UNSW Embryology
Neural System Development
© Dr Mark Hill (2011)
Introduction
The early developing brain and spinal cord (dorsal view)
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Neural development is one of the earliest systems to begin and the last to be completed after birth. This development generates the most complex structure within the embryo and the long
time period of development means in utero insult during pregnancy may have consequences to development of the nervous system.
The early central nervous system begins as a simple neural plate that folds to form a groove then tube, open initially at each end. Failure of
these opening to close contributes a major class of neural abnormalities (neural tube defects). |
Sonic Hedgehog expression (white) in both the notocord (pale circular) and neural tube floorplate (bright triangle).
(Image- Lance Davidson)
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Within the neural tube stem cells generate the 2 major classes of cells that make the majority of the nervous system : neurons and glia. Both these classes of cells differentiate
into many different types generated with highly specialized functions and shapes. This section covers the establishment of neural populations, the inductive
influences of surrounding tissues and the sequential generation of neurons establishing the layered structure seen in the brain and spinal cord. |
Neural development beginnings quite early, therefore also look at notes covering Week 3- neural tube and Week 4-early nervous system.
Development the neural crest and sensory systems (hearing/vision/smell) are only briefly introduced in these notes and are covered in detail in another notes sections.
(More? Neural Crest Notes | Senses Notes)
Page Links: Introduction | Some Recent Findings | Reading | Computer Activities |
Podcasts | Objectives | Learning activities | Development Overview |
Human Neuralation - Early Stages | Late Neural Development | Gliogenesis and Myelination |
Postnatal Neural |
References | Glossary | Terms
Related Pages:
Abnormalities |
Stage 13/14 |
Stage 22 |
Stage 22 Brain |
Stage 22 Spinal Cord |
Ventricular System |
Cerebrospinal Fluid |
Week 10 |
Fetal |
Gliogenesis |
Pain |
Molecular |
Postnatal Neural |
Postnatal Neural Assessment
| Folic Acid and Neural Tube Defects |
Iodine Deficiency |
Endocrine Development - Thyroid |
Fetal Alcohol Syndrome |
Heavy Metals - Lead |
Some Recent Findings
Tawk M, Araya C, Lyons DA, Reugels AM, Girdler GC, Bayley PR, Hyde DR, Tada M, Clarke JD.
A mirror-symmetric cell division that orchestrates neuroepithelial morphogenesis.
Nature. 2007 Mar 28; [Epub ahead of print]
"Pard3 is localized to the cleavage furrow of dividing neural progenitors, and then mirror-symmetrically inherited by the two daughter cells.
This allows the daughter cells to integrate into opposite sides of the developing neural tube. Furthermore, these mirror-symmetric divisions have powerful morphogenetic influence:
when forced to occur in ectopic locations during neurulation, they orchestrate the development of mirror-image pattern formation and the consequent generation of ectopic neural tubes."
Neural Stem Cell Differentiation Goetz AK, Scheffler B, Chen HX, Wang S, Suslov O, Xiang H, Brustle O, Roper SN, Steindler DA.
Temporally restricted substrate interactions direct fate and specification of neural precursors derived from embryonic stem cells.
Proc Natl Acad Sci U S A. 2006 Jul 10; PNAS Link | Stem Cell Notes
"Upon evaluating distinct growth-permissive substrates in an embryonic stem cell–neurogenesis assay, we found that laminin, fibronectin, and gelatin instruct neural fate and alter the
functional specification of neurons when applied at distinct stages of development."
Reading
- Human Embryology (2nd ed.) Larson Ch5 p107-125
- The Developing Human: Clinically Oriented Embryology (6th ed.) Moore and Persaud Ch18 p451-489
- Essentials of Human Embryology Larson Ch5 p69-79
- Before We Are Born (5th ed.) Moore and Persaud Ch19 p423-458
- Human Embryology, Fitzgerald and Fitzgerald
- History of Science- Brain and Mind, Brain Structure,
Camille Golgi, S. Ramon y Cajal
Objectives
- Understand the formation of spinal cord
- Understand the formation of the brain; grey
and white matter from the neural tube.
- Understand the role of migration of neurons
during neural development.
