Neurulation Flashcards
How many layers is our embryo at the end of week 1?
One layer.
Called the inner cell mass
What is another name for the inner cell mass?
Embryoblast
How many layers is our embryo at the end of week 2?
Two layers.
Epiblast and hypoblast.
How many layers is our embryo at the end of week 3?
Three: germ cell layers
Ectoderm
Mesoderm
Endoderm
What layer of germ cells does the epiblast become?
Ectoderm
What does the septum transversum give rise to?
Gives rise to our diaphragm.
What layer of germ cell gives rise to the septum transversum?
Mesoderm
Cardiogenic area gives rise to what?
Heart
What layer of germ cell gives rise to the cardiogenic area?
Mesoderm
What is the pre-chordial plate?
The pre-chordial plate gives rise to our mouth.
What layer of germ cells is the prechordial plate derived from?
Ectoderm and endoderm
What is the chloachal membrane?
The chloachal membrane creates the opening for our [urinary],
[digestive] and [reproductive system].
What layer(s) of germ cells give rise to our chloachal membrane?
- Ectoderm and
2. Endoderm
What is gastrulation?
Gastrulation is the creation of our trilaminar embryonic disk: 3 germ cell layers. In this process, cells from the epiblast will migrate to the primitive streak and form the primary germ layers.
When does gastrulation occur?
Week 3
Gastrulation begins with the formation of the ______ during week 3.
Primitive streak.
What is the primitive streak?
The primitive streak is a site on the epiblast where cells will begin to migrate during gastrulation.
What makes up our primitive streak?
Primitive pit
Primitive node
Primitive groove
What happens when epiblast cells begin to ingress in the primitive streak?
When ingression occurs, we will form true endoderm (replacing the hypoblast), true mesoderm and the remaining cells of the epiblast will become ectoderm.
During ingression, how do cells move into the primitive streak?
Cells will move medially to the primitive streak, go inside the groove and go back laterally.
SUMMARY OF GASTROLATION
Gastrolation is the process by where our 3 germ cell layers are created (ectoderm, mesoderm and endoderm) from the epiblast of our bilaminar disk. The endoderm made in this process will replace the hypoblast. It occurs during week 3.
For this to occur, a primitive streak must occur on the epiblast. A primitive streak is made up of a primitive pit, primitive node and primitive groove. Cells located laterally of the epiblast will move medially into the groove and out to areas that need it, forming true endoderm, true mesoderm and the remaining epiblast becomes ectoderm. During this of gastrulation, our body axes are established.
What end of the epiblast does gastrulation begin?
Gastrulation begins at the caudal end and moves to the rostral end.
___________ helps to establish our body axes.. In other words, what process is the reason why our heart is on the left side of our body?
Gastrulation
What are sacrococcygeal teratomas?
Sacrococcygeal terotomas are germ cell tumors that are derived from remnants of [pluripotent primitive streak cells].
In these tumors, all three layers of germ cells can be found at different stages of differentiation.
In one sentence, what is neurulation?
Formation of our neural tube
What induces neurulation?
In order for neurulation to occur, we must create a notochord (because will release SHH), the primary signaling center for our embryo. The notochord is a midline structure that is derived from mesodermal cells.
As we have said, it is important for the development for the rest of our body, but the structure itself is not really important.
What THREE things does the notochord do?
- Provides the longitudinal axis for our body.
- It is the template for our vertebral column
- Induced the formation of our [neural plate] and [CNS].
Formation of the notochord
- Mesodermal cells from the primitive pit and primitive node will form the notochordal process in the mesoderm. The notochordal process will migrate cephallically until it reaches the pre-chordal plate.
Thus, the this must occur from head–> tail of the embryo. - Bottom part of the notochordal process will fuse with the endoderm and form a notochordal plate. This allows the amniotic cavity and the primary yolk sac (umbilical cord to communicate.
- Notochordal plate will infold and form the notochord, which then pinch off from the endoderm.
By day ____, the notochord is formed.
20
What is the notochordal process?
A hollow tube that is derived from mesodermal cells of the primitive node and pit.
