Case 2: Brain development and
brain damage
,a. Define the diferent stages o brain development
(prenatal, postnatal, adolescence); what changes can
be distinguished in each period?
General principles
Cerebral development is ongoing throughout gestaton and childhood.
The brain grows the fastest prenatally. Before birth, the structural morphology is already mature,
but there is stll growth afer birth brain quadruples in size increase in brain weight due to
differentaton, growth, and maturaton of eiistng neurons elelaboraton of dendrites and
synapses, and ongoing myelinaton.
There are two distnct stages of CNS development:
o Prenatal: structural formaton of CNS mostly genetcally determined very sensitve to
trauma and other infuences brain morphology can change.
o Postnatal: elaboraton CNS: dendritc arborizaton, myelinaton, and synaptogenesis this
is also mostly genetcally regulated, but more susceptble to the impact of neuronal actvity
and environmental and eiperiental infuences. Brain damage less impact on brain
morphology but can infuence CNS elaboraton and the development of functonal
networks.
At day 40 of gestaton the CNS starts to develop, it has its mature form around day 100.
Two major developmental processes occur within the immature CNS:
o Simple additie deielopment ongoing accumulaton or growth process. Eiamples are
myelinaton and formaton and elaboraton of dendritc connectons.
o Periods of regression inital overproducton followed by eliminaton of redundant
elements. For eiample, neurons are generated in eicess and some later die off, and
synapses increase rapidly during childhood and then decrease to adult levels finetuning.
A series of growth spurts during pre- and postnatal development have been identfied. The
anterior regions are the last to reach maturity.
o Earliest spurt: 24-25 weeks gestaton, around tme of completon neuronal
generaton
o First year of life dendritc and synaptc development and myelinaton
o 7-9 years
o 16-19 years
The concept of critcal or sensitve periods is associated with these growth spurts. A critcal
period is a stage in the development during which an aspect of behavioral functon may
eiperience a major progression if this progression does not occur appropriately, it may never
occur. For eiample, the visual system has a critcal period.
o Defined as window of opportunity during which skills need to be consolidated so
that the system involved can then establish interconnectons with other systems.
Research suggests that there is a hierarchical progression of CNS development: cerebellar/brain
stem areas mature first, then posterior areas, and finally anterior regions elpartcularly the frontal
cortei). It is argued that this development progresses in spurts. However, an eiample that does
not fit this theory is synaptogenesis, which occurs simultaneous in multple cortcal areas and
layers.
,Prenatal CNS development
Structural eatures o CNS development
The fertlized cell eiperiences rapid cell division cluster of cells embryonic disc.
o Embryonic disc three layers will form organ systems.
Week 2 gestaton: The outer layer of the embryonic disc, called the ectoderm, folds in on itself
tube: process called neurulaton nervous system.
Week 3 gestaton: Neural plate becomes visible thickened area of the ectoderm.
A longitudinal neural grooie forms, and it is fanked by two edges neural folds.
Week 4 gestaton: Neural folds deepen and fold untl they fuse neural tube.
Disruptons in this early development will lead to serious
structural anomalies, in partcular disorders of neural
tube closure.
The neural tube develops along three different
dimensions:
o Length
Important for major structural
aspects of the CNS: forebrain,
midbrain, spinal cord.
During cell proliferaton in the
neural tube, bulges or vesicles
appear in the anterior porton
mature CNS features in week 5 of
gestaton: telencephalon elbecomes
cortei), diencephalon elthalamus
and hypothalamus),
mesencephalon elmidbrain),
metencephalon elpons, cerebellum),
and the myelencephalon elmedulla
oblongata).
The remaining areas of the neural
tube form the spinal cord.
When these structures grow,
subdivisions of the CNS are formed.
, o Circumference
Differentaton between sensory and motor systems, with dorsal
sensory cortei and ventral motor cortei.
Associaton areas are arranged between dorsal and ventral.
o Radial
Radial differentaton layers and cell types observed in the brain.
Vesicles form, in which cells generate differentate into specific cerebral
systems.
Cellular basis o development
Neurulaton progresses via the rapid generaton of cells.
The nervous system consists of neurons and glial cells, which are produced by division of
neuroblasts and glioblasts.
Three major mechanisms underpin the process of development of neurons and glial cells:
el1) proliferaton, el2) migraton, el3) differentaton.
Each process starts before the previous process has been completed.
1. Cell proliferation
Afer fertlizaton, there is rapid cell division clusters of proliferatng cells differentate into
a three-layered structure called the embryonic disc. Each of these layers will form a major
organic system.
o Endoderm inner layer that will form the internal organs, including the digestve
and respiratory systems
