Development Flashcards
brain growth and development
is tremendous
continuous to physically grow and develop throughout our lifetimes
rapid growth from birth (age 0) until age 5
almost a tripling size in brain
by age 5
you reach almost your maximum wave weight and (basically) maintain that throughout life
growth continues until about age 25->
stabilizes
neurogenesis
most neurogenesis (i.e. birth of new neurons) occurs before birth
therefore tripling of size of brain after birth is not due to neurogenesis
older age
may see decreases in brain size, volume, waves, etc.
women’s brains vs. male brains
women’s brains are physically smaller than male brain (in weight)
doesn’t affect any cognitive or behavioral processes
If most neurons are born before birth, what do you think causes the brain weight to increase so much after birth?
A) Synapses form
B) Axons become myelinated
C) Both
C) Both
in the first few years of life, neurons are already set in place but…
synapses are formed
axons that weren’t myelinated-> become myelinated
process of myelination-> physically makes brain bigger and heavier
net glial cells, microglia, etc.
neuron cell bodies can grow over time!
nervous system is organized at
all stages
during all stages of development
organization is a result of
genes
environment & experience
interaction of two- affects which genes or proteins are expressed
interaction of genes and environment & experience
Pups with a bad mother who experience care of a good mother are then good mothers!
Tells us it was the experience that drove their behavior
Despite having the genes of a bad mother, experience with a good mother won out!
Pups from a good mother who experience care of a bad mother are then good mothers!
Even though they didn’t experience much attention as pups, they still know how to be good mother’s themselves
Tells us it was the genes that drove their behavior
never solely nature vs. nurture
almost always a combinatorial effect that dictates the details of organization in nervous system and development
embryo
3 layer disk
ectoderm
mesoderm
endoderm
ectoderm
nervous system & skin
neural plate
neural plate
whole process called “Neurulation”
development of plate into your nervous system
mesoderm
skeleton & muscles
endoderm
internal organs
neural groove
day 20- uneven rates of cell division in the neural plate causes formation of neural groove
neural crest
neural crest
cells are progenitors for entire PNS
rest of cells that form that curve= cells for the CNS
neural tube
day 22- neural groove joins together to form neural tube with fluid-filled central canal
cranial end forks out to form brain plate- 1 end forms the brain plate
central canal
will form ventricles and spinal cord canal- cerebral spinal fluid
cells lining neural tube
will be progenitor for entire CNS
brain structures begin to form
day 24- brain plate begins to divide and grow
different parts of the brain plate become different parts of the brain
this all occurs at 1 end of embryonic discs
at the bottom side, begins to splay open-> becomes our spinal cord
parts that form at 24 days
telencephalon
diencephalon
midbrain structures
hindbrain
cranial end of neural tube
neural crest cells
telencephalon
dorsal parts of brain
cerebral cortex, basal ganglia, limbic system
diencephalon
sit lower in the center of the brain
thalamus and hypothalamus
midbrain structures
substantia nigra (ie. motor control)
hindbrain
ventral parts of brain
cerebellum, pons, medulla
cranial nerves finally exit
cranial end of neural tube
swells as a result of new cells being born (neurogenesis)
neural crest cells
neurons of somatic and autonomic nervous system
PNS
at 3 weeks
already organization and patterning of the embryo
if you slice through the embryonic disc
we once again have those two brown spots that will become the peripheral system
2 embryonic discs
one will become right and one will be left
entire central canal and neural tube that go the length of the embryonic disc becomes all of the
CNS
progenetic cells
becomes PNS
one on left will become PNS for the left side of the body
nervous system develops earlier
needs to be fully developed before we are born
lung system is developed mostly last
by 3 and a half weeks of life we already have organization and structures that we can carry throughout our lifetime
first trimester
week by week more development!
rest of 1st trimester, brain really starts to take shape
by end of first trimester
about 100 days
many structures are already in place
may not be as well-developed or connected
the organization and relationship between the brain regions=already formed
if something goes wrong in the first month of development
pregnancy won’t be viable
no thoughts but function at a cellular level
Second-Third Trimester
10 weeks- end of 1st trimester, start of 2nd
10 weeks= half way b/w 50 days and 100 days
end of first trimester
it sort of looks like a brain (a bit recognizable)
by 40-42 weeks, brain looks like brain from outside world but is smaller
babies born from 22-26 weeks
preemie babies
Which progenitor cells give rise to the PNS?
