Main article: Human body
Neuronal structure
The neuron cell contains the nucleus, cell body, and processes (dendrites and axons). If we can say so, then the neuron is the most "grown" cell in the human body, since its dendrites and axons stretch like wires, connecting the neuron to other neurons.
So, neurons connect to each other, forming biological neural networks. Basically, the circulation of excitement in these networks is our thinking, our feelings, this is us.
Neurons come in different sizes, ranging from 4 to 100 microns wide.
To represent their size, compare with the point in this text, its size is about 500 microns, i.e., one point can contain about 100 nerve cells.
Divergence - the ability of a single neuron to make numerous connections
Divergence is the ability of a single neuron to establish numerous connections with various nerve cells.
The video below shows the formation of neural systems. Growth of a living neural network.
Thus, each neuron can provide a wide propagation of momentum from one point to an entire organ or system. Also, thanks to the divergence process, the same cell can participate in the organization of various reactions and control more neurons.
In the course of research, the process of changing the structure of neural connections in a living organism was removed:
Synapse - connection between neurons
How nerve impulse is transmitted from one neuron to another
Contrary to popular belief, the transmission of a nerve pulse is not at all an electrical process (unlike the conduct of a pulse). All this is a chemical process that is carried out thanks to mediators.
Neurotransmitters - short-lived substances of local action; they are released into a gap between neurons and transmit a signal to neighboring cells. This whole connection of two neurons is called the synapse.
Why does the body need such synapses? Why can't you just continuously transmit a pulse? It is still impossible to say 100 percent, however, one thing is clear - such cracks allow you to better control and direct nervous processes in our body. Instead of simply conducting a pulse from point A to point B, our brain seems to arrange "checkpoints" at which it can slow down the pulse (make receptors insensitive to the neurotransmitter) or, for example, accelerate it (by increasing the number of mediator in the gap).
The entire process of transporting a neurotransmitter through a synaptic gap in animation is below:
Nerve impulses move at 402 kilometres per hour
The feeling of pain, in fact, comes instantly when you touch something hot or roll a needle. Thanks to our highly developed nervous system, a person can respond in less than a millisecond to things to stay away from.
Nerve impulses are so fast that the electrical signals responsible for sensations travel to and from the brain at an average speed of 402 kilometers per hour.
Myelin prevents nerve impulses from dissipating
The myelin sheath is an electrically insulating fatty white sheath covering the axons of many neurons.
Myelin builds up on the most commonly used pathways in the brain. Neurons with myelin transmit electrical signals 10 times faster than neurons without myelin.
Myelin is interrupted only in the area of Ranvier interceptions, which occur at regular intervals of 0.2 mm - > 1 mm. Due to the fact that ion currents cannot pass through myelin, the entry and exit of ions is carried out only in the area of interceptions. This leads to an increase in the speed of nerve impulse. Thus, for myelinated fibers, the pulse is carried out approximately 5-10 times faster than for non-myelinated fibers.
The myelin sheath is formed by glial cells: in the peripheral nervous system - Schwann cells, in the central nervous system - oligodendrocytes. The myelin sheath is formed from a flat outgrowth of the body of the glial cell, repeatedly wrapping the axon like an insulating tape.
The total length of myelin fibers of the human brain (including fibers that connect the hemispheres to each other, forming the so-called corpus callosum) is estimated at about 150 thousand kilometers. This is equal to four circles of the Earth's equator.
How neurons analyze incoming impulses
Each of the neurons is capable of receiving hundreds of messages per second
In order not to be overloaded with information, he must be able to judge the degree of its significance and do its preliminary analysis.
This computational activity takes place inside the cell. Excitatory pulses are added there and inhibitory pulses are subtracted.
And in order for the neuron to generate its own momentum, it is necessary that the sum of the previous ones be greater than a certain value.
If the addition of excitatory and inhibitory pulses does not exceed this limit, the neuron will be "silent."
Formation of new neurons
Neurogenesis and synaptic pruning
The brain has the ability to neurogenesis, that is, to form new neurons, only during intrauterine development, until the first months of life.
However, in the first three years of life it forms the maximum number of synapses. According to some studies, a baby three years old has about a million billion contacts in the brain: each neuron comes into contact with another at least 15 thousand times.
An adult retains about half of these compounds. A very curious choice of evolution: instead of accumulating connections, she chose to create an excess of them, so that she could then calmly sacrifice excess.
