Development of 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 – CNS
Neural crest – 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
Glioblasts – these become neuroglia (astrocytes + oligodendrocytes)
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
Three layers are formed
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
What can the grey matter of the neural tube be divided into?
Alar (interneurons) and Basal (interneurons and motor neurons) plates
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
Mesencephalon – future midbrain
Rhombencephalon – future hindbrain
Describe the changes that occur to these three vesicles in the week or so following their formation.
The first and third vesicles divide in two
Prosencephalon -telencephalon + diencephalon
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 outpouching from back of pons
Name the three flexures in the developing brain.
Cephalic
Pontine
Cervical
Describe the formation of the 4th ventricle.
In the neural tube in the region that will become the brainstem, 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
Describe the arrangement of motor, sensory and autonomic cranial nuclei within the brainstem.
Motor = medial Sensory = lateral Autonomic = in between
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?
Become the basal ganglia cells
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 (Incomplete closure of bones and membranes around spinal cord)
What condition occurs if neural tube doesn’t close rostrally?
Anencephaly – Near complete absence of brain and lack of skull vault (Incompatible with life)
What happens if there is herniation of the brain during development?
Results in Encephalocele (Ectopic brain substance)
What happens if there is herniation of the meninges during development?
Results in Meningocele – a CSF filled protrusion through a skull or spinal defect
What happens in the case of development of open spinal cord?
A Myelomeningocele – The open cord with a meningeal cyst that projects through white matter
Where can neural stem cells be found in adults?
Sub-ependymal areas of brain (This is where germination level was in development)
In hippocampus (No one is sure why)
What early structure develops into the vertebral column?
Notochord - A cartilaginous strip
Where do microglia originate?
Systemically - enter brain early in development
