Development of the NS Flashcards
Cortical vs Spinal Neurons
Spinal reflex arc
Bone morphogenetic protein (BMP)
Initially produced in all ectodermal cells. Induces epidermal fate, but is inhibited by Noggin from the primitive node.
Noggin
Produced by the primitive node. Induces formation of the neural plate/neuroectoderm from ectodermal epiblast by acting as a BMP antagonist.
Neurulation
Neural tube defects
When the neural tube does not close properly. Two major forms:
Anencephaly: when the cranial region does not close properly. Usually incompatibly with survival and leads to prenatal termination.
Spina bifida: when the spinal region does not close properly. May or may not cause significant functional problem.
_____ prevents the majority of NTD cases.
Vitamin B9 (folate) supplementation 3 months before and throughout pregnancy.
The notochord
Vestigial in adult humans, but plays the imporant role of inducing neural tube formation in development.
During neurulation, the notochord is _____ to induce ventral cell differentiation.
During neurulation, the notochord is necessary and sufficient to induce ventral cell differentiation.
Sonic hedgehog (Shh)
Morphogen produced by the notochord and the neural floor-plate. Acts on the neural tube. Induces differentiation of different types of neuron in a concentration-dependent manner.
Mechanism of Shh action
Roof-plate/Floor-plate diagram
The nature of ventral cell-type induced by Shh. . .
varies with rostral-caudal position.
Basic principle of axon guidance
Major families of axon guidance molecules
ephrin
netrin
semaphorin
slit
Slit is primarily chemorepellant while others may be attractant or repellant depending on context.
Comissural
Crossing the midline
Usually in reference to axons.
Spinal comissural interneurons
Netrin
Expressed by the neural floor plate throughout the spinal cord. Attracts neuron axons in the developing spinal cord towards the ventral horn.
Broad mechanisms of chemoattraction vs chemorepulsion
How semaphorin helps organize the spinal cord
Intermediate Target Axon Navigation
Floor Plate Attraction and Repulsion Mechanisms
Basic pathway of neural development
Node makes noggin → induces neural plate (neuroectodermal cells)
Retinoic acid produced by somites (which are already at the level of the spinal cord) → induces neural tube differentiation into spinal neurons
Sonic hedgehog produced by notochord → induces gradient-dependent spinal neuron fate (high concentrations yield spinal somatic motor neuron fate)
More than 70% of drosophila mRNA shows. . .
More than 70% of drosophila mRNA shows specific subcellular localization.