This process is called synaptic pruning.
The study of neurogenesis (the formation of new nerve cells - neurons) is a relatively new direction of research. In recent years, it has been proven that new neurons throughout life are formed in the brains of many mammals, but there is still no consensus in the scientific community on the issue of human neurogenesis by 2019.
New imaging techniques (such as confocal microscopy) have made it possible to prove that at least before puberty, new neurons are formed in the human hippocampus - a brain region involved in the formation of emotions and memory.
Studies show that in the dentate fascia (the part of the brain where neurogenesis occurs) there are thousands of young, not fully formed neurons in all samples, regardless of the age of people. However, the older a person is, the smaller the dentate fascia of cells that produce substances that are associated with the brain's ability to rearrange existing neural connections and form new ones.
In conclusion, we can say that after all, new neurons also appear in adulthood, but they form fewer connections with each other and other neurons, or migrate to other parts of the brain less often, so we cannot call this complete regeneration.
Effect of alcohol on foetal neurons
In moderate doses, alcohol does not kill adult neurons, but it can have a strong effect on developing nerve cells.
Since almost all neurons form and move to their places before birth, the fetal brain is very susceptible to alcohol.
Alcohol can kill newly born neurons, hinder their birth, and prevent them from moving from their birthplace to their final residence.
Even a short-term increase in blood alcohol levels can be enough for some fetal nerve cells to die.
Glial cells - glue for neurons
Glial cells really, as scientists previously thought, play the role of glue - they surround neurons and hold them in a specific place.
In addition, they supply the neurons with fuel -- nutrients and oxygen -- and work as electricians to build myelin sheaths that regulate potential transfer along axons.
They mastered glial cells and the profession of janitors - they delay pathogens and eliminate neurons that have stopped all activity.
Without these important functions of glial cells, the human brain could not function as efficiently as it does now.
How we lose nerve cells from birth
How many neurons (nerve cells) are in the human brain? We have about 85 billion of them. For comparison, the jellyfish has only 800, the cockroach has a million, and the octopus has 300 million. Many believe that nerve cells die only in the elderly, but most of them are lost by us in childhood, when the process of natural selection takes place in the child's head. As in the jungle, among neurons, the most efficient and adapted survive.
Is it true that the human brain works like a computer?
Main article: Human brain
This is not entirely true, because the human brain is much more powerful. The computer works in series, and the human brain is parallel. This is due to the fact that neurons perform all the functions of a computer at the same time - memorization, reproduction, storage.
One memory cell of a computer can have only one of two values, and the brain is much more complex in this regard. Neurons have so-called spines - processes that are responsible for connecting and obtaining connections. This is a direct analogue of zero and one in the computer's memory data cell. A single neuron can have more than 20 connections. This suggests that our brain is so perfect that computers will not be able to approach it in terms of performance, most likely never.
Rol neurons in memory
The physiological basis of memory is the "traces" of previously former nervous processes that persist in the brain. Any nerve process caused by external irritation (for example, the transfer of an image of a pattern to the brain) does not pass for the nervous tissue without a trace, but leaves a "trace" in it in the form of certain functional changes. Thus, when certain information is perceived, a connection is formed between some groups of neurons, which encodes this information. And the more often this information enters the brain, the more often the nerve impulse passes through the connection and the more the connection is "fixed."
When we see, for example, the drawing again, the nerve impulse will pass along a familiar path and the connection between certain neurons will become even stronger, and so on.
According to recent studies, the material carrier of information about different events is not the excitation of different neurons, but various complexes of neural networks, which are formed at the moment of perception of information.
Below is a recording of an experiment on this topic: here neurons form new connections between themselves right in the test tube.
Neurons specializing in facial recognition
In the visual area of the brain, there are neurons specializing in facial recognition. They analyze facial features, primarily the shape of the eyes, and classify them as "human faces."
After that, they compare these images with images stored in memory. As a result, we can quickly recognize the faces of our relatives and acquaintances.
When this area of the brain is affected, it becomes impossible to recognize faces, even the most familiar, despite the fact that vision and recognition of other objects can remain at a normal level.
Reading thoughts
Main article: Reading thoughts
Artificial neurons
2023
Nerve networks have begun to print on a 3D printer using new biotechnils
A team of Monash University researchers used biochernils containing living neurons and non-cellular materials that, when printed, formed three-dimensional neural networks. This was announced on September 20, 2023 by Monash University.
