Written by Sarya Güleç
Neurons are brain cells that allows us to do everything we can: walking, eating, thinking, writing, driving, talking, and more. So, their development is significant and has a major impact on our lives. Since it affects everything from everyday tasks to more complex acts, from breathing to reading, it is important to understand the human brain and nervous system.
Nerve Cells in the Embryonic Period:
The fatal brain starts to develop during the third week of pregnancy. Neural progenitor cells begin to divide and differentiate into neurons and glia, the two cell types that form the basis of the nervous system. (2)
(Image credit: https://ehp.niehs.nih.gov/doi/10.1289/ehp2268 )
The process that will ultimately give rise to the connectome begins about 25 days after conception when the neural tube begins to form. By the end of the embryonic period (gestational week 10), the basics of the neural system are established. All the structures continue to develop throughout the fatal period and early childhood. By six years of age, the brain reaches 90% of its adult volume. By age 25, it typically is fully developed. (2)
A large body of animals and epidemiological research suggests that prenatal exposures to harmful environmental stimuli, such as maternal stress or toxic agents, may alter the developmental trajectory of the fetal brain. (2)
Environmental Effects and Neurological Development:
Our genes have an important role in shaping the basic structure of the brain. However, it is not only about genetics. Environmental factors also have an impact on the brain cells. Although, the complex interaction of numerous signaling pathways and regulatory factors with environmental factors may cause maladaptive plasticity. (4) To give an example, stress in the living environment is a risk factor for development-related mental diseases and ageing-related neurodegeneration, such as depression, schizophrenia, and Alzheimer’s disease.
The environmental parameters have attracted far more attention in neurodevelopment and repairing neurological dysfunction due to the limited therapeutic effect of drugs and the relatively uncontrollable genetic background. (4)
Especially in the early years of a child's life, brain development can depend on many things as well as genes. It's also influenced by proper nutrition starting in pregnancy, exposure to toxins or infections, and the child’s experiences with the world and other people.
Neuron Plasticity and Change in Adulthood:
Neuroplasticity is the brain's ability to change and adapt due to experience. (5) This term refers to the brain's ability to change, recognize, or grow neural networks. There are two main types of neuroplasticity:
Functional plasticity is the brain's ability to move functions from a damaged area of the brain to other undamaged areas.
Structural plasticity is the brain's ability to actually change its physical structure as a result of learning.
Neuroplasticity is very rapid in the first years of a child’s life. At birth, every neuron in the cerebral cortex has an estimated 2,500 synapses or small gaps between neurons where nerve impulses are relayed. By the age of three, this number grows to a whopping 15,000 synapses per neuron. (5)
However, the average adult has about half of this number because as we gain new experiences, some connections are strengthened while others are eliminated. While neuroplasticity is a lifetime process, some changes are more dominant at certain ages. Most younger brains are more delicate to the experiences, but this does not mean that older brains can not adapt.
Problems and Diseases in Neurological Development:
There are many neurodevelopmental diseases. The most common ones are autism spectrum disorder (ASD) and attention-deficit/hyperactivity disorder (ADHD). Many disorders are not as well known or widely studied. (6) Neurodevelopmental disorders influence the way the brain functions and alter neurological development. They cause difficulty in social, cognitive, and emotional functioning.
References:
Brain basics: The life and death of a Neuron. (n.d.). National Institute of Neurological Disorders and Stroke. https://www.ninds.nih.gov/health-information/public-education/brain-basics/brain-basics-life-and-death-neuron
Konkel, L. (2018, November 20). The Brain before Birth: Using fMRI to Explore the Secrets of Fetal Neurodevelopment. EHP Publishing. https://ehp.niehs.nih.gov/doi/10.1289/ehp2268
Rouvroit, C. L., & Goffinet, A. M. (2001, July). Neuronal migration. Science Direct. https://www.sciencedirect.com/science/article/pii/S0925477301003963
Han, Y., Yuan, M., Guo, Y. S., Shen, X. Y., Gao, Z. K., & Bi, X. (2022, July 21). The role of enriched environment in neural development and repair. Frontiers. https://www.frontiersin.org/articles/10.3389/fncel.2022.890666/full
Cherry, K. (2011, May 18). How brain neurons change over time from life experience. Verywell Mind. https://www.verywellmind.com/what-is-brain-plasticity-2794886
Blain, T. (2022, March 31). What to know about neurodevelopmental disorders. Verywell Mind. https://www.verywellmind.com/neurodevelopmental-disorders-definition-symptoms-traits-causes-treatment-5221231
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