Neuro 1: Development of the CNS Flashcards
Describe the early development of the CNS
- you get proliferation of ectoderm in dorsal midline of the embryonic disc (neural plate)
- neural plate thickens and starts to fold up on the sides
- eventually the 2 neural folds fuse dorsally –> to form a tube
- space in middle of tube = neural canal
- small bunch of cells at tip of neural fold = neural crests
- neural crest separates from the neural tube (doesn’t fuse)
- at end: neural tube lines in midline dorsally in the embryo, and on either side, you have 2 strips of neural crest tissue.
THE NEURAL TUBE + CREST = 2 INDEPENDENT SOURCES OF NERVOUS TISSUE
Neural tube = all PNS/CNS cells
Neural crest = all PNS/CNS cells
Neural tube = all CNS cells
Neural crest = all PNS cells
What is the wall of the neural tube called?
neuroepithelium
What are the 3 types of cell that comes from neuroepithelium?
- neuroblasts
(all neurons with cell bodies within CNS) - glioblasts
(becomes neuroglia - astro/oligodendrocytes) - ependymal cells
(lines ventricles + central canal)
List the 4 differentiation of neural crest cells.
- sensory neurones of dorsal root ganglia + cranial ganglia
- postganglionic autonomic neurones
- schwann cells
(myelinating cells) - non - neural derivatives (e.g melanocytes)
common feature = can migrate long distances
Describe the process of differentiation of the neuroepithelium.
- cells withdraw from outer memb –> towards inner memb
- then goes through mitosis
- one of daughter cells stays attached to inner cell membrane
- it gets bigger –> and goes into cell cycle again
- other daughter cell migrates away from inner memb –> develops into neuroblasts
- they develop processes, and these axons are directed away from inner memb
- this occurs over + over –> forms 3 layers
- one layer (inner) –> mitosis occurring
one layer –> mainly cell bodies
one layer –> mainly axons
note: ependymal cells just remains in the ependymal layer.
does glioblasts develop axons?
NO
but they do develop processes.
List the layers of the neural tube
- ependymal layer surrounds neural canal
- roof plate = most dorsal part of neural canal
- floor plate = most ventral part of neural canal
What controls differentiation?
describe this controlling process.
- signalling molecules are secreted by surrounding tissues
- they interact with receptors on neuroblasts
- migration + axonal growth = controlled by attraction + repulsion
- depends on conc gradient + timing
What 2 significant features might you find in the developing spinal cord?
- neural canal = even smaller compared to thickness of the wall
- grey matter has split into (alar plate - dorsal) and (basal plate - ventral)
note: alar plate–> becoming specialized to receive sensory information
basal plate –> development of motor + inter neurons
Describe the development of the brainstem
- roof plate proliferates rapidly
- dorsal part of brainstem expands laterally
- roof plate expands –> pushes alar plates aside
- cranial nerve nuclei within brainstem that has a motor function tends to lie more medially
SO
motor = medial
sensory = lateral
autonomic = in beteween
Describe the development of the brain
at 4weeks:
- ONLY most anterior bit of neural tube develops into brain
- differentiation of wall of anterior neural tube –> forms 3 primary vesicles
- rest becomes spinal cord
over next week:
- most anterior vesicle decides into 2
- 3rd vesicle also divides into 2
- -> producing 5 secondary vesicles
5-8 wk:
- there is expansion of top part of developing forebrain
- this telencephalon becomes the cerebral hemisphere
- lower part becomes diencephalon
- developing hindbrain divides into 2 –> pons + medulla
as development continues:
- you get more + more growth of wall of the neural tube
- space within it becomes smaller relative to wall
- -> space becomes ventricular system
- then you get development of cerebellum
differentiation of wall of anterior neural tube –> forms 3 primary vesicles
a)
b)
c)
differentiation of wall of anterior neural tube –> forms 3 primary vesicles
a) Future forebrain - prosencephalon
b) Future midbrain - mesencephalon
c) Future hindbrain - rhombencephalon
Describe the folding of the developing brain
weeks 4 - 8 weeks
- vesicles have 3 flexures
- through development, flexures become exaggerated
by 8 weeks:
- telencephalon is very big –> starts to move back
- covers the diencephalon
What are the 3 flexures in vesicles of the developing brain?
a) cephalic flexure
b) pontine flexure
c) cervical flexure