Networks can grow in the laboratory and respond to nerve signals. Researchers were able to simulate the location of "gray" and "white" matter in the human brain. Gray matter neurons were found to grow into a layer of white matter. "They used it as a highway to communicate with neurons in other layers," the authors explained.
Previously, studies used two-dimensional structures of nerve cells, but they do not fully reflect the process of neuronal growth and interaction with the environment.
 | Neural networks created as part of the study fairly accurately reflect the three-dimensional nature of neural circuits in the living brain, in which nerve cells expand processes called neurites to form connections between different layers of the cortex of the brain, said Professor John Forsyth, who leads the study. |  |
Forsyth added that the researchers not only managed to recreate the structure of the brain, but also the real behavior and actions of neurons.
Electrophysiological measurements showed neural activity in the artificial nervous network. This is a breakthrough in the fields of neuroscience and bioprinting.
Printed nerve networks can be used in research examining how nerves form and grow and their connections. This way scientists will be able to understand how various diseases affect the transmission of nervous reactions, as well as check what effects drugs have on nerve cells.
Other advances in bioprinting were recently introduced by scientists in Germany. Their bio-ink made it possible to print pulsating ventricles of the heart.[1]
Artificial neurons have been developed that can connect to those living in the human body
In mid-January 2023, information emerged that researchers at Linköping University in Sweden have developed artificial neurons that demonstrate 15 of the 20 characteristics of biological neural cells and can communicate with natural neurons in the body. The scientists called their device an "organic electrochemical conduction-based neuron" (c-OECD).
c-OECD is based on materials capable of conducting negative charge, including organic electrochemical transistors and n-type conductive polymers. By printing thousands of such transistors on a flexible substrate, the researchers were able to create artificial neurons. The device uses ions to control the flow of electricity, similar to biological neurons, and for now the Swedish team has demonstrated that it can drive the vagus nerve in mice, suggesting that it has great potential for application in. to medicine
The artificial neuron c-OECD is an example because it uses ions to control the electricity that passes through it, similar to how biological neurons do by opening and closing ion channels. Scientists hope these artificial neurons can help create more realistic neural control in a variety of medical technologies. Artificial neurons use ions to control the electricity passing through the conductive polymer inside them, resulting in voltage surges that mimic what happens in real neurons. The technology allows the device to increase and decrease current in a near-perfect bell-shaped curve in a controlled manner, which resembles electrical activity in neurons that is controlled by sodium ion channels.
For January 2023, the researchers tested the technology in mice and implanted printed neurons for the purpose of controlling the vagus nerve. Neurons successfully interacted with the vagus nerve, leading to a 4.5% decrease in heart rate in mice[2]
Researches
1860: First description of neuron Otto Deuters
This drawing was made in 1860 by the young German anatomist Otto Deuters. At that time, he was only 26 years old.
This is the first full description of the classical neuron in history, in which dendrites and axons were isolated.
Otto Deuters died of typhus at only 29 years old, but managed to do a lot in neuronanatomy.
Technologies for neuronal research
2023
In Russia, developed the technology of growing brain cells
At the end of November 2023, Belgorod State University announced the development of neuronal culture technology. Thanks to it, it will be possible to determine the influence of neurotoxins or neuroprotectors on the intensity of cell respiration.
As Gazeta.Ru was told in the Ministry of Education and Science of the Russian Federation, scientists created a method for growing a primary mixed culture of hippocampal neurons (the brain department that is responsible for short-term memory and subsequent translation of information into long-term memory) of an 18-day-old embryo and newborn rodents. In this way, it is claimed, neurons of different species can be grown. This method also avoids gliosis and acidification of the medium.
The technology can be further used in screening preclinical studies and testing of pharmacological substances. Another potential area of application of the development is the selection of the right conditions for growing neurons already at the initial stages of cell differentiation, added Marina Skorkina, project leader, senior researcher at the Laboratory of Genetic Technologies and Gene Editing for Biomedicine and Veterinary Medicine.
It is noted that in their experiment, scientists used special devices for growing cell cultures twice as much as were used before.[3]
In Russia, learned to grow brain cells from auxiliary living tissue
In Russia, they learned to grow brain cells from auxiliary living tissue. Scientists from the Institute of Cytology of the Russian Academy of Sciences (INC RAS) shared their achievement in August 2023 with colleagues from St. Petersburg Polytechnic University Peter the Great. Read more here.
