The set of nerves forms... ... Modern encyclopedia

- (Latin nervus from the Greek neuron vein, nerve), strands of nervous tissue formed mainly by nerve fibers. Nerves connect the brain and nerve ganglia with other organs and tissues of the body. The collection of nerves forms the peripheral nervous system. U... ... Big Encyclopedic Dictionary

Nerves, irritability, nerve Dictionary of Russian synonyms. nerves noun, number of synonyms: 5 white-hot (1) nerve ... Synonym dictionary

- “NERVES (short story in the film anthology “Family Happiness”)”, USSR, MOSFILM, 1969, b/w, 10 min. Comedy. Based on the story of the same name by A.P. Chekhov. Having heard enough scary stories about all sorts of mystical phenomena, Vaksin cannot sleep for a long time. And in the morning the wife... Encyclopedia of Cinema

In paleobotany mouth. syn. term veins. Geological Dictionary: in 2 volumes. M.: Nedra. Edited by K. N. Paffengoltz et al. 1978 ... Geological encyclopedia

nerves- Sick, ox-like (colloquial), lethargic, iron (colloquial), healthy, twitchy, exhausted, strong, strained, strained, wire-like (colloquial), irritated, upset, disheveled, loose, strong, weak, steely, dull , tired,... ... Dictionary of epithets

Central nervous system (CNS) * I. Cervical nerves. * II. Thoracic nerves. * III. Lumbar nerves. * IV. Sacral nerves. * V. Coccygeal nerves. / * 1. Brain. * 2. Diencephalon. * 3. Midbrain. * 4. Bridge. * 5. Cerebellum. * 6.… …Wikipedia

Books

• I'm getting on my nerves. Dear, Andrey Dyshev. The rich businessman Alexander Yudin really liked being a Mongol khan - robbing, burning, raping... The soul, yearning for special sensations, rejoiced. That's why when…
• Diamond nerves, Viktor Burtsev. Moscow of the XXI century. Have Muscovites changed? No, although they are no longer worried about the housing issue. Someone still laughs, someone falls in love, eats pies, drinks Putin vodka, someone serves in...

Nerve endings are located throughout the human body. They have a vital function and are an integral part of the entire system. The structure of the human nervous system is a complex branched structure that runs through the entire body.

The physiology of the nervous system is a complex composite structure.

The neuron is considered the basic structural and functional unit of the nervous system. Its processes form fibers that are excited when exposed and transmit impulses. The impulses reach the centers where they are analyzed. Having analyzed the received signal, the brain transmits the necessary reaction to the stimulus to the appropriate organs or parts of the body. The human nervous system is briefly described by the following functions:

• providing reflexes;
• regulation of internal organs;
• ensuring the interaction of the body with the external environment, by adapting the body to changing external conditions and stimuli;
• interaction of all organs.

The importance of the nervous system lies in ensuring the vital functions of all parts of the body, as well as the interaction of a person with the outside world. The structure and functions of the nervous system are studied by neurology.

Structure of the central nervous system

The anatomy of the central nervous system (CNS) is a collection of neuronal cells and neural processes of the spinal cord and brain. A neuron is a unit of the nervous system.

The function of the central nervous system is to ensure reflex activity and process impulses coming from the PNS.

The anatomy of the central nervous system, the main unit of which is the brain, is a complex structure of branched fibers.

The higher nerve centers are concentrated in the cerebral hemispheres. This is a person’s consciousness, his personality, his intellectual abilities and speech. The main function of the cerebellum is to ensure coordination of movements. The brain stem is inextricably linked with the hemispheres and cerebellum. This section contains the main nodes of the motor and sensory pathways, which ensures such vital functions of the body as regulating blood circulation and ensuring respiration. The spinal cord is the distribution structure of the central nervous system; it provides branching of the fibers that form the PNS.

The spinal ganglion is the site of concentration of sensory cells. With the help of the spinal ganglion, the activity of the autonomic department of the peripheral nervous system is carried out. Ganglia or nerve ganglia in the human nervous system are classified as the PNS; they perform the function of analyzers. Ganglia do not belong to the human central nervous system.

Features of the structure of the PNS

Thanks to the PNS, the activity of the entire human body is regulated. The PNS consists of cranial and spinal neurons and fibers that form ganglia.