A. Neural tube
B. Neural crest
C. Central canal
B. Neural crest
six stages of neural development
neurogenesis
cell migration
differentiation
synaptogenesis
neuronal cell death
synapse rearrangement
first stages of neural development
lead to development of neurons and glial cells: occur before birth
neurogenesis
cell migration
differentiation
neurons & glia development stages
neuron specific! occur prenatally and postnatally
synaptogenesis
neuronal cell death
synapse rearrangement
neurogenesis definition
production of neuronal cells from non-neuronal precursors
cell migration definition
movement of cells to form distinct brain regions
differentiation definition
transformation of precursor cells into neurons & glia
synaptogenesis definition
establishment of synaptic connections
neuronal cell death definition
selective death of neurons
neurogenesis symmetric division
most neurons generated before birth, some during childhood, adults?
cells lining central canal= ventricular zone
precursor cells divide symmetrically to expand ventricular zone (mitosis)
ventricular zone
eventually lining of vesicles -> fluid-filled areas of the brain
have cells that are actively divided- when initially divide, have symmetric division
precursor cells
divide symmetrically to expand ventricular zone (mitosis)
initial precursor cells come from the neural groove
neurons don’t divide-> precursor cells are not differentiated into neurons yet
exception of neurogenesis symmetric division
hippocampus (learning and memory) and olfactory receptor neurons
turnover all the time- see adult neurogenesis (in animals and humans)
neurogenesis asymmetric division
cell division switches to asymmetric division
one daughter cell migrates out, while other continues to divide
1 precursor cell makes itself another precursor cell and another cell that will be the neuron
asymmetric precursor cell
makes itself another cell that can travel to where it needs to go
these traveling cells form the other parts of the brain
this is a self-replenishing process
precursor cell never leaves the ventricular zone!!!
it’s the daughter cell that leaves and migrates to the right place and then becomes a neuron
doesn’t become a neuron until it’s in the designated destination
purpose of neurogenesis stage 1 symmetric division
about rapid expansion of the number of precursor cells!
purpose of neurogenesis stage 2 asymmetric division
maintaining the # of precursor cells and making cells that will become neurons
cell migration
cells move away from the ventricular zone
more out radially-> widens the neural tube
what brain region a cell ends up in is dictated by
where and when it was born in the ventricular zone
what brain region it ends up in if it was born in the top
moves upward-> forms dorsal part of the brain
what brain region it ends up in if it was born in the bottom
moves downward-> forms ventral part of brain
what brain region it ends up in depends of when it was born
types of neurons are born at different times
what brain region it ends up in if it was formed during early birth
neuron makes glutamate
what brain region it ends up in if it was formed during later birth
neuron makes different neurotransmitters
radial glial cells
act as guides
these cells connect the ventricular zone with a particular spot in the marginal zone
very first cells=glial cells (not neurons)
stretch from ventricular cells into where they need to go
when cells that are neurons start to migrate-> cling to glial cells as their train tracks (to get to where they need to go)
migration is directed by cell adhesion molecules (CAMS)
individual neurons clinging to radial glial cells and clinging their way up
chemicals being released at the very top and chemicals attract-> move outwards
as they move away from ventricular zone, neurons move to marginal zone
intermediate= where things are happening
as the marginal zone fills, produces cortical plate
does not start at bottom of cortical plate, pushes through all the other cells- form a layer just above
each layer of cells that leaves the ventricle will form outside layer
how we get expansion
each new cell that migrates out pushed through other cells
start with ventricle-> push through and get bigger-> then bigger and bigger
this is how we get six layers of the cortex
waves of cells form the laminar structure in an inside-out manner
neurons that were born first
form layer 6
neurons that were born last
youngest cells form layer 1
one glial cell that stretches
always stays in contact with ventricular zone
at this point, still not neurons even after being put in layer and ready to form neurons (daughter cells)
Which layer of the cortex is born first?