In Russia, for the first time in the world, it was possible to "reprogram" a single neuron in the brain
A team of Russian and foreign scientists, as part of an experiment on mice, was able to change the nature of the work of a single neuron of the brain for the first time. This was reported to the Russian Scientific Foundation (RNF) in mid-April 2023.
It is noted that this experiment confirmed the widespread ideas among scientists about the plasticity of the central nervous system. The phenomenon of plasticity plays a key role in the fact that living cells in the brain are able to simultaneously both store and process information.
| | We have shown that by artificially activating a single neuron, it is possible to change its response to the visual stimulus. This proves that neurons change their properties, for example, when learning and creating new connections between cells in the process of remembering information, "Alexey Malyshev, director of the Institute of Higher Nervous Activity of the Russian Academy of Sciences, described the results of the study. | |
At the heart of human memory, the ability to learn and change their behavior depending on the situation, is synaptic plasticity, that is, the ability of nerve cells to change the strength of connections with each other. This property is that the synapse - the place of contact between neurons - can transmit a signal from one cell to another with different efficiencies. So, for example, if we remember any information, the connections between the neurons responsible for its "preservation" become more stable and the transmission of impulses between these cells is enhanced.
Due to the fact that the mammalian brain consists of tens of millions of neurons, it turns out to be quite difficult to track the connections between individual cells. In this regard, synaptic plasticity is most often studied in simplified biological models - for example, cultures of nerve cells grown in petri dishes. However, the work of the neural network of the whole brain is much more complicated: cells are affected by various biologically active substances constantly present in the brain, such as dopamine and serotonin, as well as random signals from neighboring cells. To account for all these exposures, researchers are developing methods to investigate synaptic plasticity directly in animal brains.
To investigate the plastic properties of neurons, the researchers activated the cell through the fiber connected to it at the moment when a less preferable picture was presented. It turned out that when the mouse looked at a hundred pictures that initially caused weak activation of neurons, but combined with stimulation through fiber, the cells rebuilt and began to "consider" these images preferable.[4]
Russian scientists have created cell tomography technology that will speed up the process of detecting diseases
The cell tomography technology was proposed by a team of researchers from NUST MISIS, Moscow State University named after M.V. Lomonosov and VNIIOFI. It will overcome the limitations of phase and absorption microscopy methods, which analyze only a single cell of the correct shape. In the future, using a local tomograph, it is planned to study the subcellular structures and cytoplasm during the functioning of the neuron, which will bring scientists closer to understanding how the human brain works, representatives of NUST MISISiS told Zdrav.Expert on March 9, 2023. Read more here.
Mature neurons from stem cells first created
On January 12, 2023, American researchers from Northwestern University (Illinois) reported receiving the first highly mature neurons from induced pluripotent stem cells (iPSCs). This opens up new possibilities for the therapy of neurodegenerative diseases.
In the course of previous work, scientists have already differentiated stem cells into neurons, but they were functionally immature and resembled neurons in the early stages of development. The limited maturation that current stem cell culture techniques provide reduces the potential for neurodegeneration research. The solution to the problem was proposed by specialists from Northwestern University.
The team first differentiated human iPSCs into motor and cortical neurons, then placed them on coatings made of synthetic nanofibers containing fast-moving "dancing" molecules. The proposed technology solves several important tasks at once. It allows you to get more mature neurons that show improved electrical activity. In addition, such neurons are more disposed to establish synaptic connections. In addition, they stick together less compared to typical stem cell-derived neurons.
Mature neurons, according to the researchers, open up entirely new avenues for studying neurodegenerative diseases such as amyotrophic lateral sclerosis, Parkinson's disease, Alzheimer's disease or multiple sclerosis. In addition, neurons can be transplanted into patients with spinal cord injuries.
| | We confirmed that neurons coated with our nanofibers reach greater maturity compared to other methods. Mature neurons are better able to establish synaptic connections that are fundamental to their functioning, "said Professor Samuel I. Stupp, co-author of the study.[5] | |
Notes
- ↑ Researchers `bioprint` living brain cell networks in the lab
- ↑ Artificial Neuron Uses Ions Like the Real Thing
- ↑ Russia has proposed an effective way to grow brain cells
- ↑ Specialists for the first time "reprogrammed" a single neuron in the brain
- ↑ Mature ‘lab grown’ neurons hold promise for neurodegenerative disease
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