- To know the main derivatives of the brain
vesicles and their walls.
- To know how the nervous system is modelled,
cell death etc.
- To understand the contribution of the neural
crest.
- Understand the developmental basis of
certain congenital anomalies of the nervous
system, including hydrocephalus, spina bifida,
anencephaly and encephalocele.
Podcast
Podcast - Listen ABC Radio All In The Mind
a Radio National's weekly foray into the mental universe, the mind, brain and behaviour - everything from addiction to artificial intelligence.
Learning Activities
- Review the formation of the neural tube and its subdivision into the primary and secondary cerebral vesicles and spinal cord: (see demonstration graphics)
- Identify, in the 6-7mm pig embryo, the marginal and ventricular zone of the neural tube wall, and the developing spinal ganglia.
- In the 8-week human identify the main derivatives of the fore-, mid- and hind-brain and list the adult derivatives of these areas.
- Examine UNSW Histology slides 56, 56A and 57 for neuroectodermal derivatives: 56 Head (neonatal) rat H & E,
56A Head (neonatal) rat H & Van Gieson, 57 Cochlea guinea pig H & Phloxine (resin embedded)
- List the derivatives of neural crest tissue.
- Discuss the underlying developmental processes in the following congenital anomalies: (a) meningomyelocele (spina bifida)(b) hydrocephalus(c) anencephaly(d) encephalocele
- View a graphic on development of the nervous system.
Self-Assessment Questions
- Describe the development of the neural tube. What structures develop from neurectoderm?
- List the derivatives of neural crest tissue.
- What are the developmental differences between the brain and spinal cord?
- Describe the main features of ependymal development.
- Describe the development of brain ventricles.
- How and where is the choroid plexus developed?
- Describe the development of the cerebellum.
- Construct and label simple diagrams showing the early development of the CNS and define the following terms: (a) neural plate (b) neural groove (c) neural fold (d) neural crest (e) neuropores
- What elements of the CNS and peripheral nervous system are derived from the neural crest?
Development Overview
Human Neuralation | Neural Derivatives | Neural Genes | Neural Patterning
Trilaminar Embryo: Neuralation begins at the trilaminar embryo with formation of the Notochord and somites, which underly the Ectoderm and do not
contribute to the nervous system, but are involved with patterning its initial formation.
Notochord
- forms initially as the Axial
Process, a hollow tube which extends
from the primitive pit , cranially
to the oral membrane
- the axial process then allow
transient communication between the
amnion and the yolk sac through the
neuroenteric canal.
- the axial process then merges
with the Endodermal layer to form
the Notochordal Plate.
- the notochordal plate then rises
back into the Mesodermal layer as a
solid column of cells which is the
Notochord.
Ectoderm
- 2 parts
- midline neural plate
- lateral surface ectoderm
- cuboidal
- sensory placodes
- epidermis of skin, hair,
glands, ant. pituitary, teeth
enamel
Neural Plate
- extends from buccopharyngeal
membrane to primitive node
- forms above notochord and
paraxial mesoderm
- neuroectodermal cells
- broad brain plate
- narrower spinal cord
- 3 components form: floor plate, neural plate, neural crest
Neural Determination- Neural Plate
- neuronal populations are specified before plate folds
- signals from notochord and mesoderm
- secrete noggin, chordin,follistatin
- all factors bind BMP-4 an inhibitor of neuralation
- bone morphogenic protein acts through membrane receptor
Neural Determination- Neural populations
- neuronal populations are also specified before plate folds
- lateral inhibition generates at spinal cord level 3 strips of cells
- expression of delta inhibits nearby cells, which express notch receptor, from becoming neurons
- Delta-Notch- generates Neural strips
Neural Groove
- forms in the midline of the
neural plate (day 18-19)
- either side of which are the
neural folds
- continues to deepen until about
week 4
- neural folds begins to fuse
- at 4th somite level
Neural Tube
- fusion of neural groove extends
rostrally and caudally
- begins at level of 4th
somite
- "zips up" neural groove
- leaves 2 openings at either end-
Neuropores
- forms the brain and spinal
cord
Secondary Neuralation
- caudal end of neural tube formed
by secondary neuralation
- develops from primitive streak
region
- solid cord canalized by
extension of neural canal
- mesodermal caudal eminence
Neuropores
- cranial neuropore closes before caudal
- failure to close- Neural Tube Defects (NTD)
- severity dependent upon level, spina bifida anancephaly (More? Neural Abnormalities)
- found that supplementation of maternal diet with folate reduces incidence of NTDs
- A randomised controlled trial
conducted by the Medical Research
Council of the United Kingdom
demonstrated a 72% reduction in
risk of recurrence by
periconceptional (ie before and
after conception) folic acid
supplementation (4mg daily).