The human peripheral nervous system has a very complex structure and functions, so any slightest damage, for example, damage to blood vessels in the legs, can cause serious disruptions to its functioning. Thanks to the PNS, all parts of the body are controlled and the vital functions of all organs are ensured. The importance of this nervous system for the body cannot be overestimated.

The PNS is divided into two divisions - the somatic and autonomic PNS systems.

The somatic nervous system performs double duty - collecting information from the sensory organs, and further transmitting this data to the central nervous system, as well as ensuring the motor activity of the body by transmitting impulses from the central nervous system to the muscles. Thus, it is the somatic nervous system that is the instrument of human interaction with the outside world, as it processes signals received from the organs of vision, hearing and taste buds.

The autonomic nervous system ensures the functions of all organs. It controls the heartbeat, blood supply, and breathing. It contains only motor nerves that regulate muscle contraction.

To ensure the heartbeat and blood supply, the efforts of the person himself are not required - this is controlled by the autonomic part of the PNS. The principles of the structure and function of the PNS are studied in neurology.

Departments of the PNS

The PNS also consists of the afferent nervous system and the efferent nervous system.

The afferent region is a collection of sensory fibers that process information from receptors and transmit it to the brain. The work of this department begins when the receptor is irritated due to any impact.

The efferent system differs in that it processes impulses transmitted from the brain to effectors, that is, muscles and glands.

One of the important parts of the autonomic division of the PNS is the enteric nervous system. The enteric nervous system is formed from fibers located in the gastrointestinal tract and urinary tract. The enteric nervous system controls the motility of the small and large intestine. This section also regulates the secretions released in the gastrointestinal tract and provides local blood supply.

The importance of the nervous system is to ensure the functioning of internal organs, intellectual function, motor skills, sensitivity and reflex activity. The child’s central nervous system develops not only during the prenatal period, but also during the first year of life. The ontogeny of the nervous system begins from the first week after conception.

The basis for brain development is formed already in the third week after conception. The main functional nodes are identified by the third month of pregnancy. By this time, the hemispheres, trunk and spinal cord have already been formed. By the sixth month, the higher parts of the brain are already better developed than the spinal part.

By the time a baby is born, the brain is the most developed. The size of the brain in a newborn is approximately an eighth of the child’s weight and ranges from 400 g.

The activity of the central nervous system and PNS is greatly reduced in the first few days after birth. This may include an abundance of new irritating factors for the baby. This is how the plasticity of the nervous system manifests itself, that is, the ability of this structure to be rebuilt. As a rule, the increase in excitability occurs gradually, starting from the first seven days of life. The plasticity of the nervous system deteriorates with age.

Types of CNS

In the centers located in the cerebral cortex, two processes simultaneously interact - inhibition and excitation. The rate at which these states change determines the types of nervous system. While one part of the central nervous system is excited, another part slows down. This determines the features of intellectual activity, such as attention, memory, concentration.

Types of the nervous system describe the differences between the speed of inhibition and excitation of the central nervous system in different people.

People may differ in character and temperament, depending on the characteristics of the processes in the central nervous system. Its features include the speed of switching neurons from the process of inhibition to the process of excitation, and vice versa.

The types of nervous system are divided into four types.

• The weak type, or melancholic, is considered the most predisposed to the occurrence of neurological and psycho-emotional disorders. It is characterized by slow processes of excitation and inhibition. The strong and unbalanced type is choleric. This type is distinguished by the predominance of excitation processes over inhibition processes.
• Strong and agile - this is a type of sanguine person. All processes occurring in the cerebral cortex are strong and active. A strong but inert, or phlegmatic type, is characterized by a low speed of switching nervous processes.

The types of the nervous system are interconnected with temperaments, but these concepts should be distinguished, because temperament characterizes a set of psycho-emotional qualities, and the type of the central nervous system describes the physiological characteristics of the processes occurring in the central nervous system.

CNS protection

The anatomy of the nervous system is very complex. The central nervous system and PNS suffer due to the effects of stress, overexertion and lack of nutrition. For the normal functioning of the central nervous system, vitamins, amino acids and minerals are necessary. Amino acids take part in brain function and are building materials for neurons. Having figured out why vitamins and amino acids are needed and why, it becomes clear how important it is to provide the body with the necessary amount of these substances. Glutamic acid, glycine and tyrosine are especially important for humans. The regimen for taking vitamin-mineral complexes for the prevention of diseases of the central nervous system and PNS is selected individually by the attending physician.

