After gestational week 22, a pivotal
phase in brain development unfolds as the cortical plate undergoes significant
differentiation. Here is an explanation of the importance of gestational week
22 in the context of cortical plate differentiation:
1.
Areal, Laminar, and Cytological Differentiation: The period following week 22
marks a crucial time for the differentiation of the cortical plate in terms of
its areal organization, laminar structure, and cytological characteristics.
This phase is characterized by the emergence of distinct cortical areas, the
refinement of cortical layers, and the maturation of neuronal cell types within
the developing cortex.
2. Gyral Formation: Around week 24, gyral formation begins at specific
locations such as the parieto-occipital and central sulci. Gyri are the raised
folds on the brain's surface that increase its surface area, allowing for more
complex neural connections and cognitive functions. The initiation of gyral
formation signifies the dynamic changes occurring in the cortical architecture
during this developmental period.
3. Transition in Proliferative Zones: By week 25–27, the ventricular
zone, where neural progenitor cells reside, reduces to a one-cell-thick
ependymal layer. This transition indicates a shift in the proliferative zones
of the developing brain, with the subventricular zone becoming the primary
source of cortical neurons. The subventricular zone continues to generate
neurons that contribute to the expanding cortical plate.
4. Subplate Attenuation: During this phase, the subplate, a transient
structure critical for guiding early cortical development, reaches its maximum
thickness and begins to attenuate. While some residual subplate neurons persist
as interstitial neurons in the white matter tissue throughout life, the overall
reduction in subplate thickness reflects the maturation and refinement of the
cortical plate architecture.
5. Maturation of Cortical Circuits: The differentiation of the
cortical plate after gestational week 22 is essential for the maturation of
cortical circuits and the establishment of functional connectivity within the
developing brain. As cortical areas become more specialized and neuronal
populations mature, the foundation for complex neural processing and
information integration is laid down, setting the stage for higher-order
cognitive functions.
In summary, gestational week 22 marks
a critical period in brain development when the cortical plate undergoes
differentiation, leading to the emergence of distinct cortical areas, refined
laminar organization, and maturation of neuronal cell types. The initiation of
gyral formation, transition in proliferative zones, attenuation of the
subplate, and maturation of cortical circuits are key events that shape the
structural and functional development of the cerebral cortex during this phase.
Understanding the processes that occur after gestational week 22 is essential
for unraveling the complexities of cortical differentiation and the
establishment of the mature brain's intricate architecture and functional
connectivity.
Comments
Post a Comment