development of nervous system_newkeynote

8/9/2019 Development of Nervous System_newkeynote

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Development of theDevelopment of the

Nervous SystemNervous System


Nervous SystemNervous System

Carmelo C. Canto M.D.Carmelo C. Canto M.D.


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Did you read your book? Lets check :Did you read your book? Lets check :--))

1. What are the 5 secondary vesicles that form1. What are the 5 secondary vesicles that form

from the neural tube in the developmentalfrom the neural tube in the developmental

sequence of brain regions?sequence of brain regions?

2. What are the 3 layers of the neural tube?2. What are the 3 layers of the neural tube?

3. Name 2 tissues/structures derived from3. Name 2 tissues/structures derived from

neural crest cells.neural crest cells.


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1. Cytogenesis1. Cytogenesis cellular division andcellular division and

differentiationdifferentiation

2. Histogenesis2. Histogenesis orientation of cells andorientation of cells and

connecting tissues, cell migrationconnecting tissues, cell migration

3. Organogenesis3. Organogenesis blending of tissuesblending of tissues

into organsinto organs

MORPHOGENESISMORPHOGENESISMORPHOGENESISMORPHOGENESIS


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TheThe

BeginningBeginning

TheThe

BeginningBeginning


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FertilizationFertilization 2 celled organism2 celled organism


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Week 3 : Gastrulation forms TrilaminarWeek 3 : Gastrulation forms Trilaminar

Disc and NotochordDisc and Notochord

Neural tissue appears atNeural tissue appears at 3rd week3rd week of development (fertilization = day 1)of development (fertilization = day 1)

Epiblasts differentiate to form :Epiblasts differentiate to form : 3 primary germ layers3 primary germ layers

1.1. EctodermEctoderm -- CNS, PNS, epidermisCNS, PNS, epidermis

2.2. EndodermEndoderm -- lungs, liver, GITlungs, liver, GIT

3.3. MesodermMesoderm -- muscles, vascular structuresmuscles, vascular structures

Epiblasts also form theEpiblasts also form the NotochordNotochord

18 day old embryo18 day old embryo


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Partial Duplication ofPartial Duplication ofPrimitive streakPrimitive streak


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DiplocephalyDiplocephaly

-- Duplication of anterior primitiveDuplication of anterior primitivestreakstreak-- leads to duplication of Notochordleads to duplication of Notochord-- resulting in 2 neural tubesresulting in 2 neural tubes


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The NotochordThe Notochordformed from the mesoderm between 16formed from the mesoderm between 16 -- 21 days21 days

defines the longitudinal axis of the embryodefines the longitudinal axis of the embryo

determines the orientation of the vertebral columnsdetermines the orientation of the vertebral columns

persists as thepersists as the Nucleus PulposusNucleus Pulposus

induces formation of the neural plateinduces formation of the neural plate together withtogether with Sonic hedgehogSonic hedgehog

gene (SHH)gene (SHH)


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Nucleus PulposusNucleus Pulposus


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NeurolationNeurolation: Formation and Closure of: Formation and Closure of

theN

eural

TubetheN

eural

Tube

-- Neural PlateNeural Plate

thickensthickens

-- Neural GrooveNeural Groove

formsforms-- Neural FoldNeural Fold

-- Closes rostroCloses rostro--

caudalcaudal

-- Requires Folic AcidRequires Folic Acid

1818--20 days20 days (21(21--22 days) Middle Neuropore22 days) Middle Neuropore

2424--25 days Cranial, 2625 days Cranial, 26--27 days27 days

Caudal Neuropore ClosesCaudal Neuropore Closes


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Secondary NeurolationSecondary Neurolation

Day 20, Caudal Eminence (mass ofDay 20, Caudal Eminence (mass of

mesenchyme) condenses then hollows outmesenchyme) condenses then hollows out

Day 40 hollowed caudal eminence joins neuralDay 40 hollowed caudal eminence joins neural

tubetube

forms sacral and coccygeal spinal segmentsforms sacral and coccygeal spinal segments


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Caudal Regression Syndrome or CaudalCaudal Regression Syndrome or Caudal

DysgenesisDysgenesis

Insufficient mesoderm in caudal eminenceInsufficient mesoderm in caudal eminence

Pelvic and Lower extremity hypoplasiaPelvic and Lower extremity hypoplasia

extreme cases = Sirenomeliaextreme cases = Sirenomelia

associated with maternal DMassociated with maternal DM


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HistogenesisHistogenesis-- orientation of cells and connecting tissues,orientation of cells and connecting tissues,

cellular migrationcellular migration


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Layers of the Neural TubeLayers of the Neural Tube

