Neruo Development Flashcards
(42 cards)
What is Neurulatiom?
Begins at 16 days
2nd big develop,metal event
Layers and basis of a body plan have begun to form:
Ecto -and Nervous system
Messo- internal organs
Endo- internal linings (gut,linin,etc)
Preorganogenesis?
2 weeks
Embryonic period?
3-8 weeks
Fetal period?
9-38 weeks
What effects do external influences on neural development?
Example: alcohol
Fetal alcohol syndrome
Craniofacial defects: palate, eyes
Neural defects: IQ, numbers, failure to fold
Brainfolding problems
Explain formation of the neural plat
Growth without division
Primitive streak (PS) formation (gastrulation) sets up a new axis.
Cells move in from the PS, and anteriorly to form the notochord.
Notochord induces epithelium (ectoderm) to become neural)
Describe what happens during Primary Neurulation
●Occurs in the Anterior part of the neural tube (NT)
●Only the very end of the tube forms a different way.
●Neural crest cells sit at the edge of the neural plate
●Creation of hinge points:
●Medial: upward
●Dorsolateral: inward
●Closure and delamination
What’s is the mechanism that allows folding of the neural tube?
Majority of the neural tube
●Convergent extension to lengthen: not an increase in number
●Formation of hinge points to fold
Explain the formation of dorsolateral hinges during primary neurulatuon
●BMP involved.
●Noggin (inhibits BMP) → closure. Balance of BMP and noggin allows closure
●BMP involved in shape change: loosens junctional proteins
What happens during secondary neurulation ?
Posterior neural tube formation:
●Mesenchymal condensation then cavitation
●Evolved in vertebrates with longer tails
●Junctional/transitional zone in between
●Cavitation and migration
Explain Neural tube closure and release
Zip-like at 4 sites
- Extension of lamellipodia and filopodia
•Interlock and fuse - Release of NT from epiderm (N-cadherin and E-cadherin)
•Changes in cell adhesion properties
What are the consequences of neural tube closure failure?
This is the 2nd most common birth defects worldwide
●Spina bifida, anencephaly
●Varies in severity, defects can be significantly reduced with supplementation of Folic Acid. Must be taken early in pregnancy though: start prior to conception
What are the different defects due to neural tube closure failure called?
Neural tube failure closure in cranial ( brain)
● Anencephaly: cranial (brain)
●Craniorachischisis: brain and spinal cord affected
●Spina Bifida: cervical region down
●Lower back (lumbosacral section) NTDs more common
Anencephaly = absence of brain
What does Folate do (importance)?
■Role in DNA, RNA, protein and lipid methylation- affects activity and functionality
■DNA repair and replication. It is an enzyme co-factor.
■Also associated with craniofacial defects if not taken
What are Neural Crest cells?
●Form from the neural epithelium and are carried to sit above the neural tube
●Multipotent stem cells
●Extremely important in forming key structures: craniofacial, pigmentation, adrenal tissue
They create Parasympathetic and sympathetic neurons
What is the Role of Neural crest cells?
Sit above the neural tube for a short time. Hence neural “crest”
•Migrate to contribute to other tissues and structures
•Position along the tube relates to final outcome
What are the origins and derivatives of the Neural crest?
Cranial NC: cranial neurons, facial mesenchyme Cardiac NC: tissue wall of large arteries
Trunk NC: dorsal root ganglia- sensory, adrenal medulla, pigment cells
Vagal NC: parasympathetic ganglia
Explain the dorso-ventral patterning of the nervous system
Roof Plate (no neurons):
Dorsalising: BMP Commissural neurons ( cross from one side to the other- cell adhesion), 2 sensory neurons, associated interneurons 1 ֯sensory neurons from NC
Floor Plate (no neurons): Ventralising : SHH Motor neurons, ventral roots of spinal cord, associated interneurons
Explain the anterior posterior patterning of the nervous system
Splitting of the brain (encephalisation) into distinct regions (approx. 7 weeks)
Prosencephalon :
Telencephalon
Diencephalon
Mesencaphalon
Rhombencephalon :
Metencephalon
Myelencephalon
Patterns of gene expression set up boundaries that relate to anatomical segmentation.
Otx2: forebrain
Shh: floor plate throughout
Gbx2: hindbrain
WHat is encephalisation?
Splitting of the brain into regions
Explain the external influences that affect the patterning of the nervous system
●Patterning also comes from external tissues: node and the mesoderm
●Ie External tissues give a direction, local signals give specific directions
What are the steps in neural differentiation?
Competence
Specification
Commitment
Differentiation
Explain Neural differentiation
Neuroepithelia at the lumen of the tube give rise to neuroblasts.
Neuroblasts migrate and differentiate
Explain what happens when building a brain: msuktiole layering and multiple cell types
●Cells divide, move and differentiate
●Need to create ~170billion plus another ~ 170billion glial cells
