Jittipan Chavadej,Ph.D.Dept. of Anatomy,Fac. of Science,

Mahidol University

September,2000

Diagrams showing formation of the neural groove, neural tube and neural crest

Neural tube-neural crest

Neural tube-brain & spinal cord

Neural crest-most components of PNS

-non-neural component in the body and head.

Fundamental processes in Nervous system

formation

•Induction-Proliferation

•Migration-Differentiation

•Pattern formation

•Intercellular communication

•Stabilization or Elimination

•Development of integrated pattern

Changes in Gross Structure of NS•Closure of neural tube

24th-day -cranial neuropore 26th-day -caudal neuropore

•Cephalic end-primary brain vesicles

-procencephalon-mesencephalon-rhombencephalon•Spinal cord

3-wk. Embryo : - C shape - cephalic flexure (mesencephalon) - cervical flexure (hind brain&spinal cord)

5-wk. Embryo : - procencephalon-Telen., Dien.

-mesencephalon

-rhombencephalon-Meten., Myelen.

A-lateral view of the brain vesicles and part of spinal cord. B-diagram showing the cavities of the three brain vesicles and spinal cord

Diencephalon - optic vesicles

Mesencephalon - sharply bend by cephalic flexureRhombencephalon - Pontine flexure thin roof

Basic anatomy of the five-part human brain

Histogenesis within Nervous System

•2 major cell lineages

- Neuronal progenitor cell neurons

- Glial progenitor cell

astrocyte, oligodrendrocyte,

ependyma (neural tube)*Microglia-enter CNS from outside

Cell lineages in the developing central nervous system

Neuron-large cell body

-long processe

-axon-carry signals to

targets

-dendrites-receive input

Neurons need to “ reach out and touch “ each other by forming synapses to survive.

Development of nervous

system components

Formation of Zones

1. Ventricular zone-ependymal cellsbecome epithelial lining of central canal

2. Mantle zone-neuroblast cellsbecome gray matter of the CNS

3. Marginal zone-neuronal processesbecome white matter of the CNS

Formation of zones & fundamental organization of the developing neural tube

Note:

-ependymal zone

-mantle zone

-marginal zone

<---Sulcus limitans

Fundamental Organization of Neural

tubeDorsal portion/Alar plate/sensory

Ventral portion/Basal plate/motorRoof plate - Floor plate

A-development of regional specialization across the neural tube. B-formation of the spinal cord

Spinal cord formation

** Basic plan of neural tube is preserved in spinal cord

**•Mantle zone = H-shape of gray matter with central canal

•Marginal zone = White matter -->>myelinated nerve fibers

Spinal cord - PNS

•Neuroblasts of basal plate ->> outgrowth of axons -->ventral nerve root

•Thin processes of neuroblast of spinal ganglion-->dorsal nerve root

Dorsal aspect

Ventral aspect

Development of a peripheral nerve

A-showing motor axon, growing fiber of nerve cell in DRG. B-showing ventral motor and dorsal sensory root joining to form the trunk of spinal nerve

Myelination - in CNS -->> oligodendroglia

- in PNS -->> Schwann cell

Gross change of spinal cord•6-wk.-->full length of vertebral

column•8-wk.-->end ~Co4•14-wk.-->end ~S1•23-wk.-->end ~L4•Birth-->end ~L3•Adult--> end~L2-3-filum terminale &cauda equina

Functional components

•2 functional categories: -GSA(soma,body) & GVA(viscera)

Dorsal alar horn = Afferent neurons

Ventral basal horn =Efferent neurons•2 functional categories: GSE & GVE

Dorsal alar plate-sensory horn of spinal cord

Ventral basal plate-motor horn of spinal cord

Brain Formation

•The original organization of neural tube is altered in the formation of many regions of the brain.•Nerve cells form concentrated collections called nuclei in the brain

•Dilatations of the central lumen form ventricles in the brain

-lateral ventricle-> Telen.

-third ventricle-> Dien.

-cerebral aqueduct-> Midbrain

-fourth ventricle-> Hindbrain* CSF - choroid plexus

Development of the ventricular system of the brain

A-early embryo B-during expansion of cerebral hemisphere C-postnatal morphology of ventricular system

A

Formation of specific brain regions

Rhombencephalon - Metencephalon

- MyelencephalonMedulla oblongata-transitional zone

*-major alteration --> 4th ventricle

Basal plate&Alar plate in brainstem

Expansion of roof plate- 4th ventricle

Basal plate-->close to midline

Alar plate--> lateral

<---Sulcus limitans

Alar and basal plates in myelencephalon showing the position of nuclear groups at different stages of development

Basal plate contains three motor nuclei

-medial somatic efferent gr.=SE

-intermediate special visceral efferent gr.=SVE

-lateral general visceral efferent gr.=GVE

Alar plate contains sensory nuclei*-most lateral

special somatic afferent gr.=SSA

general somatic afferent gr.=GSA *-intermediate

special visceral afferent gr.=SVA *-medial general visceral afferent gr.=GVA

Special functional categories of cranial nuclei in the brainstem

Brain Formation

Hindbrain-meten.-->pons&cerebellum

Pons contains - fiber tracts

- cranial nerve nuclei

- pontine nuclei

Cranial end of hindbrain (meten.)expands outwards to f ormcerebellum.

