The Attention Deficit Disorders or: pay attention!

The idea that made me write this entry arose over a photograph that I took of a cardinal bird, honestly I just saw the cardinal but my good friend Roberto Estévez made me a comment: it seems the bird is looking at you!.

My response to that comment was that surely the bird was watching paying attention to every detail since they are being a wild creature there are around several predators, also because it has to compete for food.

Two days later, my husband went to a meeting to another city and when he called explained me he was surprised and upset with so many people around, because it looks like everybody was absorbed by sending messages on their cell phones and they seemed not to look at who was at their side, making any walk a struggle for space and attention. Even drivers seemed to not be pay attention or remember that there was a  junglearound them.

An extra element to write this was the constant news about how more and more children are diagnosed with Attention-Deficit Disorder all of them highlighting that is alarming the number of cases submitted.

What "experts" don’t know

Ok, who am I to say experts don’t know something?, Maybe they don’t say this because to much complexity don’t sell enough magazines, but the thing is the attentional process is given to the survival of the species (not a school term) to provide tied sensory mechanisms to protect themselves from the dangers of the environment or to provide the capacity of food and caring for the offspring.

Imagine a rabbit focused on its inteligent phone screen or just looking at the female bunny front him without paying attention to the smell of possible predators, without looking at if something strange moves around, without listening to the movement of the wind and the leaves. While you are reading this, the rabbit was already attacked byyour cat, a hawk, a more attentive rabbit fornicated with the beautiful rabbit it was trying to conquest and our rabbit lost the chance of eating and of course, it  lost its cell phone in the confusion. 

What happens when a species loses its capacity of adaptation to the environment or they are unable to respond to the warning signs?, simple, extinguishes!. Therefore the capacity of attention to the environment is so important.

Now let’s return to the attention deficit deficit issue, psychologists and teachers believe that children do not have the ability to pay attention, just because does not see me as I speak them or have no view stuck on the Board or on the display, and also dare to be multitasking! that sounds, what do  these children believe?.

Let`s go by steps: attention is not an action, it is a process which involves all the senses and other superior processes such as working memory. 

Although someone can have their eyes focused on a screen, that person can hear the click, click of the keys, other noises of the environment, as the television or Spotify, or even  he or she can smell the environment, for example if something is burning, and we can’t  forget is feeling  the position of  his or her body over the chair. 

So I am sorry but even if someone ask me to pay attention to only onething, there is no way to disconnect the cranial nerves or sensory areas and even less the information flowing between the areas of association or biochemical information flow, or erase years of evolution, that is foolish.

What you have is selective attention, which is captured naturally if a stimulus is interesting, enjoyable, or dangerous. Yes, if I see someone going to hit me I move to avoid any contact because we usually react quicklier to fast movements different than slow movements.

Selective attention is one of the problems of many children, but does not only tell someone pay attention!, when I hear that I wonder to which put attention?, do to your speech, to the intensity of your words, your choice or how you move your mouth?.

There is evidence that we evolved to looking at the lips and face of other persons to recognize emotional emphasis in speech, and of course the gestures.

But attention cannot be sustained for long time, eyes tend to move, noises of the environment will cause that there is another source of attention, and it’s not only an extreme noise, in a classroom where you can hear the thoughts, even the hint of a pencil or a pen on the paper can cause a rotation of our heads to find the focus of noise. And if someone pulls out a pencil tip during an examination?, if... we are going to flip, because naturally, the ears are intensified, since that may depend on our life.

Many people then, to forget these natural principles, but it doesn’t mean they don’t knkow it,  I believe they sometimes forget that we are not experts, but how can we avoid years of evolution and selection natural and that attention as a mean of survival depends on the environment, then says that if a child not focuses attention on one single thing  has a  damaged brain.

Schools of the 16th century, which were basically churches built to avoid the temptations, where you can hear a yawn to far because of those wonderful domes and the acoustics that allows you to hear every note of praise choir, it was clear that meditation was the best way to listen to God, but if we see them as laboratories, it was certainly possible to maintain attention because after the first time of admiration, there isn't much to see.