- Women who have one infant
with a neural tube defect have a
significantly increased risk of
recurrence (40-50 per thousand
compared with 2 per thousand for
all births)
Neural Crest (More? Notes Neural Crest)
- a population of cells at the
edge of the neural plate that lie
dorsally when the neural tube
fuses
- dorsal to the neural tube, as a
pair of streaks
- pluripotential, forms many different types of cells
- cells migrate throughout the embryo
- studied by quail-chick chimeras
- transplanted quail cells have
obvious nucleoli compared with
chicken
Neural Crest Derivitives
- dorsal root ganglia
- autonomic ganglia
- adrenal medulla
- drg sheath cells, glia
- pia-arachnoid sheath
- skin melanocytes
- connective tissue of cardiac
outflow
- thyroid parafollicular
cells
- craniofacial skeleton
- teeth odontoblasts
Early Brain Structure- 3 primary vesicles
- rostral neural tube forms 3
primary brain vesicles (week 4)
- prosencephalon (forebrain)
- mesencephalon (midbrain)
- rhombencephalon (hindbrain)
Early Brain Structure- 5 secondary vesicles
From the 3 primary vesicles developing to form 5 secondary vesicles
- prosencephalon
- telencephalon (endbrain, forms cerebral hemispheres)
- diencephalon (betweenbrain, forms optic outgrowth)
- mesencephalon
- rhombencephalon- metencephalon (behindbrain), myelencephalon (medullabrain)
Ventricles (More? Notes Chorioid Plexus)
- cavity within tube will form the
contiguious space of the ventricules
of the brain and central canal of
spinal cord
- this space is filled initially
with amniotic fluid, later with
CerebroSpinal Fluid (CSF)
- CSF is secreted by a modified vascular structure, the Chorioid Plexus, lying within the ventricles
Brain Flexures
- rapid growth folds the neural tube forming 3 brain flexures
- cervical flexure - between brain stem and spinal cord
- midbrain flexure - pushes mesencephalon upwards
- pontine flexure - generates 4th ventricle
Neural Layers
- neural stem cells lie in the
layer closest to the ventricular
space, the ventricular layer
- this layer generates both
neuroblasts and glioblasts
- neuroblasts arise first and
migrate along radial gial
- their migration stops at
cortical plate
Spinal Cord Axes
- Experimental manipulation of interactions.
- Initial experiments looked at how isolated tissues may influence the development of the spinal cord.
- Repositionining of specific tissues both in vivo and in vitro
- specific markers of or alteration of differentiation.
Notocord Induction
- Ventral- Sonic Hedgehog
- notochord secretes sonic hedgehog
- Gene expression studies (ISH) showed shh gene expression occured in a subset of inducing tissues
- has a patterning role elsewhere (limb, sclerotome, lung)
- 2 signaling activities acting (locally and at a distance)
Ventral- Sonic Hedgehog
- Binds to cell surface receptor patched
- without shh, patched (Ptc) binds smoothened (Smo)
- with shh shh-Ptc releases Smo activating G protein pathway
Gene Diseases
- shh Human mutation- holoprosencephaly 3
- characteristic facies of the severe form of HPE which included a single fused eye (cyclopia) and a nose-like structure (proboscis) above the eye
- Downstream targets of Sonic hedgehog signalling: transcription factors like Gli3 (responsible for Greigs polycephalosyndactyly in humans),
d Hoxd13 (responsible for polysyndactyly)
Dorsal
- Dorsalin, growth factor controls patterning in embryonic mesoderm (frog)
- Transforming Growth factor beta, (TGF b), related factors BMP-2, BMP-4, BMP-7, radar (flies related protein determines dorsoventral)
- homology search of vertebrate library identified protein of same family.
