Development of the nervous system Flashcards
What is the first thing that happens in the early stages of CNS development
You get a proliferation of the ectoderm in the dorsal midline of the embryonic disc- this is called the neural plate
What happens after the neural plate is created
It thickens and starts to fold up on both sides
What happens next after the neural plate has started to fold up and thus what is the neural canal
The two neural folds eventually fuse together dorsally to form a tube, the neural canal is the space in the middle of the tube
What are neural crests
A little bunch of cells at the tip of the neural fold- they separate from the neural folds and don’t take part in the fusion
The neural tube and crest are sources of two different types of nervous tissue, which ones are responsible for which?
Neural tube= all CNS cells
Neural crests= all PNS cells
What is neuroepithelium
Wall of the neural tube
What three types of cell come from neuroepithelium and what are they?
Neuroblasts- All neurones that have their cell bodies within the CNS
Glioblasts- these become neuroglia (astrocytes and oligodendrocytes)
Ependymal cells- Lining of ventricles and central canals
What cells are formed by differentiation of neural crest cells
Sensory neurones of dorsal root ganglia and cranial ganglia
Initially, in proliferation of neuroepithelium, cells are attached to both the inner and outer membrane, what is the first step of differentiation after this?
Cells withdraw from the outer membrane towards the inner membrane and go through mitosis
One of the daughter cells will stay attached to the inner membrane and go through the cell cycle again, what happens to the other daughter cell?
It migrates away from the inner membrane and develops into neuroblasts. The neuroblasts will develop processes which will then develop into axons. Eventually you will have three layers: White matter (axons), grey matter and ependymal layer
What controls this process of differentiation and migration
Signalling molecules
Where do signalling molecules come from and what do they interact with
They are secreted either from tissues surrounding the developing neural tube or sometimes from cells within the neural tube and they interact with receptors on the developing neuroblasts
What else do signalling molecules guide?
The developing axons- they can cause either attraction or repulsion and the response depends on the concentration gradient
What are the two key factors to do with signalling molecules
Concentration and timing
What are two significant features later in development
The neural canal is smaller compared to thickness of wall
The grey matter has split into two different types:
Alar plate- dorsal
Basal plate- ventral
What is the difference between the alar and basal plates
Alar- interneurons are becoming specialised to receive sensory information and the information comes from the developing dorsal root ganglia that have developed from the neural ganglia
Basal- Some interneurons and development of motor neurones
What happens to the neural canal, basal plates and alar plates in a developed spinal cord
The neural canal becomes the central canal carrying CSF and the basal plate develops into ventral horns and alar plate develops into dorsal horns
What is the notochord and where is it found?
It is found just below the basal plate in the developing neural tube. It produces several signalling molecules and concentration gradient is established with the highest concentrations near the notochord. The cells within the neural tube that are closest to the source are induced to become motor neurones
What do other signalling molecules produced by the ectoderm do?
They establish a conc gradient and tend to inhibit differentiation of cells into motor neurones
What does the brain develop from
The most anterior part of the neural tube
What are the three primary vesicles that the wall of the anterior neural tube differentiates into after 4 weeks?
Prosencephalon- future forebrain
Mesencephalon- future midbrain
Rhombencephalon- future hindbrain
The rest becomes the spinal cord
What happens over the next week after the differentiation of the wall of the anterior neural tube ?
The most anterior vesicle divides in two and third vesicle also divides in two to produce 5 secondary vesicles: Telencephalon Diencephalon Midbrain Pons Medulla
What does the telencephalon become when it expands enormously?
The cerebral hemispheres
As development continues, you get more growth of the wall of the neural tube and the space within it has become smaller, what does this space become?
The ventricular system
Where does the cerebellum develop from
The back of the pons
As the vesicles aren’t in a straight line, there are three flexures, what are they called?
Cephalic flexure, pontine flexure and cervical flexure. As you go through development they become exaggerated
What happens with the telencephalon at 8 weeks
It has become so big it begins to move back and cover the diencephalon
What is the first thing that happens in the region that becomes the brainstem
The development of the 4th ventricle
What sort of matter makes up the core of the brain
White matter, grey matter is around the outside
