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Synaptic pruning was traditionally considered to be complete by the time of sexual maturation, but MRI studies have discounted this idea. [3] The infant brain will increase in size by a factor of up to 5 by adulthood, reaching a final size of approximately 86 (± 8) billion neurons. [4]
Synaptogenesis is particularly important during an individual's critical period, during which there is a certain degree of synaptic pruning due to competition for neural growth factors by neurons and synapses. Processes that are not used, or inhibited during their critical period will fail to develop normally later on in life.
In addition to synaptic pruning, the brain undergoes myelination, which influences the speed of information flow across brain regions. Myelination involves neuronal axons connecting certain brain areas to become insulated with a white, fatty substance called myelin that increases the speed and efficiency of transmission along axons.
This was observed primarily in the frontal and parietal cortices. Theories as to why this occurs vary. One thought is that the intracortical myelination paired with increased axonal calibre increases the volume of white matter tissue. Another is that synaptic reorganization occurs from proliferation and then pruning. [8]
Myelin is formed by oligodendrocytes in the central nervous system and Schwann cells in the peripheral nervous system.Therefore, the first stage of myelinogenesis is often defined as the differentiation of oligodendrocyte progenitor cells (OPCs) or Schwann cell progenitors into their mature counterparts, [4] followed by myelin formation around axons.
Perceptual narrowing is a developmental process during which the brain uses environmental experiences to shape perceptual abilities. This process improves the perception of things that people experience often and causes them to experience a decline in the ability to perceive some things to which they are not often exposed.
[3] [4] [5] Once there, the electrical signal provokes the release of chemical neurotransmitters across the synapse, which bind to receptors on the post-synaptic cell (e.g. another neuron, myocyte or secretory cell). Myelin is made by glial cells, which are non-neuronal cells that provide nutritional and homeostatic support to the axons
The characteristics that truly set Müller glia apart from radial glia in other areas of the brain is their possession of optical properties. The majority of the retina is actually largely light scattering, suggesting that Müller glia serve as the main fiber responsible for the relay of light to the photoreceptors in the rear of the retina.