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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 flexure
Rhombencephalon - 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 cells
become epithelial lining of central canal
2. Mantle zone-neuroblast cells
become gray matter of the CNS
3. Marginal zone-neuronal processes
become white matter of the CNS
Formation of zones
& fundamental
organization of the
developing neural
tube
Note:
-ependymal zone
-mantle zone
-marginal zone
Fundamental Organization
of Neural tube
Dorsal portion/Alar plate/sensory
<---Sulcus limitans
Ventral portion/Basal plate/motor
Roof 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
Ventral aspect
•Neuroblasts of basal plate ->>
outgrowth of axons -->ventral nerve
root
Dorsal aspect
•Thin processes of neuroblast of
spinal ganglion-->dorsal nerve root
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
Dorsal alar horn = Afferent neurons
•2 functional categories:
-GSA(soma,body) & GVA(viscera)
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
A
Development of the ventricular system of the
brain
A-early embryo B-during expansion of cerebral hemisphere
C-postnatal morphology of ventricular system
Formation of specific brain regions
Rhombencephalon - Metencephalon
- Myelencephalon
Medulla oblongata-transitional zone
*-major alteration --> 4th ventricle
Expansion of roof plate- 4th ventricle
Basal plate&Alar plate in brainstem
Basal plate-->close to midline
<---Sulcus limitans
Alar plate--> lateral
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 form
cerebellum.
Cerebellum - specialization of alar
plates --> 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
Colliculi =relay nuclei for auditory
& visual systems
Tegmentum -cranial motor nuclei
-2 prominent relay
nuclei=red nucleus &
substantia nigra
Cerebral peduncle=fiber tracts from
cerebrum > cerebellum > spinal cord
Cross section-early&later developing
mesencephalon (blue-sensory, red-motor)
Forebrain-->dien. & telencephalon
Dien. 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
Midline -epiphysis
Pituitary gl.-downgrowth of hypotha.
+ upgrowth of pharyngeal ectoderm
*Craniopharyngioma-remnant of Rathke’s pouch
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 expansion
Cerebral 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 lobes
Convolutions - 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
Cerebral aqueduct
3rdventricle
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
Meninges
from 2 sources
Outer dura - mesoderm surrounding
neural tube
Arachnoid & Pia-cranial
-caudal
neural
crest cells
mesoderm
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.
Herniation in the cranial region
Occipital meningocele
Frontal encephalocele
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