prenatal development Flashcards
neonate =
less than 1 month old
give some of the indirect methods to study prenatal development
loud sounds on surface of abdomen and report foetus movement, inferences from non human animal models, studies of embryos and foetuses during autopsy, perception and memory of neonates
give some of the direct methods to study prenatal development
ultrasound, brain activity via fMRI
what are the 3 prenatal periods?
germinal, embryonic, fetal
a single cell zygote develops into morula and then blastocyst. period from conception to attachment to uterine wall 8-10 days later. what period is this?
germinal
attachment to end of 8th week and all major organs have taken primitive shape and sexual differentiation occurs. what period is this?
embryonic
9th week until birth. what period is this?
fetal
how long does the embryonic period last?
about 6 weeks
what is the process where the simple ball of cells forms into a more complex embryo with three distinct germ layers?
gastrulation
in what ways does the embryo in the embryonic period start responding to the environment?
turns head in response to light, touches around mouth
makes up the skin, brain, NS =
ectoderm
bones, muscles, heart, circulatory system, internal sex organs =
mesoderm
inner lining of some systems, some organs (liver, pancreas) =
endoderm
what happens to the ectoderm during brain development?
becomes neural plate > differentiates into cells that become the forebrain, midbrain, hindbrain > neural plate folds to become the neural tube
how many x in size does the brain grow during the foetus period (week 9-birth)?
6x in size
at how many weeks does the foetus reach the “age of viability”?
22
the age of viability =
the age a preterm baby can survive
at 5-6 weeks what happens to the neural tube and brain hemispheres?
neural tube starts to differentiate into different parts of CNS, 2 hemispheres start to develop
what is seen at 7-14 weeks?
division of the 2 halves on the brain become visible
what is seen at 6 months?
nerve cell generation complete, cortex begins to wrinkle, myelination
what are the 5 phases of brain development?
neural plate induction, neural proliferation, migration/aggregration, axon growth and synapse formation, cell death and synapse rearrangement
when does neural plate induction take place?
2-3 weeks after conception
what induces development during neural plate induction?
chemical signals (growth factors)
totipotent =
not specialised zygote
multipotent =
develop into any type of NS cell
pluripotent =
5 days after fertilisation > blastocyst forms
during neural proliferation, what will the 3 swellings at the anterior end become?
forebrain, midbrain, hindbrain
what happens during migration?
neutrons move away from ectoderm, differentiation begins as migration occurs, develop NT making ability, start generating Paps
what act as guide wires for the migration of neurons?
radial glia
cells that are done migrating align themselves with other cells to form structures =
aggregation
axons (with growth cones on the end) and dendrites form a ______ with other neurons or tissue
synapse
what is critical for synaptogenesis to occur?
growth cones and chemo-attractants
creation of new synapses =
synaptogenesis
what does synaptogenesis depend on?
presence of glial cells (especially astrocytes)
why do a lot of neurons die after migration?
due to failure to compete for chemicals provided by targets
what is the chemical called that neutrons compete for?
neurotrophins
what does neurotrophin do?
promote growth and survival, guide axons, stimulate synaptogenesis
does myelination begin in the CNS or the PNS?
PNS
do motor or sensory roots become myelinated first in the PNS?
motor roots
myelination begins in the spinal cord at __ weeks and proceeds according to a craniocaudal gradient
11
in 3rd trimester, myelination begins to occur in the CNS but what is the difference than the PNS?
first seen in the sensory tracts (not motor) ie. visual system
when does myelination in complex association pathways in the cerebral cortex occur?
after birth
during infancy and early childhood, the cerebral cortex overproduces _______. how is this corrected?
synapses, pruning > experience shapes and solidifies these synapses
inherited form of mental retardation in males =
fragile X syndrome
what is the cause of fragile X syndrome?
defective FMR1 gene suppresses the production of proteins that stimulate prancing so excess synapses not pruned sufficiently > leads to ‘noise’ in neural system that causes MR and AD attention deficit symptoms
why is immaturity at birth an adaptive feature?
brains develop as we have contact with the world so can adapt it to different environments > early experiences create architecture of brain > form new connections
cerebral hemispheres begin to develop = how many weeks?
9
what are early behaviours in early foetal movements due to before the cerebral cortex develops?
largely reflexive controlled by simpler circuits in midbrain
cells in cerebral cortex proliferate and migrate = how many months?
4
sulci and gyri develop, capacity to learn and show basic forms of memory = how many months?
6
foetus behaviour becomes more organised with _______
gestation
at how many weeks does the foetus have distinct periods of rest and activity and is no longer continually moving?
34 weeks
foetus’ from 34 weeks spend most of their time in ______ sleep
active
what behaviours are involved in fetal active sleep?
HR and breathing = irregular, responsive to sensory stimuli in uterine environment, eyes show movement, more responsive to touch and sound
what are the features of a foetus at 38 weeks (end of pregnancy)?
not spend as much time in active sleep, brain is more mature, more inhibitory pathways developed (further reduces amount of movement)
foetus have a period of rest and activity in cycles throughout the day. when is there is a peak in activity?
when the mother is asleep
