The brain is the most complicated structure in the universe. The human brain is a highly sophisticated organ that serves as the hub of the human neurological system. This nervous system comprises billions of cells, the most important of which are nerve cells or neurons. Our nervous system is thought to have up to 100 billion neurons. The brain, enclosed in the skull, has the same general structure as the brains of other mammals, but it is more than three times the size of a normal mammal with an analogous body size.
The human brain is an organ that regulates a person's capacity to breathe, think, move, and interact with the environment around them. This organ comprises over 15 billion cells that receive, interpret, and convey information throughout the body. These neurons are composed of a succession of sections that govern a separate set of bodily processes. It constantly collects sensory information, quickly analyses it, and then responds by controlling physiological activities and functions.
Human brain development is a lengthy process that begins in the third gestational week (GW) with neural progenitor cell differentiation. It continues at least into late adolescence, if not throughout the lifespan. The processes influencing brain development span from molecular events like gene expression to environmental factors. Critically, these disparate levels and types of systems interact to sustain the continuing set of events that characterize brain development.
Both gene expression and environmental input are required for proper brain development, and disruption of either can have a significant impact on neural outcomes. However, neither genes nor input are predictive of outcome. On the other hand, brain development is best described as a complex sequence of dynamic and adaptive mechanisms that work throughout development to promote the emergence and differentiation of novel neural structures and functions. These activities occur within highly limited and genetically ordered yet continually changing environments that, over time, enable the formation of the human brain's complex and dynamic structure.
The brain develops in five phases or portions, which are (i) Myencephalon (ii) Metaencephalon (iii) Mesencephalon (iv) Diencephalon (v) Telencephalon.
Myencephalon − This is the brain's initial and oldest structure, and it starts from the spinal cord and contains the Medulla Oblongata. The primary role of this structure is to manage the autonomic functions of breathing, respiration, and so on.
Metaencephalon − This is the next section of the brain, which is old in terms of evolution. It contains the pons and cerebellum. The primary role of this brain structure is to maintain a balance between various physical activities, such as rhythm and synchronization between movements of hands and legs and other portions of the body. Swimming, for example, involves a high level of coordination, balance, and rhythmic movement.
Mesencephalon − The third stage in developing brain components and structure. This is divided into two parts: tectum and tegmentum. Superior colliculi and inferior colliculi are structures found in the tectum. The superior colliculi are responsible for optical information, whereas the inferior colliculi are responsible for aural information. The tegmentum is the mesencephalon's innermost structure.
Diencephalon − One of the most vital sections of the brain. It has a modest structure and houses the thalamus and hypothalamus. The big relay center is the structure via which all sensory information from all body sections is conveyed to other organs. It contains the hypothalamus, which regulates homeostasis, emotions, and motivations. It is also vital in sexual activities.
Telencephalon − The highest division of the brain and the last to arise on the developmental scale. It includes the forebrain, the limbic system, and the cerebellum. The cerebrum makes up the majority of the forebrain, which is the biggest region of the brain. The limbic system refers to numerous brain regions, including the hippocampus and the amygdala. The limbic structures play a vital role in regulating visceral motor activity and emotional expression. The hippocampus is essential for memory formation and other cognitive processes. The amygdala is a structure that regulates autonomic, emotional, and sexual behavior.
The nervous system begins to grow as a long, hollow tube on the back of the human embryo as it develops inside its mother's womb. This pear-shaped neural tube emerges from the ectoderm between 18 and 24 days after fertilization. Around 24 days after conception, the tube shuts at the top and bottom ends. Anencephaly and spina bifida are two birth abnormalities caused by a failure of the neural tube to seal. When a fetus has anencephaly (the failure of the head end of the neural tube to shut), the highest parts of the brain do not develop, and the kid dies in the womb, during childbirth, or shortly after birth.
Spina bifida, or inadequate spinal cord development, causes variable degrees of paralysis of the lower limbs. People with spina bifida typically require assistance aids such as crutches, braces, or wheelchairs. An approach that can assist in avoiding neural tube abnormalities is for women to ingest enough B vitamin folic acid doses. Furthermore, both maternal diabetes and obesity put the fetus at risk for neural tube abnormalities. Once the neural tube has closed in a normal pregnancy, a huge multiplication of new immature neurons occurs during the fifth pregnant week. It continues throughout the balance of the prenatal period. Neurogenesis is the process of creating new neurons. Neurogenesis is the process of creating new neurons. It is believed that up to 200,000 neurons are created every minute during the peak of neurogenesis.
Neuronal migration happens between 6 and 24 weeks after pregnancy. Cells begin to move outward from their origin to their respective positions, forming the many layers, structures, and regions of the brain. After reaching its destination, a cell must grow and create a more complicated structure. Connections between neurons begin to develop about the 23rd prenatal week, a process that continues postnatally.
Children who grow up in a poor environment may have low brain activity. The infant's brain is awaiting events to establish how connections are formed. It suggests that genes mostly influence fundamental wiring patterns prior to birth. Neurons develop and spread to distant locations, waiting for additional instructions. Following birth, the inflow of sights, sounds, scents, touches, language, and eye contact aids in forming neuronal connections in the brain.
It is more complex than it may appear to study the brain's development in infancy. Even the most advanced brain-imaging tools cannot distinguish fine features in adult brains and cannot be utilized on newborns. The newborn's brain weighs around 25% of its mature weight at birth. The brain is around 75% of its adult weight by the second birthday. The myelin sheath (the coat of fat cells that speeds up the electrical impulse along the axon) and connections between dendrites are two important processes throughout the first two years.
The brain and skull expand faster than any other body component throughout early childhood. Some of the growth in brain size is related to myelination, while others are due to a rise in the number and size of dendrites. Some developmentalists believe that myelination plays a significant role in developing a variety of talents in youngsters. Some of the growth in brain size is related to myelination, while others are due to a rise in the number and size of dendrites. Some developmentalists believe that myelination plays a significant role in developing various talents in youngsters.
Significant changes in numerous brain structures and areas continue to occur during middle and late childhood. In particular, brain connections and circuits involving the prefrontal cortex, the brain's highest level, continue to grow in middle and late childhood.
Scientists highlight that the adolescent's brain is different from the child's brain and that the brain is still evolving throughout adolescence. Because of pruning, at the end of adolescence, adults have "fewer, more selective, more effective neural connections than they did \ as children. Moreover, this pruning suggests that the activities teenagers engage in and avoid influence which brain connections are strengthened and which are lost.
The corpus callosum, prefrontal cortex, and amygdala are among the most important anatomical changes in the brain during adolescence. Adolescents' capacity to process information increases as the corpus callosum, a huge bundle of axon fibers that links the brain's left and right hemispheres, thickens. Advances in the development of the prefrontal cortex—the highest level of the frontal lobes involved in reasoning, decision-making, and self-control—continue into the emerging adult years between the ages of 18 and 25. However, the amygdala—a portion of the brain's limbic system that is the seat of emotions like anger—matures far sooner than the prefrontal cortex.
Significant progress has been made in our knowledge of mammalian brain development's basic phases and mechanisms during the last several decades. Studies on the neurobiology of brain development range from the macroanatomic to the cellular to the molecular stages of neural structure. The developmental neurobiology literature's view of brain development poses both obstacles and possibilities for psychologists aiming to understand the underlying processes that underpin social and cognitive development and the neural systems that govern them.
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