(4) Development of CNS Flashcards
when does the nervous system arise
3rd week of life
- when 3 principal layers are being generated by process of gastrulation
what are the 3 principal layers of the nervous sytem
ectoderm
medoderm
endoderm
what happens during gastrulation?
- outer cells (epiblast) of embryo detach, migrate through primitive streak (groove) –> mesoderm and ectoderm are generated
- remaining outside cells (epiblast) form ectoderm, from which NS develops. Later becomes epidermis
what happens at the beginning of the 3rd week of development to the ectoderm layer
in response to signals from midline tissues (notochord and prechordal mesoderm)
the ectoderm layer begins to thick and form neural plate
what do the cells of the neural plate do? (2 things)
- invaginate and form canal (basis of NS)
- make up neuroectoderm and their induction represents the initial event of neurulation
what is neurulation
formation of the nervous system
in which way does the NS mature?
top to bottom
the CNS begins initially from….
uniform sheet of cells= neuroepitheliu m
when is the neural plate formed and how
3rd week of development
- longitudinal band of ectoderm thickens to form the plate
how is the neural groove formed
neural plate folds inwards forming neural groove, flanked by neural folds
how is neural tube formed
as neural groove deepens, the folds move medially and begin to fuse forming the neural tube
what is the function of notochord?
instruct NS to become ventral
what do somites give rise to
give rise to skeleton, skin, and specialized cells called melanocytes
– they are called dermomyotome
rostral vs caudal
rostral= top/upper
caudal= bottom/lower
cephalic and caudal ends of neural tube comminicate with…
until the fusion is complete, they communicate with amniotic cavity by way of cranial (anterior) and caudal (posterior) neuropores
what happens at day 25
closure of cranial neuropore
18-20 somites
what happens at day 27
closure of caudal neuropore
25 somites
close of neural tube sensitive to… (2)
- environmental agents
- aberrant gene activity
failure of proper closure leads to neural tube defects
neural tube separating from the ectoderm
as the tube closes (fusion occuring rostrally and caudally), it separates from overlying ectoderm
notochord involved in … and becomes
it is the transient axial mesodermal structure
- involved in ventral patterning of NS
- becomes incorporate in developing intervertebral disks of the skeleton
mesoderm-derived somites will form…
most of the vertebral column and segmental units of muscle (myotomes) and dermis (dermatome)
what happens at day 24 and 26
24: tube is closed at rostral end
26: closed at caudal end, local enlargements (primary vesicles) are apparent
3 primary vesicles
prosencephalon
mesencephalon
rhombencephalon
in early development, 2 types of tissues
epithelium (have basement membrane)
mesenchyme
what does the sulcus limitans do during closing of neural tube
separates dorsal and ventral tubes
neural tube defects frequency (live births)
occurs in 1 per 1000 live births
3 types of neural tube defects
cranioarchischisis
anencephaly
spina bifida
cranioarchischisis
- open spinal cord and spine
- CNS is abnormally open on dorsal surface
- complete failure neural tube fusion
anencephaly
- failure rostral end of neural tube to close
- fetus born no/reduced head
spina bifida
- failure of caudal end of neural tube to close
- caudal walls are continuous with skin of the back, the cord and meninges are displaced into a saclike cavity on back
- vertebrate fail to form over lesion
- can be corrected by surgery
how does a primary vesicle form a secondary vesiscle
have specializations of primary vesicles to form secondary vesicles
cephalic and cervical flexure
- pockets of space
Cephalic= anterior, between mesencephalon and rhombencephalon
- secondary: between mesencephalon and metecephalon
Cervical= between rhombencephalon and spinal cord
- secondary: between myelencephalon and spinal cord
prosencephalon secondary vesicles
prosencephalon= forebrain
- Telencephalon
- Diencephalon
Derivative of telencephalon
cerebrum
derivatives of diencephalon (4)
thalamus
hypothalamus
retina
other midbrain structures
secondary vesicles of mesencephalon
(midbrain)
- secondary vesicles= mesencephalon
derivative of mesencephalon
midbrain
rhombencephalon secondary vesicles
(hindbrain)
- Metencephalon
- Myelencephalon
Metencephalon derivatives (2)
pons
cerebellum
myelencephalon derivative
medulla
list 5 secondary vesicles
telencephalon diencephalon mesencephalon metencephalon myelencephalon
fusion between diencephalon and telencephalon
part of cortical development
- rapid expansion of cerebral hemispheres in 2nd month, results in downward folding of basal ganglia
- by 3rd month, telencephalon and diencephalon have fused
development of ventricular system
as each cerebral hemisphere grows in a C-shaped manner, so does its lateral ventricle
flexures forming in ventricular system
as NS grows, spaces get trapped inside growing brai
and get different parts of ventricular system
- ex: lateral ventricle, 3rd ventricle
choroid plexus function
- regulates fluid in ventricular system
- continuation of blood supply in brain
- initially start as blood vessels, then start making choroid plexus
week 3 major developments (4)
- neural groove and folds
- 3 primary vesicles visible
- cervical and cephalic flexures
- motor neurons appear
week 3 malformations
neural tube defects
week 4 major developments (6)
- neural tube starts to close (day 22)
- rostral end of tube closes (day 24)
- caudal end of tube closes (day 26)
- neural crest cells begin to migrate
- secondary neurulation starts
- motor nerves emerge
week 4 malformations (2)
- neural tube defects
- holoprosencephaly
week 5 major developments (8)
- optic vesicle, pontine flexure
- 5 secondary vesicles visible
- sulcus limitans, sensory ganglia
- sensory nerves grow into CNS
- rhombic lips
- basal ganglia begin
- thalamus, hypothalamus begin
- autonomic ganglia, lens, cochlea start
week 5 malformations (2)
holoprosencephaly
sacral cord abnormalities
week 6-7 major developments (6)
- telencephalon enlarged
- basal ganglia prominent
- secondary neurulation complete
- cerebellum and optic nerve begin
- choroid plexus
- insula
week 8-12 major developments (5)
- neural proliferation and migration
- cerebral and cerebellar cortex begin
- anterior commissure, optic chiasm
- internal capsule
- reflexes appear
week 8-12 malformations
migration/proliferation problems
e.g. abnormal cortex/gyri
week 12-16 major developments (3)
- neuronal proliferation and migration
- glial differentiation
- corpus callosum
week 12-16 malformations
migration/proliferation problems
e.g. abnormal cortex/gyri
week 16-40 major developments (4)
- neuronal migration
- cortical sulci
- glial proliferation, some myelination
- synapse formation
week 16-40 malformations
- hemmorrhage
other destructive events
neurocrest arises between
ectoderm and neuroectoderm
neural crest cells
as neural tube separates from ectoderm, it leaves behind a group of cells that were at the crest of each neural fold
where are cells born?
at the junction and migrate
neural crest cells migrate and give rise to… (4)
- sensory neurons (dorsal root ganglia of spinal nerves, some cranial nerves)
- all post-ganglionic neurons of ANS
- the adrenal medulla
- Schwann cells
major difference between cranial and trunk neural crest cells is…
- cranial neural crest cells have ability to form cartilage and bone
sulcus limitans divides…
developing neural tube into posterior alar plate
- and anterior basal plate
that will give rise to sensory and motor areas of spinal cord and brainstem
