lecture 1 - development of the cns Flashcards
when is the pre-embryonic period?
describe organ system development at this point.
- weeks 1-2
- no distinct organ systems
when is the embryonic period?
describe organ system development at this point.
- weeks 3-7
- most of the body systems develop during this period (CNS, heart, arms, legs, ears, eyes, teeth, palate, external genitalia) - means its the most ! tetragenic !
when is the fetal period?
describe organ system development at this point.
- weeks 8-38
- continuation of development of organ systems from embryonic period (except heart, arms, legs) as the baby grows in size
what is fertilization? where does it most commonly ocur?
sperm joins egg - ampulla of uterine tubes, travles to endometrium where it implants
what is fusion?
makes zygote
what is cell cleavage?
zygote –> morula
what is a morula? when does it typically form?
- 16 cell mass
- day 4
what is blastulation?
morula –> blastula
what are blastomeres?
divisions of genetic material
what is a blastula? when does it typically form?
- 100 cell mass
- day 5-8
is blastulation before or after implantation?
before
what is occuring (in more detail) during blastulation?
- embryoblast and trophoblast differentiation (simultaneously)
- formation of blastomere cavity in the centre of the blastomere
the trophoblast goes on to become what?
the placenta
the embryoblast goes on to become what?
the fetus
what is the trophoblast composed of?
cytotrophoblasts and syncytiotrophoblasts
are cytotrophoblasts mono- or multi-nucleated?
mono
are syncytiotrophoblasts mono- or multi-nucleated?
multi
describe the cytotrophoblasts
surrounds primitive yolk sac, then embryo
describe the syncytiotrophoblasts
froms through movement, fuses with maternal sinusoids to form trophoblastic lacunae (part of blood supply to embryo)
what do the cytotrophoblasts connect?
embryo to mom via blood
what do the syncytiotrophoblasts connect?
mom to embryo
whar does the embryoblast develop into?
bilaminar disc
describe the development of the embryoblast into the bilaminar disc
- starts at day 9
- day 12: embryoblast splits into:
- – epiblast (surrounds amniotic cavity – embryo proper)
- – hypoblast (surrounds exocoelomic cavity – yolk sac/allantois)
what is gastrulation?
blastula –> gastrula
what is a grastrula?
multilayered and multidemensional cell structure
what does gastrulation establish? what does this mean
- the cranio-caudal axis
- first time we have direction in the fetus
where does gastrulation occur?
at the bilaminar disc
what marks the begining of gastrulation?
the primitive streak
describe gastrulation
- as the primitive streak advances, the primitive node forms, which eventually turns into the primitive pit
- along the primitive streak, the epiblast begins to undergo ingression through the primitive pit
During ingression, invaginating cells have four destinations - what are they?
(i.e., what is formed during gastrulation?)
- ectoderm
- mesoderm
- endoderm
- notocord
where do invaginating cells for the ectoderm end up?
remain in epiblast
what will the ectoderm become?
NS, epidermis, hair, nails, teeth, and sensory epithelium of eyes/ears/nose
where do invaginating cells for the mesoderm end up?
between the former hypoblast and the epiblast
what will the mesoderm become?
muscles, bone, cartillage blood, bvs, notocord
where do invaginating cells for the endoderm end up?
replacing the hypoblast
what will the endoderm become?
lining of GI and respiratory tracts, accessory digestive organs, urinary organs, endocrine glands
describe the notocord as a destination of invaginating cells
- some ascend to oropharyngeal membrane
- most form fetal primitive backbone (for structural integrity), which eventually develops into the nucleus pulposus (which is gelatenous tissue btween the discs in the adult back)
neurulation spans which days of development?
~19-28
describe day 19 of neurulation
- epiblast begins to thicken cranially, forming the neural plates
- lateral edges of the neural plates elevate, while the midline depresses
describe day 20 of neurulation
- neural fold begins to fold dorsally in the middle of the craniocaudal axis forming the neural groove
- folding proceeds both cranially and caudally
describe day 22 of neurulation
- neural tube begins to close at the middle
- fusion proceeds both cranially and caudally
describe day 23 of neurulation
neuropores begin to close (last part)
when does the cranial neuropore close?
day 26
when does the caudal neuropore close?
day 28
what happens when the neuropores fail to close?
neural tube defect
what (specifically) results when the cranial neuropore fails to close?
anencephaly - born without sections of the frontal lobe, cerebrum, and skull (because it develops around the developing brain)
what (specifically) results when the caudal neuropore fails to close?
spina bifida - neural tube doesn’t close all the way in the spinal cord - bulges out - can cause movement problems
what are neural crest cells?
during neural folding, cells from the neural folds break off and migrate to form other structures
what do neural crest cells become?
- dorsal root ganglia
- autonomic chain ganglia
- adrenal medulla
- schwann cells of PNS
- melanocytes
- dermis, sm and adipose of the face
breify decsribe the development of the sc
neuroepithelium divides into neuroblasts (primitive nerve cells), forming:
( 1) deep mantle layer (gray matter) (neural tube itself)
(2) superficial merginal layer (white matter)
the deep mantla layer can be further subdivided into:
alar plate (sensory, dorsal) basal plate (motor, ventral) sulcus limitans
what distinguishes the alar and basal plate?
sulcus limitans
the neural tube dilates to form 3 primary vesicles:
prosencephalon (forebrain)
mesencephalon (midbrain)
rhombencephalon (hindbrain)
what are the secondary vesicles of the prosencephalon?
telecephalon, diencephalon
what does the telecephalon form?
cerebrum
what does the diencephalon form?
thalamus and hypothalamus
what are the secondary vesicles of the mesencephalon )?
mesecephalon
what does the mesencephalon form?
midbrain
wheat are the secondary vesicles of the rhombencephalon?
metencephalon, myelencephalon
what does the metecephalon form?
pons and cerebellum
what does the myelencephalon form?
medulla oblongata
which secondary vesicle forms the lateral ventricles?
telencephalon
which secondary vesicle forms the third ventricle?
diencephalon
which secondary vesicle forms the cerebral aqueduct?
mesencephalon
which secondary vesicle forms the fourth ventricle?
rhombencephalon
which secondary vesicle forms the central canal?
mesencephalon
what are the 3 spinal flexures?
cephalic, cervical and pontine
where is the cephalic flexure?
exists entirely in the mesencephalin
where is the cervical flexure?
exists at the end of the vesicles - distinguishes the brain and spinal cord
where is the pontine flexure?
distinguishes metencephalon and myelencephalon
what is the first flexure to form?
cephalic
what is the last flexure to form?
pontine
describe the ‘C-shape’
- neurons in the neocortex (telencephalon) proliferate, migrate and begin to devlop connections rapidly
- causes C-shape rotation because the skull cannot contain all of these new connections
what signals the end of fertilization?
implantation (development of fibrin coagulum)
what is the result of increased cortical convolutions?
(gyri and sulci) - increased surface area
summarize the events of week 1
- fertilization
- cleavage
- implantation begins
summarize the events of week 2
- embryoblast differentiation
- trophoblast differentiation
- implantation is complete - fibrin coagulum
summarize the events of week 3
ingression (ectoderm, mesoderm, endoderm, notocord)
when does the embryo become asymetric?
week 3
summarize the events of week 4
neurulation
when, specifically, does brain development occur?
end of the 1st trimester
