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PRE LECTURE QUIZ WILL BEPRE LECTURE QUIZ WILL BE
GIVEN ON:GIVEN ON: BRAIN DEVELOPMENTBRAIN DEVELOPMENT
CRANIAL NERVESCRANIAL NERVES
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The Human EmbryoThe Human Embryo
ZygoteZygote
EmbryoEmbryo (first 8 weeks)(first 8 weeks)
endoderm (bodily linings)endoderm (bodily linings)
mesodermmesoderm (connective tissues)(connective tissues)
ectoderm (nervous system)ectoderm (nervous system)
FetusFetus (after 8 weeks)(after 8 weeks)
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Emergence ofthe Nervous SystemEmergence ofthe Nervous System
Neural plate becomes neural tubeNeural plate becomes neural tube
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Emergence ofthe Nervous SystemEmergence ofthe Nervous System
Walls ofneural tubeWalls ofneural tube
become neurons andbecome neurons and
glialcellsglialcells
Cavity ofneural tubeCavity ofneural tubebecomes ventricularbecomes ventricular
systemsystem
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Emergence ofthe Nervous SystemEmergence ofthe Nervous System
Neural tube defectsNeural tube defects
anencephalyanencephaly
spinaspina bifidabifida
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AnencephalyAnencephaly
cephalic disordercephalic disorder
that results from athat results from a
neural tube defectneural tube defect
occurs when the cephalic(head) end ofthe neural tube
fails to close
usually between the 23rd and 26th day ofpregnancy, resulting in the absence ofa major portion ofthe brain,
skull, and scalp.
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Children with this disorder are born withoutChildren with this disorder are born without
a forebrain, the largest part ofthe braina forebrain, the largest part ofthe brain
consisting mainly ofthe cerebralconsisting mainly ofthe cerebralhemispheres (which include thehemispheres (which include the neocortexneocortex,,
which is responsible for higherwhich is responsible for higher--levellevel
cognition, i.e., thinking).cognition, i.e., thinking). The remaining brain tissue is oftenThe remaining brain tissue is often
exposedexposednot covered by bone or skin.not covered by bone or skin.
AnencephalyAnencephaly
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A baby born with anencephaly is usuallyA baby born with anencephaly is usually
blind, deaf, unconscious, and unable to feelblind, deaf, unconscious, and unable to feel
pain.pain.
Although some individuals withAlthough some individuals with
anencephaly may be born with a main brainanencephaly may be born with a main brain
stem, the lack ofa functioning cerebrumstem, the lack ofa functioning cerebrumpermanently rules out the possibility ofeverpermanently rules out the possibility ofever
gaining consciousness.gaining consciousness.
Reflex actions such as breathing andReflex actions such as breathing andresponses to sound or touch occur.responses to sound or touch occur.
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SpinaSpina bifidabifida developmental birth defect caused by thedevelopmental birth defect caused by the
incomplete closure ofthe embryonic neuralincomplete closure ofthe embryonic neuraltubetube
cleft spine, which is an incomplete closurecleft spine, which is an incomplete closure
in the spinalcolumn.in the spinalcolumn.
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Some vertebrae overlying the spinalcord are notSome vertebrae overlying the spinalcord are not
fully formed and remainfully formed and remain unfusedunfused and open.and open.
Ifthe opening is large enough, this allows aIfthe opening is large enough, this allows aportion ofthe spinalcord to protrude through theportion ofthe spinalcord to protrude through the
opening in the bones.opening in the bones.
There may or may not be a fluidThere may or may not be a fluid--filled sacfilled sac
surrounding the spinalcord.surrounding the spinalcord.
Other neural tube defects includeOther neural tube defects include anencephalanencephalyy
encephalocele, which results when other parts of, which results when other parts of
the brain remainthe brain remain unfusedunfused..
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The Developing BrainThe Developing Brain
Rostral part ofneural tube becomes brainRostral part ofneural tube becomes brain
Caudal part ofneural tube becomes spinalCaudal part ofneural tube becomes spinal
cordcord
Differentiation ofbrain into 3 parts:Differentiation ofbrain into 3 parts:
prosencephalon (forebrain)prosencephalon (forebrain)
mesencephalon (midbrain)mesencephalon (midbrain)
rhombencephalon (hindbrain)rhombencephalon (hindbrain)
Further differentiation ofthese 3 partsFurther differentiation ofthese 3 parts
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The Developing Spinal CordThe Developing Spinal Cord
2 major zones ofcells:2 major zones ofcells:
alar platealar plate (dorsal)(dorsal)
sends sensory projections to brainsends sensory projections to brain
basal platebasal plate (ventral)(ventral)
motor neuron developmentmotor neuron development
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Formation ofNeurons and Glial CellsFormation ofNeurons and Glial Cells
Single layer ofcells withinSingle layer ofcells withinneural tubeventricularlayerneural tubeventricularlayer
DaughtercellsDaughtercells
Migration first to marginalMigration first to marginal
(outer) layer(outer) layer
Migration then toMigration then to
intermediate layerintermediate layer
Migration to cortical plate &Migration to cortical plate &
subventricularlayersubventricularlayer
Some remain in ventricularSome remain in ventricularlayer(ependymalcells)layer(ependymalcells)
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Cell Formation and MigrationCell Formation and Migration
NeurogenesisNeurogenesis: formation of: formation of
new neuronsnew neurons
Neural migration guided by:Neural migration guided by:
radial glialcellsradial glialcells
glycoproteinsglycoproteins