1. Neuroepithelial (Germinal) Layer1. Neuroepithelial (Germinal) Layer -- contains rapidlycontains rapidly

dividing cells, produce neuroblasts or primitive nerve cellsdividing cells, produce neuroblasts or primitive nerve cells

2. Mantle Layer2. Mantle Layer -- zone formed by neuroblasts fromzone formed by neuroblasts fromsurrounding germinal layer; forms gray mattersurrounding germinal layer; forms gray matter

3. Marginal Layer3. Marginal Layer -- formed by nerve fibers coming fromformed by nerve fibers coming from

axons of neuroblasts in mantle layer; forms white matteraxons of neuroblasts in mantle layer; forms white matter


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Neuroepithelial Cell DifferentiationNeuroepithelial Cell Differentiation

Neuroepithelial cells produce nerve cellsNeuroepithelial cells produce nerve cells

(neuroblasts) and supporting cells (macroglia or(neuroblasts) and supporting cells (macroglia or

neuroglia)neuroglia)


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Histogenesis : Summary of EventsHistogenesis : Summary of Events

Neuroblasts formed in periventricular (Matrix) zoneNeuroblasts formed in periventricular (Matrix) zone

Many migrate outwards to form cortex of cerebrumMany migrate outwards to form cortex of cerebrum

and cerebellumand cerebellum

remaining neuroblasts form the deep subcorticalremaining neuroblasts form the deep subcortical

nuclei and grey mater of brain and spinal cordnuclei and grey mater of brain and spinal cord


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Failure of Neuronal MigrationFailure of Neuronal Migration

Lissencephaly (Smooth Brain)Lissencephaly (Smooth Brain)


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Neural Crest CellsNeural Crest Cells

-- Ectodermal in originEctodermal in origin

-- anyany neuronneuron outsideoutside ofof thetheCNSCNS isis derivedderived fromfrom neuralneuralcrestcrest


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Neural Crest DerivativesNeural Crest Derivatives

-- connective tissue of bones of face and skullconnective tissue of bones of face and skull-- dorsal root gangliadorsal root ganglia

-- cranial nerve ganglia (V, VII, IX and X)cranial nerve ganglia (V, VII, IX and X)-- odontoblastsodontoblasts-- Schwann cellsSchwann cells-- adrenal medullaadrenal medulla-- sympathetic chain and preaortic gangliasympathetic chain and preaortic ganglia-- parasympathetic ganglia of GITparasympathetic ganglia of GIT-- leptomaningesleptomaninges-- melanocytesmelanocytes


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Development of the Spinal CordDevelopment of the Spinal Cord

-- Basal PlateBasal Plate -- ventral thickening; will form motor neurons of ventralventral thickening; will form motor neurons of ventralhornhorn

-- Alar PlateAlar Plate -- dorsal thickening; will form the sensory neurons of thedorsal thickening; will form the sensory neurons of theposterior hornposterior horn

-- Sulcus LimitansSulcus Limitans -- boundary between motor and sensoryboundary between motor and sensory


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-- Dorsal Root formed by Dorsal RootDorsal Root formed by Dorsal RootGanglion derived from neural crest cellsGanglion derived from neural crest cells

Spinal NerveSpinal Nerve

-- Ventral Root formed from somatic and autonomicVentral Root formed from somatic and autonomic

motor neuronsmotor neurons


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Clinical CorrelationClinical Correlation

9 months9 months AdultAdult


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MyelinationMyelination

-- Myelination ofMyelination ofperipheral nerveperipheral nerve brought about by neurilemma cells or cells ofbrought about by neurilemma cells or cells ofSchwannSchwann

-- Schwann cellsSchwann cells originate fromoriginate from neural crestneural crest

-- 4th month of fetal life, myelin deposition occurs4th month of fetal life, myelin deposition occurs

-- Myelin sheath ofMyelin sheath ofperipheral of nerve fibersperipheral of nerve fibers are formed byare formed by cells of Schwanncells of Schwann

-- Myelin sheath ofMyelin sheath ofnerve fibers within the spinal cordnerve fibers within the spinal cord and the rest ofand the rest ofCNSCNSare produced byare produced by oligodendrogliaoligodendroglia

