1E - Development (4) Flashcards
Neural plate, fold, groove
longitudinally oriented structures
Where does thin surface ectoderm fuse?
Midline
Lateral edges of neural tube have what shape cells?
Columnar
Does the neural tube have a thicker columnar epithelium?
Yes
On thin surface ectoderm, what shape cells are there?
Squamous-shape epithelium
What is the point at which fusion occurs?
Neural crest
Does the neural tube fold above notochord?
Yes
Is surface ectoderm above neural crest?
Yes
What does neural crest give rise too?
- PNS
- adrenal glands
- pigment cells of Iris
Why do neural crest cells migrate away from neural crest?
Different migratory streams from neural crest form variety of tissues
Where do columnar cells thicken?
Where nuclei are (located on outer surface of neural tube)
What effect does outer surface neural tube nuclei have on shape?
- Apex of triangle points at lumen of neural tube
- Base (flat) part of triangle puts to external surface of tube
- This shape pattern allows neural tube to fold
Voussior blocks form what?
arch
Hinge regions act like what?
Voussoir blocks
There are 3 hinge regions of what kind?
2 lateral
1 ventral
How do hinge regions affect invagination of neural tube?
- hinge regions causes initial bending/folding of neural tube surface
- extensive growth of external thin surface epithelium
- once neural plate buckles at hinge regions, inward pressure cases neural plate to bend/invaginate further and to the 2 sides to approximate
Surface ectoderm thickens to form what?
neural plate
Notochord secretes Noggin and Chordin. Functions?
- Act on surface epithelium to thicken it
- Reach by diffusion
- Different regions of surface ectoderm get different doses of compounds
Effect of compound is dose-dependent
- Region above notochord gets high dose of noggin and chordin
- Region farther away = lose dose
Effect of compound is dose-dependent PART. 2
- Low dose lateral to neural plate = not enough to do anything
- Edges of neural plate = enough to thicken
- Edges of neural plate form protoneural crest
protoneural crest
low dose of chordin, noggin
High dose found in the medial of the neural plate which forms a specialized region in the neural tube
Floorplate
signaling (organizing centers)
-region of embryo that secretes special chemicals that play a role in development
Morphogens
- Affect growth of tissues around them
- Can appear and disappear
- Chemicals secretes from signaling centers are morphogens
Edges of neural tube are darker
Due to Larger amount of tissue
where is primitive streak located
caudal (posterior) to neural folds
Where does notochord terminate? This structure is between border of forebrain and midbrain
Infundibulum
Hensen’s node is front of?
Primitive streak
Notochord is under what?
Neural tube( is on top)
Enlarged areas of neural tube become what?
brain
back part of neural tube forms what?
spinal cord
condensations of mesoderm that occur lateral of neural tube
somites
Problems if neural tube fusion does not take place completely
1: Spina Bifida Occulta
2: Meningocele
3: MyeloMeningocele
Spina Bifida Occulta
- Veterbrae incomplete
- Incomplete fusion of spinal cord
- not visible at surface
- problem with closure of vertebral column
Meningocele
-CNS surrounded by membranes called meninges
-surface tissue not closed
-herniation bubble occurs
some meninges herniate out
MyeloMeningocele
-primitive spinal cord tissue herniating out
-spinal cord extending outside of body into Meningocele
-can be surgically closed
-long-term motor/sensory problems
-skin is not closed across midline
walls of sac made of meninges
Myeloschisis
- surface tissue does not fuse
- edges of neural fold don’t use
- most serious form of spina bifida
- inside of neural tube is continuous with outside
Encephalocele
- brain tissue herniating out
- similar to MyeloMeningocele
- rarae survival
- retardation
Encephalocele
- brain tissue herniating out
- similar to MyeloMeningocele
- rare survival
- retardation