But today at any place away from home or school, children face the streets, where cars are moving at a certain speed, there are many people talking, they must  pay attention to traffic lights or the movement of the cars to know when crossing the streets, and pay attention to so many other persons around and even notice if the light is red or if a driver may decide that being in a hurry is worther than a life. Also  if mom is  texting while crossing street, so she is not careful while people is crossing and hit eachother, and there is a bicycle in the opposite direction... and trees move and birds singing…

Attention on the natural environment

We have asked children to  focus  on something or someone, do not you look anything else!, and at the same time have increased the transit accidents, in particular those fatal accidents because people are not able to attend all stimuli a round such as number of passengers in the car, number of cars around, number of hours of monotonous journey or level of danger at the intersections  are factors of the most serious accidents.

To this we must be add that we learned to pay attention to the voice that speaks or the screen. Ups, if you drive don't send text messages!.

What do happen to children in the family environment?, children vie for attention of parents or caregivers that are between the cell phone, Facebook, twitter, television, problems at work, trying to finish a proposal while cooking, the dog barks, siblings yells, brother shouts stronger and if they ask for a little attention with the wonderful phrase as “look what I did!”, sometimes only receives a: “not now”,  “I can't answer”, “leave me alone”, “perhaps later”, and sometimes a good!, without even looking at what the child  did, or sometimes only receives a grunt in response. Who can meet the request of the child when there are many things by turning at the same time?.

Teachers complain that they are between 15 and 20 children, all looking for their  attention, talking, making noises, of course they want a little peace!, but their  reaction is to say to everybody: if you sit down and cab be quiet, you will look prettier!, and if any of them dare to stand up without permission no doubt some children will win a visit to the and a flight non stop with all expenses paid to the psychologist’s office, who is faithful friend of the ignorance of the neurodevelopmental but who knows very well how not only apply harmless tests and without context, also know how to ask money for them as if they  are useful.

Attention to the brain

I won't say that attention-deficit disorder does not exist, the brain studies show differences in anatomical and electrophysiological brain mechanisms in children affected with one of three types of 3 attention deficit disorders. Hey! Wait a second: 3?  everyone is talking only about deficit of attention disorder!, when have you seen a happy meal with three toys?. The popular side of the disorder usually don’t talk  about it, but there are three types, the hyperactivity, inattention, and the combined type attention deficit disorder.

Neurological studies show that children with attention deficit have a slow brain development a lower overall, but specifically the cerebellar, volume especially in portions postero inferior (lobes VIII to X) as well as the vermix, the volume of the nigra substance in the right frontal gyrus and putamen are at the same time lower than the brains of healthy children, however it is worth mentioning that this can not be seen with a test in a doctor's Office.

The main problem with the diagnosis of the call children epidemics, i.e attention deficit deficit  and never well recognized autism, is that manuals of diagnostic observed clinical and non-neurological shunts, what I mean is diagnostics are based on subjective observations reported by parents, teachers based on questionnaires that analyze the inattention, impulsiveness, and hyperactivity under criteria such as "often"regardless of the contexts in which behaviors are manifested.

Occasionally apply two or three tests, is observed to the child, and as an immediate response to the problem, it prescribes a pill, and is sent to the world with a diagnosis that for better or for worse will follow throughout all  life.

But, what if the child was not the problem?, andif the problem is the environment?, and if rather than ask parents how the child behaves asked how parents and teachers to behave with the child?, what do happen when children ask something? Do we ignore them?, if when children speak they are ignored  so we push them to  do something extrem like a stop breathing and vomiting the carpet so that caregivers give them 2 seconds of attention.

Yes, because like the screen that jumps so we notice we have received a new message, an update or a new email, the child jumps, makes noise, not to disturb the world, but to say: "here I am,  pay me attention!".

The environment is chaotic, certainly to survive must pay attention to many stimuli, but is not the case  that we are becoming psychotic, reality is that way, or  the car will run and hit us, the boss asks us something that we don't know how to do because we lost the sticky note where we detailed instructions, overflowing emails and accounts invoices do not stop. The reality is that each one must find a way to adapt to the environment and does not expect the environment adapts to each of us.

References:

Bernfeld, j. (2012) ADHD and factor analysis Are there really three distinct subtypes of ADHD? Applied Neuropsychology Child. 1 (2) 100-104.

Fernandez Perrone, a., Fernández - Mayoralas DM, & Fernandez-jaen, a. (2013) of attention deficit/hyperactivity disorder: inattentive to the restrictive type type. Revista de Neurología. 56 (Supl 1) S77-S84.

Kiyonaga, a., & Egner, T. (2013) Working memory as internal attention: Toward an integrative account of internal and external selection processes. Psychonomic Bulletin & Review. 2 (2) 228-242.