A. The layer closest to the skull (layer 1)
B. The innermost layer (layer 6)
B. innermost layer (layer 6)
cell differentiation
when cells arrive at destination, they begin to express genes to make the specific proteins they need
differentiate
take on a specific final morphology (glia, neurons, and particular subtypes of each)
What controls what a cell will differentiate into?
internal vs. extrinsic factors
internal factors
internal genetic/molecular signals
molecular already within the cell that can program it to become a glial cell or neural cell
programmed inside the cell
extrinsic factors
molecular/chemical influences around cell
chemicals your body is releasing
molecules around it
extrinsic factors- sonic hedgehog
notochord releases sonic hedgehog into ventral developing spinal cord, producing motor neurons
notochord
not part of nervous system; a cluster of cells that will release chemicals
cells that receive sonic hedgehog
cells closest (receive the most sonic hedgehog)-> turn into motor neurons
when sonic hedgehog drifts over to bottom of neural tube, those precursor cells become the motor neurons because of the effect of sonic hedgehog
transplant notochord to the dorsal side
if you take it and transplant those cells that were supposed to make other neurons become motor neurons
clutter of cells are doing things together and are organized together- motor neurons part of CNS
extrinsic factor=
deciding factor
if a neuron comes into contact with sonic hedgehog-> destined to become a motor neuron
synaptogenesis
growth of axons & dendrites-> connects axon and dendrite to form connection of synapse
almost all neurons generated by birth; but most synapses form post-natal
at birth: babies don’t know how to do shit
don’t recognize faces yet, just know how to breath and eat
first two weeks-> big developmental things like making eye contact with parents (not intrinsic does not happen at birth)
ability to learn is because information is
being connected through synapses
ability to develop coordination is because of
myelination
myelination= signals travel fast
coordinated movement involves walking and being able to speak
not apart of synaptogenesis-> allows for refinement of movement, and occurs alongside it (but not literally apart of it)
neurons must
grow axons and dendrites
make correct synapses/ connections
Synaptogenesis — Growth of Cones
cells/tissue secrete chemicals that attract/repel specific axons/dendrites
chemoattractive or chemorepulsize molecules (CAMS)
two structures that should be connected share a common
chemical substrate that lays down the pathway between them
dendrite and synapse that need to come in contact=attracted by same molecules and repelled by the same molecules- forces them to come together over time
neuronal cell death
initial neurogenesis overproduces cells
selective elimination of those not necessary
depends on if it receives neurotrophic factors from target cells that it synapsess with
apoptosis
unneeded cells are instructed to die via a phenomenon of programmed cell death, or apoptosis
process of apoptosis
Ca2+ influx causes Diablo protein to be released
Diablo blocks inhibitors of apoptosis proteins (IAPs)
causes widespread biochemical changes, leading to cell death
Synapse Rearrangement/Remodeling
initial synaptogenesis overproduces synapses
pruning
selective formation of new synapses (continues for life)
regulated by neuronal activity (action potentials)
pruning
selective elimination of overproduced synapses
transferring information will stay in place- ones that are there and not doing anything- will be pruned
adolescents
biologically programmed to make not smart decisions, be moody and pull away from family- be impulsive and take risks
auditory cortex
in the process of being pruned- language learning is easier at a younger stage compared to adults
brain maturation continues into adulthood
decrease of grey matter axon terminals/dendrites
increase of myelination/white matter- information sent between cortexes is faster- can catch along faster than a 6 year old
importance of each of these stages of nervous system development
is demonstrated by the functional effects of abnormal brain development
