L10- Neuromodulation and synaptic integration

Question 1

What are 3 possible mechanisms for altering the efficacy of synaptic transmission?

Answer 1

1. Pre-synaptic: amount of NT released per AP
2. Post-synaptic; response of receptor to NT
3. Post-synaptic: excitibility of postsynaptic cell

Question 2

What are retrograde NT and signals?

Answer 2

Neurochemical released by postsynaptic neurone which then modulates function of presynaptic neurone

Question 3

Give an example of retrograde signalling?

Answer 3

Endogenous cannabinoids are released in reponse to postsynpatic Calcium influx.
Then feedback modulated presynaptic NT release via effects on the Calcium channels in the PRE synaptic membrane.
Endocannabinoid goes back and changes presynaptic.

Question 4

Name 4 allosteric modulators of GABAa receptor?

Answer 4

1.Barbituates- CNS depressant. Anti- anxiety, anti convulsant (epilepsy).
Increased duration of GABA channel opening. Means more inhibition.

2.Benzodiazepines- sedative, anti-anxiety, anti-consulvant. Increased frequency of GABA channel opening– so more inhibition.

Question 5

What do barbituates do?

Answer 5

Barbituates- CNS depressant. Anti- anxiety, anti convulsant (epilepsy).
Increased duration of GABA channel opening. Means more inhibition.

Question 6

What do bensodiazepines do?

Answer 6

Benzodiazepines- sedative, anti-anxiety, anti-consulvant. Increased frequency of GABA channel opening– so more inhibition.

Question 7

What is an example of postsynaptic neuromodulation in a mammalian hippocampal neurone?

Answer 7

Noradrenline increases excitability of postsynaptic cell.

Noradrenaline-> cAMP-> closes K+ channels in postsynaptic membrane.

Question 8

WHat is synaptic integration?

Answer 8

Where PSPs are summed on the postsynaptic cell. add up

Question 9

What do IPSPs do?

Answer 9

Take membrane potential further from the threshold. Inhibit.

Question 10

What are PSPs?

Answer 10

graded electrical signals

Question 11

Where is the final decision made about whether to fire an AP?

Answer 11

At action potential initiation zone. At the axon hillock. It has high density of VSNa channels so a low threshold.

Question 12

How do graded PSPs travel to the axon hillock?

Answer 12

In a passive decremental fashion. Inputs furhter away from the axon hillock have less influence on final output.

Question 13

Why is the location of the synapse key?

Answer 13

Further from axon hillock, the weaker the signal is when it reaches it.

Question 14

What does the spread of a PSP along the membrane depend on?

Answer 14

1. time constant τ (tau
2. length constant λ
3. diameter
4. membrane resistance Rm
5. internal resistance Ri

1 and 2 are of the membrane
3,4,5 are of the dendrite. Dendritic cable properties.

Question 15

Which dendritic cable properties affect the spread of PSP along the membrane?

Answer 15

diameter, membrane resistance, inernal resistance

Question 16

What is the length constant? λ

Answer 16

The distance over which PSP travels to reach 37% of its original size.

Question 17

What is the time constant (tau)

Answer 17

The time taken for the PSP to decay to 37% of its peak value

Question 18

What can temporary ichanges in the Rm via gated ion channels lead to?

Answer 18

Rm = membrane resistance.

leads to Changes in passive spread of PSPs.

Question 19

What does synaptic integration involve?

Answer 19

Summation of EPSPs and IPSPs on the postsynaptic membrane.

Axon hillock acts as a read-out if the membrane is above the AP threshold

Question 20

What is spatial summation?

Answer 20

A few post-synaptic neurones coming together on post synaptic neurone. Their APs add up to enough to fire an AP>

Question 21

What is temporal summation?

Answer 21

APs fired frequently on presynaptic neurone. Enough to reach threshold.

Question 22

What is shunting inhibition?

Answer 22

An inhibitory synapse, located close to the soma, can switch off all other inputs to that dendrite.

Question 23

What is a disease which shows the importance of inhibition in the CNS?

Answer 23

Hyperekplexia; Startle Disease.
Jumping Frenchmen of Maine.

Single AA mutation in the glycine receptor- Cl ion channel. Inhibtion of the CNS is reduced. So get bigger shock.

Question 24

What is AM and FM at the axon hillock?

Answer 24

AM- Graded PSP

FM- action potentials. ( AP either there or not.)

Question 25

Which code do neurones use?

Answer 25

An FM code. The frequency and pattern of APs conveys information.