Klauer, SG., dinghys, TA., Neale, VL., Sudweeks, JD., Ramsey, DJ. (2006) The impact of driver vigilance on near-crash risk: An analysis using the 100-Car naturalistic driving study data. Available at: http://trid.trb.org/view.aspx?id=786825

Koziol, LF, Budding, & D. (2012) ADHD and sensory processing disorders: Placing the diagnostic issues in context. Journal of Applied Neuropsychology Child. 1 (2) 137-144.

Mules, f., Gandia, r., rock, p., Etchepareborda MC., Abad, l. (2012) update drug of attention deficit/hyperactivity disorder: intervention models and drugs. Revista de Neurología. 54 (Suppl 3) S41-S53.

Ramos-Quiroga, JA., Chalita, PJ., Vidal, r., Bosch, r., Palomar, g., Prats, l., and houses, M. (2012) diagnosis and treatment of attention deficit disorder / hyperactivity in adults. Revista de Neurología. 54 (Supl 1) S105-S115.

Schmidt, EA., Schrauf, M., Simon, M., Fritzsche, M., Buchner, j., Kincses, WE. (2009) Drivers' misjudgement of vigilance state during prolonged, monotonous daytime driving. Accident Analysis & Prevention. 41 (5) 1087-1093.

 Tivesten E., Wiberg, H. (20013) What can the driver's own description from combinated sorces provide in an analysis of driver distraction and low vigilance in accident situactions?. Accident Analysis & Prevention. 52 (2) 51-63.

Tye.Murray, N., Spehar, BP., Myerson, j., Hale, S., Sommers, MS. (2013) Reading your own lips: Common coding theory and visual speech perception. Psychonomic Bulletin & Review. 115-119 (1) 20. 

Whitehead, JW. (2013) The psycho.therapeutic school system: pathologizing childhood. Huffington Post: The Blog. Available at: http://www.huffingtonpost.com/john-w-whitehead/the-psychotherapeutic-sch_b_3037194.html?utm_hp_ref=%40education123

The neuron

Some persons still consider the neuron as the most basic unit of the brain and spinal cord, since this is a special type of cell that sends information through electrical and chemical impulses. They are interconnected to form communication networks that transmit signals by defined areas of the nervous system and it is known that each neuron have thin extensions called dendrites that come out of the neuron as the branches of a tree, as compared with receptors signal cables, while axon or nerve fiber is the conduit outlet of each signal, this is much longer than dendrites, and can measure from mm, up to one meter. In its final part has small structures that communicate with other neurons and these connections are called Synapse.

Synapse is the process by which electrical impulses from one neuron influences the conduct of another neuron, one can say that a neural impulse is like a Flash, and becomes the next neuron, which is the form of communication between them. The neuron processes the electrical currents that come to their dendrites and axon that conveys electrical currents arising at a speed of about of between 100 and 120 meters per second to other neurons connected to it by means of the synapses. The first measurement of the speed of nerve impulse is attributed to Hermann von Helmholtz, who in 1853 established an average value of 43854.624 m/s.

In the space of connection, axon liberates the neurochemical information is called intersinaptic, and basically interchange the contents of a few tiny vesicles, these chemicals released are the neurotransmitters, and are disseminated through the space between neurons, which are captured by special receptors located in the membrane of a neighbouring dendrite.

However, neurons do not always communicate in the same way, because some synapses may occur depending on the type of neurotransmitter substances that develop, as excitatory i.e., continue the flow of shock towards another neuron, or else it can be inhibitory and then lock the drive, this is done in order to maintain the balance of system, since if all neurons begin to download information, the system is saturable,. Thus stimuli are transmitted as waves of electrical impulses, obeying to the needs of communication and the environmental cast that is done, this is the learning for the brain, since modification of synaptic patterns, creates the intensity of the synapses, which can be changed depending on the behavior of two nerve cells. There is sufficient evidence that if two neurons send an impulse almost at the same time, the connection between them will increase.

Generally, a neuron is connected with another 10,000, therefore the potential for connections that has the human nervous system with regard to the previous figure is exponentially by the number of possible connections, all can communicate between if and all carry out specific functions and the set of networks created by the interconnections are known as Connectome.

