Structure . Anatomically divided into central and peripheral, the central nervous system includes the brain and spinal cord, the peripheral - 12 pairs of cranial nerves and 31 pairs of spinal nerves and nerve nodes. Functionally, the nervous system can be divided into somatic and autonomous (vegetative). The somatic part of the nervous system regulates the work of skeletal muscles, the autonomous part controls the work of internal organs.
Nerves can be sensitive (visual, olfactory, auditory) if they conduct excitation to the central nervous system, motor (oculomotor) if excitation comes from the central nervous system along them, and mixed (vagus, spinal) if excitation along one fiber goes into one -, and on the other - in the other direction.
The conduction function is carried out due to the ascending and descending paths of the white matter. Along the ascending paths, excitation from the muscles and internal organs is transmitted to the brain, along the descending paths - from the brain to the organs.
The structure and functions of the brain
1 - large hemispheres; 2 - diencephalon; 3 - midbrain; 4 - bridge; 5 - cerebellum ; 6 - medulla oblongata; 7 - corpus callosum; 8 - epiphysis.
There are five divisions in the brain: the medulla oblongata, the posterior, which includes the bridge and the cerebellum, the middle, diencephalon, and forebrain, represented by the cerebral hemispheres. Up to 80% of the mass of the brain falls on the cerebral hemispheres. The central canal of the spinal cord continues into the brain, where it forms four cavities (ventricles). Two ventricles are located in the hemispheres, the third in the diencephalon, the fourth at the level of the medulla oblongata and the bridge. They contain cranial fluid. The brain is surrounded by three membranes - connective tissue, arachnoid and vascular (Fig. 231).
Medulla is a continuation of the spinal cord, performs reflex and conduction functions.
Reflex functions are associated with the regulation of the work of the respiratory, digestive and circulatory organs; here are the centers of protective reflexes - coughing, sneezing, vomiting.
Bridge connects the cerebral cortex with the spinal cord and cerebellum, performs mainly a conductive function.
Cerebellum formed by two hemispheres, outside covered with a bark of gray matter, under which is white matter. The white matter contains nuclei. The middle part - the worm connects the hemispheres. Responsible for coordination, balance and affects muscle tone. With damage to the cerebellum, there is a decrease in muscle tone, a disorder in the coordination of movements. After some time, other parts of the nervous system begin to perform the functions of the cerebellum and the lost functions are partially restored. Together with the bridge, it is part of the hindbrain.
midbrain connects all parts of the brain. Here are the centers of skeletal muscle tone, the primary centers of visual and auditory orienting reflexes. These reflexes are manifested in the movements of the eyes, head towards stimuli.
AT diencephalon There are three parts: visual tubercles (thalamus), epithalamic region (epithalamus, which includes the epiphysis) and hypothalamic region (hypothalamus). In the thalamus there are subcortical centers of all types of sensitivity, excitation from the sense organs comes here, from here it is transmitted to various parts of the cerebral cortex. The hypothalamus contains the highest centers of regulation of the autonomic nervous system, it controls the constancy of the internal environment of the body. Here are the centers of appetite, thirst, sleep, thermoregulation, i.e. all types of metabolism are regulated. Neurons of the hypothalamus produce neurohormones that regulate the functioning of the endocrine system. In the diencephalon there are also emotional centers: centers of pleasure, fear, aggression. Together with the hindbrain and medulla, the diencephalon is part of the brainstem.
1 - central furrow; 2 - lateral furrow.
forebrain represented by the cerebral hemispheres, connected by the corpus callosum (Fig. 232). The surface is formed by the crust, the area of which is about 2200 cm2. Numerous folds, convolutions and furrows significantly increase the surface of the cortex, the surface of the convolutions is more than two times smaller than the surface of the furrows. The human cortex has from 14 to 17 billion nerve cells arranged in 6 layers, the thickness of the cortex is 2 - 4 mm. Accumulations of neurons in the depths of the hemispheres form subcortical nuclei. In the cortex of each hemisphere, the central sulcus separates the frontal lobe from the parietal, the lateral sulcus separates the temporal lobe, and the parietal-occipital sulcus separates the occipital lobe from the parietal.
