Lec 8: Brain Development (The Early Years) Flashcards
what were the consequences of the atomic bomb (Hiroshima)?
cranium size of children were smaller as a consequence of this bomb (because of radiation)
- inc in amount of seizures
brains are shaped by the interaction between ____ and _____
genetics & experience
3 types of development that are highly interrelated?
social
emotional
cognitive
is brain architecture and skills built in top-down or bottom-up sequence?
bottom-up
brain plasticity and ability to change behaviour INC/DEC over time?
decrease
what are the 3 core concepts of development?
1) brain architecture is established early in life and supports lifelong learning, behaviour and health
2) stable, caring relationships and “serve and return” interaction shape brain architecture
3) toxic stress in the early years of life can derail healthy development
what is the timespan for development of the CNS??
3 weeks –> 20 years
at what week gestation does the CNS begin to form?
3 weeks gestation
what is the first neural element that begins to develop in the ‘early beginnings’?
the neural tube
compare the weight of the brain at birth VS 1 year
birth= 350g
1 year= 1000g
4 steps/processes in the growth and development of neurons
- proliferation (production of new cells)
- migration (move towards final destination)
- differentiation (form axons and dendrites)
- myelination (addition of insulating sheath)
–> inc in methylation
name the 4 stages of development
prenatal
infancy
childhood
adolescence
when is the prenatal phase?? what occurs during this phase?
conception–> birth
- rapid physical growth
what is the infancy stage?? what occurs during this phase?
birth –> 2 years
- motor development
what is the childhood stage?? what occurs during this phase?
2-12 years
- abstract reasoning
what is the adolescence stage?? what occurs during this phase?
13-25 years
- identity creation
what is the main ‘highlight’ after the adolescence stage?
development of ‘judgement’
- risk taking behaviour is high in 20-25 year olds
- directly related to the maturation of the Prefrontal Cortex
what is Piaget’s Object Permanence task?
- infant sees toy, investigator places barrier in front of toy
- infants younger than 9mo fail to reach for hidden toy
- up to 4 years old, do not remember anything, no good connection between prefrontal cortex and hippocampus
- tasks that require a response to a stimulus that is no longer present depend on the prefrontal cortex (slow to mature)
what occurs during the prenatal phase of development?
- ovum + sperm = zygote
- once zygote implants in uterus= embryo (composed of germinal layers of cells from which various organs derive later)
- weak 8 –> birth = fetus
prenatal brain development is primarily ____
structural
when does cell creation and movement occur in prenatal development?
during first 5 months
what are the 5 phases of brain development?
1) neural plate induction
2) neural proliferation
3) migration and aggregation
4) axon growth & synapse formation
5) cell death and synapse rearrangement
embryonic stage of development includes the process of ____
organogenesis
what is organogenesis?
transformation from embryo to a body structure including defined organs
what forms on day 16 (gestation), and what is its function?
primitive streak
- provides axis which other structures can organize
what is formed on day 21?
neural groove
name the 3 germinal layers of the embryo
ectoderm
mesoderm
endoderm
the process of ____ in embryos forms the NS and vertebral column
neurulation
the process of neurulation in embryos generates a dorsal rod shaped structures termed a _____
notochord
the notochord is generated from what structure?
primitive streak
the notochord serves as a ______ ____, which is later replaced by the ___ _____
serves as a primitive skeleton
later replaced by the vertebral column
the NS develops from the _____ (layer) which is located above/below the notochord?
ectoderm
above the notochord
explain the basic steps of neurulation
- neural folds form from neural plate
- folds fuse
- neural tube forms
NS development proceeds from the generation of the neural ___ to neural ____, which eventually develop into the neural ____
neural plate
neural folds
neural tube
___ days after conception the embryo begins to implant in the uterine wall
(induction of neural plate)
18 days
- this becomes the patch of tissues on the dorsal surface of the embryo that will become the NS
thickening of the ____ germ layer leads to the development of the neural_____
ectoderm
neural plate
when does the neural groove begin to develop?
20 days
during the induction of the neural plate, what occurs at 22 days?
neural groove closes along the length of the embryo making the neural tube
during the induction of the neural plate, what occurs a few days after day 22 and neural tube production?
brain subdivides into the:
- forebrain
- midbrain
- hindbrain
what structure(s) are included in the forebrain
telencephalon
diencephalon
what structure(s) are included in the midbrain?
mesencephalon
what structure(s) are included in the hindbrain?
rhomencephalon
what does proliferation mean?
generation of new cells
____ cels are the stem cells of the NS
neuroepithelial cells
what occurs during the 2nd step of brain developmentL neural proliferation
neuroepithelial cells of the ectoderm proliferate
- 3 swellings at the anterior end in humans become forebrain, midbrain, hindbrain
- after mitosis, “daughter” cells become “fixed” post mitotic
where does mitosis/proliferation occur????
