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Neurodevelopment (week 11) - Coggle Diagram
Neurodevelopment (week 11)
Developmental origin of the central nervous system
Early embryonic layers
Gastrulation leads to the formation of
three
embryonic layers: ectoderm, mesoderm, and endoderm.
Ectoderm is the top layer and is the
origin
of neural tissue
Sequence of events in the development of the central nervous system(this order)
Neural induction
Specific cells
in the
ectoderm
become
neural
Signaling molecules
from surrounding tissues (mesoderm and endoderm) and nearby ectodermal cells induce the ectodermal cells to
differentiate into neural cells
Results: leads to the
formation of the neural plate
, a region in the ectoderm capable of becoming neural tissue
Neurulataion
Neural plate
transforms into the
neural tube
, which develops into the
brain and spinal cord
Neural folds
, which are elevated regions of the neural plate,
lift up and fuse together
, forming the
neural tube
Neural crest cells, originating from the border of the neural plate and ectoderm,
migrate away
and contribute to various cells in the
peripheral nervous system
Zippering mechanism
Closure of the neural tube occurs thru it
Neural tube fuses 1st in middle & zippers up from both end
Proper zippering is crucial; failure in this process can result in
neural tube defects
like spina bifida or problems in brain development
After neurulation, the neural tube differentiates into
distinct brain regions
: forebrain, midbrain, hindbrain, & spinal cord.
These regions form
vesicles
, with the
forebrain being the largest
and developing into the cerebral cortex.
The cerebral cortex undergoes folding (gyri and sulci formation) to increase surface area, allowing for efficient neural processing
Clinical significance
:
Neural tube defects
can occur if the neurulation process is disrupted, emphasizing the
importance of proper nutrition
, including
folate supplements
, in
preventing these defects
, especially in
pregnant women
.
Neurogensis
Initial Neural Plate and Tube:
One cell thick
,
extensive cell division
required for brain and spinal cord formation.
Bipolar Cells: Cells have a
central cell body
with processes extending
inward
(
ventricular surface
) and
outward
(pial surface).
Progenitor cells
proliferate to become
neuroblasts
Types of divisions
Symmetrical: produces two more progenitor cells
Asymmetrical:
Type1: progenitor cells produce
one neuron
(or neuroblast) and
another progenitor cell
.
Type 2: progenitor cells generate an
intermediate progenitor
(basal progenitor) and a neuron
Neuron migration
Radial migration
: neurons migrate radially, like spokes on a wheel,
away from the ventricular surface
toward the brain's outer layers.
Gripping onto apical processes: Neuroblasts (developing neurons) use the apical processes, extending from the ventricular surface, as a guide for migration.
Inside-Out Manner: younger neurons migrate further out, forming outer layers, while
older neurons remain deeper inside the cortex
Axon guidance & synaptogensis
Axon guidance
Growth Cone: developing axons have growth cones at their tips. These growth cones are dynamic structures essential for guiding axons toward their appropriate target locations
Important factors: substrate (extracellular matric, other cells), guidance cues, and attraction/repulsion
Types of guidance signals
Long range signals
: act as cues that
attract
or
repel
axons over a
significant distance
. ie, the smell of chocolate cake can be an analogy for a long-range attractive cue
Short range signals
: involve
direct contact
bt the growth cone and other cells or components of the extracellular matrix. These signals can be either
repulsive or adhesive
, guiding axon growth in a localized manner
Synaptogensis
Initial contact
: begins with the initial contact between the
axon terminal and the dendrite
(or another appropriate target). Initially, there are few synaptic vesicles present at the pre-synaptic terminal
Maturation process
: recruiting
various synaptic machinery
, including neurotransmitter-containing vesicles + forming appropriate cytoskeletal structures
Pre- and Post-Synaptic Maturation: pre-synaptic maturation, involving the
development of neurotransmitter release capabilities
, often occurs before post-synaptic maturation. Neural activity plays a vital role in regulating these processes, ensuring the synapse becomes functional
Synaptic plasticity
: ability of synapses to
change strength
in response to activity is crucial. Neural activity influences whether a synapse is
retained or eliminated
, allowing for the adaptation of neural circuits based on experiences and learning. ie responsible for remembering & forgetting info
Developmental events that continue postnatally with regard to motor control
Brain developments: important processes in brain development continue after birth. Development can be influnced by genes & environment
Synaptogensis, axon growth & purning, dendirte development & purning, electrophysiological changes, learning & plasticity, ongoing myelination
Developmental origin of glial cells in the central nervous system
Neural plate progenitor cells
: Glial cells, specifically
astrocytes and oligodendrocytes
, originate from
progenitor cells
within the neural plate
Initial neuronal development
: progenitor cells initially produce
neurons and neuroblasts
through specific signals that instruct them to form neurons
Transition to Glial Cells
:
Over time, signaling cues change, leading the progenitor cells to transition from producing neurons to
generating glial cells
, particularly astrocytes and oligodendrocytes.
