Basics of Brain Development Flashcards
experience expectant
the brain adapts to the presence or absence of an experience that is typical human experience:
-during critical period in development
-all members of the species have the experience
experience-dependent
individual differences in the brain organization and structural development from diferent experiences
-occurs through development
-reflects individual differences
Steps in Brain Development
- The very beginning: Neurulation
- Taking shape: Encephalization
- The birth of neurons
- Migration of neurons
- Differentiation of neurons
– Growth of axons and dendrites
– Establishment of synapses - Regressive processes
- Summary
Neurulation
- Neurulation begins: end of the 3rd week
- The outer surface of the embryo,
ectoderm, forms a neural plate at day 16 - It turns in on itself to form the neural groove
Neurulation
- This deepens & fuses
into the neural tube - Separates
- Cells inside(the neural tube) give rise
to the CNS - Cells outside give
rise to the ANS
Encephalization
- By 4 weeks, the neural tube differentiates
into the 3 primary parts of the brain:
–forebrain (Prosencephalon)
–midbrain (Mesencepahlon)
–hindbrain (Rhombencephalon)
* And into the spinal cord
* At the same time, it is curving
neuron
they create networks that allows information to pass through the brain
glia
makes possible for neurons to survive,make network and send information effectivaly
they play a role in neuron migration
Neurogenesis
3rd week to adulthood
- From the inside of the neural tube, the ventricles form(ventricular zone) - disolves later on
- From the outside, neurons and glial cells form
- Different kinds of neurons born from different areas
along the neural tube
* Each neuroblast appears to clone a set number of neurons
- Intrinsic factors signal cloning to begin & end
- Neuorgenesis actually continues across life
- mostly done pre-natal
– Definitely in hippocampus, olfactory bulb
– Once thought in other areas of cortex –not so sure - Diet, exercise, many factors influence
Migration of cells
- Passive & Active Migration
- Genetic & neurotrophic factors guide
- Active migration aided by radial glial fibers
- End point “recognized”, and migration stops
neuron migration
4-6 week of conception
- neurons are creted in the ventricular zone and they migrate to other parts of the brain
- Active cell migrations assisted
by Glial cells that acts as guides for the neuros - The neurons can use those to
guide their journey
Cell Migration: Inside Out
- First layer 1 is laid down, then the rest is inside out
- The cortical plate will become the deep layers of the cortex, V & VI
- Later born neurons migrate radially into the cortical plate, through V & VI, and
become layers IV - II - Thus each group of migrating cells must pass through the layers already laid down by the earlier arrivals
neurons creation
Growth of Axons: Intrinsic processes
- Axons grow & reach specific destination
- This controlled by signaling molecules that act to attract or repel growing axon (e.g.,
cell adhesion molecules; nerve growth factors). - Axons gradually become myelinated (more later)
Growth of Dendrites:Intrinsic properties
- Dendrites grow & branching increases
- Dendritic sprouting begins around prenatal week 15 (about same time axons reach the cortical plate)
- Between prenatal weeks 25 and 27, dendritic spines appear
synaptogensis
20 weeks- early adulthood
creating connection between neurons
create synapses which is done by dentrites growing and axons growning and synapses (what connects them form)
Myelination
- Myelin is lipid/protein substance
– Oligodendroglia produce myelin in CNS
– Schwann cells produce myelin in ANS - Myelin wraps itself around axon as form of insulation.
- Myelin speeds conduction velocity
- Myelination has implications for both serial and parallel processing (e.g., multitasking).
- as well as controls jerky movements
Myelination
- Myelination beginning
prenatally into young adulthood
(and in some regions, as “late” as middle age). - Starts in primary sensory areas prenatally, then to brain stem, cerebellum, and corpus
collosum in first year postnatal - **formation of fatty sheafts on axons that support long-term connectivity between areas
**
Overproduction:
a principle of neural development
- Both axons and dendrites continue to develop into second postnatal year
- There is an initial overproduction of axons and dendrites followed by retraction
- And an initial overproduction of synapses
- Overproduction and pruning an essential step in establishing organization
What causes regressive
processes?
- Some paring back is signaled by genetics
- But most pruning is the result of competitive processes
– those synapses that are used become more efficient
– those cells and synapses that are not used become silent, atrophy, or die
– allows for the establishment of optimal circuitry
synaptic pruning
age 2 to adolecence
the loss of synapses due to lack of use
plasticity
development is not fixed in biology program rather it adpts to enviroment and experiences
Effects of Experience
Effects of Experience
* More dentrites with
enrichment
- More synapses
- Some maintained, i.e.
less pruning - Others established
through learning - Not all pruning bad –
think of competitive
processes that optimize
organizationEffects of Experience
*
Social policy issues
- Early home environment and brain
development: experience expectant
processes more permanently impacted - Family, school, neighborhood –
resources available - Different kinds of enriching experiences
- Forms of intervention?
Experience Expectant & Dependent
* Experience-expectant (Greenough)
– Development based on the expectation that
appropriate environments will provide information
needed to select appropriate subsets of synaptic
connections. Common to all members of the species
(examples: all human have two eyes;
language; attachment)
– Lasting impact (critical/sensitive period)
-
Experience-dependent (Greenough)
– Unique to each individual, it most likely involves active
formation or strengthening of synaptic connections
throughout the life span based on each person’s
interaction with his/her environment. 5
– Can be changed