Damage to bundles of nerve fibers, congenital pathologies and abnormalities of brain development, as well as the action of infections and viruses - all this leads to disruption of the central nervous system and PNS and the development of various pathological conditions. Such pathologies can cause a number of very dangerous diseases - immobility, paresis, muscle atrophy, encephalitis and much more.

Malignant neoplasms in the brain or spinal cord lead to a number of neurological disorders. If an oncological disease of the central nervous system is suspected, an analysis is prescribed - histology of the affected parts, that is, an examination of the composition of the tissue. A neuron, as part of a cell, can also mutate. Such mutations can be identified by histology. Histological analysis is carried out according to the doctor’s indications and consists of collecting the affected tissue and its further study. For benign formations, histology is also performed.

The human body contains many nerve endings, damage to which can cause a number of problems. Damage often leads to impaired mobility of a body part. For example, an injury to the hand can lead to pain in the fingers and impaired movement. Osteochondrosis of the spine can cause pain in the foot due to the fact that an irritated or compressed nerve sends pain impulses to receptors. If the foot hurts, people often look for the cause in a long walk or injury, but the pain syndrome can be triggered by damage to the spine.

If you suspect damage to the PNS, as well as any related problems, you should be examined by a specialist.

It is an organized set of cells specialized in conducting electrical signals.

The nervous system consists of neurons and glial cells. The function of neurons is to coordinate actions using chemical and electrical signals sent from one place to another in the body. Most multicellular animals have nervous systems with similar basic characteristics.

Content:

The nervous system takes in stimuli from the environment (extrinsic stimuli) or signals from the same organism (intrinsic stimuli), processes the information, and generates different responses depending on the situation. As an example, we can consider an animal that, through cells sensitive to light in the retina, senses the proximity of another living being. This information is transmitted by the optic nerve to the brain, which processes it and emits a nerve signal and causes certain muscles to contract through the motor nerves to move in the opposite direction of the potential danger.

Functions of the nervous system

The human nervous system controls and regulates most body functions, from stimuli through sensory receptors to motor actions.

It consists of two main parts: the central nervous system (CNS) and the peripheral nervous system (PNS). The central nervous system consists of the brain and spinal cord.

The PNS is made up of nerves that connect the CNS to every part of the body. The nerves that carry signals from the brain are called motor or efferent nerves, and the nerves that carry information from the body to the central nervous system are called sensory or afferent nerves.

At the cellular level, the nervous system is defined by the presence of a cell type called a neuron, also known as a "nerve cell." Neurons have special structures that allow them to send signals quickly and accurately to other cells.

Connections between neurons can form circuits and neural networks that generate perceptions of the world and determine behavior. Along with neurons, the nervous system contains other specialized cells called glial cells (or simply glia). They provide structural and metabolic support.

Malfunction of the nervous system can occur as a result of genetic defects, physical damage, due to injury or toxicity, infection, or simply through aging.

Structure of the nervous system

The nervous system (NS) consists of two well-differentiated subsystems, on the one hand the central nervous system and on the other the peripheral nervous system.

Video: Human nervous system. Introduction: basic concepts, composition and structure

At the functional level, the peripheral nervous system (PNS) and somatic nervous system (SNS) are differentiated into the peripheral nervous system. The SNS is involved in the automatic regulation of internal organs. The PNS is responsible for capturing sensory information and allowing voluntary movements such as shaking hands or writing.

The peripheral nervous system consists mainly of the following structures: ganglia and cranial nerves.

Autonomic nervous system

Autonomic nervous system

The autonomic nervous system (ANS) is divided into the sympathetic and parasympathetic systems. The ANS is involved in the automatic regulation of internal organs.

The autonomic nervous system, together with the neuroendocrine system, is responsible for regulating the internal balance of our body, decreasing and increasing hormone levels, activating internal organs, etc.

To do this, it transmits information from the internal organs to the central nervous system through afferent pathways and radiates information from the central nervous system to the muscles.

It includes the cardiac muscles, smooth skin (which supplies hair follicles), smooth eyes (which regulates contraction and dilation of the pupil), smooth blood vessels, and smooth walls of internal organs (gastrointestinal system, liver, pancreas, respiratory system, reproductive organs, bladder...).