- dorsalin-1 (dsl-1) Basler, Cell 73, p687, 1993
Dorsalin-1
- From overlying ectoderm
- Naming comes from the obvious
reason that it promotes the
differentiation of neural crest
cells.
- Also signal for dorsal signal of
neural tube.
- Inhibits the differentiation of
motoneurons.
- Implication is that dsl-1 and
shh act antagonistically, or
competitively to establish d-v axis
of neural tube.
Rostro-Caudal Axis
- What about the third pattern axis?
- Brain rostro-caudal axis is generated by differential expression of Hox genes (transcriptional activators)
- corresponding to genetic order on chromosome.
- Wilkinson, Nature, 341, p405, 1989.
Hox Genes
- Stands for Homeobox domain Genes
- A family of transcription factors
- Discovered in flies and
conserved between all species.
antennapedia
- Expressed in sequence along the
embryo rostro-caudal axis.
- Regulate many other aspects of
development.
- 180aa region binds DNA and
regulate gene expression
- large family of genes organized
and expressed in sequence on the
chromosome
- Nkx-2.2 first detected at 1
somite stage
- Lim hox gene expressed at spinal
cord level
Early Development and Neural Derivatives
- bilaminar embryo- hyoblast
- trilaminar embryo then ectoderm layer, neural plate, neural groove, neural tube and neural crest
- cranial expansion of neural tube- central nervous system
- caudal remainder of neural tube- spinal cord
- neural crest
- dorsal root ganglia
- parasympathetic / sympathetic ganglia.
- ectodermal placodes- components of the special senses: otic placode (otocyst), nasal placode, lens placode
Neural tube and Genes: neural specification- Notch/Delta, patched receptor. Border- fibroblast growth factor (fgf), BMP (BMP4, msx1)
Rostral border- Dlx5
Neural tube patterning
- segmented along its length- Hox/Lim gene expression
- ventral identity- sonic hedgehog, BMP7/chordin interaction
- dorsal identity- dorsalin
Human Neuralation - Early Stages
The stages below refer to specific Carneigie stages of development.
stage 8 (about 18
postovulatory days) neural groove and
folds are first seen
stage 9 the three main
divisions of the brain, which are not
cerebral vesicles, can be distinguished
while the neural groove is still
completely open.
stage 10 (two days later)
neural folds begin to fuse near the
junction between brain and spinal cord,
when neural crest cells are arising
mainly from the neural ectoderm
stage 11 (about 24 days) the
rostral (or cephalic) neuropore closes
within a few hours; closure is bidirectional, it takes place from the dorsal and terminal lips and may occur in several areas simultaneously.
The two lips, however, behave differently.
stage 12 (about 26 days) The caudal neuropore takes a day to close
- the level of final closure is
approximately at future somitic pair
31
- corresponds to the level of
sacral vertebra 2
stage 13 (4 weeks) the neural tube is normally completely closed
Secondary neurulation begins at stage 12
- is the differentiation of the caudal part of the neural tube from the caudal eminence (or end-bud) without the intermediate phase of a neural plate.
(Text modified from: Neurulation in the normal human embryo. O'Rahilly R, Muller F Ciba Found Symp 1994;181:70-82)
Late Neural Development
Three-dimensional magnetic resonance imaging and image-processing algorithms have been used to quantitate between 29-41 weeks volumes of: total
brain, cerebral gray matter, unmyelinated white matter, myelinated, and cerebrospinal fluid (grey matter- mainly neuronal cell bodies; white matter- mainly neural processes and glia). A
study of 78 premature and mature newborns showed that total brain tissue volume increased linearly over this period at a rate of 22 ml/week. Total grey matter also showed a linear increase in
relative intracranial volume of approximately 1.4% or 15 ml/week. The rapid increase in total grey matter is mainly due to a fourfold increase in cortical grey matter. Quantification of
extracerebral and intraventricular CSF was found to change only minimally. (text modified from Huppi etal., (1998) Quantitative magnetic resonance imaging of brain development in premature and mature newborns.Ann Neurol 43(2):224-235.)