In the cortex, sensitive, motor zones and associative zones are distinguished.
Sensitive zones are responsible for the analysis of information coming from the sense organs: occipital - for vision, temporal - for hearing, smell and taste, parietal - for skin and joint-muscular sensitivity. And each hemisphere receives impulses from the opposite side of the body. The motor zones are located in the posterior regions of the frontal lobes, from here come the commands for contraction of the skeletal muscles, their defeat leads to muscle paralysis. Associative zones are located in the frontal lobes of the brain and are responsible for the development of programs for behavior and management of human labor activity; their mass in humans is more than 50% of the total mass of the brain.
A person is characterized by a functional asymmetry of the hemispheres, the left hemisphere is responsible for abstract-logical thinking, speech centers are also located there (Brock's center is responsible for pronunciation, Wernicke's center for understanding speech), the right hemisphere is responsible for figurative thinking, musical and artistic creativity.
Due to the strong development of the cerebral hemispheres, the average mass of the human brain is on average 1400 g. But abilities depend not only on mass, but also on the organization of the brain. Anatole France, for example, had a brain mass of 1017g, Turgenev 2012.
autonomic nervous system
The parasympathetic nervous system has the opposite effect, the "stop system". Prenodal neurons are located in the middle, medulla oblongata and in the sacral spinal cord, postganglionic - in the nodes near the internal organs. The mediator secreted by synapses in both types of neurons is acetylcholine (Fig. 234). Functions: - reverse.
Thus, depending on the circumstances, the autonomic nervous system either enhances the functions of certain organs or weakens them, and at each moment either the sympathetic or parasympathetic parts of the autonomic nervous system show greater activity.
Nervous system consists of tortuous networks of nerve cells that make up various interconnected structures and control all the activities of the body, both desired and conscious actions, and reflexes and automatic actions; the nervous system allows us to interact with the outside world, and is also responsible for mental activity.
The nervous system consists of various interconnected structures that together make up an anatomical and physiological unit. consists of organs located inside the skull (brain, cerebellum, brain stem) and spine (spinal cord); is responsible for interpreting the state and various needs of the body based on the information received, in order to then generate commands designed to obtain appropriate responses.
consists of many nerves that go to the brain (brain pairs) and spinal cord (vertebral nerves); acts as a transmitter of sensory stimuli to the brain and commands from the brain to the organs responsible for their execution. The autonomic nervous system controls the functions of numerous organs and tissues through antagonistic effects: the sympathetic system is activated during anxiety, while the parasympathetic system is activated at rest.
central nervous system Includes the spinal cord and brain structures.
The entire nervous system is divided into central and peripheral. The central nervous system includes the brain and spinal cord. Nerve fibers - the peripheral nervous system - diverge from them throughout the body. It connects the brain with the sense organs and with the executive organs - the muscles and glands.
All living organisms have the ability to respond to physical and chemical changes in the environment. Stimuli of the external environment (light, sound, smell, touch, etc.) are converted by special sensitive cells (receptors) into nerve impulses - a series of electrical and chemical changes in the nerve fiber. Nerve impulses are transmitted along sensitive (afferent) nerve fibers to the spinal cord and brain. Here, the corresponding command impulses are generated, which are transmitted along the motor (efferent) nerve fibers to the executive organs (muscles, glands). These executive organs are called effectors. The main function of the nervous system is the integration of external influences with the corresponding adaptive response of the body.
The structural unit of the nervous system is a nerve cell - a neuron. It consists of a cell body, a nucleus, branched processes - dendrites - along them nerve impulses go to the cell body - and one long process - an axon - along it a nerve impulse passes from the cell body to other cells or effectors. The processes of two adjacent neurons are connected by a special formation - a synapse. It plays an essential role in filtering nerve impulses: it passes some impulses and delays others. Neurons are connected to each other and carry out joint activities.
