Synaptic integration and plasticity

Question 1

Give two examples of coincidence detectors

Answer 1

Sound localisation (comparing timing difference between two ears)
Visual processing (combining simple shapes to recognise complex features)

Question 2

What is silent post-synaptic inhibition?

Answer 2

When neurotransmitter release causes the activation of ion channels in the post-synaptic membrane with a reversal potential which is the same as the resting membrane potential. This means that there is no net movement of ions but the membrane resistance has been changed.

Question 3

What is Ohm’s Law?

Answer 3

V = R x I
Where V = change in membrane potential
R = membrane resistance
I = current

Question 4

What is the main inhibitory neurotransmitter in mammals?

Answer 4

GABA

Question 5

Define synaptic facillitation

Answer 5

Two close impulses pre-synaptically increasing post-synaptic activity

Question 6

What acts as the calcium sensor in the SNARE complex?

Answer 6

Synaptogamin

Question 7

How does repeated stimulation of a low probability neuron lead to longer APs? (3)

Answer 7

Longer presynaptic depolarisation
More calcium influx
More neurotransmitter release

Question 8

In what two ways can heterosynaptic modulation work?

Answer 8

On the presynaptic membrane it can alter neurotransmitter release
On the post synaptic membrane, it can alter sensitivity to neurotransmitter

Question 9

Give two examples of postsynaptic modulation

Answer 9

Activation of a GPCR can activate PKA which can phosphorylate GABAa receptors and alter their activity
Insulin binding to its receptors activates certain pathways, one of which increases the number of GABAa receptors in the membrane

Question 10

What are the mechanisms of pre and post synaptic modulation?

Answer 10

Pre:
Altered vesicle release
Altered calcium entry
Altered neurotansmitter recycling

Post:
Altered receptor function
Altered receptor number

Question 11

Define synaptic plasticity

Answer 11

The ability of a synapse to change its strength

Question 12

What is a strong synapse?

Answer 12

A synapse where the post synaptic neuron needs a minimal amount of impulses to reach threshold

Question 13

Describe the theory behind Hebbian plasticity

Answer 13

When neurons fire at the same time, the connections between them are strengthened (LTP) which makes them more likely to fire again in the future
When two neurons fire asynchronously, the connections are weakened (LTD) making them more likely to fire independently of each other
‘Neurons that fire together, wire together’

Question 14

Define spike timing dependent plasticity

Answer 14

A biological process adjusting the strength of synapses depending on whether or not the pre-synaptic neuron fires within the critical window which is 20ms before or after the post-synaptic neuron fires

Question 15

What do the values of a paired pulse ratio as short term plasticity show?

Answer 15

PPR >1 = Paired pulse facilitation

PPR <1 = Paired pulse depression

Question 16

What is non-synaptic plasticity?

Answer 16

Any change in transmission that occurs somewhere other than the synapse e.g. membrane potential or neuronal excitability

Question 17

What is homeostatic plasticity?

Answer 17

The capacity of neurons to regulate their own excitability to keep it at a target firing rate
Acts by opposing changes in network activity

Question 18

Where are APs initiated?

Answer 18

Axon initial segment

Question 19

What are the two types of homeostatic plasticity?

Answer 19

Synaptic (at synaptic terminals) and non-synaptic (at the axon initial segment or changing ions channel density)

Question 20

What type of homeostatic plasticity occurs in pyramidal cells?

Answer 20

Distance of the axon initial segment from the soma is increased with repeated stimulation because it is the most excitable part of the neuron and this allows more time for decay of the EPSP
The length of the the axon initial segment can also be modified