development part 3 Flashcards
Axon guidance is ______ between intermediate targets
dynamic
Layered on top of _________, receptor expression can _____ in response to the environment.
antagonistic gradients. change. In this way axons can be attracted and repelled by the same structure.
Normal development requires______.
pruning
In many developmental situations, extra cells/tissues are formed, which are pruned back during later development.
Input neurons ______ for target neurons
compete.
By competing, the strongest and best placed cells survive.
Trophic factors
Target neurons secrete trophic factors that help keep cells alive.
Trophic factors induce pro-survival activities,
while their absence causes pro-apoptotic activities.
The default behavior for many developing neurons is to die! These trophic factors keep them alive.
Rita Levi-Montalcini,
Got her medical degree in 1936 from the University of Turin
she began working as a research assistant in neurobiology
Why did Rita Levi-Montalcini lose her jobafter only 2 years of working?
Italy’s fascist regime barred Jews from
working in major professions.
What did Rita Levi-Montalcini do after she got owned?
she set up a makeshift laboratory in her bedroom where she began studying the development of chicken embryos, which would later lead to her scientific breakthrough.
What did Rita Levi-Montalcini do in 1943, when the Nazis invaded Italy?
She fled to Florence and lived underground, assuming false identities.
what did Rita Levi-Montalcini discover and where?
By 1947, Levi-Monalcini was based at Washington University in St Louis, Missouri, where she eventually became a full professor.
It was here that she continued her work into cell development and discovered the nerve growth factor.
Maturation
Multiple axons from motor neurons can innervate a single muscle fiber.
Maturation involves pruning extra axonal projections so
there is one motor nerve per muscle fiber.
What happens to trophic factors encountered by the axon?
Trophic factors encountered by the axon are transported back on the axon to the cell body.
Muscle fiber stimulation _______ the elimination of all but
____ input.
accelerates.
one.
Synapse elimination at the NMJ requires_____.
activity
Blocking a small subset of post-synaptic acetylcholine
receptors leads to
recptor loss and axon retraction.
What does blocking muscle activity prevent?
loss of excess synapses
insufficient receptor activation in an otherwise
active neuromuscular junction leads to ______.
synapse pruning.
Context matters – without on-going synaptic activity,
inactive synapses are not pruned.
cortical thickness ______ after development, while number of synapses __________.
doesnt change.
dramatically decreases.
Synaptic rearrangement alters ______
the balance of synaptic input.
what happens during maturation in terms of inputs and capacity?
During brain maturation the balance of synaptic inputs may
change, while the total synaptic capacity is unaltered. This
synaptic rearrangement requires synaptic transmission.
molecular guidance molecules.
Allows for long range connections can be established without the need for synaptic activity early in development
when does activity dependent refinement of synaptic
connections occur?
later in development, and through maturity.
Retinal axons enter the LGN diffusely, but eventually what happens?
They segregate such that each eye targets specific structures. This requires synaptic activity, but not light
Brain dervied Nerotropic factor (BDNF)
is synthesized in the cortex and its co-release with glutamate is critical for striatal neuron survival.
Neurotrophins stimulate complex signals
The interaction of neurotrophins with their receptors stimulate complex intracellular signaling cascades, which are largely based regulation of transcription.
Synaptic rearrangement can be dynamic (AGRP/POMC)
In response to peripheral hunger signals (e.g. leptin and ghrelin) the balance of excitatory and inhibitory synapses on AGRP/POMC neurons in the hypothalamus switches.
NPY stimulates appitite.
POMC inhibits appetite.
“Hebbian” synapses in the LGN
Initially, input from each eye targets multiple layers of cells in the LGN.
Correlated firing in neurons from the same retina strengthens connections with active post-synaptic neurons, which subsequently fire.
Lack of correlated firing in non-target neurons leads to synapse loss. The net effect is segregation of synaptic inputs into their appropriate layers.
Neural precursor cells in the ventricular zone replicate their DNA after sending a projection where?
towards the pial surface
When do Neural precursors replicate?
They replicate their DNA while their soma moves towards the pial surface and back.
Once replicated and back at the ventricular surface they divide _____ or _________.
horizontally or vertically
how could you make a neuron grow towards cues faster?
Increase their expression for certain receptors.