The efferent fibers are organized into two distinct systems called the sympathetic and parasympathetic systems.

Sympathetic nervous system is primarily responsible for preparing us to act when we perceive a significant stimulus, activating one of our automatic responses (such as running away or attacking).

Parasympathetic nervous system, in turn, supports optimal activation of the internal state. Increase or decrease activation as needed.

Somatic nervous system

The somatic nervous system is responsible for capturing sensory information. For this purpose, it uses sensory sensors distributed throughout the body, which distribute information to the central nervous system and thus transfer it from the central nervous system to the muscles and organs.

On the other hand, it is a part of the peripheral nervous system associated with the voluntary control of bodily movements. It consists of afferent or sensory nerves, efferent or motor nerves.

Afferent nerves are responsible for transmitting body sensations to the central nervous system (CNS). Efferent nerves are responsible for sending signals from the central nervous system to the body, stimulating muscle contraction.

The somatic nervous system consists of two parts:

• Spinal nerves: arise from the spinal cord and consist of two branches: a sensory afferent and another efferent motor, so they are mixed nerves.
• Cranial Nerves: Sends sensory information from the neck and head to the central nervous system.

Both are then explained:

Cranial nervous system

There are 12 pairs of cranial nerves that arise from the brain and are responsible for transmitting sensory information, controlling some muscles, and regulating some glands and internal organs.

I. Olfactory nerve. It receives olfactory sensory information and transfers it to the olfactory bulb located in the brain.

II. Optic nerve. It receives visual sensory information and transmits it to the brain's vision centers through the optic nerve, passing through the chiasm.

III. Internal ocular motor nerve. It is responsible for controlling eye movements and regulating pupil dilation and contraction.

IV Intravenous-trilateral nerve. It is responsible for controlling eye movements.

V. Trigeminal nerve. It receives somatosensory information (eg warmth, pain, texture...) from sensory receptors on the face and head and controls the muscles of mastication.

VI. External motor nerve of the optic nerve. Control of eye movements.

VII. Facial nerve. Receives information about the taste of the tongue (those located in the middle and anterior parts) and somatosensory information from the ears, and controls the muscles necessary to perform facial expressions.

VIII. Vestibulocochlear nerve. Receives auditory information and controls balance.

IX. Glossaphoargial nerve. Receives taste information from the very back of the tongue, somatosensory information from the tongue, tonsils, pharynx, and controls the muscles needed for swallowing (swallowing).

X. Vagal nerve. Receives sensitive information from the digestive glands and heart rate and sends information to organs and muscles.

XI. Dorsal accessory nerve. Controls the muscles of the neck and head, which are used for movement.

XII. Hypoglossal nerve. Controls the muscles of the tongue.

Spinal nerves connect the organs and muscles of the spinal cord. Nerves are responsible for transmitting information about sensory and visceral organs to the brain and transmitting orders from the bone marrow to skeletal and smooth muscle and glands.

These connections control reflexive actions that are performed so quickly and unconsciously because the information does not have to be processed by the brain before a response is produced, it is directly controlled by the brain.

There are a total of 31 pairs of spinal nerves that exit bilaterally from the bone marrow through the space between the vertebrae, called the intravertebral foramina.

central nervous system

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

At the neuroanatomical level, two types of substances can be distinguished in the central nervous system: white and gray. White matter is formed by the axons of neurons and structural material, and gray matter is formed by the neuronal soma, where the genetic material is located.

This difference is one of the reasons on which the myth is based that we only use 10% of our brain, since the brain is made up of approximately 90% white matter and only 10% gray matter.

But although the gray matter appears to be composed of material which only serves to make connections, it is now known that the number and manner in which connections are made have a marked influence on the functions of the brain, since if the structures are in an ideal state, but between there are no connections between them, they will not work correctly.

The brain consists of many structures: the cerebral cortex, basal ganglia, limbic system, diencephalon, brainstem and cerebellum.

Cortex

The cerebral cortex can be divided anatomically into lobes separated by grooves. The most recognized are the frontal, parietal, temporal and occipital, although some authors argue that there is also a limbic lobe.

The cortex is divided into two hemispheres, right and left, so that halves are present symmetrically in both hemispheres, with right frontal lobe and left lobe, right and left parietal lobe, etc.

The hemispheres of the brain are separated by an interhemispheric fissure, and the lobes are separated by various grooves.

