Synaptic plasticity LTD n LTP 26/11 Flashcards
What is the name of the structure of where neurons communicate?
Synapses
What causes the release of neurotransmitters into the synapse?
Action potential coming down from axon into axon terminal
What is a post synaptic density region?
(3 marks)
- Electron dense structure that is positioned after the synaptic cleft
- Keeps shape of spine of synapses
- Anchors/ keeps receptors in synaptic zone
What is Hebb’s postulate?
(2 marks)
- When axon of cell A is near enough to excite cell B it takes part in firing it repeatedly
- Growth processes or metabolic change takes place in one or both cells such that A’s efficiency as one of the cells firing B is increased
What is Hebb’s learning rule? (explanation of his postulate)
(2 marks)
- Correlated pre and post synaptic activities cause synapse strengthening and stabilization by action potential coming down axon to post synaptic neuron - this may be the basis of information storage
- Uncorrelated activity between synaptic partners would weaken the connection - cells that fire together wire together
What is an action potential?
Large, brief depolarisation of the membrane potential - unit of transmission
What is ‘synaptic potential’?
Depolarizing or hyperpolarising potentials due to activation of NT receptors . Many receptors on post-synaptic membrane are ionotropic causing change in potential
What is an EPSP?
Excitatory post synaptic potential - current measure of strength of synapse
What can many EPSPs do together?
Summate together - lots of AP coming in at onetime on same neuron and if big enough can fire action potential
Which brain structure was LTP first found in?
Hippocampus
Why is the hippocampus the chosen area to study LTP?
(4 marks)
Highly laminus structure with 3 interlocked sheets:
- Cells in dendate gyrus - glutamatergic excitatory cells
- CA3 pyramidal cells - connected by 3 different pathways
- CA1 region - all dendrites in laminus structure
How are the 3 groups of cells in the hippocampus connected?
What pathways are involved?
(4 marks)
- Perforant pathway from the entorhinal cortex - axons from here join onto dentate granule cells
- Dentate granule cells send fibres in mossy fibre pathway
- ^^axons infringe on dendrites of CA3 cells
- CA3 cells infringe in bundle called Schaffer collateral and bind to CA1 cells
- From this can make recordings in post synaptic cells
Explain how the results were generated in this image.
(7 marks)
- Signal given to stimulate perforant pathway and then measured EPSPs
- Plotted max amplitude of deflection from the max response
- Given pathway a high frequency stimulation at 0 mins at 100hz per second
- ^^ known as Tetanus - train of bursts
- Rapidly see bigger change in response in EPSPS
- Bigger response for every stimulation they do after they’ve given brief high frequency stimulation than before
- Provided first evidence that nunch of synapses can change in response to an activity after stimulation
What are th 2 phases LTP is divided into?
(2 marks)
Induction: occurs during brief tetanus
Expression: way in which synapses are altered after LTP
What is input specifity?
LTP only occured in tetanized pathway
What is cooperativity?
(2 marks)
- Weak input in which only few excitatory synapses were tetanized, failed to induce LTP, whereas a strong input reliably produced LTP
- Weak induction - only few synapses will be active - causes few seconds of potenciation
What is associativity?
- Simultaneous activation of 2 seperate synapses, one of which is weak and fails to undergo LTP on its own but is able to exhibit LTP and potenciation when tetanized together with a strong input
What can prevent LTP?
(2 marks)
Hyperpolarisation - shows LTP has 2 requirements of LTP: synaptic stimulation and post synaptic depolarisation
What receptors is excitatory neural transmission dependent on?
NMDA & AMPA receptors - LTP critically dependent on activation of NMDA receptors
Describe in detail what are NMDA receptors?
(6 marks)
- Multimeric ion channel
- Ionotropic receptors
- Binds glutamate
- Co-agonist glycine binds to receptor but ions won’t flow in
- Mg2+ blocks pore unless depolarised
- Are ligand and voltage gated calcium permeable receptors NMDA
How can you remove the block of Mg2+ on NMDA receptor?
(4 marks)
- By binding glutamate
- Opens NMDA receptor (unless membrane sufficiently depolarised)
- Relieving Mg2+ block and receptor lets in Na+ and Ca2+
- Influx of Ca2+ improtant for induction of LTP
Why is the influx of Ca2+ important for LTD?
(2 marks)
- Causes activation of CamKII
- Can increase AMPA insertion into dendritic spine and also in some forms of LTD and see w/ drawal of AMPA receptors
What are two mechanisms that are also responsible for long-lasting potentiation?
(2 marks)
- Increase in efficiency of synaptic transmission at perforant pathways
- Increase in the excitabliilty of granule cell population
