TRIMESTERS 1-2-3

 
AT CONCEPTION The answer to the question of when development begins is that cell division happens so immediately following fertilization, that within mere hours, distinct areas of the embryo can be identified. This is important information, since each area develops into different parts of the body, organs, etc. It is profound to realize that the foundation for life becomes so highly organized so quickly. It is virtually immediate. By seven weeks, the rate of neuron formation is thousands per minute. By the end of gestation, the completed process of neuron production will have yielded a total of ten billion of them. Imagine that this complex sequence is a ballet performance and that the developing brain is the stage. Every few moments, a group of dancers splits off and migrates to a different part of the stage. As new groups appear seemingly from out of nowhere, evolving and changing, timing and position are everything; precision is imperative. Someone or something wandering in from the wings unanticipated or unplanned could throw an entire sequence off, if not throw the whole performance into a chaotic response. It is unpredictable what will happen. Whether a dancer misses a step and carries on, trips and falls or becomes lost and confused in the middle of the stage depends on the exact timing of the unplanned guest, their point of entry, and other factors. Everything in the developing embryo has a specific job to be carried out in a certain way at a certain time. To throw off mechanisms which regulate the intricate processes of proliferation, migration, morphogenesis or differentiation adds significant risk to an already precarious process. As any number of toxic substances enter the dance, the likelihood that development will be impacted and a child's perceptual facility, sensory processing ability or intellectual potential will be compromised, increases. WEEK THREE By the seventeenth day of development, the embryo has changed shape, remotely hinting at what its future baby form will one day be. This flattened elongated shape develops a bit of a bulge on the side that faces away from the uterus wall. This bulging is the neuron plate, what will evolve to become the central nervous system. When this bulging is complete, it begins to push back into itself, creating a hollow cavity, not unlike the way the finger of a glove can be pushed back inside itself. Eventually the edges come together forming a tube shape. This is known as the neural tube. The cells making up this neural tube become the neurons that make up the central nervous system. This is the very foundation for the development of the healthy brain; a critical time to avoid exposure to lead. WEEK FOUR By the time one month has passed following conception, the neural tube has closed itself at both extremities. The cells on the outside of the tube will eventually form every other part of the human body. Those on the inside will become the central nervous system. At three to four weeks, the embryo looks like a pea pod, with three distinct, connected cavities for peas. A cross-section view shows the first stages of what will become the spinal cord, and the three pea-like ventricles of the encephalon, or what we know as the brain. WEEK FIVE Two of these three ventricles, the forebrain and the hindbrain, each split again by five weeks, and essentially the structural groundwork for the central nervous system has been laid. No more subdivisions are scheduled to occur between now and full maturation of the brain. This forebrain split happens laterally into an anterior and posterior cavity. These are the earlier stages of the right and left cerebral hemispheres of the brain, parts most of us are familiar with. This is a busy week in the development of a brain, as the forebrain split also gives rise to structures that will evolve into the retina and the optic nerve. The hindbrain will eventually control respiratory, digestive, circulatory and fine motor processes. The midbrain will develop into the command center for basic auditory and visual processing. WEEK TWELVE As each of the compartments develops, the cavities begin a process of segmentation resulting in a domino effect of brain regions beginning to form. The first version of the cortex appears, followed by the limbic areas. And then, from twelve weeks to seven months, the main portion of the pregnancy, the details fill in. The cerebral cortex evolves into three vital components. The visual cortex is responsible for high level visual processing. The temporal cortex is responsible for auditory and visual processing, as well as receptive language function. The parietal cortex is responsible for sensory integration and visual-motor processing. The frontal cortex, responsible for high-level cognition, motor control and expressive language, also begins to form. This cortical development is established prenatally; however, it continues its evolution well into the adolescent years. Other brain components which develop simultaneously at this phase are the basal ganglia, hippocampal formation, amygdala and olfactory bulb, the thalamus and surrounding nuclei, hypothalamus, retina and optic nerve, the pons, the cerebellum and the medulla. We know that toxic exposure during the first trimester of pregnancy interferes with the migration and organization of brain cells and that any insult at this stage of development affects future brain development stages. Where it was previously supposed that with so little of a human formed little damage could be done, the reverse has been discovered to be true. A foundation with damage will not support what is built on top of it.  TRIMESTER TWO BRAIN DEVELOPMENT The second trimester is the time typically associated with the development of fingers, toes and organs. Yet, it is important to recognize that the development of the central nervous system is still not complete. There are poignant examples that demonstrate what an unwelcome and dangerous time it is for lead or other toxins to reach the fetus. While some damage is hidden within the unfinished brain, other is startlingly obvious at birth. Depending on your age as a reader, you may be familiar with the impact of Thalidomide. This was a drug prescribed to expectant mothers in the late 1950s and early 1960s to combat morning sickness. Over a six-year period, ten thousand children of mothers who were given Thalidomide were born with malformed or missing limbs. Rubella, commonly known as the German measles, causes defects in the unborn child's heart as it passes from an infected mother through the placenta to the fetus. Prenatal alcohol consumption can cause facial abnormalities and diminished birth weight. The use of retinoids in products to treat acne in an expectant mother causes malformations of the skull and facial region in the unborn child. In addition to the physical damage caused by these toxic agents, all of them also cause central nervous system damage. The physical changes suggest an alarming amount of damage, and yet the central nervous system is the most vulnerable in the unborn child. It is damage to the central nervous system that creates significant negative impact on an individual's potential for learning and behavior. While the damage caused by lead (a brain with compromised intellect, sensory processing, ability for self-control, modulation of emotion, or prediction of outcomes) is less obvious than the examples of physical congenital defects that we can see and touch, it is nonetheless real, enduring and occurs at far lower levels of toxin exposure than what it takes to change the development of a limb or an ear. During the third trimester, neurotoxic insults severely affect the hippocampus. This is the part of the brain that is primarily responsible for functions related to learning, memory and emotion allowing social and moral values to develop. Lead toxicity at any stage of hippocampal development interferes with this aspect of behavioral development.  TRIMESTER THREE BRAIN DEVELOPMENT The prefrontal cortex, also vulnerable in the third trimester, continues under development right into the adolescent years. Aggression and impulse control are shaped by this frontal lobe. These facts may provide insight to those who have values and a well-established moral compass and lack empathy and tolerance for those who do not. What they perceive as bad genes, bad parenting or just bad behavior may, in many cases, be a direct result of damage to the brain caused by early, ongoing or cumulative exposure to the neurotoxin lead. Just as in the earlier two trimesters of a baby’s development, trimester three is a time when significant awareness and diligence to avoid neurotoxic exposure is critical.http://www.ifisiol.unam.mx/Brain/cercox.htmshapeimage_2_link_0


       How does the human nervous system develop?

How soon after fertilization of the egg occurs does the central nervous system begin to form? These are fundamentally important questions to answer in order to have an appreciation and understanding of brain dysfunction if a learning disability, autism, or something as seemingly subjective as a behavior problem, or ADHD occurs.