(More? Late Neural Development)
Gliogenesis and Myelination
Glial cells have many different types and roles in central and peripheral neural development, though they are typically described as "supportive", and have the same early embryonic origins as neurons.
(More? Gliogenesis and Myelination)
Early in neural development a special type of developmental glia, radial glia, provide pathway for developing neuron (neuroblasts) migration out from the proliferating ventricular layer and
are involved in the subsequent lamination and columnar organization of the central nervous system.
Types of glia: radial glia, astroglia, oligodendroglia, microglia and Schwann cells.
Postnatal Neural
Neural development continues after birth with substantial growth, death and reorganization occuring during the postnatal period.
(More? Postnatal Development - Neural) The references below give a sample of some recent findings and research methods.
Cortex Matures Faster in Youth with Highest IQ (More? NIH - Cortex Matures Faster in Youth with Highest IQ)
Stern CD.
Neural induction: old problem, new findings, yet more questions. Development. 2005 May;132(9):2007-21. Review. "During neural induction, the embryonic neural plate is specified and set aside from other parts of the ectoderm.
A popular molecular explanation is the 'default model' of neural induction, which proposes that ectodermal cells give rise to neural plate if they receive no signals at all, while BMP activity directs them to become epidermis.
However, neural induction now appears to be more complex than once thought, and can no longer be fully explained by the default model alone.
This review summarizes neural induction events in different species and highlights some unanswered questions about this important developmental process."
Snook L, Paulson LA, Roy D, Phillips L, Beaulieu C.
Diffusion tensor imaging of neurodevelopment in children and young adults. Neuroimage. 2005 Jul 15;26(4):1164-73.
"Diffusion tensor magnetic resonance imaging (DTI) was used to study regional changes in the brain's development from childhood (8-12 years, mean 11.1 +/- 1.3, N = 32) to young adulthood (21-27 years, mean 24.4 +/- 1.8, N = 28).
..... These findings suggest a continuation of the brain's microstructural development through adolescence."
References
Many of the links below are to external resources and require an internet connection.
Links: Earlier References | Journals | Online Textbooks | Search Textbooks | PubMed |
Search PubMed | Books | Glossary
1999 and Earlier References:
Neuralation | Notch Articles/Reviews |
Sonic Hedgehog Articles/Reviews | Dorsal |
Clinical | Folate |
Journals
Developmental Brain Research Content Listing
Neural Development
Welcome to Neural Development |
Pubmed Central Volume 1 2006 |
Pubmed Central Volume 2 2007 |
International Journal for Developmental Neuroscience
Official Journal of the International Society for Developmental Neuroscience |
Developmental Neuroscience
Journal Homepage |
Hippocampal Development |
Vol. 29, No. 3, 2007 |
Neuroscience
Official journal of The International Brain Research Organisation (IBRO)
Neuron
Neuroscience journal published by Cell press
Online Textbooks
Developmental Biology (6th ed) Gilbert, Scott F. Sunderland (MA): Sinauer Associates, Inc.; c2000.
Formation of the Neural Tube |
Differentiation of the Neural Tube |
Tissue Architecture of the Central Nervous System |
Neuronal Types |
Snapshot Summary: Central Nervous System and Epidermis
Neuroscience Purves, Dale; Augustine, George J.; Fitzpatrick, David; Katz, Lawrence C.; LaMantia, Anthony-Samuel; McNamara, James O.; Williams, S. Mark.
Sunderland (MA): Sinauer Associates, Inc. ; c2001
Early Brain Development |
Construction of Neural Circuits |
Modification of Brain Circuits as a Result of Experience
Molecular Biology of the Cell (4th Edn) Alberts, Bruce; Johnson, Alexander; Lewis, Julian; Raff, Martin; Roberts, Keith; Walter, Peter. New York: Garland Publishing; 2002.
Neural Development |
The three phases of neural development
Health Services/Technology Assessment Text (HSTAT) Bethesda (MD): National Library of Medicine (US), 2003 Oct.