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Cell DifferentiationCell Differentiation
Creation ofdifferent cellCreation ofdifferent cell
typestypes
2 types:2 types:
cellcell--autonomousautonomous
differentiation (genetic)differentiation (genetic)
induction (dependent uponinduction (dependent upon
influence ofothercells)influence ofothercells)
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Glial Cell DevelopmentGlial Cell Development
Begins in embryonicBegins in embryonicperiodperiod
Most intense glialMost intense glial
production after birthproduction after birth
Myelination (wrappingMyelination (wrappingaxon in myelin sheath)axon in myelin sheath)
spinalcord thenspinalcord then
hindbrain thenhindbrain then
midbrain thenmidbrain then
forebrainforebrain
sensory then motorsensory then motor
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Formation ofNeural ConnectionsFormation ofNeural Connections
Axons grow towards target cellsAxons grow towards target cells
Axon emerges from growth coneAxon emerges from growth cone
(containing filopodia)(containing filopodia)
Filopodia are attracted to target cell throughFilopodia are attracted to target cell through
chemical signalchemical signal
neurotrophinsneurotrophins
Abrupt changes in direction ofgrowth dueAbrupt changes in direction ofgrowth due
to guidepost cellsto guidepost cells
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Importance ofNeural ActivityImportance ofNeural Activity
Axonal remolding (Shatz, 1992)Axonal remolding (Shatz, 1992)
neurons grow to manyneurons grow to many
addressesaddresses
correct address...remaincorrect address...remain incorrectincorrect
address...eliminatedaddress...eliminated
Neurons that fire together wireNeurons that fire together wire
togethertogether
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Neuron Cell DeathNeuron Cell Death
Theories:Theories:
Competition to attain connections with targetCompetition to attain connections with target
cellscells Need to receive certain qualitity ofNeed to receive certain qualitity of
neurotrophins for survivalneurotrophins for survival
Examples:Examples: Motor neuronMotor neuron--muscle fiberconnections (PNS)muscle fiberconnections (PNS)
Purkinje cells ofcerebellum (CNS)Purkinje cells ofcerebellum (CNS)
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Failures ofNeural DevelopmentFailures ofNeural Development
Genetic defectsGenetic defects
DownDown SyndromeSyndrome -- trisomytrisomy 21, is a chromosomalcondition21, is a chromosomalcondition
caused by the presence ofall or part ofan extra 21st chromosome.caused by the presence ofall or part ofan extra 21st chromosome.
PhenylketonuriaPhenylketonuria (PKU(PKU)) -- autosomalautosomal recessive metabolicrecessive metabolicgenetic disordercharacterized by a deficiency in the hepatic enzymegenetic disordercharacterized by a deficiency in the hepatic enzyme
phenylalaninephenylalanine hydroxylasehydroxylase (PAH)(PAH)
PAH : convertsPAH : converts phenylalanine ('phenylalanine ('PhePhe') to the amino acid tyrosine.') to the amino acid tyrosine.
hyperphenylalaninemiahyperphenylalaninemia (HPA) was associated with mental retardation(HPA) was associated with mental retardation..
Fragile XFragile X SyndromeSyndrome
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Fragile X SyndromeFragile X Syndrome
genetic syndrome which results in agenetic syndrome which results in a
spectrum ofcharacteristic physical andspectrum ofcharacteristic physical and
intellectuallimitations and emotional andintellectuallimitations and emotional and
behavioralfeatures which range from severebehavioralfeatures which range from severe
to mild in manifestation.to mild in manifestation.
expansion ofa singleexpansion ofa single trinucleotidetrinucleotide genegene
sequence (sequence (CGG)CGG) on theon the X chromosome, andchromosome, and
results in a failure to express the proteinresults in a failure to express the proteincoded by thecoded by the FMR1 gene, which is requiredne, which is required
for normal neural development.for normal neural development.
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ExternalfactorsExternalfactors
MalnutritionMalnutrition
Fetal Alcohol SyndromeFetal Alcohol Syndrome -- next slidenext slide
Failures ofNeural DevelopmentFailures ofNeural Development
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(Andrew Syndrome) is a pattern ofmental(Andrew Syndrome) is a pattern ofmental
and physical defects that can develop in aand physical defects that can develop in a
fetus when a woman drinks alcohol duringfetus when a woman drinks alcohol during
pregnancy.pregnancy.
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Redevelopment ofthe Nervous SystemRedevelopment ofthe Nervous System
Damage to cell body ofnerve...death; damage to axon...degenerative changes,Damage to cell body ofnerve...death; damage to axon...degenerative changes,sometimes deathsometimes death
anterograde degeneration (from point ofinjury to axon terminals)anterograde degeneration (from point ofinjury to axon terminals)
retrograde degeneration (between point ofinjury and cell body)retrograde degeneration (between point ofinjury and cell body)
chromatolysis (degeneration ofcell body)chromatolysis (degeneration ofcell body)
transneuronal degeneration (damage to connecting neurons)transneuronal degeneration (damage to connecting neurons)
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...Redevelopment ofthe Nervous System...Redevelopment ofthe Nervous System
Regeneration occurs within PNS onlyRegeneration occurs within PNS only
Collateral sprouting within CNSCollateral sprouting within CNS
Research on recovery ofCNS functioningResearch on recovery ofCNS functioning
collateral sproutingcollateral sprouting
suppression ofgrowthsuppression ofgrowth--inhibiting chemicalsinhibiting chemicals
fetal tissue transplantationfetal tissue transplantation
Compensatory strategies after CNS damageCompensatory strategies after CNS damage
rehabilitationrehabilitation
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