Embryology 2 - Neurulation, Folding, and Development of Nervous System (Week 8) Flashcards
What are the roles of the notochord?
1) Establishes the longitudinal axis of the embryo and gives it some rigidity
2) Provides signals for the development of axial MSK structures and the CNS
3) Contributes to the intervertebral discs
How does the notochord form?
Note: this process occurs @ approx. day 16, 17, and 18
- mesenchymal cells “dive” into the primitive pit, migrating towards the cephalad region
- they stop at the prechordal plate (acts as “stop signal” from developing too far anteriorly)
- in doing so, these cells form the notochordal process
The notochordal process develops a lumen called the __________
Once this canal forms, the floor of the notochordal process fuses with the endoderm, replacing whatever endoderm was there with the notochord process.
notochordal canal
Once the notochordal canal disappears and becomes the notochordal plate, we also get the ___________ canal, which allows for communication between the amniotic cavity and the umbilical vesicle.
neurenteric
Note: was once the primitive pit –> becomes neurenteric canal
As the notochordal plate proliferates and folds into itself, it forms the ___________
@ ~ middle of 3rd week
notochord
Note: notochord is like a tube
True or False: Notochord formation starts caudally and progresses cranially
False.
Notochord formation starts cranially (cephalad) and progresses caudally
After the notochord is fully developed, the _____________ is fully obliterated
neurenteric canal
True or False: The neural groove is a groove that is part of the ectoderm that is located on top of the notochord. On either sides of the groove, there are neural folds.
True
What serves as the central axis of the embryo, dividing right from left?
the notochord
What does the prechordal plate develop into?
the oropharyngeal membrane
The oropharyngeal membrane is a two-layer membrane that includes an ________ and ________, but NO ____________
ectoderm and endoderm,
mesoderm
What eventually becomes the future site of the anus?
cloacal membrane
The cloacal membrane is a two layered membraned that includes an ____________ and ___________, but NO ___________
ectoderm and endoderm,
mesoderm
Note: similar to the oropharyngeal membrane
True or False: The cloacal membrane forms caudal to the primitive streak
True
A small, vascularized diverticulum (outpouching) from the caudal wall of the umbilical vesicle, extending into the connecting stalk
allantois
What is the allantois involved with?
- early blood formation
- bladder development
The ________ is a tube that extends from the bladder to the belly button (umbilical region) that closes after birth and becomes the ________________ in adults
urachus,
median umbilical ligament
The notochord induces the overlying ectoderm to develop into the ____________
neural plate
The process by which the neural tube is formed is called what?
neurulation
Note: begins with neural plate formation
The neuroectoderm gives rise to what?
- the CNS
- retina
- tissues that arise from the neural crest
True or False: As the organism matures, the neural plate extends beyond the notochord
True
On day 18, the neural plate invaginates to form the _____________, whereby neural folds are found on either side
neural groove
When the neural folds fuse together, they form the ___________
neural tube
When is neurulation complete?
By the end of the 4th week, when the tube becomes completely closed
____________ are a subset of neuroectodermal cells that originate at the apex of the neural folds, lose affinity to the epithelium and neighbouring cells, and migrate widely on either side of the tube, throughout the mesenchyme
neural crest cells
What do the neural crest cells give rise to?
the peripheral nervous system (PNS)
What are some derivatives of the neural crest cells?
- ganglia of CN V, VII, IX, and X
- spinal ganglia (dorsal root ganglia)
- autonomic nervous system ganglia
- neurolemma (Schwann) sheaths of peripheral nerves
- contribute to arachnoid and pia mater
- adrenal medulla
- melanocytes
- craniofacial bone and cartilage
- portions of the heart
Intraembryonic mesoderm proliferates to form a thick column of mesoderm on either side of the notochord, called __________
paraxial mesoderm
The ____________ is found just lateral to the paraxial mesoderm
intermediate mesoderm
The ____________ is found just lateral to the intermediate mesoderm
lateral mesoderm
During the 3rd to 5th week, the paraxial mesoderm “bulks up” to form what?
somites
What are somites?
cuboidal masses of mesoderm on either side of the notochord, that give rise to most of the axial skeleton and associated musculature (e.g., erector spinae), as well as the dermis in those areas
During the 3rd week, mesenchymal cells migrate anteriorly, lateral to the notochordal process to eventually form the ____________
cardiogenic mesoderm
Note: eventually gives rise to the embryonic heart primordia (aka the primordial heart)
REVIEW: what is a coelum?
a fluid-filled cavity
True or False: By about day 21, isolated coelomic spaces in the lateral mesoderm and cardiogenic mesoderm join together and form a single horseshoe-shaped intraembryonic coelom
True
The intraembryonic coelom is in the middle of and separates what two layers in the lateral mesoderm?
1) somatopleure (the somatic mesoderm and the overlying ectoderm; forms the body wall)
2) splanchnopleure (the splanchnic mesoderm and the underlying intraembryonic endoderm; forms the embryonic gut)
During the 2nd month, the intraembryonic coelom develops into what 3 body cavities?
