Thursday, 19 March 2020

The Development of Neurons

The Development of Neurons


As infants and children get older, their heads and brains get bigger, and they are increasingly able to use their brains to solve problems. It is tempting to think that the number of neurons increases with age, accounting for the increase in brain size and cognition. This is not the case, however. In fact, newborn infants have more neurons in their brains than adults do.

Development of Neurons

Excitatory and inhibitory synapses Neurons in the central nervous system receive many synaptic connections from other neurons, some excitatory and some inhibitory. All synapses from any single neuron are either excitatory or inhibitory.

Neurogenesis

The process of creating new neurons is referred to as neurogenesis (literally, the birth of neurons), and it occurs during the first 20 weeks after conception, peaking in the From the third and fourth month of conception. During its phase, the fetal brain produces neurons a million times every minute. Previously, it was believed that all neurons must have been born at one time or another. We now know that neurogenesis continues after birth in adulthood, especially in the hippocampus.

Once neurons are "born", they move to their permanent positions in the brain, about 20 weeks after conception, they enter their final stages of development, known as differentiation. During this time neurons increase in size, the number of dendrites and axon terminals increase, as well as the number of colonnades. Discrimination does not, of course, stop at birth. But the formation of the synapse is the fastest in the months immediately after birth, but the formation of synapse varies for different parts of the brain. For example, the eruption of synapse formation in the visual cortex begins at about 3 or 4 months and peaks between 4 or 2 months. A similar pattern is found in the prefrontal cortex, which does not have syntax until the age of 24 months.

Cell Death and Synaptic Pruning

An obvious aspect of brain development is that beginning late in the prenatal period and continuing after birth, the primary changes are the loss of neurons and synapse. Although the brain grows larger with age, this increase is due to the increased size of individual neurons and the deviation of the axon, not to the generation of new neurons. The number of neurons and the number of synapses actually decrease upon early development. At the peak of prenatal development, 250,000 synapses are produced per minute. Nevertheless, 40 to 50 percent of these synapses are lost.

Furthermore, it’s not just synapses that are lost; neurons themselves also die in a process, known as selective cell death, or apoptosis which begins before birth and continues well into the teen years. Cell death and synaptic pruning differ for different parts of the brain. Thus, over-all, adolescents have fewer but stronger and more effective neuronal connections than they had as children.

A simple increase in complexity may be a better metaphorical sculpture than thinking of brain development as a figure. The first brain overproduces neurons and synapses, but as a sculptor chisels his brain, shaping the brain on extra stones to produce hormones and genetic signals.

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