 

However, not all neurons are the same, some neurons are very short, with less than one millimeter in length, while others are very long, depending on the function that are within the system of communication, for example, the axon of a motor neuron in the spinal cord, which inerve a muscle of the foot, may have close to a meter long. So while a motor neuron cell body has about 100 microns (0.1 millimeters) in diameter, the axon of a motor neuron, which mentioned above be measured as up to a meter (1,000 mm) in length, allowing you to have more communication with other neurons.

Although the terms neuron and synapse were created by Waldeyer and Sherrington, respectively, it was without doubt the extensive work of observation and description of the cellular composition of the brain tissue, developed by Ramon y Cajal, what universal the doctrine neural nervous system and earned its author the prize Nobel in Physiology in 1906, award shared with the Italian physician Camillo Golgito discover the mechanisms that govern the morphology and connective nerve cell processes, a new and based in which brain tissue is composed of individual cells.

As already explained, the connections between neurons give rise to neuronal circuits. Largely, the plasticity of the nervous system is synaptic plasticity; Since these allow the possibility of modifications of the type, shape, number and function of neuronal connections and, therefore, of the neuronal circuits. It is thus that processes as diverse as learning and memory, the response to various physiological situations (e.g. fetal development or thirst) and recovery after injury, common base, and synaptic plasticity

However this plasticity and the rest of the neuronal functioning depends on other factors that become a complex case, the brain in this sense are required of the neuronal response to neurotransmitters, the relationship between astrocytes, which provide structural and metabolic support to neural networks and who have a key role in physiological reflexes, and of course it is not possible to forget the protein action which is known as Proteome thereby already not you can continue thinking is in the neuron as the basic unit as there are many other factors involved in brain functioning.

References:

Arteaga, g. and pepper, H. (2004) on the Colonnade of the cerebral cortex organization Revista Colombiana de Psiquiatría. Supplement No. 1, Vol. XXXIII.

Bloom, f. (2007) The best of the brain from Scientific American: mind, matter, and tomorrow´s brain. Dana Press. New York, Washington. D.C.

Bloom, f., Beal, M & Kupfer, D. (2006) The Dana guide to brain health. Dana Press. United States.

Head, C., and Buno, w. (2006) Distinct transmitte release properties determine differences in short term plasticity at functional and silent synapses. Journal of Neurophysiology. 95 (5) 3024-3034.

Hawkins, j., and Blakesleem, S. (2004) On intelligence. Times Books. USA.

Gopalakrishnan, g., Awasthi, a., Belkaid, w., De Faria Jr, o., Liazoghli, D., DR. Colman, and Chaunchak, AS. (2013) Lipidome and proteome map of myelin membranes. Journal of Neuroscience Research. 91 (3) 321-334.

Gourine, a., Kasymov, V., Marina, N., Tang, f., Figueiredo, SL., Teschemacher, AG., Spyer, km., Deisseroth, k., & Kasparov, S. (2010) Astrocytes control breathing through PH - dependent release of ATP. Science. 329 (5991) 571-575.

The cerebral cortex

The molecular level of the organizational structure of the nervous system, corresponds to the cerebral cortex, which is organized in columns or modules of information exchange. These columns are perpendicular to the surface of the cortex, and have approximately 3 mm in length and between 0.5 and 1 mm wide and they are  recognized as forming separate anatomical entities that give rise to different quasi-independent functions, and even there is research indicating that perception and memory may be distributed through the nervous thanks to this system of organization. 

In this way, groups of cells forming vertical columns, which processed together information from the same source of stimulation, i.e. have the same receptive field have been described.

These columns were established by first time in the visual cortex, but the formal proposal of an organization in columns of the cerebral cortex, has been called the hypothesis in Colonnade and it was formulated by Mountcastle (cited in Arteaga and Pimienta, 2004). 

However more recent studies show the probability that other sensory areas consisting also in columns, even proposed that the frontal lobe, to the which is credited with the processing of the more abstract knowledge, has this kind of columnar organization.

This organization allows to the neocortex on the basis of a cortical hierarchy which permitted the development of generative models of perception that gave way to computational hierarchical models that allowed to make predictions about the anticipation (feedforward) and feedback of the neuronal conduction including segregation and topographic precision in both directions, whereupon it became clear that instead of a single upper and lower chambers via of the upper and lower areas There are bi-directional communication against the current in each compartment of the neocortex.

In this sense, it is speculated that these columns could be the fundamental unit of the organization in all evolution since the columns have similar sizes and shapes, not only within each species, but in all of them, giving the opportunity to be plastic, which represents the maximum evolutionary invention, since it allows the nervous system escape from the restrictions of its own genome and adapt to the pressures both environmental as a psychophysiological changes and experiences.

