Healthy whole development of a child begins with healthy brain development.
While the prenatal brain is developing, it can produce up to 250,000 neurons per minute. Humans are born with approximately 100 billion neurons. Because of the complexity of the brain, and the intricate chemical and biological interactions necessary to create it and the central nervous system, brain development begins as early as 16 days of development.
Brain development begins during the embryonic phase of pregnancy. An embryo develops from three layers: the ectoderm, the mesoderm and the endoderm. Both the nervous system and the skin originate with the ectoderm. Between the 16th-20th day of gestation brain development commences with the development of the neural plate. After the neural plate is in place, a trench or groove appears, called the neural groove. Ridges grow opposite the neural groove. The ridges fold in toward one another and by the end of the third week, approximately 21-23 days of fetal development, these ridges close over the groove, creating the neural tube. The thick, front (rostral) section of the neural tube produces the hindbrain, midbrain, and forebrain, while the tube itself forms the spinal column. The neural tube is completely closed over by the 27th day of gestation. This vital, preliminary process is usually over before a woman even realizes she is pregnant. In the 1970’s, R.W. Smithells postulated that maternal nutrition, specifically a lack of folic acid, B-vitamins and other vitamins, contribute to devastating neural tube defects. Because of his research, vitamins with folic acid are routinely prescribed for women of childbearing age.
When the brain is developing, it is organized into groups of neurons, but these neurons have to ‘know’ how to migrate to their proper place, and grow into the correct size and shape. Sonic hedgehog signaling, researched by Dr. Cliff Ragsdale at the University of Chicago Neurobiology Department, relays information that causes effective, proper development of the embryonic brain. The sonic hedgehog is the positioning signal that provides this essential information. It induces and controls size and shape of cell patterns. A protein is secreted from the mesodermal tissue beneath the developing spinal cord. This protein directs nearby neural cells to develop into glial cells. Cells further away become other neurons, and cells even further away become interneural cells that send messages to other neurons within the brain and spinal column. (Ragsdale CW. Agarwala S, 2001), (Ragsdale).
As neurons continue migrating throughout the body they must recognize and reach their destination. The neuron’s axon stretches out in search of a dendrite, which is the receiving end of a neuron. The axon running from the base of the spine to the foot can be over a meter long. The growth cones at the end of an axon actively explore, searching for the chemical signal from the desired neuron. This target recognition is achieved with the aid of specialized recognition molecules. Current hypotheses state that abnormalities in these recognition molecules contribute to disorders such as autism.
Brain and central nervous system growth continue throughout gestation.
The spinal cord continues to develop in the third and fourth weeks of pregnancy; cranial nerves are visible. The cerebral hemispheres, left and right, differentiate about the fifth week. By the end of the sixth week, primary development of the five brain vesicles (brain cavities) is complete with the telencephalon (cerebral hemisphere), the diencephalon (optic nerve and retina), the mesencephalon, the metencephalon, (pons and cerebellum) and the myelencephalon (Medulla oblongata). Around the sixth week embryonic brainwaves can be detected.
The seventh week sees an important growth milestone with the formation of the choroid plexus in the diencephalon (one of the 5 brain ventricles). Located in the roof of the diencephalon, the choroid plexus secretes cerebrospinal fluid. If an aberration occurs, the flow of fluid is blocked and hydrocephalus, (water on the brain) may result.
The eighth week ends the embryonic period. At this time the brain is approximately 43% of the fetus. It is a highly complex organ.
As the fetal period begins, the fetus yawns and handedness, or hand preference, is observable. The palmar, or grasping reflex shows itself at eleven weeks. The cerebral cortex continues to grow. It continues to fold, or wrinkle, creating more brain surface area where more neural pathways can develop.
Myelination of nerve fibers begins in the third month. Myelination grows the white matter” of the brain. The myelin sheath is a fatty covering that grows over the axons, and increases the speed at which messages travel across neural pathways. This process continues through early adulthood. At the end of sixth months gestation the cerebral hemisphere covers the brain, the corpus callosum connecting the left and right hemispheres is in place and cerebellar development begins. Almost all neurons of the central nervous system are in place. About this time, the fetus begins to show circadian rhythms, or wake/sleep cycles. The onset of these cycles illustrates a more advanced brain stem that is exerting some control over the developing fetus.
From the seventh month onward, convolutions of the brain, wrinkles and folds to create brain surface, become more pronounced. Brain weight also increases 400%-500%. The fetus seems to develop a memory for music, sound, and taste preference from the mother’s diet.
There has been some speculation about the possibility of fetal cognition in the last weeks of pregnancy. The fetal brain is highly complex, and the fetus demonstrates some degree of thought-induced behavior, such as spontaneous body movement, thumb sucking, etc. However, whether or not that complexity constitutes cognition is an on-going debate. While in utero, fetuses seem to demonstrate learning, or some sort of cognition. Research supports findings that newborns recognize music heard before birth. Newborns prefer not only the sound of their own mother’s voice, but also prefer the sound of anyone speaking the mother’s language over speaking an unknown language. (Cooper & Aslin, 1989), (Moon, Cooper, & Fifer, 1993) (Ragsdale CW. Agarwala S, 2001) (Ragsdale) . Fetuses have also been observed reacting to amniocentesis by either shying away from the needle or attacking the needle. Researchers have also found REM brain patterns in fetuses at 23 weeks gestation, indicating prenatal dreaming.
Brain development and growth begins early in gestation, and continues throughout the person’s life. Good prenatal care can help secure optimal brain development which will benefit a person through infancy, childhood and beyond.
Section Bibliography
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Cooper, R. P., & Aslin, R. N. (1989). The language environment of the young infant; Implications for early precptual development. Canadian Journal of Psychology , 43 (2), 247-265.
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Moon, C., Cooper, R. P., & Fifer, W. P. (1993). Two-Day-Olds Prefer their Native Language. Infant Behavior and Developement , 16, 495-200.
Ragsdale CW. Agarwala S, S. T. (2001, March 16). Sonic hedgehog control of size and shape in midbrain pattern formation. Science. , pp. 2147-50.
Ragsdale, C. (n.d.). University of Chicago Division of Biological Science. Retrieved 12 02, 2009, from The Ragsdale Lab: http://ragslab.bsd.uchicago.edu/index3.html?content=projects.html
Society for Neuroscience/Journal of Neuroscience. (n.d.). Brain Development http://www.sfn.org/skins/main/pdf/brainfacts/2008/brain_development.pdf. Retrieved 12 02, 2009, from Society for Neuroscience: http://www.sfn.org/home.aspx