The central nervous system consists of the brain and spinal cord. The brain is divided into the brainstem and the forebrain. The brain stem consists of the medulla oblongata and midbrain. The forebrain is divided into intermediate and final.
All parts of the brain have their own functions. Thus, the diencephalon consists of the hypothalamus - the center of emotions and vital needs (hunger, thirst, libido), the limbic system (in charge of emotional-impulsive behavior) and the thalamus (performing filtering and primary processing of sensory information).
In humans, the cerebral cortex is especially developed - the organ of higher mental functions. It has a thickness of 3 mm, and its total area is on average 0.25 sq.m. The bark is made up of six layers. The cells of the cerebral cortex are interconnected. There are about 15 billion of them. Different cortical neurons have their own specific function. One group of neurons performs the function of analysis (crushing, dismemberment of a nerve impulse), the other group performs synthesis, combines impulses coming from various sensory organs and parts of the brain (associative neurons). There is a system of neurons that keeps traces of previous influences and compares new influences with existing traces.
According to the features of the microscopic structure, the entire cerebral cortex is divided into several dozen structural units - fields, and according to the location of its parts - into four lobes: occipital, temporal, parietal and frontal. The human cerebral cortex is a holistically working organ, although its individual parts (areas) are functionally specialized (for example, the occipital region of the cortex performs complex visual functions, the frontotemporal region - speech, the temporal region - auditory). The largest part of the motor zone of the human cerebral cortex is associated with the regulation of the movement of the labor organ (hand) and speech organs.
All parts of the cerebral cortex are interconnected; they are also connected to the underlying parts of the brain, which carry out the most important vital functions. Subcortical formations, regulating innate unconditional reflex activity, are the area of those processes that are subjectively felt in the form of emotions (they, according to I.P. Pavlov, are “a source of strength for cortical cells”).
The human brain contains all the structures that arose at various stages of the evolution of living organisms. They contain the "experience" accumulated in the process of the entire evolutionary development. This testifies to the common origin of man and animals. As the organization of animals at various stages of evolution becomes more complex, the importance of the cerebral cortex grows more and more.
The main mechanism of nervous activity is the reflex. Reflex - the reaction of the body to external or internal influences through the central nervous system. The term "reflex" was introduced into physiology by the French scientist René Descartes in the 17th century. But to explain mental activity, it was used only in 1863 by the founder of Russian materialistic physiology, M.I. Sechenov. Developing the teachings of I.M. Sechenov, I.P. Pavlov experimentally investigated the features of the functioning of the reflex.
All reflexes are divided into two groups: conditioned and unconditioned.
Unconditioned reflexes are innate reactions of the body to vital stimuli (food, danger, etc.). They do not require any conditions for their development (for example, the blink reflex, salivation at the sight of food). Unconditioned reflexes are a natural reserve of ready-made, stereotyped reactions of the body. They arose as a result of a long evolutionary development of this species of animals. Unconditioned reflexes are the same in all individuals of the same species; it is the physiological mechanism of instincts. But the behavior of higher animals and humans is characterized not only by innate, i.e. unconditional reactions, but also such reactions that are acquired by a given organism in the course of its individual life activity, i.e. conditioned reflexes.
Conditioned reflexes are a physiological mechanism for adapting the body to changing environmental conditions. Conditioned reflexes are such reactions of the body that are not innate, but are developed in various lifetime conditions. They arise under the condition of constant precedence of various phenomena to those that are vital for the animal. If the connection between these phenomena disappears, then the conditioned reflex fades away (for example, the growl of a tiger in a zoo, without being accompanied by its attack, ceases to frighten other animals).