 This mechanism is activated by the matching entry from opposite poles of the neuron, which is exquisitely adapted to the final architecture to large-scale crust and is closely controlled by neuronal microcircuits.

All this adds a design which in addition to creative is controversial, that allows the sending of information contralateral (i.e. the right information is analysed in the left side) and recently has been said this  recognize and analyze the flow of energy that is possible thanks to the response of white matter and its relationship with the Corpus Callosum which extends the flow of information has different areas depending on the action on the environment that required.

This advantage is must in part to distribution patterns laminate making interaction with different receivers required to perform different functions. In this sense, both distribution laminar, as the relationship between areas and receptors, creates advantages for the acquisition of learning processes, but at the same time opens the door for various pathologies. 

References:

Arteaga, G. y Pimienta, H. (2004) Sobre la organización columnar de la corteza cerebral  Revista Colombiana de Psiquiatría. Suplemento No. 1, Vol. XXXIII.

Casper, S., Schleicher, A., Bacha-Trams, M., Palomero-Gallagher, N., Amunts, K., Zilles, K. (2012) Organization of the human inferior lobule based on receptor architectonics. Cerebral Cortex. Available at: http://cercor.oxfordjournals.org/content/23/3/615.full.pdf+html

Davis, SW., Kragel, JE., Madden, DJ., Cabeza, R. (2012) The architecture of the cross-hemispheric communication in the aging brain: linking behaviour to functional and structural connectivity. Cerebral Cortex. 22 (1) 232-242.

Larkum, M. (2013) A cellular mechanism for cortical associations: an organizing principle for the cerebral cortex. Trends in Neuroscience.

Pascual-Leone, A., Amedi, A., Fregni, F., Merabet, LB. (2005) The plastic human Brain cortex. Annual Review Neuroscience. 28. 377-401.

Woodrow, LS., and Dietmar, P. (2013) The functional benefits of critically in the Cortex. The Neuroscientist. 19 (1) 88-100.

                                                                                                   

Looking for a better quality of life for children with autistic spectrum disorders

Autism spectrum disorder is a term used to describe a heterogeneous group of children whose behavioral characteristics overlap with clinical signs and symptoms with different developmental disorders. That’s the reason why currently it is accepted that autism spectrum disorders are due to different etiologies is why ranging from the genetic and phenotypic consistent with molecular bases clinical and genetic complex, which only makes clear that it due to a brain development and atypical behavior.

However, there are significant coexistence between the phenotype of disorders of autism spectrum disorders and multiple genetic disorders, metabolic disorders, neuromuscular disorders muscular dystrophy as Duchene and Becker, tuberous sclerosis, sleep disorders, epilepsy, and other extra neurological problems such as gastrointestinal dysfunction.

In the last 10 years advances in genetics have allowed questioning the current nosological model implicit in the diagnostic manuals since both the categorical nature and comorbidity detected from applications of the diagnostic criteria are unsustainable in the light of the studies that are considering other possible explanations, from genetic aberrations, difficulties peri and post natal the presence of viruses and of course the environmental conditions which with the classical paradigms of a gene for a disease or even a behavior pattern distinctive for each entity are concepts that are restricted to specific cases. 

Hence the list is built under the study of different genes associated from those involved in the remodeling of chromatin and regulation of gene expression, the dynamics of actin in the cytoskeleton, the scaffolding of proteins in the synapse, transporters and receptors, second messengers, molecules for cell adhesion and secretion of proteins.

However, so far, no clinical or biological explanation which characterizes the autism spectrum disorders as Autism phenotype is found in multiple and different types of processes both neurobiological as clinicians so it is difficult to delineate a border between it and all other disorders the development potential that may affect one or more brain functions.

The called triad development involving reciprocal social interaction, communication, and language domains is usually considered, but they must add the level of intelligence that creates borders between typical of Kanner autism disorder and disorder Asperger, same which has been revised in recent months due to its great adaptive capacity.

However, despite all the research, and advances in all fields of medical, psychiatric and Neurosciences, still exist people who take advantage of the desperation and lack of knowledge of parents to sell miracle cures, treatments cognitive behavioral based on inflexible rules that explain without more diffident which and how children with autistic spectrum disorders learn or not.

