LTP Flashcards
What is an Engram?
the physiological representation of learning and memory
What is consolidation?
The process of producing the physiological change/ The formation of the engram
What is synaptic facilitation
it is the “strengthening” of the synapse between the pre-synaptic neuron and the post-synaptic neuron
What is Donald Hebb’s theory for the formation of an engram
Repeated excitation of particular synapse: often/fast enough stimulation to strengthen
Simultaneous firing of 2 neurons
What does “strengthened” synapses mean?
it means when the pre-synaptic neuron released NT that the post-synaptic neuron is more likely to fire an action potential next time it is stimulated by that specific neuron
What is co-occurence?
if cells are active at the same time often enough, long-term changes in the synapse facilitate subsequent transmission
Explain what Stronger means in reference to the synapse
It means that when the particular pre-synaptic neuron activates the post-synaptic neuron it is more likely to reach the threshold to create an action potential in relation to a normal non-strengthened neuron activating the same post-synaptic neuron
Using Pavlov’s experiment with his dogs. Explain a simple model of how a UCS(food) and a CS(bell) interact to create a UCR(salivation) that can be used to explain Hebbian Synapses
the CS(bell) is on neuron(pre-s) and the UCS(food) is the other neuron(pre-s) both of these neurons have synapses on the UCR(salivation) neuron(post-s). When the dog has shown the food, the UCS neuron fires and activates the UCR neuron making the dog salivate. When the UCS neuron is paired with the CS neuron, both fire simultaneously and activate the UCR neuron. As this happens repeatedly, the synapse between the CS and the UCR neuron is strengthened when “naturally” it wouldn’t be. After the dog has been conditioned when the CS fires alone and is not paired with the activation of the UCS the dog’s UCR neuron is triggered and the dog salivates.
What are ways of synaptic facilitation?
Increase the number of receptors
Increase the number of synapses
Increase the NT release from pre-s
Change the sensitivity of the post-s membrane
What is EPSP?
Excitatory post-synaptic potential: the potential of the neuron to reach the threshold and fire and action potential
What is a tetanized input?
It is an input that happens very rapidly and is artificial and does not occur physiologically
What are the three main structures of the Hippocampus?
Dentate Gyrus, CA3, and CA1
Where does the Entorhinal cortex go to?
Synapse on the Dentate Gyrus via the perforant pathway
Where does the Dentate gyrus granule cells synpase?
CA3 pyramidal cells via the mossy fibers
Where does CA3 synapse?
CA1 via the schaffer fibers
Contralateral CA3 and CA1 via commissural fibers
What happens if you stimulate the mossy fibers?
the CA3 pyramidal cells will be activated
What happens if you stimulate the Schaffer collaterals?
You will activate the CA1 as well as the contralateral CA3 & CA1
What do Hebbian, Homosynpatic, and Associative induced LTP to have in common?
Stimulation of afferent neurons
all induce LTP
All in essence do Hebbian: they all depolarize the cell enough that when it is activated again it has a larger effect on EPSP
What is the cooperative characteristic of LTP?
With HFS(high frequency stimulation), need a certain minimum number of presynaptic fibers activated
What is the input-specific characteristic of LTP?
LTP changes excitability at particular synapses, not the whole neuron
What is the associative characteristic of LTP?
LTP can result from the concurrent activation of converging inputs
What is homosynaptic induced LTP?
Repeated, rapid stimulation of 1 set of afferents (tetanic stimulation)
What is Associative Induced LTP?
Simultaneous. stimulation of 2 sets of afferents
Cooperative characteristic of LTP
with HFS, need certain minimum number of presynaptic fibers activated
Input-Specific Characteristic of LTP
LTP changes excitability at particular synapses, not the whole cell
Associative characteristic of LTP
LTP can result from concurrent activation of converging inputs
What is early phase LTP?
1 stimulus, no protein synthesis required
What is late phase LTP?
4 stimulus trains over a period of time(repetition is important), and protein synthesis required(changing the morphlogy)
what is In vitro?
Neurons grown in a class dish
What is ex vivo?
Neurons taken from a brain and experimented on in a glass dish(hippocampal slice)
what mechanism of LTP is NMDA dependant?
Associative LTP in CA1
What is metabotropic?
Not direct it is a 2nd messenger system
What is the major characteristic of NMDA?
Voltage and ligand gated
What does it mean to be voltage and ligand gated receptor?
The response to GLUT depends on post synaptic membrane potential
Not depolarized: Mg2+ blockade prevents Ca2+ influx
Depolarized: Mg2+ blockage is removed, glut binding produces Ca2+ influx
Characteristic of AMPA receptor?
Ligand gated
GLUT binds -> Channel Opens -> Na+ influx -> depolarization
What is Non-Coincident stimulation?
AMPA receptor activated, NMDA not
what happens when LTP is induced?
Repeated/Simultaneous stimulation of AMPA -> depolarization -> Mg2+ block is removed -> Ca2+ influx thru NMDA
What do retrograde messengers do?
They give feedback from post to pre-synaptic changes: protein kinases
What is the mechanism of maintenance of pre-synaptic mechanism?
Ca2+ -> Calmodulin Activation -> activation of various kinases -> release of retrograde messengers -> activation of pre-syn protein kinases -> increased GLUT release
What is the mechanism for post-syn LTP mechanisms?
Ca2+ influx -> Ca2+/Calmodulin kinase activation -> Exocytosis of AMPA -> phosphorylation of AMPA receptors -> increased excitability
What is a filopodia?
an immature dendritic spine
How do filopodia turn into mature dendritic spines?
The filopodia forms postsynaptic density from ambient glutamate, It then releases retrograde signaling that then creates and active zone on the axon of a nearby cell. This active zone then releases NTs that active the postsynaptic membrane. Which then releases retrograde signaling and the synapse is strengthened
What are the changes in morphology of existing spines in late-phase LTP.
Few mins after LTP: increased receptors and glut release
30mins after: spine head enlarges: synaptic strengthening
Big synapses break apart and form a double-headed spine and then those split and form two spines
What criteria does LTP meet to be a mechanism for learning?
Detectability: learning induces LTP
Mimicry: LTP induces learning
Anterograde Alteration: block LTP, block Learning; induce LTP, induce learning
Retroade Alteration: erase LTP, erase memory