Developmental Disorders Associated with Failure to Thrive
Search NLM Online Textbooks- "neural development" :
Developmental Biology |
The Cell- A molecular Approach |
Molecular Biology of the Cell |
Endocrinology
PubMed
Reviews
Gotz M, Huttner WB
The cell biology of neurogenesis.
Nat Rev Mol Cell Biol. 2005 Oct;6(10):777-88.
Articles
Villa-Cuesta E, Modolell J.
Mutual repression between msh and Iro-C is an essential component of the boundary between body wall and wing in Drosophila. Development. 2005 Aug 10
Goto M, Piper Hanley K, Marcos J, Wood PJ, Wright S, Postle AD, Cameron IT, Mason JI, Wilson DI, Hanley NA.
In humans, early cortisol biosynthesis provides a mechanism to safeguard female sexual development.
J Clin Invest. 2006 Apr;116(4):953-60.
Books
Note: books are listed for educational and information purposes only and does not suggest a commercial product endorsement.
Molecular and Cellular Approaches to Neural Development
The Embryonic Human Brain: An Atlas Of Developmental Stages, 3rd Edition
Modeling Neural Development
The Female Brain
Search PubMed
Search Mar2007 "neural development" 9,393 reference articles of which 2,047 were reviews.
Search PubMed: term= neural development |
Sonic Hedgehog |
Hox |
abnormal neural development
Neural Development Terms
Only brief descriptions are given below, more complete definitions can be found in the glossary.
- 3DMRI Three-dimensional magnetic resonance imaging. A new technique that allows 3D analysis of embryonic structures.
(More? Prenatal Diagnosis - Magnetic Resonance Imaging)
- 3rd ventricle ventricular cavity within the diencephalon.
- 4th ventricle ventricular cavity within the rhombencephalon.
- accessory nerve-
- adenohypophysis anterior pituitary= 3 parts pars distalis, pars intermedia, pars tuberalis
- alar plate afferent, dorsal horns
- anlage (German = primordium, structure or cells which will form a future structure.
- arachnoid- (G.) spider web-like
- basal ganglia-
- basal plate efferent, ventral horns
- brachial plexus mixed spinal nerves innervating the upper limb form a complex meshwork (crossing).
- brain general term for the central nervous system formed from 3 primary vesicles.
- buccopharyngeal membrane (=oral membrane) at cranial (mouth) end of gastrointestinal tract (GIT)
where surface ectoderm and GIT endoderm meet. (see also cloacal membrane)
- cauda equina- (=horse's tail) caudal extension of the mature spinal cord.
- central canal lumen, cavity of neural tube within the spinal cord. Space is continuous with ventricular system of the brain.
- cerebral aqueduct ventricular cavity within the mesencephalon.
- cervical flexure most caudal brain flexure (of 3) between spinal cord and rhompencephalon.
- choroid plexus specialized vascular plexus responsible for secreting ventricular fluid that with further additions becomes cerebrospinal fluid (CSF).
- cloacal membrane at caudal (anal) end of gastrointestinal tract (GIT) where surface ectoderm and GIT endoderm meet forms the
openings for GIT, urinary, reproductive tracts. (see also buccopharyngeal membrane)
- cortex-
- cortical plate outer neural tube region which post-mitotic neuroblasts migrate too along radial glia to form adult cortical layers.
- cranial flexure (=midbrain flexure) most cranial brain flexure (of 3) between mesencephalon and prosencephalon.
- diencephalon the caudal portion of forebrain after it divides into 2 parts in the 5 secondary vesicle brain (week 5).
(cavity- 3rd ventricle) Forms the thalmus and other nuclei in the adult brain.
- dorsal root ganglia (=spinal ganglia) sensory ganglia derived from the neural crest lying laterally paired and
dorsally to the spinal cord (in the embryo found ventral to the spinal cord). Connects centrally with the dorsal horn of the spinal cord.
- dura mater-
- ectoderm the germ layer which form the nervous system from the neural tube and neural crest.
- ependyma epithelia of remnant cells after neurons and glia have been generated and left the ventricular zone
- floorplate early forming thin region of neural tube closest to the notochord.
- ganglia (pl. of ganglion) specialized neural cluster.
