Term
| What does the patch-clamp technique allow? |
|
Definition
| characterise ion channel properties and their contribution to neuronal firing patterns |
|
|
Term
| Describe a cell attached patch-clamp configuration |
|
Definition
| membrane patch is left intact |
|
|
Term
| Describe a whole cell patch-clamp configuration |
|
Definition
| membrane patch is disrupted by briefly applying strong suction. The interior of the pipette becomes continuous with the cytoplasm |
|
|
Term
| Describe an inside out patch-clamp configuration |
|
Definition
| patch pipette is attached to cell membrane and is then retracted to break off a patch of membrane |
|
|
Term
| Describe an outside out patch-clamp configuration |
|
Definition
| pipette is retracted during the whole-cell configuration, causing a rupture and rearrangement of the membrane |
|
|
Term
| At what threshold are M-type K+ channels activated? |
|
Definition
|
|
Term
| What does M channel activity define? |
|
Definition
|
|
Term
|
Definition
| A reduction of charge separation, leading to a less negative membrane potential |
|
|
Term
|
Definition
| An increase in charge separation, leading to a more negative membrane potential |
|
|
Term
| What are graded potentials? |
|
Definition
Changes in membrane potential that do not lead to the opening of gated ion channels
Passive responses of the membrane |
|
|
Term
| What type of current comes from a positive current flow out of the cell? |
|
Definition
|
|
Term
| What type of current comes from a negative current flows in to the cell? |
|
Definition
|
|
Term
| What type of current comes from a negative current flow out of the cell? |
|
Definition
| If negative current flows out of the cell e.g. Cl- flow out of the cell, then this is effectively a positive current. |
|
|
Term
| What type of current comes from a positive current flows in to the cell? |
|
Definition
| If positive current flows into the cell e.g. K+ flow into the cell, then this is effectively a negative current. |
|
|
Term
Describe the driving force and therefore the flow direction for K+ at:
a) -10mV
b) -110mV
c) -100mV |
|
Definition
c) at -10mV, there will be a positive driving force so K+ will flow outwards.
b) at -110mV, there will be a negative driving force so K+ will flow inwards.
c) -100mV, there will be no driving force so K+ will not flow. |
|
|
Term
Describe the driving force and therefore the flow direction for Na+ at:
a) +80mV
b) 0mV
c) +70mV |
|
Definition
a) +80mV, there will be a positive driving force so Na+ will flow outwards.
b) 0mV, there will be a negative driving force so Na+ will flow inwards.
c) +70mV, there will be no driving force so Na+ will not flow. |
|
|
Term
Describe the driving force and therefore the flow direction for Cl- at:
a) +50mV
b) -100mV
c) -50mV |
|
Definition
a) +50mV, there will be a positive driving force so Cl- will flow outwards.
b) -100mV, there will be a positive driving force so Cl- will flow inwards.
c) -50mV, there will be no net driving force so Cl- will not flow. |
|
|
Term
Describe the driving force and therefore the flow direction for Cl- at:
a) >0mV
b) <0mV
c) 0mV |
|
Definition
a) at voltages > 0mV, there will be a positive driving force so cations will flow outwards.
b) at voltages < 0mV, there will be a negative driving force so cations will flow inwards.
c) at 0mV, there will no net driving force on any cation. |
|
|
Term
| What are the 4 basic types of neuronal firing? |
|
Definition
1. phasic neurone
2. tonic neurone
3. accommodating neurone
4. spontaneously active neurone |
|
|
Term
| Describe and draw a phasic neurone |
|
Definition
| a neurone that fires in ‘bursts’ or ‘pulses’. |
|
|
Term
| Describe and draw a tonic neurone |
|
Definition
| a neurone that is constantly – ‘tonically’ – active as long as an input is detected. |
|
|
Term
| Describe and draw an accommodating neurone |
|
Definition
| a neurone with multiple discharges but with decrementing (decreasing gradually) frequency. |
|
|
Term
| Describe and draw a spontaneously active neurone |
|
Definition
| a neurone that fires or ‘bursts’ at a constant frequency. Example: pacemaker potential. |
|
|
Term
| What are firing properties of neurones defined by? |
|
Definition
| their ion channel expression profile |
|
|
Term
|
Definition
| a type of non-inactivating potassium current |
|
|
Term
|
Definition
- a voltage-gated K+ channel
- activity defines firing patterns |
|
|
Term
| When is an M-channel open? |
|
Definition
| at rest and even more likely to be open during depolarisation |
|
|
Term
| What happens when the muscarinic acetylcholine receptor (MAChR) is activated? |
|
Definition
|
|
Term
| How does M-channels prevent an AP? |
|
Definition
1. Initial depolarisation of a neurone increases the likelihood that M-channels will open.
2. M-channels generate an outward K+ current.
3. K+ efflux counteracts Na+ influx in action potential. Overall result: full action potential is prevented. |
|
|
Term
| How does ACH cause M-channel inhibition? |
|
Definition
1. 1 molecule of ACh binds to mAChR.
2. Gq G-protein causes the hydrolysis of PIP2 to IP3.
and IP3 dissociates from the membrane into the cytoplasm. When M-current is restored, it moves back to the membrane.
3. IP3 causes intracellular increase in Ca2+
4. inhibitor |
|
|
Term
| What effect does mAChR have by inhibiting M-channels? |
|
Definition
| excites sympathetic neurones |
|
|
Term
| How do mAChR inhibit cardiac muscle cells? |
|
Definition
| by activating G-protein-coupled inwardly rectifying K+ (GIRK) channels. When opened, these K+ channels result in hyperpolarisation of the cell. |
|
|
Term
| In simple terms, what effect does ACh have when it binds to M1 receptors? |
|
Definition
| M1 -> Gq -> M current inhibition -> excitation |
|
|
Term
| In simple terms, what effect does ACh have when it binds to M2 receptors? |
|
Definition
| M2 -> Gi -> GIRK activation -> inhibition |
|
|
Term
| How can rhythmic activity be generated? |
|
Definition
| by a combination of currents with various voltage-depedent and ion selectivity |
|
|
Term
| In addition to your ‘minimal’ set of voltage-gated Na+ and K+ channels, what else would you need? |
|
Definition
1. Voltage-gated Ca2+ channels to raise intracellular Ca2+ after the burst of action potentials.
2. Ca2+-activated K+ channels to provide long-lasting afterhyperpolarisation.
3. Hyperpolarisation-activated non-selective cation channels (“Ih”) to stop and invert repolarisation.
4. T-type Ca2+ channels to ‘pick-up’ Ih-mediated depolarisation. |
|
|
Term
| What do GABAA-mediated postsynaptic responses depend upon? |
|
Definition
|
|
Term
| How can opening of Cl- be inhibitory? |
|
Definition
| In ionotropic GABAA receptors, binding of GABA molecules to their binding sites in the extracellular part of the receptor triggers opening of a chloride ion-selective pore. The increased chloride conductance drives the membrane potential towards the reversal potential of the Cl¯ ion which is about –65 mV in neurons, inhibiting the firing of new action potentials. |
|
|
Term
| Can opening of Cl- be excitatory? |
|
Definition
|
|