The brain does not go on about only current influences. He plans, anticipates the future, carries out an anticipatory reflection of the future. This is the main feature of his work. The action must achieve a certain future result - the goal. Without preliminary modeling by the brain of this result, regulation of behavior is impossible. So, brain activity is a reflection of external influences as signals for certain adaptive actions. The mechanism of hereditary adaptation is unconditioned reflexes, and the mechanism of individually variable adaptation is conditioned reflexes, complex complexes of functional systems.
Neuron, types of neurons
Neuron (from the Greek nuron - nerve) is a structural and functional unit of the nervous system. This cell has a complex structure, is highly specialized and contains a nucleus, a cell body and processes in structure. There are over one hundred billion neurons in the human body. The complexity and diversity of the functions of the nervous system are determined by the interaction between neurons, which, in turn, are a set of different signals transmitted as part of the interaction of neurons with other neurons or muscles and glands. Signals are emitted and propagated by ions, which generate an electrical charge that travels along the neuron.
Types of neurons.
By localization: central (located in the central nervous system); peripheral (located outside the central nervous system - in the spinal, cranial ganglia, in the autonomic ganglia, in the plexuses and intraorganically).
On a functional basis: receptor (afferent, sensitive) are those nerve cells through which impulses go from receptors to the central nervous system. They are divided into: primary afferent neurons - their bodies are located in the spinal ganglia, they have a direct connection with receptors and secondary afferent neurons - their bodies lie in the visual tubercles, they transmit impulses to the overlying sections, they are not connected with receptors, they receive impulses from others neurons; efferent neurons transmit impulses from the central nervous system to other organs. Motor neurons are located in the anterior horns of the spinal cord (alpha, beta, gamma - motor neurons) - provide a motor response. Neurons of the autonomic nervous system: preganglionic (their bodies lie in the lateral horns of the spinal cord), postganglionic (their bodies are in the autonomic ganglia); intercalary (interneurons) - provide the transmission of impulses from afferent to efferent neurons. They make up the bulk of the gray matter of the brain, are widely represented in the brain and its cortex. Types of intercalary neurons: excitatory and inhibitory neurons.
It is an organized set of cells specialized in conducting electrical signals.
The nervous system is made up 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 captures stimuli from the environment (external stimuli) or signals from the same organism (internal stimuli), processes the information, and generates different responses depending on the situation. As an example, we can consider an animal that senses the proximity of another living being through cells that are sensitive to light in the retina. 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 bodily 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 CNS is made up 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 CNS are called sensory or afferent.
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 quickly and accurately send signals to other cells.
Connections between neurons can form circuits and neural networks that generate the perception 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.
Nervous system malfunction can result from genetic defects, physical damage, injury or toxicity, infection, or simply 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: The human nervous system. Introduction: basic concepts, composition and structure
At a functional level, the peripheral nervous system (PNS) and the somatic nervous system (SNS) differentiate 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, lowering and raising hormone levels, activating internal organs, etc.
To do this, it transmits information from the internal organs to the CNS through afferent pathways and emits information from the CNS to the muscles.
It includes cardiac muscle, smooth skin (which supplies the hair follicles), smoothness of the eyes (which regulates pupil contraction and dilation), smoothness of blood vessels, and smoothness of the 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 mainly responsible for preparing us to act when we feel a significant stimulus by activating one of the automatic responses (such as running away or attacking).
parasympathetic nervous system, in turn, maintains 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 CNS and thus transfer from the CNS 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 sensation from the body to the central nervous system (CNS). Efferent nerves are responsible for sending signals from the CNS 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 certain muscles, and regulating certain glands and internal organs.
I. Olfactory nerve. It receives olfactory sensory information and carries it to the olfactory bulb located in the brain.
II. optic nerve. It receives visual sensory information and transmits it to the vision centers of the brain via 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-tricoleic nerve. It is responsible for controlling eye movements.
V. Trigeminal nerve. It receives somatosensory information (eg heat, pain, texture...) from sensory receptors in the face and head and controls the chewing muscles.