ventricular zone
- rate can be 250 000/min
what occurs during the 3rd phase of brain development: migration
slow movement to the right place
describe the characteristics of migrating neurons
- immature
- lacking dendrites
- only a soma and immature axon
- undifferentiated at start of migration
differentiation begins as ……
neurons migrate
- they develop NT making ability and AP (as they migrate)
(migration) neuroepithelial cells of the ventricular zone give rise to ___ ____cells that further differentiated into ____ or ____ cells
radial glial cells
neurons or glial cells (e.g. astrocytes)
function of radial glial cells?
act as guide wires for migration of neurons
- scaffolding structures
what is the process of aggregation (following migration)
cells that are done migrating align themselves with other cells and form structures
- later neuroepithelial cells= present at top
- earlier neuroepithelial cells= at the bottom
- brain develops inside-out
describe the relationship between methylation in the cell and dietary methionine
inc methylation in the cell from dietary methionine
- high methionine and high choline in diet of pregnant women= to continue methylation
- low methylation= spina bifida & cleft lips
closure of the neural tube and action of neural crest cells from neural folds is dependent on….
methylation machinery
brain regions (forebrain, midbrain, hindbrain) further divide and contain
fluid filled region= ventricle, aqueduct or canal
where do the 2 major bends/flexures occur?
midbrain and cervical
name the 3 primary brain vesicles
prosencephalon (forebrain)
mesencephalon (midbrain)
rhombencephalon (hindbrain)
name the 5 secondary brain vesicles & which primary vesicles they are derived from
prosencephalon
1) telencephalon
2) diencephalon
mesencephalon
3) mesencephalon
rhombencephalon
4) metencephalon
5) myelencephalon
which adult brain structures & ventricles are derived from the secondary brain vesicles?
1) telencephalon: cerebrum/cerebral hemispheres (cortex, white matter, basal nuclei)
- lateral ventricles
2) diencephalon: diencephalon (thalamus, hypothalamus, epithalamus)
- third ventricle
3) mesencephalon: brainstem- midbrain
- cerebral aqueduct
4) metencephalon: brainstem-
pons
- 4th ventricle
5) myelencephalon: braintem-
medulla oblongata
- 4th ventricle
what are gyri?
elevated ridges
entire surface
(BUMPS)
what are sulci?
groove separating gyri
shallow groove
what are fissures?
deeper grooves
describe how the cerebral hemispheres are forced to grow
due to space restrictions, grow posteriorly over rest of brain, envelop it
- grow into horseshoe shape
- continued growth causes creases, folds, wrinkles
what is grey matter?
neuronal cell bodies
- brown when fixed
- dendrites and axon terminals of neurons
- where all synapses are
what is white matter?
neuronal axons coated with electrical insulation= myelin
connecting different parts of grey matter to each other
what occurs during the 4th stage of brain development: axon growth/synaptogenesis?
- once migration is complete and structures have formed (aggregation), axons/dendrites begin to grow to their “mature” size/shape
- axons (with growth cones on end) and dendrites form a synapse with other neurons/tissue
- growth cones and chemo-attractants are critical for this (e.g. NCF)
name the 2 types of cells in CNS
neurons
glial cells (~10:1)
the formation of new synapses is called???
synaptogenesis
most neurons are formed halfway through gestation and have no synaptic connections, what forms these synaptic connections?
experience and interaction with environment
during what time frame does synaptogenesis occur?
through to the 2nd year of life
what % of dendritic growth occurs after birth?
83%
what is a synaptic cleft?
space between neurons at nerve synapse across which a nerve impulse is transmitted by a NT
what are dendrites?
receive messages from other cells
what are axons terminals?
passes on messages to other cells
what is a Node of Ranvier?
separate Schwann cells (glial) which are formed around axon to form axon sheath
after birth, development is ….
refinement of neuronal connections
maturity of neurons
increasing complexity of dendrite interconnections
what % of neurons made will die after migration??
40-75%
- death is normal and necessary, important to strengthen connections
why do neurons typically die?
due to failure to compete for chemicals provided by targets
what are neurotrophins?
family of proteins (e.g. NGF, BDNF)
3 functions of neurotrophins
- promote growth/survival
- guide axons
- stimulate synaptogenesis
axons not exposed to neurotrophins after making connections undergo ___
apoptosis
- preprogrammed mechanism of cell death
describe ‘use it or lose it’ (neural darwinism)
- neurons and synapses must get hooked together properly to develop specific skills and abilities in humans
- during infancy and early childhood, developing cortex overproduces synapses (2X as needed)
- overproduction leads to competition for survival of fittest synapses (competition for neurotrophin, NGF)
- after maturity, apoptoci mechanisms become dormant
- neurons no longer need neurotrophins for survival
- neurotrophins inc the branching on axons and dendrites throughout life
when does synaptogenesis and pruning occur?
