Lecture 1: Development Flashcards
When does myelination of axons occur during development
Postnatally by oligodendrocytes
When does the most neuronal cell proliferation occur?
First 5 months since birth
What causes the differentiation of different types of neurons (Eg. dopaminergic vs. GABAergic) and glial cells?
A plethora of different combinations and concentrations of various signalling molecules
What are bone morphogenic proteins (BMPs)
Signalling molecules released by the ectoderm next to the neural groove which cause formation of the sensory neurons via the alar plate of the neural tube (dorsal part of the spinal cord)
How many layers of neurons are there in the adult cerebral cortex?
How do they develop?
Cerebral cortex consists of 6 layers. They develop in an “inside out” fashion. Radial glial cells provide a scaffold (that extends from the ventricular surface to the pial surface) in which neuroblasts can migrate along.
- The first cell layer to develop is layer 6 (which is the inner most layer). The cells migrate through the intermediate zone and past the subplate to arrive at the cortical plate.
- The next group of cells migrate past layer 6 to become what becomes layer 5 and so on.
- The last cells to migrate are layer 1
What is meningomyelocele
The most severe case of spina bifida where elements of the spinal cord, cauda equina and meninges herniate through a defect in the vertebral column. Has severe consequences to motor function and sensation to lower limbs
What are the 4 types of glial cells?
Astrocytes, oligodendrocytes, microglia and ependymal cells
How is neuronal proliferation regulated? And when does this occur?
Neuronal proliferation occurs between 5 weeks to 5 months - and is regulated by two signalling molecules within the neuroblast
- Notch-1 (sits on the pole of the neuron closest to the pial surface)
- Numb (sits closest to the ventricular surface)
They occupy a polar position within the neuroblast (as above). When a neuroblast undergoes verticle cleavage - both notch-1 and numb are maintained. When a neuroblast undergoes horizontal cleavage, Notch-1 and Numb-1 are contained in separate daughter cells and the Notch-1 cell will migrate and be unable to proliferate (when notch-1 is expressed on its own it causes the migration to the pial surface).
Numb inhibits notch when contained in a single cell during vertical cleavage.
When do secondary vesicles appear?
Weeks 5 to 6
What are names of the vesicles in red, pink, green, blue and purple? and what do they give rise to?
What is 1, 2 and 3?
A. Telencephalon: Cerebral hemispheres, hippocamous, amygdala and basal ganglia
B. Diencephalon: thalamus, hypothalamus and retina
C. Mesencephalon: midbrain
D. Metencephalon: pons and cerebellum
E. Myelencephalon: medulla
- Cervical flexure
- Pontine flexure
- Cephalic flexure
How are neural crest cells formed?
As the neural folds come together, some neural ectoderm cells get pinched off to form neural crest cells
What is the function of sonic hedgehog (SHH)
Cause differentiation of the cells which go on to form the ventral part of the spinal cord via the basal plate of neural tube(to form motor neurons)
Which flexures of the primary vesicles exist in the adult?
The cervical flexure does not exist in the adult - it straightens out. The cephalic flexure still exists in the adult which is why there is an angle where the brain stem meets the cerebrum.
What happens when the rostral end of the neural tube fails to develop?
Failure of the rostral end is a catastrophic developmental defect (anencephaly) where the foetus lacks much of the forebrain and cranium and results in death
What causes spina bifida?
Spina bifida is a neural tube defect that results from the failure of the caudal end of the neural tube to close (and can vary in severity.
Describe the formation of the neural groove
Midline mesoderm (notochord) releases signalling molecules that lead to the thickening of the overlying ectoderm to form the neural plate. The lateral edges of the neural plate become elevated and move together to form the neural fold. The neural fold moves inwards to form he neural groove. The neural groove eventually closes to form the neural tube
What is different in the pattern of differentiation between that on other parts of the neural tube and the rhombencephalon
The neural tube develops in a dorsoventral gradient of sonic hedghog (basal plate, to form ventral spinal cord and motor neurons) and bone morphogenic proteins (alar plate to form dorsal spinal cord and sensory neurons)
The rhombencephalon develops in a rostrocaudal pattern of differentiation via FGF8 (rostral) and Retinoic Acid (caudal). Differential concentrations of these two signalling molecules causes a differing pattern of HOX genes to be transcribed. This results in the diffential pattern of development in the rhombencephalon. Resulting in rhombomeres which are segments of the rhombencephalon. Every rhombere is driven in its development by the expression of a different set of HOX genes. And its the differing concentrations of FGF8 and retinoic acid that results in different combinations of HOX genes. Note: this happens very early on in development, around day 29
What is A, B and C?
The Primary Vesicles:
A. Prosencephalon
B. Mesencephalon
C. Rhombencephalon
What is this image showing? What type of MRI is this?
This is a T2 weighted MRI, where CSF is bright and myelin is dark. This is showing that myelination of neurons occurs posnatally, and you can see the increased white matter 24 months since birth.
Neuronal connections continue to form postnatally: TRUE/FALSE
true
When does formation of the neural groove occur?
3rd week
Which of the primary germ layers gives rise the the nervous system?
The ectoderm (also gives rise to the skin)
What divides the alar and basal plate?
sulcus limitans
What lines the ventricles (and neural tube)?
Ependymal cells (a type of glial cell)