Inside of the tube is called the notochordal canal.
What is a notochord?
Notochord is solid rod that is derived from the primitive node (mesodermally derived).
When is the notochordal plate formed?
As our notochordal process is moving from the primitive node–> prechordal plate, the bottom part of it will fuse with the endoderm and create a notochordal plate.
The notochord will extend from where to where?
Oropharyngeal membrane–> primitive node.
Do we keep our notochord forever?
No. As our vertebral bodies form, our notochord will degenerate and form the [nucleus pulposus] of our [intervertebral disks]
What are chordomas?
Chordomas are SLOW-growing aggressive bone cancers caused by remnants of the notochord.
Where do chordomas occur?
They occur in the axial skeletons in the [spheno-occipital] region of the [skull and sacrum].
What is an allantois?
The allantois is a diverticulum (pouch) that comes off of the wall of the yolk sac.
The allantois is a ____________-midline structure that is derived from what germ cell layer?
The allantois is a posterior-midline structure that is derived from the ENDODERM.
What does the allantois do?
- Serves as the TEMPLATE for our [umbilical arteries and veins].
- Eventually becomes the urachus.
What is the primary signaling center for our embryo?
Notochord
What are the three types of mesoderm?
- Paraxial mesoderm
- Intermediate mesoderm
- Lateral plate of the mesoderm
Where is our paraxial mesoderm located?
Either side of the notochord
What does our paraxial mesoderm gives rise to?
Somites
- Muscle (myotome)
- Skeleton (sclerotone)
- Dermis of the skin (dermatome)
Where is our intermediate mesoderm located?
NExt to the paraxial mesoderm
What does our intermediate mesoderm give rise to?
Urogenital structures
- Kidneys
- Gonads
Where is the lateral plate of mesoderm located?
Above and below the intraembryonic coelom.
Lateral plate of the mesoderm located ABOVE the intraembryonic coelum?
Somatic layer of the lateral plate mesoderm
Lateral plate of the mesoderm located BELOW the intraembryonic coelum?
Splanchnic layer of the lateral plate mesoderm
*located next to the endoderm
What does the lateral plate of the mesoderm give rise to?
Connective tissue
- blood
- lymph
- mesentaries
- cardiovascular
The primitive streak forms extra-embryonic mesoderm. What is this?
The extra-embroyonic mesoderm formed by the mesoderm will go to the connecting stalk and help to form our placenta.
When does neurulation occur?
Week 3.
When do we develop the CNS and neural crest cells?
Week 3
Neural plate forms what?
CNS
Neurulation process
- Notochord will release SHH, which goes to the ectoderm, causing it to thicken and flatten, forming our neural plate
- Our neural plate will then invaginate and form neural folds, and a neural groove (the depression)
- Our neural folds come together to form our NEURAL TUBE
- and neural crest cells migrate away.
What is the neural plate made up of?
neural folds and neural crest cells
What comes from SURFACE ectoderm?
- hair
- nails
- sweat glands
- EPIDERMIS of the skin
What comes from neuroectoderm?
Neural tube
CNS (brain and spinal cord)
Our neural crest cells came from what?
Neuroectoderm
Did our neural crest cells come from our neural tube?
Nooooo
How can we tell how old a embryo is?
By counting the somites.
Where does our neural tube close?
around the 4th-5th somite. It will then ZIPPER close in the caudal region
Our neural tube closes at the 4th and 5th somite and zippers close. Thus, we what problem do we have?
We need to close the openings at the very end called the
- Rostral neuropore
- Caudal (posterior) neuropore.
when does the rostral neuropore close?
day 25
When does the caudal neuropore close?
day 28
What is primary neurulation?
Closure of the neural tube at the rostal and caudal neuropore (at the brain and lumbar region)
What is secondary neurulation?
Sacral and coccyx region closure.
Occurs when the [caudal eminence] fuses with the [caudal neuropore] to form our sacral and coccyx regions.
What is the caudal eminence?
The caudal eminence will fuse with the caudal neuropore and create our sacrum and coccyx (tail bone)