Cerebellum - specialization of alarplates --> Rhombic lips

Two cerebellar hemispheres+Vermis

Motor and sensory nuclear groups in the basal and alar plates of caudal part of metencephalon

The development of the cerebellum.- Dorsal view

Note: 3 apertures - Foramen of Magendie(1-median)

-Foramen of Luschka(2-lateral)

Formation of the cerebellum or cerebrum involves formation of multiple neuronal layers in the cortex

There is a second wave of proliferation fron the inner ventricular layer-->Germinal layer and give rise to cerebellar cortex

A-D=development of cerebellum

A&B=development of cerebellar cortex

Glia play an important role in migration of cortical neurons

Radial glia-->for guidance neurons to their destination

The external cortical neurons-layers * The cerebellar hemispheres undergo extensive folding = Folia

Radial glial cells and their association with peripherally migrating neurons during development of the brain

DEVELOPMENT of

Nervous System (cont.)

Dr. Jittipan Chavadej

Anatomy Department

yr,2000

Mesencephalon

The alar region forms 4 swellings called corpora quadrigemina

The ventral region forms

-gray matter in tegmentum

-white matter in cerebral peduncles

Dorsal view of the midbrain & hindbrain

Tegmentum -cranial motor nuclei

-2 prominent relay nuclei=red nucleus

& substantia nigra

Colliculi =relay nuclei for auditory & visual systems

Cerebral peduncle=fiber tracts from cerebrum > cerebellum > spinal cord

Cross section-early&later developing mesencephalon (blue-sensory, red-motor)

Forebrain-->dien. & telencephalonDien. forms midline brainstem regions from its alar plate-contain relay nuclei.

Dorsal -thalamus & epithalamus

Ventral -hypothalamus

Medial surface & X-section of prosencephalon. Note:corpus striatum bulge from the floor of lateral ventricle

A -medial surface of telencephalon & diencephalon

B -X-section

Note:thalamus,hypothalamus & corpus striatum

*Craniopharyngioma-remnant of Rathke’s pouch

Midline -epiphysis

Pituitary gl.-downgrowth of hypotha. + upgrowth of pharyngeal ectoderm

Functions

Thalamus-relay center for cerebral cortex

Epithalamus -olfactory input

Pineal gl.-extension of epithalamus

*-neurosecretory cell-->melatonin

Hypothalamus-receiving input from many CNS areas.

-regulates autonomic visceral fn. including sleep,body temp.,digestion

-regulates endocrine secretions of pituitary gland

Telencephalon forms the cerebral hemispheres by bilateral expansionCerebral cortex-waves of migration to form cerebral cortex=neocortex

-intermediate zone-->white matter *Forming multiple synaptic connections is important to the development of the brain*

*The cerebral hemispheres fold into lobes and gyri->begin 14 weeks

Fetal period-frontal,parietal, temporal and occipital lobes

Sulcus/sulci separate some lobesConvolutions - gyrus/gyri

-begin betw.6&8months

Showing the development of gyri and sulci on the lateral surface of the cerebral hemisphere

A=7 months B=9 months

Corpus striatum formation

•At the base of telencephalic vesicle

•Dorsal to the thalamus

C -shaped corpus striatum

-caudate nucleus

-lentiform nucleus

A -medial surface of telencephalon & diencephalon

B -X-section

Note:corpus striatum -caudate&lentiform nucleus

-internal capsule

Commissures

**Lamina terminalis** •1st - antr commissure

•2nd- hippocampal commissure

•3rd - corpus callosum-biggest

-postr & habenular commissures

(pineal gland) -optic chiasm

Medial surface showing various commissures

Meninges form a protective coating around the entire CNS

Meninges -3 layers of CNT

1. Tough outer coat = Dura mater

2. Middle layer = Arachnoid mater

3. Inner layer = Pia mater

Subarachnoid space is filled with CSF, forming a protective cushion for the brain.

CSF Lat. ventricle

3rdventricle

Cerebral aqueduct

4thventricle

Foramen of Magendie

Foramen of Luschka

B-showing the lateral and medial apertures in the roof of the 4th

ventricle

Development of the ventricular system of the brain

Outer dura - mesoderm surrounding neural tube

Arachnoid & Pia-cranial

neural crest cells

-caudal

mesoderm

Meninges

from 2 sources

Congenital defects of the CNS

•Mental retardation-no detectable brain abnormality

•Gross morphological defects

-spina bifida/occulta/cystica-meningocele/

meningomyelocele /meningoencephalocele-rachischisis

Congenital malformations of the NS

Rachischisis

-no cranial bones covering the brain.

-spinal cord is exposed.

Occipital meningocele

Frontal encephalocele

Herniation in the cranial region

PNS development

PNS consists of the neural tissue outside CNS•ganglion/ganglia-neurons•peripheral nerve-nerve cell process

Neural crest forms most of the PNS

Organization of ANS at thoracic

level

Neural crest

Neural crest forms most of the PNS

Two types of ganglia

sensory ganglia

autonomic motor ganglia

Major neural crest migratory P’W