VI. External motor nerve of the ophthalmic nerve. Eye movement control.
VII. facial nerve. Receives taste information of the tongue (those located in the middle and previous parts) and somatosensory information about the ears, and controls the muscles necessary to perform facial expressions.
VIII. Vestibulocochlear nerve. Receives auditory information and controls balance.
IX. Glossopharyngeal nerve. Receives taste information from the very back of the tongue, somatosensory information about the tongue, tonsils, pharynx, and controls the muscles needed for swallowing (swallowing).
X. Vagus nerve. Receives sensitive information from the digestive glands and heart rate and sends the information to the organs and muscles.
XI. Dorsal accessory nerve. Controls the muscles of the neck and head that are used for movement.
XII. hypoglossal nerve. Controls the muscles of the tongue.
The spinal nerves connect the organs and muscles of the spinal cord. Nerves are responsible for transmitting information about the sensory and visceral organs to the brain and relaying orders from the bone marrow to the skeletal and smooth muscles and glands.
These connections control the reflex actions that are performed so quickly and unconsciously because the information does not have to be processed by the brain before a response is given, it is directly controlled by the brain.
There are a total of 31 pairs of spinal nerves that emerge bilaterally from the bone marrow through the space between the vertebrae, called the foramen magnum.
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 CNS: white and gray. The white matter is formed by the axons of neurons and structural material, and the gray matter is formed by the neuronal soma, where the genetic material is located.
This difference is one of the reasons behind the myth that we only use 10% of our brain, since the brain is made up of about 90% white matter and only 10% gray matter.
But although gray matter seems to be made up of material that only serves to connect, it is now known that the number and manner in which connections are made have a marked effect on brain function, because if the structures are in perfect condition, but between they don't have connections, they won't work correctly.
The brain is made up 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 state that there is also a limbic lobe.
The cortex is divided into two hemispheres, right and left, so that the halves are present symmetrically in both hemispheres, with right frontal lobes and left lobes, right and left parietal lobes, 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 attributed to the functions of the sensory cortex, the association cortex, and the 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 certain point in the cortex, which forms 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, compared to the size of 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 located in the occipital lobe (in the groove) and this information has a retinotopic organization.
The primary auditory cortex is located in the temporal lobe (Brodmann's 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 sheath, while the olfactory cortex is located in the piriform cortex.
The association cortex includes primary and secondary. Primary cortical association is located next 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 root of the secondary association is located in the parietal operculum and processes the 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 processing high-level information and integrating sensory information with motor actions that are performed in such a way that they correspond to the perceived stimulus.
In addition, they perform a number of complex, usually human tasks called executive functions.
Basal ganglia
The basal ganglia (from the Greek ganglion, "conglomerate", "knot", "tumor") or basal ganglia are a group of nuclei or masses of gray matter (clumps of bodies or neuronal cells) that lie at the base of the brain between the ascending and descending white matter tracts and riding on the brainstem.
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 structures, the hippocampus.
The amygdala is almond-shaped and consists of a series 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 processes, attention, and some perceptual mechanisms.
The hippocampus, or hypocampal formation, is a seahorse-like cortical region (hence the name hippocampus, from the Greek hypos: horse and monster of the sea) and communicates in two directions 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, that 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, 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 the central and peripheral nervous systems 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, bulge, and mesencephalin.
This structure receives most of the 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 mainly from the cerebral cortex. Its main functions are coordination and adaptation of 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 link the CNS to the SNS, for example by receiving motor commands from the brain to the nerves that innervate the muscles so that they give a motor response.
In addition, he can initiate automatic responses by receiving some very important sensory information such as a prick or a burn.
Neurons – they are the workhorses of the nervous system. They send and receive signals to and from the brain through a network of interconnections so numerous and complex that it is quite impossible to count them or draw a complete diagram of them. At best, you can roughly say that there are hundreds of billions of neurons in the brain and many times more connections between them.Figure 1. Neurons
Brain tumors that arise from neurons or their precursors include embryonic tumors (previously called primitive neuroectodermal tumors - PNETs), such as the medulloblastoma and pineoblastoma.
