3.8 Development of multicellular organisms 2 Flashcards
How many phases are there in neural development?
3
What happens in phase 1?
Different cell types develop independently at widely separate location in embryo according to local program and are unconnected.
what happens in phase 2?
axons and dendrites grow along specific routes setting up a provisional but orderly network of connections between various parts of the system.
What happens in phase 3?
continues into adult life, connections are adjusted and refined through interaction with distant regions via electric signals.
Neurons are produced in association with what cells?
glial
Neurons and glial cells devlop from where?
ectoderm
What consists of the CNS?
brain spinal cord, retina
What consists of the PNS?
nerves, sensory nerves
The CNS is derived from what?
neural tube
The PNS is derived from what?
neural crest.
What does the sonic hedgehog do?
Activate latent genes, Transcription repression to activation. Depend on proteoglycans for function.
What does BMP do?
pattern formation, differentiation, secretion of extracellular matrix
The neural crest cells originate at what end of the neural tube?
dorsal end.
What 3 cell types does the neural crest produce?
neurons and glial cells of PNS. Epinephrine cells of adrenal gland. Skeletal and connective tissue components of the head.
Fate of the neural crest cells depends on what?
Where they migrate and settle
What is the structure of a neuron?
cell body, long axon, and dendrites
Where is the growth cone?
Tip of axon/dendrite
What forms the axon?
one of the growth cone starts migrating fast and develops axon specific proteins
How is growth cone behavior dictated by?
its cytoskeltal machinery
What 2 things do growth cones throw out?
filopodia and lamelopodia
What two monomeric GTPases control the assembly and disassembly of actin filaments, which control movement of growth cone?
rho and Rac
how do growth cones know where to find their way? 2 ways
extracellular matrix environment and chemotactic factors.
How does the extracellular matrix environment work via growth cones?
Sensed by receptors present on membrane
How do chemotactic factors work via growth cones?
Released by neighboring cells. Attract or repulse.
What is contact guidance?
path taken by other cells that growth cones often follow
the extracellular matrix is mediated by what molecules?
homophilic cell adhesion molecules
What are the 2 classes of homophilic cell adhesion molecules?
immunoglobulin superfamily and cadherin family.
Extracellular matrix provides a mechanism for what two things?
selective guidance and recognition
Matrix molecules such as laminin favor what?
axonal outgrowth
Chondroitin sulfate proteoglycans inhibit what?
growth
Dorsal neurons of spinal cord receive and relay sensory info from what
sensory neurons located in the periphery of the body
Ventral clusters of spinal cord neurons develop as what?
motor neurons
What do motor neurons do?
send out long axons to connect with specific subset of muscles
Intermediate location has inter neurons that do what?
connect specific set of nerve cells to each other
What are chemotactic factors?
secreted by cells, act as guidance factors at stretegic points along path
What are 3 ex of chemotactic factors?
Slit, Semaphorin and Netrin
What does the first stage of commissural neuron guidance depend on?
Secretion of netrin by cells of the floor plate
binding of netrin to its receptor causes what?
opening of TRPC channels.
opening of TRPC channels allows for what?
entry of extracellular calcium
After calcium has entered, what does this lead to?
Lead to activation of machinery for filopodia and movement of growth cone.
What neurons do not have netrin receptors?
Non commissural neurons
Since non commissural neurons in neural tube dont have netrin receptors, what does this mean?
non commissural neurons dont migrate towards floor plate
What cells secrete slit?
midline cells
Whats the name of the slit receptor that is present on commissural neurons?
roundabout
What does slit do?
repels growth cones and blocks entry to the midline
What is semaphorin?
a repulsive signal that gets growth cones to become sensitive
Why do growth cones travel in a narrow track?
Because they are trapped between 2 sets of repellents
Do axonal growth cones reach their target cells?
yes
When axonal growth cones reach their target cells what happens?
they halt, communicate and make synapses with target cells
Signal from target tissue regulate what?
which growth cones synapse and where
What two rules is synaptic remodeling dependent on?
- Axons from cells in dif regions of retina compete for tectal neurons. 2. Axons from neighboring sites which are excited at same time cooperate/collaborate to retain and strengthen synapses with tectal neurons
What two things does activity dependent synaptic remodeling depend on?
electrical activity and synaptic signaling.
Posterior retinal neuron axons prefer what type of tectal neurons?
anterior
Anterior retinal neurons prefer what type of tectal neurons?
no preference.
Neurons that fire together also what together?
wire together
Synapses are strengthened by what?
external events that cause 2 or more neurons to be activated at the same time.
What triggers lasting change in synaptic strength?
enty of calcium through the NMDA receptor
