Jittipan Chavadej,Ph'D'

1
EMBRYOLOGY NERVOUS SYSTEM
Jittipan Chavadej,Ph.D.
Dept. of Anatomy,Fac. of Science, Mahidol
University
September,2000
2
Diagrams showing formation of the neural groove,
neural tube and neural crest
3
Neural tube-neural crest
Neural tube-brain spinal cord
Neural crest-most components of
PNS -non-neural component
in the body and head.
4
Fundamental processes in Nervous system formation

• Induction-Proliferation
• Migration-Differentiation
• Pattern formation
• Intercellular communication
• Stabilization or Elimination
• Development of integrated pattern

5
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

6
3-wk. Embryo - C shape - cephalic flexure
(mesencephalon) - cervical flexure (hind
brainspinal cord)
5-wk. Embryo -
procencephalon-Telen., Dien. -mesencephalon
-rhombencephalon-Meten., Myelen.
7
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
8
Diencephalon - optic vesicles
Mesencephalon - sharply bend by
cephalic flexure
Rhombencephalon - Pontine flexure
thin roof
9
Basic anatomy of the five-part human brain
10
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
11
Cell lineages in the developing central nervous
system
12
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.
13
Development of nervous system components
14
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
15
Formation of zones fundamental organization of
the developing neural tube
Note -ependymal zone -mantle zone -marginal zone
16
Fundamental Organization of Neural tube
Dorsal portion/Alar plate/sensory
lt---Sulcus limitans
Ventral portion/Basal plate/motor
Roof plate - Floor plate
17
A-development of regional specialization across
the neural tube. B-formation of the spinal cord
18
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
  --gtgtmyelinated nerve fibers

19
Spinal cord - PNS
Ventral aspect

• Neuroblasts of basal plate -gtgt outgrowth of axons
  --gtventral nerve root

Dorsal aspect

• Thin processes of neuroblast of spinal
  ganglion--gtdorsal nerve root

20
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
21
Myelination - in CNS --gtgt oligodendroglia
- in PNS --gtgt Schwann cell
22
Gross change of spinal cord

• 6-wk.--gtfull length of vertebral column
• 8-wk.--gtend Co4
• 14-wk.--gtend S1
• 23-wk.--gtend L4
• Birth--gtend L3
• Adult--gt endL2-3-filum terminale
  cauda equina

23
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

24
Dorsal alar plate-sensory horn of spinal
cord Ventral basal plate-motor horn of spinal
cord
25
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

26

• Dilatations of the central lumen form ventricles
  in the brain
• -lateral ventricle-gt Telen.
• -third ventricle-gt Dien.
• -cerebral aqueduct-gt Midbrain
• -fourth ventricle-gt Hindbrain