Type II brain cells are called neuroglia. In the literal sense, this word means “glue that holds the nerves together” - thus, the auxiliary role of these cells is already visible from the name itself. Another part of neuroglia contributes to the work of neurons, surrounding them, nourishing and removing their decay products. There are many more neuroglial cells in the brain than neurons, and more than half of brain tumors develop from neuroglia.
Tumors arising from neuroglial (glial) cells are generally referred to as gliomas. However, depending on the specific type of glial cells involved in the tumor, it may have one or another specific name. The most common glial tumors in children are cerebellar and hemispheric astrocytomas, brainstem gliomas, optic tract gliomas, ependymomas, and gangliogliomas. Types of tumors are described in more detail in this article.
The structure of the brain
The brain has a very complex structure. There are several large sections of it: large hemispheres; brain stem: midbrain, pons, medulla oblongata; cerebellum.
Figure 2. The structure of the brain
If you look at the brain from above and from the side, we will see the right and left hemispheres, between which there is a large furrow separating them - the interhemispheric, or longitudinal fissure. Deep in the brain is corpus callosum– a bundle of nerve fibers that connects the two halves of the brain and allows information to be transmitted from one hemisphere to the other and vice versa. The surface of the hemispheres is indented by more or less deeply penetrating fissures and furrows, between which convolutions are located.
The folded surface of the brain is called the cortex. It is formed by the bodies of billions of nerve cells, because of their dark color, the substance of the cortex was called "gray matter". The cortex can be viewed as a map, where different areas are responsible for different functions of the brain. The cortex covers the right and left hemispheres of the brain.
It is the hemispheres of the brain that are responsible for processing information from the senses, as well as for thinking, logic, learning and memory, that is, for those functions that we call the mind.
Figure 3. The structure of the cerebral hemisphere
Several large depressions (furrows) divide each hemisphere into four lobes:
- frontal (frontal);
- temporal;
- parietal (parietal);
- occipital.
frontal lobes provide "creative", or abstract, thinking, expression of emotions, expressiveness of speech, control arbitrary movements. They are largely responsible for the intellect and social behavior of a person. Their functions include action planning, prioritization, concentration, memory, and behavior control. Damage to the anterior frontal lobe can lead to aggressive antisocial behavior. At the back of the frontal lobes is motor (motor) zone where certain areas control different types of motor activity: swallowing, chewing, articulation, movements of the arms, legs, fingers, etc.
Sometimes, before brain surgery, stimulation of the cortex is done to get an accurate picture of the motor area with an indication of the functions of each area: otherwise there is a danger of damage or removal of tissue fragments important for these functions.
parietal lobes are responsible for the sense of touch, the perception of pressure, pain, heat and cold, as well as for computational and speech skills, and the orientation of the body in space. In front of the parietal lobe is the so-called sensory (sensitive) zone, where information about the influence of the surrounding world on our body converges from pain, temperature and other receptors.
temporal lobes largely responsible for memory, hearing and the ability to perceive oral or written information. They also have additional complex objects. So, amygdala (tonsils) play an important role in the occurrence of such states as excitement, aggression, fear or anger. In turn, the amygdala is connected to the hippocampus, which facilitates the formation of memories from experienced events.
Occipital lobes- the visual center of the brain, analyzing the information that comes from the eyes. The left occipital lobe receives information from the right visual field, while the right lobe receives information from the left. Although all lobes of the cerebral hemispheres are responsible for certain functions, they do not act alone, and no single process is associated with only one particular lobe. Due to the huge network of interconnections in the brain, there is always communication between different hemispheres and lobes, as well as between subcortical structures. The brain functions as a whole.
