KIDS: DisCover the Genesis of the HuMan Brain

Its tools: 100 billion neurons and an incalculable number of connections. Its "language": minimum electrical currents and about 50 chemicals. Its functions: supervise the work of the body, process outbound signals from the outside, store memories and, above all, allow us to reason. Is the sole reason of our existence is called the BRAIN

It is the most complex and mysterious organ you know: 1,300-1,500 grams of gelatinous tissue, made up of 100 billion cells (the neurons ) each of which develops on average 10,000 connections to neighboring cells. Here is, in summary, how it is shaped, how it is organized, how it defends and how the brain works .

ALL IN EIGHT MONTHS

During fetal life , the body produces no fewer than 250,000 neurons per minute. But 15 to 30 days before birth, production stops and for the brain begins a second phase that will last for a lifetime: the creation of cell connections. In this process, the cells that fail connect are eliminated, so that at the time of birth they are already halved.

THE THREE BRAINS

The human brain is the result of overlapping the three types of brain that emerged during the evolution of the vertebrates.

From the bottom (to the base of the skull), the oldest brain , specializing in the control of involuntary functions such as vigilance, breathing, circulation and muscle tone. It includes the cerebellum and the parts of the spinal cord that stretch in the brain.

There is also mesencephalon : a small portion of nervous tissue consisting of the so-called brain stems and the quadrilateral lamina.

Lastly, there is the prosencephalon , the most "modern" part, subdivided into Diencephalon and telencephalon. The first, also called "limbic system" , contains structures such as thalamus , hypothalamus , hypophysis and hippocampus , from which sensations come as hunger, thirst or sexual desire. Finally, the most recent part: the bark (Also known as cerebral cortex), where the functions of intelligence and language are based.

The bark occupies most of the skull, so its volume is easily perceived. It is difficult, however, to imagine how extensively it is. The bark is in fact covered by deep fissures (cerebral circumcisions) so that if we could "stretch it" it would occupy an area many times greater than that of the head.

The deeper slit is the one that separates the two hemispheres, combined with the callous body , a very heavy texture of nerve fibers: if they recessed, the two hemispheres would no longer communicate. The other major slots distinguish the so-called "lobes". The major ones are temporal (hearing and balance), frontal (voluntary movements), parietal (tactile sensitivity and taste) and occipital (vision).

To wrap the encephalus, we find the membranes called meninges (mother palm, arachnoid and hard mother): Contrary to what the phrases are suggested, they do not need to think, but to nourish and protect the real brain.

Always for a protective purpose, the encephalus is finally passed through a series of cavities full of liquid (Cerebrospinal fluid) which creates a sort of "floating effect" useful to counteract the force of gravity and accelerations due to the rapid movements of the head.

There is finally a brain defense that, unfortunately, makes it difficult to lose weight by command. If a fast tends to squeeze more muscles than fat mass, it is because the brain defends itself.

Its nourishment is sugars, and neurons are not able to demolish the fats to make sugars. Therefore, those available immediately in the liver, use the proteins (meanwhile the body also crushes the fat) and stomach the muscles. Better so, because most of the nerve fibers are "isolated" by a sleeve - the myelin sheath - made up of fat ... if the neurons could "eat" them, as in a disease called multiple sclerosis it would be impossible to do the activity cerebral.

NEURON: THE CELL-BASE

Let us come to the bones of the brain, neurons : cells specialized in collecting, processing and transferring nerve impulses. From their cellular body they spread different branches: dendrites , and a larger branch of the axon . The first receive of incoming signals, the second outputs which is the outgoing messages. Thanks to dendrites and axons, the total number of connections that a human brain's neurons can achieve exceeds the number of all celestial bodies in the universe.

The existence of these connections, or synapses , was discovered at the end of the nineteenth century by English physiologist Charles Scott Sherrington, although this is not a physical connection because a microscopic slot is always interfered between two neurons. To overcome this passage, the signals change: from electric to chemical. Termination of the axon releases substances, called neurotransmitters, which are harvested by the appropriate receptors present on the lens cell membrane.

Taken the neurotransmitter, the chemical message is converted into electric impulse. To make the trip faster, on the ax, the impulse will leap. In fact, the axon is covered with an insulating material called "myelin sheath", which, however, reveals a few points: the knots of Ranvier. And "jumping" from one knot to the other, the impulse reaches 400 km / h.

CHEMICAL MESSAGES

The neurotransmitters are like the words of a language limited but very complex, consisting of just fifty words, but able to provide detailed instructions. Unfortunately, there is not yet a vocabulary to translate chemical messages, but we can at least group neurotransmitters into two distinct groups: fast acting ones and slow action.

Among the first are molecules such as acetylcholine , adrenaline , noradrenaline , dopamine , serotonin : small molecules, which have the task of causing immediate responses, from the perception of a perfume to the reaction (for example, a smile ).

Of the second group are the " neuropeptides " (the most known are somatostatin and beta-penicillins): large molecules, slow to act but capable of inducing lasting changes. They give shape to the synapses, for example, but they can also reduce receptors for a certain neurotransmitter, making the neurons "deaf" to certain commands.