The cerebral cortex can also be classified as a function of the sensory cortex, association cortex, and frontal lobes.

The sensory cortex receives sensory information from the thalamus, which receives information through sensory receptors, with the exception of the primary olfactory cortex, which receives information directly from sensory receptors.

Somatosensory information reaches the primary somatosensory cortex, located in the parietal lobe (in the postcentral gyrus).

Each sensory information reaches a specific point in the cortex, forming a sensory homunculus.

As can be seen, the areas of the brain corresponding to the organs do not correspond to the same order in which they are located in the body and they do not have a proportional ratio of sizes.

The largest cortical areas, relative to the size of the organs, are the hands and lips, since in this area we have a high density of sensory receptors.

Visual information reaches the primary visual cortex of the brain, located in the occipital lobe (in the sulcus), and this information has a retinotopic organization.

The primary auditory cortex is located in the temporal lobe (Brodmann area 41), responsible for receiving auditory information and creating tonotopic organization.

The primary taste cortex is located in the anterior part of the impeller and in the anterior shell, and the olfactory cortex is located in the piriform cortex.

The association cortex includes primary and secondary. The primary cortical association is located adjacent to the sensory cortex and integrates all the characteristics of the perceived sensory information such as color, shape, distance, size, etc. of the visual stimulus.

The secondary association root is located in the parietal operculum and processes integrated information to send it to more “advanced” structures such as the frontal lobes. These structures place it in context, give it meaning and make it conscious.

The frontal lobes, as we have already mentioned, are responsible for high-level information processing and the integration of sensory information with motor actions that are performed so that they correspond to the perceived stimulus.

They also perform a number of complex, typically human tasks called executive functions.

Basal ganglia

The basal ganglia (from Greek ganglion, "conglomerate", "nodule", "tumor") or basal ganglia are a group of nuclei or masses of gray matter (clusters of cell bodies or neuronal cells) that are found at the base of the brain between the ascending and descending white matter tracts and riding on the brain stem.

These structures are connected to each other and together with the cerebral cortex and association through the thalamus, their main function is to control voluntary movements.

The limbic system is formed by subcortical structures, that is, below the cerebral cortex. Among the subcortical structures that do this, the amygdala stands out, and among the cortical ones, the hippocampus.

The amygdala is almond-shaped and consists of a number of nuclei that emit and receive afferents and outputs from different regions.

This structure is associated with several functions, such as emotional processing (especially negative emotions) and its influence on learning and memory, attention, and some perceptual mechanisms.

The hippocampus, or hypocampal formation, is a seahorse-shaped cortical area (hence the name hippocampus from the Greek hypos: horse and monster of the sea) and communicates bidirectionally with the rest of the cerebral cortex and with the hypothalamus.

Hypothalamus

This structure is especially important for learning because it is responsible for memory consolidation, which is the transformation of short-term or immediate memory into long-term memory.

Diencephalon

Diencephalon located in the central part of the brain and consists mainly of the thalamus and hypothalamus.

Thalamus consists of several nuclei with differentiated connections, which is very important in the processing of sensory information, since it coordinates and regulates information coming from the spinal cord, the brain stem and the brain itself.

Thus, all sensory information passes through the thalamus before reaching the sensory cortex (with the exception of olfactory information).

Hypothalamus consists of several nuclei that are widely interconnected. In addition to other structures both central and peripheral nervous system, such as the cortex, spinal cord, retina and endocrine system.

Its main function is to integrate sensory information with other types of information, such as emotional, motivational or past experiences.

The brain stem is located between the diencephalon and the spinal cord. It consists of the medulla oblongata, convexity and mesencephalin.

This structure receives most peripheral motor and sensory information, and its main function is to integrate sensory and motor information.

Cerebellum

The cerebellum is located at the back of the skull and is shaped like a small brain, with a cortex on the surface and white matter inside.

It receives and integrates information primarily from the cerebral cortex. Its main functions are coordinating and adapting movements to situations, as well as maintaining balance.

Spinal cord

The spinal cord passes from the brain to the second lumbar vertebra. Its main function is to communicate between the central nervous system and the central nervous system, for example by taking motor commands from the brain to the nerves that innervate the muscles so that they produce a motor response.

In addition, it can initiate automatic responses by receiving some very important sensory information such as a prick or burning sensation.