- glia supporting, non-neuronal cells of the nervous system. Generated from neuroepithelial stem cells in ventricular zone of neural tube. Form astrocytes, oligodendrocytes.
- glossopharyngeal ganglion-
- grey matter neural regions containing cell bodies (somas) of neurons. In the brain it is the outer layer, in the spinal cord it is inner layer. (see white matter)
- growth factor usually a protein or peptide that will bind a cell membrane receptor and then activates an intracellular signaling pathway.
The function of the pathway will be to alter the cell directly or indirectly by changing gene expression. (eg shh)
- hox (=homeobox) family of transcription factors that bind DNA and activate gene expression. Expression of different Hox
genes along neural tube defines rostral-caudal axis and segmental levels.
- intervertebral foramina-
- isthmus- (G. narrow passage)
- lamina terminalis anterior region of brain where cranial neuropore closes.
- lumbar
plexus mixed spinal nerves innervating the
lower limb form a complex meshwork
(crossing).
- mantle
layer layer of cells generated by first
neuroblasts migrating from the ventricular zone
of the neural tube. Layers are rearranged during
development of the brain and spinal cord.
- marginal
zone layer of processes from neuroblasts in
mantle layer.
- mater (L.
mother)
- meninges
mesenchyme surrounding neural tube forms 3 layer
(Dura-, pia-, arachnoid- mater) connective
tissue sheath of nervous system.
- mesencephalon
(=midbrain), the middle portion of the 3 primary
vesicle brain (week 4).
- metencephalon
the cranial portion of hindbrain after it
divides into 2 parts in the 5 secondary vesicle
brain (week 5). Forms the pons and cerebellum in
the adult brain.
- myelencephalon
the caudal portion of hindbrain after it divides
into 2 parts in the 5 secondary vesicle brain
(week 5). Forms the medulla in the adult brain.
- neural
tube neural plate region of ectoderm
pinched off to form hollow ectodermal tube above
notochord in mesoderm.
- neural
tube defect (NTD) any developmental
abnormality that affects neural tube
development. Commonly failure of neural tube
closure.
- neuroblast undifferentiated neuron
found in ventricular layer of neural tube.
- neurohypophysis
(=posterior pituitary=pas nervosa)
- neuron The cellur
"unit" of the nervous system, transmitting
signals between neurons and other cells. The
post-mitotic cells generated from
neuroepithelial stem cells (neuroblasts) in
ventricular zone of neural tube.
- neuropore
opening at either end of neural tube:
cranial=rostral=anterior, caudal=posterior. The
cranial neuropore closes (day 25) approx. 2 days
(human) before caudal.
- notochord rod
of cells lying in mesoderm layer ventral to the
neural tube, induces neural tube and secretes
sonic hedgehog which "ventralizes" the neural
tube.
- olfactory bulb (=cranial nerve I, CN I) bipolar neurons from nasal epithelium project axons through cribiform palate into olfactory bulb of the brain.
- optic cup-
- optic nerve (=cranial nerve II, CN II) retinal ganglion neurons project from the retina as a tract into the brain (at the level of the diencephalon).
- otocyst (=otic vesicle) sensory placode which sinks into mesoderm to form spherical vesicle (stage 13/14 embryo) that will form components of the inner ear.
- pars (L. part of)
- pharyngeal arches (=branchial arches, Gk. gill) form structures of the head. Six arches form but only 4 form any structures. Each arch has a pouch, membrane and cleft.
- pharynx uppermost end of GIT, beginning at the buccopharyngeal membrane and at the level of the pharyngeal arches.
- pia mater-
- placode specialized regions of ectoderm which form components of the sensory apparatus.
- pontine flexure middle brain flexure (of 3) between cervical and cranial flexure in opposite direction, also generates thin roof of
rhombencephalon and divides it into myelencephalon and metencephalon. (
sc-^V^
)
- prosencephalon (=forebrain), the most cranial portion of the 3 primary vesicle brain (week 4).
- Rathke's pouch a portion of the roof of the pharynx pushes upward towards the floor of the brain
forming the anterior pituirary (adenohypophysis, pars distalis, pars tuberalis pars intermedia). Where it meets a portion of the brain pushing
downward forming the posterior pituitary (neurohypophysis, pars nervosa). Rathke's pouch eventually looses its connection with the pharynx.
