Plasticity and Regeneration Flashcards
Neurogenesis
the growth and development of nerve tissues
What is the germ layer that gives rise to the nervous system?
Ectoderm which forms in week 3 of gestation
Neural Tube Development
The neural crest are migratory cells that
give rise to diverse cell types: melanocytes etc
Stem Cells Definition
capable of self-renewal, indefinite number of cell divisions, can differentiate into any cell type
Progenitor Cells Definition
more specialised than stem cells, can differentiate towards a limited number of cell types
go through a limited number of cell divisions priot to differentiation
Neural Epithelial cells are stratified cells.
True or False?
False
columnar cells
Cells of the neural crest are
stem cells
give rise to all cell types in the nervous system including neurons, oligodendrocytes and astrocytes
Neural Progenitor cells emerge after
neural stem cell asymmetric self-renewal
Neural Progenitor Cells:
What regulates the differentiation of neuroblasts?
the notch receptor of the notochord regulates the differentiation of progenitor cells
notch signaling promotes the formation of astrocytes while it inhibits the formation of neurons and oligodendrocyte
The growth cones are
the growing tips of axon
Growth Cone and Filopodia: Next step after differentiation in development in the CNS:
- growth cones are growing tips of
axons - growth cones are rich in
microtubules and mitochondria and
other organelles: which are the
driving force for growth - growth cones extent to filopodia and
sense environmental signals - within the growth cone and filopodia
myosin molecules act a motor of
actin filaments - the filopodia receive environmental
signals through the receptor and
respond by either advancing,
retracting or turning
Filopodia are
slender cytoplasmic projections
Chemoattraction vs Chemorepulsion:
guidance of commissural neurons across the ventral midline
commissural neuron axons cross the midline that separates the two hemispheres of the developing brain
the protein netrin-1 is such a chemoattractant = causes formation of neurons that cross the midline/between two hemispheres hence commissural
Slit signal is a chemorepulsion
INSERT DIAGRAM
Which of the terms neuroblast/glioblast, neurostem cells, progenitor cells and neuroepithilial cells are interchangable?
- Neuroblasts/glioblasts and
progenitor cells are the same - neurostem cells and neuroepithelial
cell
Delta-Notch Signaling Pathway determines and label
whether a neuroepithelial cell will follow the glial or neuronal pathway
Cellular events in neuronal development are and regulated by
- in embryonic development approx
double the number of neurons are
produced compared to the mature
brain and spinal cord - increased apoptosis ensures the
removal of excess neurons - this process is regulated through the
action of neurotrophins nerve
growth factor (NFG), brain derived
growth factor (BDNF) and the
fibroblast growth factor (GFG)
Cortex formation begins in —— development, and when are the six layers of the neocortex formed?
- embryonic development
- six (unequal) layers are formed at
birth
Which of the six layers in cortex development has the most myelin and hence axons?
layer six
decreases on the way to layer one
How does the cortex develop?
Inside out cortical development
Inside-out Cortical Development:
- newly formed neurons migrate
towards the cortical plate with the
help of radial glial cells - migration is achieved through the
action of cytoskeletal microtubules - this leads to the formation of the 6
cortical layers of the cerebellum - this movement is called radial glial
migration - first lower layers develop
*radial glial cells are differentiated
neuroepithelial cells
insert diagram
Adult Neurogenesis:
- locations
- subventricular zone (SVZ)
- hippocampal dentate gyrus
Ventricular System:
Adult Neurogenesis:
- why not common?
- what allows neurogenesis
- neurons are post-mitotic cells but
two exceptions (SVZ, hippocampus) - neural crest cells are found and
hence stem cells which can still
regenerate
Adult Neurogenesis Process: Replace Olfactory Neurons:
- neural crest stem cells = neuroblasts
- differentiate into immature neurons
- migrate to the olfactory bulb along
the Rostral Migratory Stream - then integrate into the already
formed neuronal network - migration is guided by the cellular
environment, molecular and
chemical signals - migration also depends on
cytoskeletal rearrangements
CNS vs PNS Regeneration:
- Neurons of the CNS have a different
outcome following injury compared
to PNS - in CNS oligodendrocyte myelinate
axons but in PNS schwann cells
myelinate - axons can still grow even if damaged
but oligodendrocytes will not
regenerate myelin sheath but
schwann cells will reform the sheath - in CNS hindered as it is a
compromise to keep networks stable
as there is immediately phagocytic
activity and invasion of astroctyes - glial scar is formed and axon in CNS
can not grow
The Critical Period Concept:
- time during postnatal neural
development where neuronal
plasticity depends on environmental
signals - more accurate to have different
critical periods for different brain
functions - ***critical periods are charcaterised
by increased plasticity - strictly: sensitive period, the time
when a sensory signal is received
and followed by a period of
increased neuronal plasticity - if something is learnt outside of the
critical period the learning will not be
as great later in life
Examples of Critical Period in Development:
- language skills
- accent learning
- bird imprinting: hatchling
immediately attached to a moving
entity and important for survival of
new bird - primates can see early social
interactions are essential for social
development
Cortical Plasticity:
- adult brain characterised by low
incidence of regeneration - some degree of ***plasticity in the
somatosensory cortex located in the
postcentral gyrus - when fingers are amputated there
are changes in the cortical area to
reflect that, cortical areas
corresponding to missing fingers
now respond to stimulations from
adjacent skin areas - cortical plasticity diminishes with age
Primary Somatosensory Cortex:
- somatotopic representation of the
different body areas of the cortex - resembles a homunculus
- some body regions have a high
number of sensory receptors and are
assigned a larger cortical area while
other regions with low density of
sensory receptors correspond to a
smaller cortical area
Computational Theories of Memory:
- recording new memories rely on the
emergence of newly formed
neuronal cells in the hippocampal
dentate gyrus - older memories are encoded in the
pre-existing neuronal network
Axon guidance is regulated by specific signalling cues that cause chemoattraction or chemorepulsion.
True or False?
True
Neuronal differentiation relies on the formation of growth cones, microtubule supported cell migration, signalling pathways, apoptosis of surplus cells.
True or False?
True
Neurogenesis in the hippocampus has been shown to assist formation of new memories.
True or False?
True
(hippocampal dentate gyrus)
Some neuronal axons (PNS) are characterised by regenerative capacity, while few cortical neurons exhibit plasticity even in the adult CNS.
True or False?
True
Neurogenesis begins early in embryonic development with the formation of the neural tube and the differentiation of neural stem cells towards glial cells and neurons.
True or False?
True