- in cortex, synapses begin to form after neuronal migration (23 weeks prenatal)
- most synapses form after birth (form randomly)
- flourish, and selectively prune by levels of NT (up to 100 000 synapses pruned per second)
what are the 2 types of synapse development?
1) experience-expectant development
2) experience-dependent development
what is experience-expectant development?
- overproduces synapses, prune with experience
- ‘experiences leads to LESS’
- tied to critical/sensitive periods
- organizes brain to process info, behaviours EXPECTED for humans (sensory processes, parental attachment, eye-hand coordination, language capacity)
pruning leads to more/less cells?
LESS
what is experience-dependent development?
- new synapses formed, maybe some pruning
- ‘experience leads to MORE’
- continues throughout life
- codes experiences/learning that is person-specific (particular language, specific knowledge, memories, skills)
result of enriched housing in INFANT rats
- enrichment REDUCED synapse density
- facilitated pruning of excess synapses in experience-expectant development
prune > gain
(synaptic gain is less, when dec synapse density)
result of enriched housing in ADULT rats
- enrichment INCREASED synapse density
- facilitate growth of new synapses in experience-dependent development
Gain > prune
(more gain of synapse density, compared to loss of pruning)
experience influences pruning and growth of new synapses in ____ ___ manner
age dependent ***
- has to do with # of structures formed (e.g. in regions of cortex)
what occurs during synapse rearrangement?
- release and uptake of neurotrophic factors
- neurons receiving insufficient neurotrophic factor die
- axonal processes compete for limited neurotrophic factor
what are active synapses?
receive enough neurotrophic factor to remain stable
what are inactive synapses?
receive too little neurotrophic factor to remain stable
what is the process of myelination?
- glial cells (formed by oligodendrocytes in CNS and Schwann cells in PNS) wrap themselves around axons
- inc speed of AP conduction down axon
when does myelination occur?
- begin at birth
- rapidly inc to 2 years
- continue to inc slowly to 30 years old
glial cells in CNS are formed by
oligodendrocytes
glial cells in PNS are formed by
schwann cells
what is the function of myelin?
- in adults, dendritic growht and synapse refinement are coated with myelin
- serves as an electrical insulation
myelination slows/speeds the travel of impulses and makes travel more/less efficient?
speeds up
more efficient
correlation between myelination and breastfeeding?
- myelin composed of 15% cholesterol, 20% protein
- myelin content and speeds of electrical signals INC with breasfeeding
SUMMARY: name the 8 phases of embryonic and fetal development at a cellular level **
1) mitosis/proliferation
2) migration
3) differentiation
4) aggregation
5) synaptogenesis
6) neuron death
7) synapse re-arrangement
8) myelination
postnatal growth is a consequence of … (3)
1) synaptogenesis
2) inc dendritic branches
3) myelination (prefrontal cortex continues into adolescence)
overproduction of synapses may underlie the greater ____ of the young brain
plasticity
- young brain more able to recover function after injury, as compared to older brain
name the 3 structures that compose the forebrain
- cerebrum (cortex)
- thalamus
- hypothalamus
(part of limbic system)
name the 2 structures that compose the midbrain
tectum & tegmentum
name the 3 main structures that compose the hind brain
- cerebellum
- pons
- medulla
what structures are referred to as the brainstem?
midbrain, pons, medulla
the frontal lobe is responsible for
- self-regulation
- problem solving
- goal setting
- social cognition
- judgement, decisions, planning, creativity
occipital lobe is responsible for
vision and perception
- processes visual input that is sent to the brain from retinas
the parietal lobe is responsible for
sensory motor perception
spatial abilities
- main sensory inputs from skin (touch, temp, pain receptors) relay through thalamus to parietal lobe
the temporal lobe is responsible for
hearing
language
memory
social-emotional function
brainstem is important for which 4 basic functions?
- HR
- breathing
- sleeping
- eating
(“survival”)
limbic system is responsible for….
emotion
cerebellum is responsible for…
movement
what are the frontal lobes executive functions?
governing emotions judgement planning organizing problem solving impulse inhibition abstraction analysis/synthesis self-awareness self-concept identity spirituality
maturation occurs from ___ to ___ of the brain
back to front
early development of back of brain and later development of front of brain leads to… (in adolescents)
- preference for physical activity
- less than optimal planning and judgement
- more risky, impulsive behaviours
- minimal consideration of negative consequences
describe frontal lobe development
- very sensitive to early experience
- long process beginning prenatally, continue until early adulthood
- altered by range of positive and negative experiences (e.g. parent-infant interactions, drugs, stress)
describe neuroplasticity in adults
- where is neurogenesis?
- mature brain changes and adapts
- neurogenesis (birth of new neurons) seen only in olfactory bulb and hippocampus of adult mammals
