Development of the Nervous System Flashcards
What is the name given to the proliferation of the ectoderm in the dorsal midline?
Neural plate
What happens to the neural plate as it thickens?
It folds up the sides and eventually the two neural folds fuse to form a tube The space in the middle is the neural canal
What is the name given to the bunch of cells at the tip of the neural fold that are excluded in the fusion?
Neural crest
Which cells do the neural tube and neural crest cells give rise to?
Neural tube – all cells of the CNS Neural crest – all cells of the PNS
What is the name given to the wall of the neural tube?
Neuroepithelium
What three types of cells do neuroepithelium give rise to?
Neuroblasts – all cells with cell bodies in the CNS, this includes motor neurone and interneurons as their cell bodies are in the CNS, whereas sensory neurons do not come from neuroblasts but from the neural crest cells
Glioblasts – these become neuroglia (astrocytes + oligodendrocytes ONLY, not microglia which has a different source. Ependymal cells are a type of glial cell but they have a separate lineage outlined below)
Ependymal cells – line the ventricles and the central canal
Are motor neurons produced from neuroepithelium?
Yes – although most of their axons are outside the CNS, their cell bodies are within the spinal cord
State four cell types that neural crest cells can differentiate into.
Sensory neurons of dorsal root ganglia and cranial ganglia
Autonomic post-ganglionic neurons
Schwann cells
Non-neuronal cells e.g. melanocytes
Describe the arrangement of the neuroepithelium.
Neuroepithelium has an inner layer and an outer layer Most cells are connected to both the inner and outer layer but the nuclei are at different positions
Describe the differentiation of the neuroepithelium.
Firstly, you get cells withdrawing away from the outer membrane towards the inner membrane where it undergoes mitosis One of the daughter cells will remain attached to the inner membrane and the other daughter cell will move away from the inner membrane and become a neuroblast. The neuroblast will develop processes and one will become the axon. These axons are directed away from the inner membrane. Eventually, three layers are formed with the neuroblast cell body in the grey matter layer and its axon in the white matter layer
What are the three layers formed by the differentiation of the neuroepithelium?
Ependymal, grey matter and white matter AKA germinal layer, mantle layer, marginal layer
Glioblasts show a similar pattern of differentiation to neuroblasts. State one difference.
Glioblasts can migrate into the white matter NOTE: glioblasts do not develop axons (but they do develop processes)
What guides the process of differentiation and migration?
Signalling molecules
Which factors are important with regards to signalling molecules?
Concentration and timing
there is no point producing signalling molecules if the developing neurones don’t have the right receptors. Also, Some of the signalling molecules have different effects at different stages of development
What can the grey matter of the neural tube be divided into?
Alar plates and basal plates
Which types of neurons do the alar plate and basal plate give rise to?
Alar plate – interneurons Basal plate – interneurons and motor neurons
Which structures around the neural tube release signalling molecules and what effect do they have on the cells in the neural tube?
Notochord and ectoderm Notochord releases signalling molecules that induce the cells nearest to it to differentiate into motor neurons Ectoderm produces signalling molecules that inhibit the cells nearest to it from differentiating into motor neurons
Around 4 weeks, you get differentiation of the wall of the anterior neural tube to form three primary vesicles. Name these primary vesicles.
Prosencephalon – future forebrain (prosen= leaning forwards)
Mesencephalon – future midbrain (mesen=middle)
Rhombencephalon – future hindbrain (rhombus shaped)
Describe the changes that occur to these three vesicles in the week or so following their formation.
The first and third vesicles divide into two
- Prosencephalon - telencephalon (future cerebral cortex) + diencephalon (thalamus and hypothalamus)
- mesencephalon stays the same (becomes midbrain)
- Rhombencephalon - pons + medulla
What important structure begins to appear quite late in development (around 8 weeks) and where does it appear from?
Cerebellum – appears as an out pouching from the back of the pons
Name the three flexures in the developing brain.
Cephalic Pontine(related to pons) Cervical
Describe the formation of the 4th ventricle.
In the neural tube in the region that will become the brainstem (rhombencephalon), the roof plate rapidly proliferates and causes the alar plates to split apart so that they are lateral to the roof plate The space left from the proliferation of the roof plate will become the 4th ventricle
Picture plate shows what I am saying
Describe the arrangement of motor, sensory and autonomic cranial nuclei within the brainstem.
Motor = medial Sensory = lateral Autonomic = in between
What structure divides the motor nuclei from the sensory nuclei in the brainstem?
Sulcus limitans
How do neuroblasts migrate from the inner membrane to the outer membrane in the brain?
They attach themselves to radial glial cells and climb up them towards the outer membrane Radial glial cells have their cell bodies anchored to the inner membrane and have a single long process to the outer membrane
What happens to neuroblasts that stay in the middle of the cortex?
They become the basal ganglia
How many layers of cells are there within the cerebral cortex?
SIX
What can a deficiency of folic acid in pregnancy lead to?
Spina bifida
What is anencephaly
Neural tube needs to close at both ends. Anencephaly is when the rostral end does not close and you essentially get no brain/little brain that is open and lacks a skull to protect it
anencephaly= without
What is encephalocele
rostral end of neural tube doesn’t close completely causing Herniation because part of the skull in the occipital area didn’t fuse properly so contents herniate out
encephalo= brain
cele= hernia/tumour/swelling
what is iniencephaly
extreme retroflexion of head ( bend back) caused by incomplete closure of the rostral end of the neural tube
from anatomy- inion is at the back of the skull on the occipital bone
What are the three types of spina bifida
Spina bifida: incomplete closure on the caudal part of neural tube. the bony surrounding around the spinal cord is not completely closed. It has three types:
- spina bifida occulta,
- meningiocele and (herniation of the meninges)
- myelomeningocele. (herniation of the meninges and spinal cord(myelo))
- Spina bifida occulta: occulta means hidden. This means that there is no herniation through the opening in the vertebral spine despite the incomplete closure.
- Meningiocele: meninges have herniated through (see pic above). The spinal cord doesn’t herniate
- Myelomeningiocele: meninges + spinal cord both herniate through the opening (myelo=spinal cord or bone marrow)
what is craniorachischisis
Craniorachischisis: most severe form of neural tube defect. This is when both ends of the neural tube do not close, causing an open and exposed brain and spinal cord (see pics online)
Cranio=brain
Rachi=spine
Schisis= split