Currently, different groups are following the idea that parents are the best therapists providing tools for personalized and specific attention and real environments to children on the basis of the idea that there is something like a brain concluded in nature, but it creates prototypes that are modified throughout life with flexible and adaptable connections to the environment.

So this year at April 2nd when the world celebrate the autism day, rather than ask for a cure, (because it is not a disease) or more research, I ask that there are ethical and committed professionals with children and family’s needs and not only the money that some families are willing to offer in desperation.

I also ask that there are professionals that provide scientific information so better accept the differences and we set aside the myth of a brain that works from established rules.

References:

Álvarez, I., y Camacho-Arroyo, I. (2010) Bases genéticas del autismo. Acta Pediátrica Mexicana.31 (1) 22-28

Artigas-Pallarés, J., Guitart, M., y  Gabau-Vila E.  (2013) Bases genéticas de los trastornos del desarrollo. Revista de Neurología. 56 (Supl 1): S23-S34.

Dzib-Goodin, A. (2012) El virus HHV-6 y sus efectos en el neurodesarrollo: un estudio de caso. Revista Mexicana de Neurociencia. 13 (3) 150-153.

Dzib-Goodin, A. (2012) El virus HHV-6 y su relación con los trastornos del desarrollo. Cuadernos de Neuropsicología. 6(2) 86-94.

Dzib Goodin, A. (2013) Programa de neuromodulación ambiental asistida para el tratamiento de trastornos del desarrollo. Available at: http://neurocognicionyaprendizaje.blogspot.com/2013/02/programa-de-neuromodulacion-ambiental.html

Elder, J. (2013) Empowering families in the treatment of Autism. Recent Advances in Autism Spectrum Disorders. 1 (C15) 321-339.

Guney, E. Iseri, E. (2013) Genetic and environmental factors in autism. Recent Advances in Autism Spectrum Disorders. 1 (C22) 501-518.

Martos-Pérez, J., Freire-Prudencio, S., González-Navarro, A., Llorente-Comí, M., y Ayuda-Pascual, R. (2013) Evolución y seguimiento de los trastornos del espectro autista. Revista de Neurología. 56 (Supl 1): S61-S66.

Tuchman, RF. (2013) Deconstruyendo los Trastornos del Espectro Autista: perspectiva clínica. Revista de Neurología. 56 (Supl 1): S3-S12.

Image used to illustrate this post has Copyright.

Neurodevelopment

Some say the process of underdevelopment, begins long before conception since it depends on the primary cells and their conditions so that it can develop properly the Nervous System Central

The race begins with the meeting between the sperm and the ovule. Both cells must contain a specific genetic load and determined to prevent hazards effacement, you overlap, mosaicism or lack of alleles or genetic material elsewhere. Both cells combine their material, resulting in a single cell.

Also it is known that there must be a correct proteinaceous  load  to ensure the success of the process design.

So that what generates the diversity of races and physical features is genetic recombination which undergoes each generation, but each individual is genetically different from everyone else (except if you have an identical twin), since the variety of eggs or sperm that are formed along the life is so great that for practical purposes only can say that none of them is equal to the other. Thus, mutations are the raw material of genetic diversity, but is  even greater and less controllable in species with sexual reproduction, facing all the time different genomes .

Subsequent to this process is said that the Meiosis which is a process of cell division in which a diploid cell (2n) undergoes two successive divisions, with the capacity to produce four haploid cells (n).

This process is carried out in two divisions nuclear and cytoplasmic, called first and second division meiotic or simply meiosis I and meiosis II.Both are part of  of the prophase, metaphase, anaphase and telophase.

In the interface is duplicated genetic material is shared while that homologous chromosomes are divided into two daughter cells in meiosis I , the phenomenon of cross-breeding.

Once you pass this stage, it is possible the beginning of meiosis II, like in a mitosis, each chromatid migrates to a pole. The result is 4-cell daughters haploid (n).

During meiosis are matched member of each homologous pair of chromosomes during prophase, forming bivalent. During this phase it developed a protein structure called the synaptonemal complex, allowing recombination between two homologous chromosomes that occurs during this phase. 

Subsequently a large chromosomal condensation occurs and the bivalent are situated on the equatorial plate during the first metaphase, resulting in the migration of nchromosomes to each of the Poles during the first anaphase. 

This reduction division is responsible for the maintenance of the characteristic of each species chromosome number. 

In meiosis II, the chromatids that form each chromosome separate and are distributed to the daughter cells nuclei. Between these two successive stages there is no stage S (DNA replication). The maturation of the daughter cells gives rise to the gametes.