-- Some motor fibers descending from higher centers do not become myelinated untilSome motor fibers descending from higher centers do not become myelinated until 1st week of postnatal life1st week of postnatal life

-- The tracts of the nervous system become myelinated by the time they begin functionThe tracts of the nervous system become myelinated by the time they begin function


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BrainstemBrainstem BrainBrain

cerebellumcerebellum

cerebral hemispherescerebral hemispheres

MedullaMedulla

PonsPons

MidbrainMidbrain

DiencephalonDiencephalon


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Developmental Sequence of Brain Regions : 3Developmental Sequence of Brain Regions : 3

Vesicle and 5 vesicle StagesVesicle and 5 vesicle Stages


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to maintain a largeto maintain a large

surface area in a smallsurface area in a small

containercontainer

Development ofFlexures, Sulci, FissuresDevelopment ofFlexures, Sulci, Fissures

Surface area of brain =Surface area of brain =SoccerFieldSoccerField


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Myelencephalon : Development of MedullaMyelencephalon : Development of Medulla

Alar Plate (Sensory Neurons)Alar Plate (Sensory Neurons)-- laterallateral

-- sensory nuclei of CN V, VIII, IX, Xsensory nuclei of CN V, VIII, IX, X

Basal Plate (Motor Neurons)Basal Plate (Motor Neurons)-- MedialMedial

-- Motor nuclei of CN IX, X, XI, andMotor nuclei of CN IX, X, XI, and

XIIXII


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MetencephalonMetencephalon

2 Parts2 Parts1. Pons1. Pons -- ventral portionventral portion

-- connects cord, cerebral cortexconnects cord, cerebral cortex

and cerebellumand cerebellum

a. Pontine Tegmentuma. Pontine Tegmentum

b, Basis Pontisb, Basis Pontis

2. Cerebellum2. Cerebellum -- dorsal portion;dorsal portion;

coordination center for posture andcoordination center for posture and

movementmovement


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Metencephalon: PonsMetencephalon: Pons

Basal PlateBasal Plate

-- medially locatedmedially located

-- motor nuclei of CN V, VIImotor nuclei of CN V, VII


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Metencephalon: PonsMetencephalon: Pons

Alar PlateAlar Plate

-- laterallateral

-- Sensory Nuclei of CN V, VII, VIII, IX and XSensory Nuclei of CN V, VII, VIII, IX and X

-- Pontine NucleiPontine Nuclei


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Metencephalon: CerebellumMetencephalon: Cerebellum

-- Rhombic lips form cerebellar plateRhombic lips form cerebellar plate

-- cerebellar plate divides into a midline vermiscerebellar plate divides into a midline vermisand 2 hemispheresand 2 hemispheres


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Mesencephalon: MidbrainMesencephalon: Midbrain

Morphologically the most primitive ofMorphologically the most primitive ofthe brain vesiclesthe brain vesicles


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Midbrain: Alar PlateMidbrain: Alar Plate

-- Superior Colliculus serves as reflex center for visualSuperior Colliculus serves as reflex center for visual

impulsesimpulses-- Inferior Colliculus serves as synaptic relay station forInferior Colliculus serves as synaptic relay station for

auditory impulsesauditory impulses


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Midbrain: Basal PlateMidbrain: Basal Plate

Basal Plate Motor Nuclei:Basal Plate Motor Nuclei:

1. Oculomotor (CN III), Trochlear (CN IV)1. Oculomotor (CN III), Trochlear (CN IV)

2. Edinger Westphal Nucleus2. Edinger Westphal Nucleus -- pupillarypupillary

constrictionconstriction


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DiencephalonDiencephalon

Develops from medial portion ofDevelops from medial portion of

ProsencephalonProsencephalon

Consist of 2 alar plates, a roof plateConsist of 2 alar plates, a roof plate

and the 3rd ventricleand the 3rd ventricle


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gives rise to choroid plexus of 3rd ventriclegives rise to choroid plexus of 3rd ventricle

pineal body or epiphysispineal body or epiphysis

epithalamusepithalamus

Diencephalon: Roof PlateDiencephalon: Roof Plate


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Diencephalon: Thalamus andDiencephalon: Thalamus and

HypothalamusHypothalamus

Alar PlatesAlar Plates form lateral walls and floor of Diencephalonform lateral walls and floor of Diencephalon

Hypothalamic SulcusHypothalamic Sulcus divides Alar Plate into adivides Alar Plate into a dorsaldorsalthalamusthalamus andand ventral hypothalamusventral hypothalamus


