The human brain contains about 86 billion neurons. Each of these neurons connects to other cells, forming trillions of compounds. The contact site of two neurons or a neuron and a signal-receiving cell is called a synapse. Through these synapses, a nerve impulse is transmitted.
All this has been known to science for a long time. Scientists more than hundred years ago have found out, that each neuron works as the centralized excited element. Inside it, first incoming electrical signals accumulate, and then, when they reach a certain limit, the neuron generates and sends a short electrical impulse to the numerous branches – dendrites. At their ends are membrane outgrowths – spinules. An impulse is sent from these spinules. When the spines of one neuron are connected to the spines of the other, a synapse is formed. But this is only one of the types of contact. Synapses are also formed by the contact of the dendrites themselves, as well as the bodies of the neurons.
Nevertheless, a new study conducted by Israeli specialists from the Bar-Ilan University and published by the scientific journal Scientific Reports disproves the classical notions about the work of neurons.
1907, the French neuroscientist Louis Lapic proposed a model according to which the voltage in the dendritic spines of neurons increases as electrical signals accumulate. When a certain maximum is reached, the neuron responds with a burst of activity, after which the voltage is released. This also meant that if the neuron had not yet "collected" a sufficiently strong electrical signal, then it would not send momentum.
The next hundred years, neurobiologists studied brain cells based on this model. However, within the framework of new types of experiments, scientists proved that Lapik was wrong.
The old scheme of the work of neurons as a combined excitable unit (left image) and a new one with sensitivity to the right, left and bottom (right image)
, that each neuron functions not as a set of excitable elements. In fact, its dendritic processes can act in different ways. Roughly speaking, the "left" and "right" dendrites do not wait for the accumulation of signals to summarize them and generate an impulse. On the contrary, each of them "works" in its direction, creating completely different impulses.
"We came to this conclusion using a new experimental setup, but in principle, these results could be detected using technologies that existed since 1980 -ies. Belief in scientific discoveries of a hundred years ago led to this delay, "commented the leader of the work, Professor Ido Kanter.
Researchers decided to study the nature of the neural impulse itself – a burst of electrical activity. In one experiment, an electric current was applied to a neuron from different sides, and in another experiment scientists used the effect of multiple input signals.
The obtained results indicate that the direction of the received signal can significantly affect the neuron response. For example, a weak signal "on the left" and the same weak signal "on the right" the neuron does not add up and does not respond with an impulse. However, if a more powerful signal comes from one side, even he alone can trigger the neuron response.
According to Kanter, it is necessary to abandon the traditional notions and re-study the functional capabilities of the brain cells. First of all, it is extremely important for understanding the nature of neurodegenerative diseases. Perhaps neurons that are unable to differentiate between "left" and "right" can be the starting point for discovering the origin of these diseases.
New experiments also questioned the "spiky sorting" method used by hundreds of scientific groups around the world. The method helps to measure the activity of many neurons at once, but like others, it is based on assumptions that may soon be officially recognized as obsolete.
However, the primary task for neuroscientists was to understand how neurons "sort" incoming signals and on the basis of this form their "feedback". In addition, the authors note that they conducted experiments with only one type of nerve cells – pyramidal neurons. Although they are also pear-shaped, stellate, granular, irregular and fusiform.
In addition to medical applications, the discovery can be of great benefit for the sphere of creating more advanced artificial neural networks, scientists say.