1brain development

8/3/2019 1brain Development

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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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Walls ofneural tubeWalls ofneural tube

become neurons andbecome neurons and

glialcellsglialcells

Cavity ofneural tubeCavity ofneural tubebecomes ventricularbecomes ventricular

systemsystem


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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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