development of the CNS Flashcards
what are the stages the CNS development?
neurulation
neural proliferation
neural migration
apoptosis
synaptogenesis
myelination
what is gastrulation?
single-layered blastula reorganizes into a multi-layered structure called the gastrula, which forms the basis for the development of the three primary germ layers of the embryo: the ectoderm, mesoderm, and endoderm
when does gastrulation begin?
3 weeks of pregnancy
what process creates the 3 germ layers?
involution- cells of surface of embryo fold inwards
what is the ectoderm?
cells that remain on the outer surface of the embryo form the ectoderm, which will give rise to the skin, nervous system (including the brain and spinal cord), and sensory organs
what is the mesoderm?
cells that move inward between the ectoderm and endoderm form the mesoderm, which will become muscles, bones, the circulatory system, kidneys, and other internal structures
what is the endoderm?
cells that move deepest into the embryo form the endoderm, which will become the lining of the digestive and respiratory systems, including organs like the liver, pancreas, and lungs
what is neurulation?
process during early embryonic development in which the neural tube is formed from the neural plate
when does neurulation occur?
3-4th week of gestation
stages of neurulation
- formation of neural plate
- shaping of neural plate
- formation of neural tube
- closure of neural tube
- formation of neural crest
neural plate formation
after gastrulation, the ectoderm forms the neural plate
the neural plate is a thickened region of ectoderm that appears on the midline of the dorsal embryo
shaping of neural plate
neural plate begins to fold at its lateral edges, which gradually move toward each other=neural folding
the central region of the neural plate forms a groove called the neural groove
neural tube formation
neural folds continue to move closer to each other, eventually fusing at the midline
this fusion process forms the neural tube, a hollow structure that will give rise to the brain and spinal cord.
the anterior (cephalic) part of the neural tube will become the brain
the posterior part will form the spinal cord
closure of neural tube
begins in the middle of the embryo and proceeds anteriorly and posteriorly
completed at 4th week of development
neural crest formation
neural crest is made by the folds of the edges of the neural tube
neural crest cells migrate away from the neural tube and give rise to a wide variety of structures, including sensory neurons, ganglia, schwann cells and parts of the skull (PNS)
what are the two most common NTD (neural tube defects)?
anencephaly and spina bifida
what is anencephaly?
anterior part of the neural tube fails to close resulting in the absence or undevelopment of major parts of the brain
closure of the anterior neuropure occurs at around day 25-28
those born with anencephaly die very quickly or are stillborn
what is spina bifida?
posterior part of neural tube fails to close resulting in the incomplete development of the spinal cord and the vertebral column
posterior neuropore closes at around day 27
what are the types of spina bifida?
spina bifida occulta
spina bifida cystica (meningocele and myelomeningocele)
what is spina bifida occulta?
mild form where vertebrae are deformed but cord and nerves are unaffected
what is meningocele?
severe form in which meninges bulge out through vertebrae but spinal cord stays in place
myelomeningocele
most severe form where spinal cord and meninges protured through opening in the vertebrae
how to prevent NTDs?
folic acid supplementation (synthetic form of folate)
supplementation at least one month before conception and during the first trimester of pregnancy
what are the three primary brain vesicles?
prosencephalon, mesencephalon and rhombencephalon
when do the vesicles begin to develop?
following the development of the neural tube (4th week)
when does the prosencephalon divide into the telencephalon and the diencephalon?
week 5
when do the telencephalon and diencephalon diffrentiate?
week 6 and beyond
when does the rhombencephalon divide into the myelencephalon and metencephalon?
4-5 weeks
when does the myelencephalon develop the medulla?
5-7 weeks
what plates form the dorsal and ventral parts of the spinal cord?
alar plate forms the dorsal
basal plate forms the ventral
at around 4-6 weeks
what layers are the grey and white matter formed by?
mantle layer forms grey
marginal layer forms the white
at 6-10 weeks
when do spinal nerves and ganglia form?
6-12 weeks
what condition impacts formation of neural crest?
foetal alcohol syndrome
how does FAS affect the neural crest?
neural crest cells are highly migratory and alcohol interferes with the signals that guide migration
e.g Wnt Notch and Sonic Hedgehog (Shh) pathways
can also induce oxidative stress which leads to apoptosis of neural crest cells
disrupts cell proliferation adn progenitor cells which generate neurons and glial cells