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Thalamus/HypothalamusThalamus/Hypothalamus

-- Thalamus bulge into lumen of diencephalonThalamus bulge into lumen of diencephalon

-- may fuse in midline to form Masa Intermediamay fuse in midline to form Masa IntermediaThalamic Nuclear groups:Thalamic Nuclear groups:

1. Dorsal1. Dorsal -- for reception and transmission of auditoryfor reception and transmission of auditory

impulsesimpulses2. Ventral2. Ventral -- serves as passage and relay station for higherserves as passage and relay station for higher

centerscentersHypothalamic Nuclear GroupsHypothalamic Nuclear Groups

1. Hypothalamic Nuclei centers for regulation of visceral functions (sleep, body1. Hypothalamic Nuclei centers for regulation of visceral functions (sleep, body

temperature etc.)temperature etc.)

2. Mamillary Bodies2. Mamillary Bodies -- part of Limbic System concerned with memory recognitionpart of Limbic System concerned with memory recognition


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Diencephalon: HypophysisDiencephalon: Hypophysis

Anterior or AdenohypophysisAnterior or Adenohypophysis

-- develops from Rathkes pouch andevelops from Rathkes pouch an

out pouching of the stomodaeumout pouching of the stomodaeum(oral cavity)(oral cavity)

Posterior orNeurohypophysisPosterior orNeurohypophysis-- develops from the infundibulum adevelops from the infundibulum a

downward extension of the diencephalondownward extension of the diencephalon


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Telencephalon: Cerebral HemispheresTelencephalon: Cerebral Hemispheres

Telencephalon gives riseTelencephalon gives rise

to:to:

-- anterior part of 3rdanterior part of 3rdventricleventricle

-- cerebral hemispherescerebral hemispheres

Cerebral hemispheres:Cerebral hemispheres:

-- Frontal, Temporal, Parietal, Occipital lobesFrontal, Temporal, Parietal, Occipital lobes

-- lateral ventricles and its choroid plexuslateral ventricles and its choroid plexus

-- falx cerebri and tentorium cerebellifalx cerebri and tentorium cerebelli

-- Corpus Striatum and Lenticular NucleusCorpus Striatum and Lenticular Nucleus

-- Ascending and Descending tractsAscending and Descending tracts

-- Internal capsule, External capsuleInternal capsule, External capsule


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Choroid Plexus and the VentricularChoroid Plexus and the Ventricular

SystemSystem

Choroid Plexus is a single layer ofChoroid Plexus is a single layer of

ependymal cells covered with vascularependymal cells covered with vascularmesenchymemesenchyme

-- CSF production and circulation,CSF production and circulation,

nourishmentnourishment


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CommissuresCommissures

Fiber bundles that connect theFiber bundles that connect the

left and right sides of the brainleft and right sides of the brain

1.1.Anterior CommissureAnterior Commissure

-- 1st to appear at 3rd month, connect olfactory bulb and left and right1st to appear at 3rd month, connect olfactory bulb and left and right

temporal lobestemporal lobes

2.2. FornixFornix -- 2nd to appear and connects hippocampus with each hemisphere2nd to appear and connects hippocampus with each hemisphere

3.3. Corpus CallosumCorpus Callosum -- appears 10th weekand connects all nonappears 10th weekand connects all non--olfactory areasolfactory areas

of hemisphereof hemisphere

4.4. PosteriorPosterior,, HabenularHabenularCommissures,Commissures, Optic ChiasmOptic Chiasm


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Clinical NotesClinical Notes

Neural Tube DefectsNeural Tube Defects

-- caused by failure of closure of anteriorcaused by failure of closure of anterior

and/or posterior neuroporeand/or posterior neuropore

-- 1 in 1000 live births1 in 1000 live births

-- early diagnosis by Ultrasound orearly diagnosis by Ultrasound or

elevated alpha feto proteinelevated alpha feto protein


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AnencephalyAnencephaly

failure of closurefailure of closure

anterior neuroporeanterior neuropore

can be born alivecan be born alive

and live for few hrsand live for few hrs

to daysto days

females/male 4:1females/male 4:1


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Spina BifidaSpina Bifidafailure of closure of posteriorfailure of closure of posterior

neuroporeneuropore


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Spina Bifida OccultaSpina Bifida Occulta

MeningomyelocoeleMeningomyelocoele

MyelochisisMyelochisis


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HydrocephalusHydrocephalus


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