8 - Synaptic Integration

Question 1

Dendrites integrate info….

Answer 1

Spatially and temporally

Question 2

Is a single presynaptic AP that produces a small EPSP sufficient to produce an AP in post-synaptic neuron?

Answer 2

No - usually insufficient

Question 3

EPSPs associated w/ simultaneous inputs…

Answer 3

From multiple neurons sum

Question 4

EPSPs associated w/ sequential inputs from…

Answer 4

A single neuron can sum over time

Question 5

Will neurotransmitter be released if there’s no extracellular Ca+2?

Answer 5

No — Ca+2 influx needed to initiate presynaptic neurotransmitter release

Question 6

Neurotransmitter vesicle release is…

Answer 6

Quantal and PSPs reflect release of many vesicles

Question 7

Does each vesicle contain different amount of neurotransmitter?

Answer 7

No — each contain similar amount and produce similar PSP

Question 8

Miniature PSPs

Answer 8

Voltage change due to a single vesicle

Question 9

Why is PSP smaller at soma than at synapse?

Answer 9

Passive ion diffusion dominant in dendrites (no APs). PSP reduced in amplitude at soma due to leakage of charge in dendrites from passive diffusion.

Question 10

What’s most important consideration about whether an AP generated?

Answer 10

Depolarisation at trigger zone

Question 11

Trigger zone

Answer 11

Contain highest density of Nav channels and easiest place to generate an AP

Question 12

Passive conduction in dendrites

Answer 12

EPSP decays w/ distance from synapse due to leakage of ions, reducing size of depolarisation

Question 13

Assuming there are no voltage-gated channels…

Answer 13

• effect of injected current decays exponentially w/ distance
• length constant -> distance at which depolarisation decays to 1/e of max size

Question 14

What does length constant depend on?

Answer 14

• internal resistance (diameter, which increases towards soma)
• membrane resistance (density open channels, which varies)

Question 15

Do signals propagate unidirectionally in dendrites?

Answer 15

No - bidirectional

Question 16

For PSPs of same size synapses closer to soma have greater….

Answer 16

Influence on spiking probability

Question 17

PSP needs to reach what in order to affect spiking probability?

Answer 17

Spike initiation zone

Question 18

Active conduction always occurs in…

Answer 18

Some dendrites

Question 19

What does active conduction in dendrites depend on?

Answer 19

Voltage-gated channels, which boost membrane depolarisations

Question 20

Active conduction in dendrites improves probability that…

Answer 20

An EPSP reaches soma

Question 21

Do dendritic APs function like axonal APs?

Answer 21

No — dendritic aren’t as reliable and don’t cause as large depolarisation

Question 22

Synaptic current

Answer 22

Charge influx due to channels opening in response to neurotransmitter release

Question 23

Temporal summation is affected by…

Answer 23

Membrane time constant (how quickly it leaks charge)

Question 24

Spatial summation depends on…

Answer 24

Membrane length constant (how far charge can propagate)

Question 25

Charge leakage limits...

Answer 25

Distance over which neuron can integrate input

Question 26

Distal synapses are less effective at depolarising...

Answer 26

Soma

Question 27

Distal synapses are associated w/

Answer 27

Larger EPSPs to help counteract decay along dendrite

Question 28

Spiking threshold varies...

Answer 28

Across membrane

Question 29

What is spiking threshold determined by?

Answer 29

Minimum mempot for which an AP will occur (sufficient Nav channels need to open to initiate positive feedback)

Question 30

What’s another name for the axon hillock?

Answer 30

Trigger zone or spike initiation zone

Question 31

T/F - if Vm already at -65mV, opening more Cl channels due to influx of GABA will change Vm

Answer 31

False — because Ecl = -65mv

Question 32

Shunting inhibition

Answer 32

Inhibiting current flow from soma to axon hillock. Opening of Cl channels allows charge leakage, preventing EPSP reaching soma

Question 33

Does arrival of an AP at axon terminal guarantee vesicles will be released?

Answer 33

No - release probability < 1

Question 34

Modulating probability of vesicle release is another way to...

Answer 34

Control strength of synapse

Question 35

Pr varies between areas

Answer 35

Spinal cord motor neurons Pr = 0-1 | Motor neurons Pr = 1

Question 36

Axo-axonal synapses regulate...

Answer 36

Ca+2 entry into axon terminal, modulating vesicle release

Question 37

If a 2nd AP arrives before Ca+2 in axon terminal has cleared and not all vesicles have been released in response to 1st AP,

Answer 37

2nd AP associated w/ higher intracellular Ca+2 in pre-synaptic axon terminal, greater neurotransmitter release, larger post-synaptic change

Question 38

What are autoreceptors?

Answer 38

Pre-synaptic metabotropic receptors that monitor own levels of neurotransmitter release and can inhibit neurotransmitter release and synthesis (-ve feedback)

Question 39

Neuromodulation — metabotropic

Answer 39

Some metabotropic neurotransmitters can indirectly modify size of EPSPs associated w/ other synapses

Question 40

Decreasing K+ leakage will...

Answer 40

Increase membrane resistance and length constant (makes neuron more excitable)

Question 41

Astrocytes modulate...

Answer 41

Synaptic transmission by detecting and responding to many neurotransmitters

Question 42

Back-propagation in dendrites

Answer 42

APs can travel retrogradely in dendrites