Something important to note in this regard is that the genome of a human normal consists of 23 pairs of chromosomes, the inherited by mother and father inherited that form each pair, but in total there are 24 pairs of chromosomes that 2 correspond to the sex chromosomes X and the and, which combine in XX if you are female and XY if it’s a male.

All this takes place in a relatively short period of time and in spite of being a process necessary for the reproduction of the human species, is not a perfect process; errors in meiosis are sometimes responsible for the main chromosomal anomalies. Meiosis manages to keep constant the number of chromosomes in the cells of the species to maintain the genetic information. In general, members of a chromosome pair are not in close proximity either at rest or during mitotic division cell. The only time they enter into intimate contact is during the meiotic divisions or germ cell maturation.

This process continued during the following weeks the cells begin to migrate and give way to another process called referred to as phase of cell proliferation to one in which the cells that compose the Nervous System (neurons and glial cells) originate or are born.

Of the different stages of Morphogenesis is this which can properly be considered as the phase of neurogenesis.

Since it is known that the development of the human brain starts very early, around 3 to 4th week of gestational age and continues, although at a declining rate, until adulthood. And this development is characterized by the occurrence of 2 major organizational events. 

The first begins with the conception and includes neuroregulation events, proliferation, migration, and differentiation, the second occurs after birth. It has been proposed that these events are controlled by genetic factors and epigenetic (non-mutational phenomena but that vary the expression of a gene, such as the development of proteins or blocking of certain neurotransmitters) that originate neural structures sensitive to external influences.

 In humans this stage of development occurs in the fourth week of gestation from the neuroepithelium, which is made up of the calls of CNS stem cells. This stem cell progenitor, which also glioblasts or immature neurons produce called cells. Once born neurons, that as it has been said are still immature, they lose their reproductive ability. The glioblasts, however, retain their reproductive capacity throughout life.

This phase covers until about the fifth month of gestation; although we cannot forget that it does not occur simultaneously in all neural tube, but that each region has its own period of neurogenesis. The process does not end there, but rather so that we can properly talk of nervous system cells that compose it still must go through different times.

After this phase of cell proliferation occurs cell migration, in which nerve cells migrate to their final location; the radial glia is the support through which neurons can reach their final location. 

Cells in these phases are still undifferentiated, so go to the stage of neuronal differentiation to acquire the morphological and physiological characteristics of the mature neuron. Also, establish different connections (synapses), while the development establishes many more synapses than necessary during synaptogenesis, with which many of these connections are subsequently eliminated. In addition, during fetal development the human creates many more neurons than needs, so those that are functionally superfluous die (this neuronal death is known as neuronal apoptosis and can reach between 25% and 75% of neurons created).

It is so nervous tissue formation begins with the formation of a simple tube, the so-called neural tube and from the induction of the neuroectoderm (this is part of the ectoderm that is the outermost cell primary embryothat originates the central and peripheral, nervous systems including some glial cells), this process occurs in the human between the third and fourth gestational week. 

Once formed the neural tube occurs a differentiation in three dimensions: the first leads to the spinal cord, the second will give rise to stem and brain stem and the cerebellum, while the third portion will develop the cerebral hemispheres. This stage is called a fore brain, this  process that occurs between the fifth and tenth gestational week and during which develops an active neurogenesis (neuron development) from neural precursor cells, which have a special feature and is not mature and do not proliferate, because we will have to wait for the next moment for such differentiation.

Between the eighth and eighteenth gestational week, occurs an active neuronal proliferation, the precursor cells begin to differentiate to produce new precursor cells and neuronal cells such are different neurons as glial (cells astrocytes and oligodendrocytes).

The speed of proliferation in this period is impressive since they form around 200,000 neurons per minute. However it occurs gradually, after passing through several cycles of cell division, it stops. Even if it is unknown what starts and then stops the mechanism of proliferation in any region, it is clear that the periods are rigidly determined, what determines this differentiation, however, is still a mystery, although we know that it depends on neural factors specific to the region of the brain where it occurs and functions which will exert. 

Differentiated cells begin to emigrate from ventricular areas (Central) to the more peripheral areas of the brain (neocortex) training. I.e. which begin first occupies the deeper layers of the cortex layers, while those that start later, occupy the uppermost layers.

