Synaptic Plasticity

Question 1

What is Hebb’s theory of learning?

Answer 1

When the axon of cell A is close enough to excite cell B, and repeatedly takes part it firing it, a growth or metabolic change takes place in one or both cells that cell A becomes more efficient at firing cell B

Question 2

What is long term potentiation?

Answer 2

The strengthening of a synapse in response to high frequency of stimulation

Question 3

Define “Input Specificity” in relation to long term potentiation

Answer 3

The induction of long term potentiation within one synapse will not induce long term potentiation in surrounding, inactive synapses

(This is due to functional compartmentalisation by dendritic spines!)

Question 4

Define “Associativity” in relation to long term potentiation

Answer 4

If a synapse is strongly activated, a neighbouring pathway that is only weakly activated will also undergo long term potentiation

Question 5

Define “Cooperativity” in relation to long term potentiation

Answer 5

If many synapses that converge on a single patch of postsynaptic membrane are weakly stimulated, there may collectively be enough stimulation to induce long term potentiation

Question 6

Define “Persistance” in relation to long term potentiation

Answer 6

Long term potentiation is persistent, and may last from several minutes to several months

Question 7

Which receptor mediates long term potentiation?

Answer 7

NMDA receptors

Question 8

What is the meaning of NMDA being a ‘coincidence detector’?

Answer 8

NMDA receptors detect both presynaptic activity (as they bind glutamate that has been released) and postsynaptic activity (as they detect depolarisation of the cell they are on).

Question 9

Why are NMDA receptors required for long term potentiation?

Answer 9

NMDA receptors are permeable to calcium. Calcium is needed for the intracellular signalling pathways that result in long term potentiation.

Question 10

What is the intracellular signalling pathway behind long term potentiation?

Answer 10

Calcium binds to calmodulin
The calcium/calmodulin complex activates protein kinase II
More AMPA receptors are inserted into the membrane
The kinase phosphorylates AMPA receptors, increasing their conductance

Question 11

Suggest 3 presynaptic mechanisms that may contribute towards long term potentiation

Answer 11

Increased number of neurotransmitter release sites
Increased probability of neurotransmitter release
Increased neurotransmitter concentration

Question 12

Suggest 3 postsynaptic mechanisms that may contribute towards long term potentiation

Answer 12

Increased length of time for which the AMPA receptor is activated (open)
Increased probability of AMPA receptor activation
Insertion of additional AMPA receptors

Question 13

What is long term depression?

Answer 13

Reduction in the efficacy of neuronal synapses following a patterned stimulus

Question 14

What are the possible causes of long term depression?

Answer 14

Long term depression can result from strong synaptic stimulation or persistent weak synaptic stimulation

Question 15

What neurotransmitter is most commonly involved in long term depression?

Answer 15

L-glutamate

Question 16

What is the thought to be the mechanism behind long term depression?

Answer 16

Decrease in postsynaptic NMDA receptor density
Calcium activates protein kinase C, which initiates the MAPK cascade
The MAPK cascade results in phosphorylation of the AMPA receptors, which causes them to internalise via endocytosis

Question 17

Name two areas of the brain where long term depression occurs

Answer 17

Hippocampus and cerebellum

Question 18

What are the 4 ‘rules’ of long term potentiation?

Answer 18

Input specificity
Cooperativity
Associativity
Persistence