10 - Learning and Memory - LTD<P mechanisms Flashcards
What is procedural memory?
Skills and association largely unavailable to the conscious mind.
What is declarative memory?
Memory that is available to the conscious mind can be encoded in symbols and language.
What is explicit memory?
Memory that can be consciously recalled. eg declarative
What is implicit memory?
Memory that cannot be consciously recalled. eg procedural memory, classical conditioning.
What are some advantages that simple systems have?
- Their neuronal size
- Circuit complexity
- Mapping tools
What are 2 simple forms of memory?
Habituation and sensitisation.
What is habituation?
- A form a memory where the amplitude of response decreases when the stimulus is applied many times.
- Causes a depletion in the synaptic vesicle pool.
What is sensitisation?
A form of memory where the amplitude of response increases when the stimulus is applied many times
What kind of habituation does Aplysia Californica show?
The gill withdrawal reflex, the reflex slows down as the stimuli is repeated.
What is the neuronal basis of habituation?
When the pre-synaptic neuron is stimulated the amplitude stays the same but when the post-synaptic neuron is stimulated the amplitude starts to decrease.
- Shows reduced synaptic strength.
What is the cellular basis of habituation?
A reduced neurotransmitter release due to a depletion of the readily releasable pool (RRP).
What would be a sensitisation response from Aplysia Californica?
An increased gill withdrawal reflex evoked by the tail pinch or the shock.
What input does the sensitisation response from Aplysia involve?
Pre-synaptic input to the sensory neuron also the action of serotonin and G-Protein action.
What is the example of a neuron that senses the sensitising stimulus?
L29
What is the molecular basis of sensitisation?
pkA phosphorylates and inactivates the potassium ion channels and a longer depolarisation means more vesicular release.
What is the Hebbian synapse?
A synapse where the coordinated activity of a pre-synaptic terminal and a post-synaptic neuron strengthen the synaptic connections between them.
What is the simplified version of the hippocampal circuit?
- input comes in through the entorhinal cortex and goes to the denate gyrus in what is known as the Perforant pathway.
- Input then travels from the denate gyrus to the Ca3 through mossy fibres.
-The Ca3 to Ca1 though Schaffer collaterals - All the output then leaves via the fornix and the subiculum.
Where does LTP normally take place?
In Ca3 to Ca1 synapses which are glutamatergic.
What kind of stimulus comes from long term potentiation?
A high frequency stimulus which resembles the human Q rhythm and produces long lasting potentiation.
How does LTP show input specificity?
By only acting on the neuron that is activated, this increases the amplitude of the EPSP.
What is cooperativity in LTP?
When 2 pathways converging on the same target can both be strengthened if they fire together. (although one pathway may be quite weak)
What are the 3 types of glutamate receptors?
AMPAR (non-NMDA), NMDAR and mGluR.
What kind of receptor is the AMPA receptor?
The main ionotropic receptor which is more permeable to sodium and potassium ions.
What kind of receptor is the NMDA receptor?
An ionotropic receptor which is more permeable to calcium ions.
What kind of receptor is a mGlut receptor?
A metabotropic receptor.
How does LTP occur?
- Could be by pre-synaptic changes but evidence suggests that it is a post synaptic event
- NMDA receptors open releasing calcium ions into the post-synaptic neuron
- Calcium then activates kinases eg caMKII which phosphorylates different proteins leading to an increase in amplitude of the EPSP.
Why do NMDA receptors need to be pre-activated by a depolarising input?
Because they have a voltage gated magnesium block, the pre-activation is done by a glutamate in the allosteric site.
How is early LTP activated?
- NMDA receptor mediated calcium ions activate calmodulin kinase II (CaMKII) due to the increase in calcium ions.
- Calcium and calmodulin bind to CaMKII and cause conformational change which leads to the activation of the protein which will then be phosphorylated.
How is early LTP activated?
- NMDA receptor mediated calcium ions activate calmodulin kinase II (CaMKII) due to the increase in calcium ions, calcium and calmodulin then bind.
What does the binding of calcium and calmodulin to CaMKII cause?
Conformational change which leads to the activation of the protein which ill then be phosphorylated.
What does phosphorylation of the protein do for AMPA?
Enhances the AMPA currents which may involve AMPAfication (the increase in the number of AMPA receptors.)
How is Late LTP activated?
BY cAMP signalling, this activates pKA which may activate other proteins and translocate to the nucleus and phosphorylate proteins there.
How do we know LTP is linked to memory?
Because inhibiting LTP inhibits some memory formation
What are the LTD inputs in the cerebellum?
Positive mossy and climbing fibres.
What are the LTD outputs in The cerebellum?
Negative purkinje fibres.