Cerebellum-a smaller structure located in the lower back of the brain, under the cerebral hemispheres, and separated from them by a process of the dura mater - the so-called cerebellar tenon or tent of the cerebellum (tentorium). In size, it is approximately eight times smaller than the forebrain. The cerebellum continuously and automatically performs fine regulation of the coordination of movements and balance of the body.
If a tumor grows in the cerebellum, the patient may experience gait (atactic gait) or movement problems (sharp jerky movements). There may also be problems with the work of the hands and the eye.
brain stem descends from the center of the brain and passes in front of the cerebellum, after which it merges with the upper part of the spinal cord. The brain stem is responsible for basic bodily functions, many of which are carried out automatically, outside of our conscious control, such as heartbeat and breathing. The trunk includes the following parts:
- Medulla, which governs breathing, swallowing, blood pressure, and heart rate.
- Pons (or simply bridge), which connects the cerebellum to the cerebrum.
- midbrain, which is involved in the implementation of the functions of vision and hearing.
Runs along the entire brain stem reticular formation (or reticular substance) is a structure that is responsible for awakening from sleep and for arousal reactions, and also plays an important role in the regulation of muscle tone, respiration and heart rate.
diencephalon located above the midbrain. It includes, in particular, the thalamus and hypothalamus. Hypothalamus – it is a regulatory center involved in many important functions of the body: in the regulation of hormone secretion (including hormones from the nearby pituitary gland), in the functioning of the autonomic nervous system, digestion and sleep processes, as well as in the control of body temperature, emotions, sexuality, etc. Located above the hypothalamus thalamus, which processes a significant part of the information coming to and from the brain.
12 pairs of cranial nerves in medical practice, they are numbered in Roman numerals from I to XII, while in each of these pairs one nerve corresponds to the left side of the body, and the other to the right. The cranial nerve originates from the brain stem. They control important functions such as swallowing, muscle movements of the face, shoulders and neck, and sensations (sight, taste, hearing). The main nerves that carry information to the rest of the body run through the brainstem.
Nerve endings cross in the medulla oblongata so that the left side of the brain controls the right side of the body - and vice versa. Therefore, tumors formed in the left or right side of the brain can affect the mobility and sensation of the opposite side of the body (the exception here is the cerebellum, where the left side sends signals to the left arm and left leg, and the right side to the right limbs).
Meninges nourish and protect the brain and spinal cord. They are located in three layers under each other: immediately under the skull is hard shell(dura mater), which has the largest number of pain receptors in the body (there are none in the brain), under it gossamer(arachnoidea), and below - closest to the brain vascular, or soft shell(pia mater).
Spinal (or cerebrospinal) fluid is a transparent watery liquid that forms another protective layer around the brain and spinal cord, softening shocks and concussions, nourishing the brain and removing unnecessary products of its vital activity. In a normal situation, cerebrospinal fluid is important and useful, but it can also play a role harmful to the body if a brain tumor blocks the outflow of cerebrospinal fluid from the ventricle or if cerebrospinal fluid is produced in excess. Then the fluid accumulates in the brain. Such a state is called hydrocephalus, or dropsy of the brain. Since there is practically no free space for excess fluid inside the skull, increased intracranial pressure (ICP) occurs.
The structure of the spinal cord
Spinal cord- this is actually a continuation of the brain, surrounded by the same membranes and cerebrospinal fluid. It makes up two-thirds of the central nervous system and is a kind of conduction system for nerve impulses.
Figure 4. The structure of the vertebra and the location of the spinal cord in it
The spinal cord makes up two-thirds of the CNS and is a kind of conduction system for nerve impulses. Sensory information (touch sensations, temperature, pressure, pain) goes through it to the brain, and motor commands (motor function) and reflexes go from the brain through the spinal cord to all parts of the body. Flexible, made of bones spinal column protects the spinal cord from external influences. The bones that make up the spine are called vertebrae; their protruding parts can be felt along the back and back of the neck. Different parts of the spine are called departments (levels), there are five in total: cervical ( With), chest ( Th), lumbar ( L), sacral ( S) and coccygeal