1) pericardial cavity
2) pleural cavity
3) peritoneal cavity
REVIEW: The bilaminar embryonic disc –> trilaminar embryonic disc during gastrulation. What are the layers?
bilaminar (epiblast and hypoblast) –> trilaminar (ectoderm, mesoderm, endoderm)
Note: When the endoderm forms, the hypoblast goes away. Everything in the middle becomes mesoderm. Everything left in the epiblast becomes the ectoderm.
What are the two general planes of embryonic folding ?
1) median plane folding (aka cranial-caudal folding)
2) horizontal plane folding (aka lateral folding)
the anterior and posterior ends of the embryo move ventrally
median plane folding/cranial-caudal folding
the lateral edges of the embryonic disk move ventrally, whereby the edges roll ventrally towards the umbilical vesicle
horizontal plane folding/lateral folding
When does embryonic folding begin?
By the end of the 3rd week, but is more prominent in the 4th week
As embryo folds cranially, what appears?
- brain vesicles
- some somites
As embryo folds laterally, what forms?
the body wall
The foregut lies between the ________ and _________
forebrain, primordial heart
True or False: Part of the endoderm of the umbilical vesicle is incorporated into the embryo as the foregut
True
The __________ is the primordium of the mouth
stomodeum
The ___________ separates the foregut from the stomodeum
oropharyngeal membrane
The _____________ lies caudal to the heart and develops into the central tendon of the diaphragm, separating the abdominal cavity from the thoracic cavity
septum transversum
The pericardial coelom lies __________ (ventral/dorsal) to the heart
ventral (tummy side)
True or False: Part of the endodermal germ layer is incorporated into the embryo as the hindgut
True
Note: similar to foregut
The connecting stalk is the primordium of what?
the umbilical cord
As the tail folds, the connecting stalk moves from caudal to _________ and the allantois becomes part of the embryo
ventral
True or False: During lateral folding, as the abdominal walls form, part of the endoderm germ layer is incorporated into the embryo as the midgut
True
The foregut and hindgut form during ____________ and the midgut forms during ___________
cephalad/caudal folding,
lateral folding
After lateral folding, the midgut and umbilical vesicle are connected by the _________
omphaloenteric duct
What does the endoderm give rise to?
- epithelial lining of the digestive and respiratory tracts
- parenchyma of the tonsils
- thyroid and parathyroid glands, thymus
- liver, pancreas
- epithelial lining of the urinary bladder and most of urethra
- epithelial lining of the tympanic cavity, tympanic antrum, and eustachian tube
What does the mesoderm give rise to?
- connective tissue (cartilage, bone)
- striated and smooth muscle (heart, blood, lymphatic vessels)
- ovaries, testes, genital ducts
- serous membranes lining the body cavities (pericardial, pleural, peritoneal)
- spleen
- cortex of suprarenal glands
What does the ectoderm give rise to?
- CNS, PNS
- sensory epithelia of the eyes, ears, nose
- epidermis and its appendages (hair and nails)
- mammary glands
- subcutaneous glands
- enamel of teeth
- pituitary gland
- neural crest cells
True or False: By the end of neurulation, after the neuropores close, a basic blood circulation has been established
True
The cranial 2/3 of the neural tube forms what?
the brain
The caudal 1/3 of the neural tube forms what?
the spinal cord
What are the three zones that develop during spinal cord development?
1) ventricular zone
2) intermediate zone
3) outer marginal zone
True or False: During spinal cord development, the outer marginal zone is the first of the three layers to develop
False
The ventricular zone is the first to develop
What does the ventricular zone give rise to?
all neurons and macroglia
What does the intermediate zone become populated with?
primordial neuroblasts
What does the outer marginal zone develop into?
white matter tracts
Glioblasts are precursors to what?
glial cells
Alar plates eventually develop into?
dorsal gray horn (afferent/sensory nuclei)
Basal plates eventually develop into?
ventral gray horn (efferent/motor nuclei)
What are the spinal meninges derived from?
mesenchyme
Neuroepithelium (neuroectoderm) derivatives
- glioblasts
- astroblasts
- oligodendrocytes
- ependymal cells (provide CSF)
- neuroblasts –> eventually make neurons
Brain development occurs when?
beginning ~ week 5
What are the three primary brain vesicles?
1) forebrain (prosencephalon)
2) midbrain (mesencephalon)
3) hindbrain (rhombencephalon)
What two SECONDARY brain vesicles does the prosencephalon divide into?
1) telencephalon
2) diencephalon
What does the telencephalon give rise to?
cerebral hemispheres
What does the diencephalon give rise to?
thalami (thalamus, hypothalamus, epithalamus)
What does the midbrain give rise to?
midbrain
(easy to remember!)
What secondary vesicles does the hindbrain (rhombencephalon) divide into?
1) metencephalon
2) myelencephalon
What does the metecephalon give rise to?
pons and cerebellum
What does the myelencephalon give rise to?
medulla
During week 4, lateral outgrowths/optic vesicles give rise to what?
retinae and optic nerves
Telencephalic vesicles give rise to what?
cerebral hemispheres
and their cavities become the lateral ventricles
Three swellings develop in the lateral walls of the third ventricle, which go on to become what?
1) thalamus
2) hypothalamus
3) epithalamus
Note: these are prevalent by week 7
