Synaptic plasticity LTD n LTP 26/11

Question 1

What is the name of the structure of where neurons communicate?

Answer 1

Synapses

Question 2

What causes the release of neurotransmitters into the synapse?

Answer 2

Action potential coming down from axon into axon terminal

Question 3

What is a post synaptic density region?

(3 marks)

Answer 3

• Electron dense structure that is positioned after the synaptic cleft
• Keeps shape of spine of synapses
• Anchors/ keeps receptors in synaptic zone

Question 4

What is Hebb’s postulate?

(2 marks)

Answer 4

• 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

Question 5

What is Hebb’s learning rule? (explanation of his postulate)

(2 marks)

Answer 5

1. 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
2. Uncorrelated activity between synaptic partners would weaken the connection - cells that fire together wire together

Question 6

What is an action potential?

Answer 6

Large, brief depolarisation of the membrane potential - unit of transmission

Question 7

What is ‘synaptic potential’?

Answer 7

Depolarizing or hyperpolarising potentials due to activation of NT receptors . Many receptors on post-synaptic membrane are ionotropic causing change in potential

Question 8

What is an EPSP?

Answer 8

Excitatory post synaptic potential - current measure of strength of synapse

Question 9

What can many EPSPs do together?

Answer 9

Summate together - lots of AP coming in at onetime on same neuron and if big enough can fire action potential

Question 10

Which brain structure was LTP first found in?

Answer 10

Hippocampus

Question 11

Why is the hippocampus the chosen area to study LTP?

(4 marks)

Answer 11

Highly laminus structure with 3 interlocked sheets:

1. Cells in dendate gyrus - glutamatergic excitatory cells
2. CA3 pyramidal cells - connected by 3 different pathways
3. CA1 region - all dendrites in laminus structure

Question 12

How are the 3 groups of cells in the hippocampus connected?

What pathways are involved?

(4 marks)

Answer 12

• 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

Question 13

Explain how the results were generated in this image.

(7 marks)

Answer 13

• 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

Question 14

What are th 2 phases LTP is divided into?

(2 marks)

Answer 14

Induction: occurs during brief tetanus

Expression: way in which synapses are altered after LTP

Question 15

What is input specifity?

Answer 15

LTP only occured in tetanized pathway

Question 16

What is cooperativity?

(2 marks)

Answer 16

• 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

Question 17

What is associativity?

Answer 17

• 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

Question 18

What can prevent LTP?

(2 marks)

Answer 18

Hyperpolarisation - shows LTP has 2 requirements of LTP: synaptic stimulation and post synaptic depolarisation

Question 19

What receptors is excitatory neural transmission dependent on?

Answer 19

NMDA & AMPA receptors - LTP critically dependent on activation of NMDA receptors

Question 20

Describe in detail what are NMDA receptors?

(6 marks)

Answer 20

• 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

Question 21

How can you remove the block of Mg²⁺ on NMDA receptor?

(4 marks)

Answer 21

• 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

Question 22

Why is the influx of Ca²⁺ important for LTD?

(2 marks)

Answer 22

• 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

Question 23

What are two mechanisms that are also responsible for long-lasting potentiation?

(2 marks)

Answer 23

• Increase in efficiency of synaptic transmission at perforant pathways
• Increase in the excitabliilty of granule cell population