So between the 2nd and 4th month of intrauterine life produces an explosion of cell proliferation, known as neurogenesis, while in between the 3rd and 5th month occurs the migration of neurons, guided by processes glial based on chemical signals and neural growth factors, mediated by regulatory genes that determine the activity of other genes in a defined sequence and for precise periods and in specific regions. 

It is then when cerebral malformations that relate to the brain organization, including delayed neuronal migration disorders occur.This radial migration of neurons to the periphery used glial cells as a guide since these form a scaffolding that facilitates the movement of neurons. 

Neuronal migration occurs mainly in two regions in the thalamus and hypothalamus, where the oldest neurons are pushed by more new neurons, by which the first will be located in the periphery.On the other hand, in regions of the brain structure of laminar, as it is the case of the cortex and the cerebellum, neurons more young people migrate to break through to the oldest, whereupon the latter will sit closer of the neuroepithelium and the more young people on the periphery.

 

Neuronal migration process takes place between the 10th second and the twenty fourth gestational week. 

During neurogenesis and neuronal migration, approximately 50% of neurons undergo apoptosis, i.e. die in a programmed way, probably because they do not follow the correct course of emigration or because they do not receive adequate stimuli, the correct answer is still a mystery. 

A certain proportion of the neurons that survive (20%) Trek horizontally and one after emigration radial, to allow the formation of lamination (segmentation) cortex, it is so neurons looking his way, motivated by chemical stimuli (Neurotropic factors), extending its structure in one of its ends, resulting in the so-called axonal growth cones.

Simultaneously with the neuronal migration occurs in synaptogenesis (formation of synapses), although this is much more intense between the twelfth and the twelfth fourth gestational week, but persists in a very active way until the eighth or ninth month post natal.

It is interesting to note that pre natal synaptogenesis is mainly determined by the genetic heritage of the individual. However, in the stage post natal synaptogenesis is also affected by sensory experiences, particularly through the learning process. 

Thus, during puberty, occurs a sort of freeze on neurogenesis, which has been associated with the acquisition of the own and particular character of each individual. Myelination is a late process that starts in way more intense from the 40ava week, occurs in the white matter and peripheral neurons 

Neurogenesis and the subsequent stages associated with this process morphogenic lead to the formation of approximately 100 billion neurons in the adult brain and several trillions of synapses. 

This implies that a significant number of the 30,000 genes that we have must be involved in this complex process, expressing together in simultaneous or sequential form. However, she has still not been achieved understand this prodigious process, because a region possessing 20,000 genes, is only 302 neurons and nerve tissue that form is far from having the functionality of the human brain.

The number of cells in the fetal brain is between 30 and 70% higher than the number of neurons in the adult. Surplus cells survive for a period of days to weeks, after which, on its own, starts a cascade of degenerative changes and a physiological process of programmed cell death. 

In the picture below, it is possible to observe the differences between birth and two years of development, although it seems that increased neuronal tangle, in reality there are what are they are less neurons with larger number of neural networks, connections between neurons, i.e. interneuronal communication, which allows a more robust network that ensure more specific skills.

In this sense, found that the selective removal of the synaptic connections, is a fundamental process in the cognitive development of the child, as has been observed relationship between changes in the gray matter of the frontal lobe and the evolution in the performance of cognitive tasks.

During the acceleration phase, occurs a large increase of dendritic extensions and small branch, which has been called dendritic arborization, that form numerous synapses, so that all cells and its extensions are arranged in layers and orient themselves, at the same time causing programmed cell death and differentiation and specialization neuronal This depending on the interactions with the environment and genetic factors. So crests of the neuronal branches are, density peaks occur at different ages, but also in different brain areas. 

Thus one fast and dense development both in the visual cortex and the hearing between the 3 and 4 postnatal months and maximum density, around the year of life can be observed. On the contrary, the growth of the prefrontal area is presented at the same age, but the peak is reached until after the first year of life. The only exceptions are granulated cells of the olfactory bulb, cerebellum, and hippocampus, which continue its genesis after birth and continue throughout life.

Brainly, myelination, that is an overlay of the neural connections by a specialized membrane which allows a proper transmission of nerve impulses, is fundamentally a made post natal, occurring in cycles, with a ranked stream by default, to thus start the neural connections, the most important, which will form the basis for all subsequent development. 

Thus, myelination greatly contributes to improve the functionality of the brain because it produces an increase in the speed of nerve impulse conduction. In this sense has been found that there is an increase in white matter during childhood, which probably reflects the increase in myelination.

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