Development of the nervous system Flashcards
What are the 3 germinal layers?
endoderm, mesoderm and ectoderm
Explain the formation of the neural tube
The ectoderm proliferates and thickens to form the neural plate down the length of the back of the embryo
the neural plate folds to form neural groove which eventually fuses into the neural canal (some of the cells of the neural tube form part of the neural crests). The neuroepithelium differentiates to form the CNS while the neural crests diffrentiate to form the PNS.
Neuroepithelium differentiates into what type of cells
Neuroblasts, Glioblasts, Ependymal cells
What to the neural crest cells differentiate into?
sensory neurons (dorsal root ganglia and cranial ganglia)
post-ganglionic autonomic neurones
Schwann cells
Non-neural derivatives
Explain the differentiation of the neuroepithelium
Firstly, you get the cells withdrawing from the outer membrane towards the inner membrane and then it goes through mitosis
One of the daughter cells will stay attached to the inner cell membrane, it gets bigger and goes into the cell cycle again
The other daughter cell migrates away from the inner membrane and then develops into neuroblasts
They develop processes (one will become the axon) and these axons are directed away from the inner membrane again
What controlles this differentiation?
Signalling molecules
The signalling molecules can either cause attraction or repulsion and the direction is determined by the concentration gradient - close to the source of the signalling molecules there will be a higher concentration
What are the important features of the developing spinal cord?
The neural canal is smaller
the grey matter has split into two different types alar plate (dorsal/interneurones) and basal plate (ventral/motoneruones and interneurones)
What do these structure develop into?
The neural canal has become the central canal carrying CSF
Alar plates develop into the dorsal horns
Basal plates develop into ventral horns
The whole spinal cord is surrounded by a thick layer of white matter
Explain the development of the brain at 4 weeks
Only the most anterior bit of the neural tube develops into the brain
You get differentiation of the wall of the anterior neural tube to form THREE primary vesicles:
Prosencephalon - future forebrain
Mesencephalon - future midbrain
Rhombencephalon - future hindbrain
The rest becomes the spinal cord
Explain the development at 5 weeks
anterior vesicle divides in two and the third vesicle also divides in two
This produces 5 secondary vesicles
You get an enormous expansion of the top part of the developing forebrain and this telencephalon will become the cerebral hemispheres
There is less expansion in the lower part of the developing forebrain because that part becomes the diencephalon
The developing midbrain doesn’t expand very much
The developing hindbrain divides in two to becomes the pons and the medulla
The vesicles aren’t in a straight line - there are THREE flexures
The flexures are named based on their position
As you go through development these flexures become exaggerated
Explain the development at around 8 weeks
As development continues you get more and more growth of the wall of the neural tube
The space within it has become smaller relative to the wall and this space becomes the ventricular system
Coming quite late, you have the first development of the cerebellum - out-pouching from the back of the pons
Dsecribe the development of the brainstem
The brainstem is a tubular structure but in the middle of it you have a 4th ventricle
In the region that becomes the brainstem, the first thing that happens is the development of the 4th ventricle
The roof plate starts proliferating rapidly and the dorsal part of the brainstem expands laterally
As the roof plate expands it pushes the alar plates aside so they are no longer dorsal to the roof plate - they are actually lateral to the roof plate
Describe the development of the cortex
The brain has a core of white matter with grey matter around the outside
The grey matter consists of nuclei that have migrated from the inner membrane of the neural tube
Some of the neuroblasts will stay in the middle and form the basal ganglia
There are other neurones that then migrate towards the outer membrane
This migration takes place by the neuroblasts attaching themselves to radial glial cells - these have their cell bodies anchored in the inner membrane and have a single long process that goes to the outer membrane
The neuroblasts attach themselves to radial glial cells and climb up towards the outer membrane
You get a wave of proliferation near the inner membrane and then a wave of migration towards the other surface and then one layer of the cortex is formed
Then you get another wave of proliferation and another wave of migration forming the 2nd layer of cortex
This continues until you have SIX LAYERS of cells within the cerebral cortex
Each layer of cells has different types of cells with different functions and different connections
Explain the factor that affect the devlopment of the the nervous system and how it can affect the nervous system
This may be disrupted by genetic or environmental abnormalities
This occurs early in gestation
Schizophrenia is caused by a malfunction of neural development
Deficiency of folic acid can lead to spina bifida
Development of the nervous system starts very early in pregnancy
