Neurulation Flashcards
Week 4
Neurulation
Steps of neurulation
1.) Neuroectodermal tissues differentiate from the ectoderm and thicken into the neural plate; the neural plate border separates the ectoderm from the neural plate
2.) The neural plate bends dorsally, with the two ends eventually joining at the neural plate borders, which are now referred to as the neural crest
3.) The closure of the neural tube disconnects the neural crest from the epidermis; neural crest cells differentiate to form most of the peripheral nervous system
4.) The notochord degenerates and only persists as the nucleus pulposus of the intervertebral discs; other mesoderm cells differentiate into the somites, the precursors of the axial skeleton and skeletal muscle
Neurulation highlights
- notochord induces overlying ectoderm to develop into the neural plate
- the neural plate folds into the neural tube and the neural crests are pinched off
- the neural tube derives the CNS
- the neural crests derive the PNS and select other cells
During gastrula (week 3 development), the body axis is formed
- bilateral symmetry
- left and right
- dorsal and ventral
- cranial and caudal
Week 3
- triploblastic/trilaminar disc
What germ layers are formed during gastrulation?
- ectoderm
- mesoderm
- endoderm
Notochord
Sonic Hedge Hog (SHH)
The mesoderm differentiates into how many types?
3
Primitive streak becomes
primitive groove
Primitive node becomes
primitive pit
The notochord secretes SHH, which dictates what?
cellular involvement
Neural plate
- neural groove
- neural folds
During neurulation, the neuroectodermal cells transform into what?
neural tube
Neural tube becomes what?
brain and spinal cord
The neural tube activates what?
- neural crest cells
- further differentiation of ectoderm, mesoderm, and endoderm
Central Nervous System (CNS)
- brain
- brain stem
- spinal cord
Peripheral Nervous System (PNS)
- cranial nerves
- peripheral body nerves
- ganglion
- sensory and motor
Steps at ectoderm: primitive area makes
primitive streak –> groove
primitive node –> pit
Primitive node
“Hensen’s node” or “Spemann-Mangold Organizer”
- notochord and SHH and axial mesoderm
Notochord and SHH and Axial mesoderm stimulates what?
Neural plate (replaces primitive streak at day 25)
Neural plate makes
- neural groove
- neural folds
which makes the neural tube
Steps at ectoderm: Cells at primitive NODE (let’s make a tube)
- they direct organization
- cells that DIVE through groove and travel CRANIALLY become the prechordal plate and notochord (which stimulate neurulation)
Steps at ectoderm: Cells at primitive NODE
Ectoderm: neural plate –> _______ ____
Ectoderm: surrounding plate –> ______
neural tube; epidermis
At primitive NODE, what happens to the cells at the cranial end?
they proliferate
At the primitive NODE, once plate is formed it undergoes __________ by _______ _______
elongation; convert extension
Neural plate
communication
How do germ cells communicate at the neural plate?
induction
At the neural plate, mesoderm causes overlaying ectoderm to undergo molecular and cellular changes
1.) Cells proliferate (increase mitosis)
2.) Cells express new sets of mRNA’s specific for neural development “markers” including CAM’s (cell adhesion molecules)
If cells transplant incorrectly—
two-headed organism
Neural plate – communication – cell movement
cells undergo shape and behavioral changes
- columnarization
- apical constriction
- convergent extension
- cell crawling
Neural plate –> hinge and close –> neural tube
1.) The sheet bends at a median hinge joint, creating neural folds
2.) The sheet bends further at lateral hinge joints, closing at the top to form the neural tube
3.) Neural crest cells detach from the epithelial tube and become wandering mesenchyme cells