Postsynaptic Function

Question 1

What is the name of the post synaptic structure that excitatory synapses form on?

Answer 1

Dendritic spines

Question 2

What is the theory of functional compartmentalisation?

Answer 2

Dendritic spines restrict the biochemical changes that result from calcium influx, to just one synapse. They prevent the events at one synapse from having a ‘sphere of influence’ on surrounding synapses.

Question 3

Where are dendritic spines found?

Answer 3

On the dendrites of only excitatory post synaptic membranes.

Question 4

What is the main form of glutamate?

Answer 4

L-glutamate

Question 5

Is glutamate essential or non-essential?

Answer 5

It is classified as a ‘non-essential’ amino acid as it can be synthesised by the body - we don’t need to eat it.

Question 6

What is VGLUT?

Answer 6

VGLUT is the vesicular glutamate transporter. It transports cytoplasmic glutamate into vesicles, using the proton gradient.

Question 7

What are the core principles for defining a neurotransmitter?

Answer 7

Process for synthesis
Stored in synaptic vesicles
Calcium-dependent release mechanism
Specific protein (receptor) targets
Process for removal from synaptic cleft

Question 8

How is glutamate removed from the synaptic cleft?

Answer 8

Glutamate transporters on both the pre and and postsynaptic terminals
Glutamate transporters on astrocytes

Question 9

What is the distance of the synaptic cleft?

Answer 9

20nm

Question 10

What determines if an AMPA receptor is permeable to calcium or not?

Answer 10

If there is presence of a GluA2 subunit within the AMPA receptor, it will be impermeable to calcium.

Question 11

Give an example of a synthetic, selective, competitive antagonist of AMPA receptors.

Answer 11

NBQX

Question 12

Give an selective agonist of GABA-b receptors.

Answer 12

R-Baclofen

Question 13

Give an example of a selective, competitive antagonist of GABA-b receptors

Answer 13

CGP55845

Question 14

Give an example of a selective NMDA antagonist

Answer 14

D-AP5

Question 15

What is the difference between and EPSP and an action potential?

Answer 15

An EPSP is depolarisation of a cell caused by entry of sodium ions. EPSPs have an additive effect. If you have enough EPSPs, you may reach the action potential threshold and initiate a full action potential.

Question 16

How large, roughly, is a single EPSP?

Answer 16

Only a few millivolts

Question 17

What is the voltage threshold for the removal of the magnesium block in NMDA receptors?

Answer 17

-35mV

Question 18

What is the difference between EPSPs from AMPA receptors and NMDA receptors?

Answer 18

Activation of AMPA receptors initiates a fast EPSP.

Activation of NMDA receptors initiates a slow-rising, longer laster EPSP.

Question 19

How is GABA synthesised?

Answer 19

GABA is synthesised from Glutamate, by Glutamate Decarboxylase

Question 20

What two membrane transporters remove GABA from the synaptic cleft?

Answer 20

GAT1 and GAT3

Question 21

Why are dendritic spines not needed on the postsynaptic membrane for inhibitory neurotransmission?

Answer 21

Inhibitory receptors (GABA receptors) do not allow entry of calcium into the cell. Therefore they do not result in any biochemical changes - just voltage changes.

Question 22

Why are IPSPs longer and biphasic, compared to EPSPs?

Answer 22

The initial ‘dip’ is mediated by the influx of chloride ions from the fast, ionotropic GABA-a receptor.
The second, shallower dip is mediated by efflux of potassium ions, mediated by the slower, metabotropic GABA-b receptor.

Question 23

What is an autoreceptor?

Answer 23

A receptor for a neurotransmitter present on the presynaptic terminal