Week 1 Lecture 4

Question 1

What are the two types of post-synaptic receptors?

Answer 1

Ionotropic and metabotropic

Question 2

What is an ionotropic receptor

Answer 2

Directly open channels

Question 3

What is a metabotropic receptor?

Answer 3

Initiates a signalling cascade which activates enzymes

Question 4

What is ionotropic effects?

Answer 4

Binding of transmitter to post-synaptic membrane opens ion channels which result in changes in the post-synaptic membrane potential called post-synaptic potential (PSP)

Question 5

What are the two types of post-synaptic potentials?

Answer 5

EPSPs (excitatory) and IPSPs (inhibitory)

Question 6

What do EPSPs correspond to?

Answer 6

the opening of ion channels specific for cations, Na+ and K+, depolarizing

Question 7

What do IPSPs correspond to?

Answer 7

the opening of ion channels specific to Cl- or K+, hyperpolarizing

Question 8

What are nicotinic receptors?

Answer 8

The ionotropic receptor for acetylcholine

Question 9

What are the ligands for ionotropic receptors?

Answer 9

Acetylcholine, glutamate, GABA and glycine

Question 10

What is GABA?

Answer 10

An inhibitory transmitter, generates IPSPs, drugs that enhance the effect of GABA (i.e. benzodiazepines) are often used to treat anxiety and insomnia, reduce the communication between synapses

Question 11

Can the ligand that act on ionotropic receptors also act on metabotropic receptors?

Answer 11

Yes, all the ligands that act on ionotropic receptors can act on metabotropic receptors. The transmitter does not determine the effect, the receptor does

Question 12

What is metabotropic effects?

Answer 12

Binding of a ligand to the post-synaptic metabotropic receptor activates an enzyme, that is usually G-protein coupled, that either produces or destroys 2nd messengers.

Question 13

What are examples of second messengers?

Answer 13

cAMP, cGMP, InP3

Question 14

What do second messengers do?

Answer 14

activate enzymes like phopshokinases, which phosphorylates proteins

Question 15

Why is the phosphorylation of proteins significant?

Answer 15

The phosphorylation of proteins results in a conformational change that changes the function of the protein e.g. the phosphorylation of ion channels may open/close them

Question 16

What is the difference between the ionotropic and metabotropic effect?

Answer 16

• The ionotropic effect is fast while the metabotropic effect takes time
• The ionotropic effect results in a change in membrane potential while with the metabotropic effect there does not have to be a change in membrane potential

Question 17

What is the beta-andrenoreceptor?

Answer 17

The metabotropic receptor for Noradrenalin (NA)

Question 18

What is the signalling cascade associated with the beta-adrenoreceptor? (4)

Answer 18

• Binding of NA activates adenyl cyclase via conformational change in G-coupled protein
• Adenyl cyclase produces cAMP
• cAMP activates kinases which phosphorylate Ca++ channel protein which increases Ca++ influx

Question 19

What are beta-blockers?

Answer 19

Block interactions between NA and beta-adrenoreceptors which decreases calcium availability resulting in less activity

Question 20

What are ligands for metabotropic receptors?

Answer 20

ACh = muscarinic receptor
Peptides = substance P, beta-endorphin
Catecholamines = noradrenaline and dopamine
Serotonin
Purines = adenosine, ATP
Gases: NO, CO

Question 21

Where are PSPs generated?

Answer 21

They are generated in inexcitable membrane e.g. neuronal dendrites and cell bodies where there is not a high density of voltage-gated Na+ channels

Question 22

What is the trigger zone?

Answer 22

The nearest excitable membrane at the beginning of the axon

Question 23

How are PSPs generated?

Answer 23

The binding of transmitter

Question 24

How do PSPs spread?

Answer 24

PSPs spread across the membrane through passive conduction to get to the trigger zone.

Question 25

Why is a single EPSP not enough to bring the trigger zone to threshold?

Answer 25

Biological tissue is not conductive, potential is lost while it moves across the membrane. Therefore, many PSPs summating is required to reach threshold

Question 26

What are the two types of PSP summation?

Answer 26

Spatial and temporal summation

Question 27

What is spatial summation?

Answer 27

Large number of EPSPs have to be activated simulataneously

Question 28

What is temporal summation?

Answer 28

EPSPs last 30-40 ms, thus successive inputs generates EPSPs that add pre-existing EPSPs, high frequency EPSPs required

Question 29

Where are IPSPs usually located and why is the location significant?

Answer 29

At the cell soma, which is between where EPSPs are generated and the trigger zone. This is location gives IPSPs an advantage since they can shunt EPSP potentials

Question 30

How do IPSPs shunt depolarizing EPSP potentials?

Answer 30

IPSPs involve the opening of Cl- channels which have a equilibrium potential of -70 mV (very close to RMP) which brings the membrane potential back to -70mV when the membrane is depolarized, essentially preventing excitation.

Question 31

Which is more important IPSPs or EPSPs and why?

Answer 31

IPSPs, because there are precise and control/shape information

Question 32

What is a spike train?

Answer 32

The sustained depolarization of the trigger zone associated with the continuous stream of action potentials.

Question 33

What does a spike train tell the brain?

Answer 33

That there is a very strong and prolonged stimulus present

Question 34

What is necessary for a spike train to be generated?

Answer 34

Hyperpolarization is required for a spike train to occur because following an AP voltage-gated Na+ channels are closed and can only be opened once the RMP is reached therefore hyperpolarization is required to re-open them quickly