(Martin Heinrich Rathke 1973-1860, embryologist and anatomist)
- rhombencephalon (=hindbrain), the most caudal portion of the 3 primary vesicle brain (week 4).
- roofplate early forming thin region of neural tube closest to the overlying ectoderm.
- spinal
cord caudal end of neural tube that does
not contribute to brain. Note: the process of
secondary neuralation contributes the caudal end
of the spinal cord.
- spinal
ganglia (=dorsal root ganglia, drg) sensory
ganglia derived from the neural crest lying
laterally paired and dorsally to the spinal cord
(in the embryo found ventral to the spinal
cord). Connects centrally with the dorsal horn
of the spinal cord.
- spinal
nerve mixed nerve (motor and sensory)
arising as latera pairs at each vertebral
segmental level.
- sonic hedgehog
(=shh) secreted growth factor that binds patched
(ptc) receptor on cell membrane. SHH function is
different for different tissues in the embryo.
In the nervous system, it is secreted by the
notochord, ventralizes the neural tube, inducing
the floor plate and motor neurons.
- sulcus (L.
furrow) groove
- sulcus
limitans longitudinal lateral groove in
neural tube approx. midway between roofplate and
floorplate. Groove divides alar (dorsal) and
basal (ventral) plate regions.
- sympathetic ganglia-
- telencephalon
the cranial portion of forebrain after it
divides into 2 parts in the 5 secondary vesicle
brain (week 5). (cavity- lateral ventricles and
some of 3rd ventricle) Forms the cerebral
hemispheres in the adult brain.
- thalamus (G.
thalamos= bedchamber) cns nucleus,
lateral to 3rd ventricle, paired (pl
thalami).
- transcription
factor a factor (protein or protein with
steroid) that binds to DNA to alter gene
expression, usually to activate. (eg steroid
hormone+receptor, Retinoic acid+Receptor, Hox,
Pax, Lim, Nkx-2.2)
- trigeminal ganglion
(=cranial nerve V, CN V) first arch ganglion,
very large and has 3 portions.
- vagal ganglion-
(=cranial nerve X, CN X) fourth and sixth
arch ganglion, innervates the viscera and
heart.
- ventricles
the fluid-filled interconnected cavity system
with the brain. Fluid (cerebrospinal fluid, CSF)
is generated by the specialized vascular
network, the choroid plexus. The ventricles are
directly connected to the spinal canal (within
the spinal cord).
- ventricular
zone Neuroepithelial cell layer of neural
tube closest to lumen. Neuroepithelial cells
generate neurons, glia and ependymal cells.
- vestibulocochlear
nerve (=cranial nerve VIII, CN VIII, also
called statoacoustic)
- white
matter neural regions containing processes
(axons) of neurons. In the brain it is the inner
layer, in the spinal cord it is outer layer.
(see grey
matter)
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Comments
Development of the neural system continues throughout our entire life, from the early trilaminar embryo, through embryonic,
fetal, newborn, and postnatally continues to be remodelled at the synaptic level.
2010 - New
Neural Notes
We form from a simple plate region of the ectoderm, then fold a simple neural tube, to
differentiate into the complex structure of the spinal cord and brain.
Use this page to get an overview of the online resources available and notes to follow through early stages of development.
Note: These current neural notes cover mainly early events of development, additional region-specific notes are in preparation. Additional notes are available for Neural Crest and Sensory Systems (hearing/vision/smell) and only briefly introduced in these current notes.
Next look at the neural structure and distribution in the Carnegie stage 13 and then the stage 22 embryos.(use righthand menu Internal Links)
Then look at the later Week 10 embryo sagittal sections which show further development of the brain features and flexures.
Note that the edge of the neural plate forms the neural crest which contributes the cranial ganglia, peripheral sympathetic
and parasympatheic nervous system as well as many non-neural tissues (this part of the nervous system is covered in
Neural crest Notes).
Please email Dr Mark Hill if you wish to make a comment about this current project.
Notochord
