Development of the CNS Flashcards
What are the layers for the development of the CNS? Draw this.
See diagram. endoderm, mesoderm + notocord, ectoderm (neural plate)
What happens to the ectoderm in the embryonic disk around 3 weeks?
There is proliferation of the ectoderm in the dorsal midline called the neural plate
What happens to the neural plate?
The neural plate folds together. When the neural folds come together it forms the neural canal. On the tips of the neural folds you get a bunch of cells called the neural crest. The neural crest separates from the neural tube.
What are the two independent sources of nervous tissue?
Neural tube - CNS cells
Neural crest - PNS cells
What is the name given to the wall of the neural tube
Neuroeptithelium
What are the different cell types that come from the neuroepithelium?
Neuroblasts - precursor to all cells have cell bodies in the CNS
Glioblasts - precursor to neuroglia (astrocytes and oligodendroytes)
Ependymal - line the ventricles, central canal and neural tube. Inner layer of the neural tube
Where do motor neurones originate from in terms of the cell types derived from the neuroepithelium?
They are neuroblasts. They have cell bodies in the CNS even though most of their axons are in the PNS
What are the different cell types that come from the neural crest?
Sensory neurones of the dorsal root ganglia and cranial ganglia
Postganglionic autonomic neurones
Schwann cells
Non-neuronal derivatives e.g melanocytes
Describe the cellular organisation of the neuroepithelium
The cells are attached to both the inner and outer membranes
Describe the differentiation of the neuroepithlieum
See diagram. Neuroblasts.
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
Glioblasts have a similar pattern of differentiation and migration to neuroblasts but glioblasts can migrate into white matter as well. Remember glioblasts are support neuronal cells
What are the layers formed from the differentiation of the neural epithelium?
Ependymal Layer - Layer by the inner membrane - where mitosis occurs - germinal layer
Grey Matter - Layer of cell bodies - mantle layer
White Matter - Layer of axons - marginal layer
This is the beginning of the difference between grey and white matter. Grey matter = cell bodies White matter = axons
What do glioblasts develop?
Processes NOT axons
What are the roof and floor plate?
These show the most dorsal and ventral parts of the canal
What is the process of differentiation and migration controlled by?
Signalling molecules that are secreted from the tissues surrounding the neural tube or by cells within the tube.
They interact with receptors on neuroblasts controlling migration and axonal growth by attraction and repulsion.
Depends on the concentration gradient and timing. Higher concentration when the signalling molecules are close to the source
See notes - Dorso-ventral patterning
Draw the layers of the neural tube in cross section
Draw diagram
During later stages of development what the grey matter split into?
Alar plate - dorsal; INTERNEURONES specialised to receive sensory information coming from the dorsal root ganglia (neuronal crest)
Basal plate - ventral; Some INTERNEURONES mainly developing MOTOR NEURONES
These terms are only used for the embryonic nervous system - neural tube
What do the different parts of the neural tube develop into? (The mature spinal cord)
Neural canal –> central canal - carries CSF
Alar plate –> dorsal horn
Basal plate –> ventral horn
The whole spinal cord is surrounded by a thick layer of white matter
How does the brain stem develop?
See notes. 4th Ventricle, Roof plate, Alar plates,
Draw the structure of the brain at 4 weeks and label the sections
See diagram
What are the primary vesicles of the anterior neural tube that will form the brain?
Prosencephalon - Future forebrain - divides into two
Mesencephalon - Future midbrain
Rhombencephalon - Future hindbrain - divides into two
What do the primary vesicles divide into to form the secondary vesicles?
Telencephalon Diencephalon Mesencephalon - stays the same Pons Medulla
Separation of the vesicles happens at 5 weeks
What happens at 8 weeks of brain development?
See diagram. Ventricles
What are the flexures of the three vesicles?
Cephalic flexure - By 8 weeks the telencephalon has got so big its started to move back and cover the diencephalon
Pontine flexure
Cervical flexure
What is the organisation of matter in the brain?
White matter inside and grey matter outside
This occurs due to the migration of neurones from the inner membrane where they proliferate along radial glial cells.
How is the basal ganglia formed?
From neurones migrating and stopping in the middle
Describe the orientation of radial glial cells
They have their cell bodies anchored in the inner membrane and have a single long process that extend out to the outer membrane.
How many layers are there in the cerebral cortex?
6 layers - wave of proliferation and migration. Each layer has different types of cells with different functions and different connections
Developmental disorders of the nervous system
Normal development depends on the coordinated completion of several complex processes (e.g. proliferation, differentiation, migration, axon growth and synapse formation)
Genetic mutation and environmental factors such as the mother’s lifestyle, diet and teratogens can interfere with these processes
See slide 27
- Craniorachischisis
- Anencephaly
- Encephalocele
- Iniencephaly
- Spina bifida occulta
- Closed spinal dysraphism
- Meningocele
- Myelomeningocele