MEMORIES AND THERE "FACILITATED" ROUTES

We have already seen that two neurons, to communicate, exchange chemicals that induce them to generate particular electrical impulses. Imagine you repeat this process millions of billions of times, and you have described, albeit in a simplified way, the transfer of information (visual, acoustic ...) within a neuronal circuit of the human brain. But what does this have to do with learning, memorizing, and remembering processes?

Let us see a simple case. Let's imagine, for example, catching a flower never seen before and featuring a delightful scent. This type of information will travel from the olfactory mucosa membrane (the inside of the nose that "smells"), along the olfactory nerve, to the part of the cerebral cortex organized to analyze and understand perfumes. In doing so, the information will cross a huge number of synapses by creating the equivalent of a neuronal "path". By repeating the experience, the information will travel again along the same path, reinforcing it even more, just as the passage of many people into a forest creates an authentic path.

ACCUPPED MEMORIES

This process, called "facilitation" is probably the physical basis of learning and memorizing processes: when information has passed a large number of times through the same synapse sequence, the synapses themselves are so "facilitated" that even different, but relevant, signals or impulses (eg the name of the flower having a certain scent) generate a pulse transmission in the same synapsis sequence. This determines in the subject the perception of the experience many times before, that is to hear that pleasing scent even if the perfume is not actually "felt".

The same happens when you try to store a new phone number or a new number on the ATM: it will need to be recompiled several times before you can lock it into memory. Unless you use storage strategies that link the new number to already-traced paths ... it would be easy to recall a number like 191518 by linking it to the concept of "World War I" (begun in 1915 and ended in 1918).

This mechanism also explains another small mystery: why ever, when we learned a song or poem, is it so difficult to recite it from the second verse and not from the beginning? Precisely because the whole storage is part of an "easy" path: just by taking it from the beginning you can trace it without difficulty.

Obviously, the process of learning is much more complex.

BUILT IN CONSTRUCTION

But one thing is certain: at the base of memory there is " neural plasticity . With these words it is defined the ability of the brain to mold itself through the continuous remodeling of old synapses and the creation of new synapses. The brain is in constant remodeling, and that is why it is necessary to keep it in operation to ensure its efficiency.

Of course, it is legitimate to think that learning is something more than restructuring a number of synapses ... but there is a concrete proof that without neural plasticity we would no longer be able to learn. Not even to memorize the "Vispa Teresa".

First of all, the brain must be able to quickly produce new proteins. The simple expulsion of the neurotransmitter from the end of the ax requires the presence of proteins: their task here is to push the full-length neurotransmitter vesicles close to the presynaptic membrane. Other proteins have a similar function to cranes in building constructions: they move dendrites and axons into new locations where they can connect with other cells out of reach. Well, it has been noted that the use of drugs capable of blocking protein synthesis also blocks learning and memorization. The brain, in short, does not learn unless it changes.

THE PASSED WAREHOUSE

But where do we physically end the things learned and memorized? How are complex memories stored? Even here, it's not all clear. However, we know that memories are not stored in the brain as photographs, but are actually decomposed into their constituents (color, taste, movement, depth, intensity, sound, and so on).

The biggest mystery is how to make the fragments scattered in the various areas of the brain to recompense, if necessary, in a few thousandths of a second, re-emerging the full memory. Easier, however, is to understand why some memories are lost (or voluntarily disappear): it is enough for the "facilitated" path between synapses to erase or weaken, and the memory becomes inaccessible.

WHAT IS HOMUNCULUS

The brain has many other functions, in addition to learning and memory. In particular, it acts as a control center for sensations and movement. And researchers have built with a certain precision the sensory and motor map of the brain. As? A system is to apply minimal electrical stimulation in precise areas of the bark during surgical interventions in local anesthesia and to ask the patient what sensations are to test. Conversely, peripheral stimulation (for example, a puncture on one foot) produces a bark in the cortex electrical signal that can be detected, for example, to magnetic resonance imaging. The same applies to the motor cortex, whose electrical stimulation can produce a specific movement and vice versa.

Hence the homunculus was born , ie the representation of how the human body would be if all the organs were proportionate to the brain areas that controlled them: big head (with bigger tongue), huge hands, organs of meaning, genitalia tiny, insignificant muscles and so on.

BACK RIGHT AND LEFT

With the same technique, the way in which the two hemispheres of the brain, which are essentially identical, have been divided into several functions . The right hemisphere is more specialized in spatial and synthesis tasks such as reading maps, performing geometric designs, recognizing faces, and musical sensitivity.

The left hemisphere prefers the expression and understanding of language, the analysis of details, symbolic reasoning. It is also related to this differentiation between the hemispheres also some statistical differences between the two sexes : men, who mainly use the right hemisphere, are better in spatial orientation and mathematical logic, women in the vocabulary richness and in the ' manual skill.

And the remarkable difference in volume between male and female brain exists, but only because the male is bigger and has more muscles, so his brain needs more control work: however, the bark with cognitive functions, however, is the extension of the same in both sexes.

There is, however, a disparity, less known, which manifests itself in the hemispheric level: in women the two cerebral hemispheres are on average more similar to each other. Consequently, in the case of a disease affecting only a hemisphere, the recovery capacity of the woman is significantly higher than that of the male.

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