Lec6: Glutamenergic receptors

Question 1

Draw a basic diagram of a neuron. Are they polarised or unpolarised cells?

Answer 1

Polarised.

Question 2

Define a synpase.

Answer 2

Highly specialised site of neuron-to-neuron (or neuron-to-muscle or neuron-glia) contact.

Question 3

Synapses allow for what kind of communication, therefore allowing for what “structures” to be formed in the brain?

Answer 3

Rapid communication, so that brain circuits can be formed.

Question 4

What are brain circuits?

Answer 4

Area that mediates conversion transmission of neural messages, converting from electrical info (pre-synpase) to chemical info (synaptic cleft) back to electrical info (post-synapse).

Question 5

What is the name of:

1. The area at the axon terminal base where vesicular fusion occurs
2. The name of the area at the dendritic synapse base where all the receptors are located

Answer 5

1. Active zone

2. Post-synaptic density

Question 6

Draw an entire diagram showing how transmitters are released by exocytosis. Also, in the last step, neurotransmitters are recovered by the pre-synaptic terminal by what process?

Answer 6

Endocytosis.

Question 7

Draw a flowchart illustrating the process of vesicular fusion at the active zone. Name the two vesicular SNARES and the two membrane SNARES.

Answer 7

VS = Syntaxin, SNAP25
MS = Synaptobrenin, Synaptotagmin (Ca2+ binds to this one)

Question 8

Inhibitory synapses are located in the vicinity of what neuron?

Answer 8

Interneurons.

Question 9

Interneurons comprise what proportion of all neurons in the brain? Also, compare their polarisation to regular neurons.

Answer 9

1. 5%

2. Very polarised: one neuron controls many other cells

Question 10

Which neurotransmitter do interneurons release? Also, the receptors that these neurotransmitters bind to are permeable to what ion?

Answer 10

GABA and glycine. The receptors are permeable to Cl- (negative ions).

Question 11

Draw the voltage-time graph representing an influx of Cl- ions into the cell. Name the deflection and state why this makes it more difficult for the cell to be excited.

Answer 11

1. Inhibitory post-synaptic potential (IPSP)

2. RMP is decreased, so it’s more difficult to depolarise the cell to threshold to generate an action potential.

Question 12

What are the three types of glutamanergic receptors? Which are fast and slow conducting?

Answer 12

1. AMPA receptors - fast
2. NMDA receptors - fast
3. Metabotropic glutamate receptors - slow

Question 13

What ions to AMPA receptors conduct?

Answer 13

Na+ mostly, K+

Question 14

What ions to NMDA receptors conduct?

Answer 14

Ca2+ mostly, Na+, K+

Question 15

What conditions must be met before AMPA and NMDA receptors are able to open respectively?

Answer 15

AMPAR = only glutamate binding
NMDAR = Glutamate binding and depolarisation (because they are voltage-gated)

Question 16

Why must the post-synaptic membrane of a cell depolarise before NMDAR open?

Answer 16

The depolarisation causes a conformational change in NMDAR that removes Mg2+ blockage from the receptor pore, thus allowing ions to flow.

Question 17

How is the depolarisation of NMDAR achieved?

Answer 17

By strong stimulation of AMPAR allowing for a huge influx of Na+ ions causing a significant depolarisation.

Question 18

What does coincidence mean in terms of neuron activation?

Answer 18

It means there is good degree of coactivation between pre-synaptic and post-synaptic cell.

Question 19

Describe why high levels of pre and post synaptic activity a reflection of AMPAR and NMDAR being “coincident detectors?”

Answer 19

1. High post-synaptic activation = high Ca2+ influx (instead of solely Na+ influx)
2. High Ca2+ influx = high NMDAR activation
3. High NMDAR activation requires depolarisation of post-synaptic membrane = high AMPAR activation
4. High AMPAR activation = high glutamate release (due to high level of pre-synaptic activity)