Gliogenesis Process
:
Occurs
after neurogenesis
. Progenitor cells that were initially geared towards neurons shift their developmental path to become glial cells instead.
Microglia Development
:
microglia= type of glial that is present in the CNS. They originate from the
immune system and migrate into the brain
early during brain development.
Glial Cell Functions:
Astrocytes are involved in synapse formation
and development, while oligodendrocytes are
responsible for myelinating axons
, providing them with protective sheaths
Temporal Aspects of Development
:
The development of glial cells, including astrocytes and oligodendrocytes, occurs during specific timeframes, with gliogenesis happening
after neurogenesis
Origin of the peripheral nervous system
Neural crest cells
:
Group of cells that form @ border of the neural plate during embryonic development
They undergo a process of epithelial
mesenchymal transition
to allow them to break free from the neural tube & migrate
Neural crest cells= only found in
inverterbrates
. Its types are: dorsal root ganglia, sympathetic and parasympathetic ganglia and enteric nervous system
Events involved in development of the sympathetic ganglia
Epithelial-mesenchymal Transition (EMT)
EMT transition involves changes in : cell-cell adhesion, polarity, cell shape, cell matrix adhesion
Origin: Neural crest cells originate from the
dorsal neural tube
, which is the
ectodermal layer
of the developing embryo
Epithelial state: initially they are tightly packed and adhere to each other within the neural tube
EMT Initiation: Signaling molecules and transcription factors induce EMT in neural crest cells, causing them to lose their epithelial characteristics and gain mesenchymal traits
Migration of the neural crest
Delamination & migration
:
Neural crest cells undergo
delamination
,
detaching from the neural tube
These delaminated cells transform
from epithelial to mesenchymal
, allowing them to migrate away from the neural tube
Guidance cues
:
Neural crest cells follow specific pathways guided by various cues, both attractive and repulsive, in the developing embryo
Ensuring proper migration & positioning of neural crest cells in the embryo
Formation of sympathetic Ganglia
:
1) Neural crest migrate to the
dorsal aorta
2) Cells are dispersed along the aorta (no segmentation)
3) Cells aggreggate into discrete ganglia
Identify the developmental origin of glial cells in the peripheral nervous system
Glial cells in the PNS, including
Schwann cells and satellite cells
, originate from the neural crest cells during embryonic development.
These cells undergo
differentiation from multipotent neural crest cells into specific glial cell
types in the peripheral nervous system
Tumours from the peripheral nervous system
Sympathetic ganglion cells can give rise to
neuroblastoma
. Most commonly develops from neuroblasts in the
adrenal medulla
. It is the mot common solid tumout in childhood
Adva & disadv of using organoids to study brain development
Adv
Organoids provide a three-dimensional structure, allowing the study of complex tissue organization
Evolution
Specific patient mutations
Brain cancer (eg glioma)
Disadv
Vascularisation: organoids might lack certain components found in the natural brain, such as blood vessels and microglia, limiting their physiological relevance. But closer it starts getting like a brain tissue the more ethical consideration would be involved
Immune system
What are organoids: miniature organs grown in vitro that mimic the structure & function of real organs. Derived from stem cells, which can differentiate into various cell types, allowing the development of complex tissue structures resembling organs like the brain, liver, kidney, or intestine.