CSF - choroid plexus
27
A
Development of the ventricular system of the
brain A-early embryo B-during expansion of
cerebral hemisphere C-postnatal morphology of
ventricular system
28
Formation of specific brain regions
Rhombencephalon - Metencephalon -
Myelencephalon
Medulla oblongata-transitional zone -major
alteration --gt 4th ventricle
29
Expansion of roof plate- 4th ventricle
Basal plateAlar plate in brainstem
Basal plate--gtclose to midline
lt---Sulcus limitans
Alar plate--gt lateral
30
Alar and basal plates in myelencephalon showing
the position of nuclear groups at different
stages of development
31
Basal plate contains three motor nuclei -medial
somatic efferent gr.SE -intermediate special
visceral efferent gr.SVE -lateral
general visceral efferent gr.GVE
32
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
33
Special functional categories of cranial nuclei
in the brainstem
34
(No Transcript)
35
(No Transcript)
36
Motor and sensory nuclear groups in the basal and
alar plates of caudal part of metencephalon
37
The development of the cerebellum.- Dorsal
view Note 3 apertures - Foramen of
Magendie(1-median) -Foramen
of Luschka(2-lateral)
38
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--gtGerminal layer and
give rise to cerebellar cortex
39
A-Ddevelopment of cerebellum
ABdevelopment of cerebellar cortex
40
Glia play an important role in migration of
cortical neurons
Radial glia--gtfor guidance neurons to their
destination
The external cortical neurons-layers
The cerebellar hemispheres undergo extensive
folding Folia
41
Radial glial cells and their association with
peripherally migrating neurons during development
of the brain
42
DEVELOPMENT of Nervous System (cont.)
Dr. Jittipan Chavadej
Anatomy Department
yr,2000
43
Mesencephalon
The alar region forms 4 swellings called corpora
quadrigemina
The ventral region forms -gray matter in
tegmentum -white matter in cerebral peduncles
44
Dorsal view of the midbrain hindbrain
45
Colliculi relay nuclei for auditory
visual systems
Tegmentum -cranial motor nuclei -2
prominent relay nucleired nucleus
substantia nigra
Cerebral pedunclefiber tracts from cerebrum gt
cerebellum gt spinal cord
46
Cross section-earlylater developing
mesencephalon (blue-sensory, red-motor)
47
Forebrain--gtdien. telencephalon
Dien. forms midline brainstem regions from its
alar plate-contain relay nuclei.
Dorsal -thalamus epithalamus
Ventral -hypothalamus
48
Medial surface X-section of prosencephalon.
Notecorpus striatum bulge from the floor of
lateral ventricle
49
A -medial surface of telencephalon diencephalon
B -X-section Notethalamus,hypothalamus corpus
striatum
50
Midline -epiphysis
Pituitary gl.-downgrowth of hypotha. upgrowth
of pharyngeal ectoderm
Craniopharyngioma-remnant of Rathkes pouch
51
Functions
Thalamus-relay center for cerebral cortex
Epithalamus -olfactory input Pineal gl.-extension
of epithalamus -neurosecretory
cell--gtmelatonin
52
Hypothalamus-receiving input from many CNS
areas. -regulates autonomic visceral fn.
including sleep,body temp.,digestion -regulates
endocrine secretions of pituitary gland
53
Telencephalon forms the cerebral hemispheres by
bilateral expansion
Cerebral cortex-waves of migration to form
cerebral cortexneocortex -intermediate
zone--gtwhite matter
Forming multiple synaptic connections is
important to the development of the brain
54
The cerebral hemispheres fold into lobes and
gyri-gtbegin 14 weeks
Fetal period-frontal,parietal, temporal and
occipital lobes
Sulcus/sulci separate some lobes
Convolutions - gyrus/gyri -begin
betw.68months
55
Showing the development of gyri and sulci on the
lateral surface of the cerebral hemisphere A7
months B9 months
56
Corpus striatum formation

• At the base of telencephalic vesicle
• Dorsal to the thalamus

C -shaped corpus striatum -caudate
nucleus -lentiform nucleus
57
A -medial surface of telencephalon diencephalon
B -X-section Notecorpus striatum
-caudatelentiform nucleus -internal capsule
58
Commissures
Lamina terminalis

• 1st - antr commissure

• 2nd- hippocampal commissure

• 3rd - corpus callosum-biggest

-postr habenular commissures (pineal
gland) -optic chiasm
59
Medial surface showing various commissures
60
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
61
Subarachnoid space is filled with CSF, forming a
protective cushion for the brain.
Lat. ventricle
3rdventricle
CSF
4thventricle
Cerebral aqueduct
Foramen of Magendie
Foramen of Luschka
62
B-showing the lateral and medial apertures in the
roof of the 4th ventricle
Development of the ventricular system of the brain
63
Meninges
from 2 sources
Outer dura - mesoderm surrounding neural tube
Arachnoid Pia-cranial
neural crest cells
-caudal
mesoderm
64
Congenital defects of the CNS

• Mental retardation-no detectable brain abnormality

• Gross morphological defects
• -spina bifida/occulta/cystica
• -meningocele/meningomyelocele
• /meningoencephalocele
• -rachischisis

65
Congenital malformations of the NS
66
Rachischisis -no cranial bones covering the
brain. -spinal cord is exposed.
67
Herniation in the cranial region
Occipital meningocele
Frontal encephalocele
68
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
69
Organization of ANS at thoracic level
70
Neural crest
Neural crest forms most of the PNS

• Two types of ganglia
• sensory ganglia
• autonomic motor ganglia

71
Major neural crest migratory PW