Action Potential COPY

Question 1

Action potential in axon values

Answer 1

RMP: -70mV

Depolarisation peak: +30mV

Question 2

Action potential skeletal muscle values

Answer 2

RMP: -90mV

Depolarisation peak: +40mV

Question 3

SA node action potential values

Answer 3

RMP: -60mV

Depolarisation peak: +30mV

Question 4

Cardiac ventricle action potential values

Answer 4

RMP: -90mV

Depolarisation peak: +30

Question 5

How long does action potential last in axon/skeletal muscle?

Answer 5

0.5ms

Question 6

How long does action potential last in SA node/cardiac ventricle?

Answer 6

100ms

Question 7

What is conductance dependent on?

Answer 7

number of ion channels open

higher conductance = more channels open

Question 8

What happens if you increase conductance of an ion?

Answer 8

Membrane potential moves towards the equilibrium potential for that ion

Question 9

How much ion change is needed for large changes in membrane potential?

Answer 9

only small amounts (larger axons need less)

Question 10

Membrane potential during action potential

Answer 10

V gated Na+ channels open 
Na+ channels inactivate
V gated K+ channels open
Hyperpolarisation  
Na+ channels become reactivated but remain closed 
V gated K+ channels close

Question 11

What occurs when V gated channels of Na+ open?

Answer 11

Membrane gets depolarised as Na+ enters cells

Question 12

How are V gated Na+ channels reactivated?

Answer 12

After membrane gets hyperpolarised

Question 13

How can we show experimentally that Na+ is responsible for AP depolarisation?

Answer 13

If you decrease extracellular Na+ action potentials get smaller

Question 14

How can currents be measured over time at a set membrane potetnial?

Answer 14

Voltage clamp

K+ causes hyperpolarisation, Na+ causes depolarisation

Question 15

How does conductance change over action potential?

Answer 15

Na+ channels conductance changes rapidly - quickly inactivate in response to depolarisation
K+ channels are slower at closing so have a shallower curve

Question 16

How does hyperpolarisation occur?

Answer 16

Non voltage gated K+ channels are naturally open

When you pair this with open v gated k+ channels membrane gets more negative than RMP

Question 17

What causes membrane to go back RMP after hyperpolarisation?

Answer 17

Closure of V gated K+ channels

Question 18

What triggers an action potential?

Answer 18

Depolarisation to threshold at axon hillock

Question 19

What does depolarisation to threshold trigger?

Answer 19

Positive feedback to open Na+ channels and allow influx of Na+

Question 20

What does depolarisation trigger?

Answer 20

Inactivation of V gated Na+ channels

Voltage gated K+ channels open

Question 21

Is the Na+K+ATPase involved in repolarisation?

Answer 21

NOOOOOOOOO (just sets up gradients)

Question 22

What is absolute refractory period (ARP)?

Answer 22

Na+ channels are inactivated
Depolarisation cannot re-occur no matter stimulus
No other action potential can occur during this

Question 23

What is relative refractory period?

Answer 23

Na+ channels are closed (not inactivated)
If stimulus is strong, can cause opening of channels and depolarisation
V gated K+ channels are closing

Question 24

structure of V gated Na+ channel

Answer 24

1 alpha subunit
four similar sections
voltage sensor (in S4)
pore region (P)

Question 25

what is important about the S4 voltage sensor?

Answer 25

Contains positively charged amino acid residues
senses changes
conformational change

Question 26

What is located between 3rd and 4th sections of alpha subunit on Na+ channel?

Answer 26

Inactivation particle
Enters pore when membrane is depolarised
Inactivates channel so no Na+ can enter

Question 27

structure of v gated K+ channels

Answer 27

4 individual a subunits
voltage sensor (s4)
Pore region
NO INACTIVATION

Question 28

What does pore region contribute to?

Answer 28

Selectibility - only tries to allow K+ ions through

Question 29

differences V gated K+ channel and V gated Na+ channel

Answer 29

No inactivation in K+ channel

K+ is made of 4 subunits, Na+ only 1

Question 30

Phases of V gated Na+ channel

Answer 30

Closed, Open, Inactivated

Question 31

What form of anesthetic is permeable to the membrane?

Answer 31

Unprotonated

hydrophobic/lipophilic

Question 32

example of anaesthetic

Answer 32

Lidocaine

Question 33

How does lidocaine work?

Answer 33

Hydrophilic pathway (open channel block)
Hydrophobic pathway (inactivated)

(block Na+ channels)

Question 34

Hydrophilic/open channel pathway

Answer 34

Channel must be open
Drug crosses membrane (uncharged hydrophobic)
Gets protonated inside cell
Enters Na+ channel
Blocks

Question 35

Hydrophobic pathway

Answer 35

Drug crosses membrane (uncharged hydrophobic)
Moves into Na+ channel within membrane (across)
Gets protonated
Blocks Na+ channel
STRONGEST

Question 36

When is block in strongest form?

Answer 36

When the Na+ channel is in inactivated state

Question 37

How is unblocking occur?

Answer 37

Channel must be closed

Drug gets deprotonated

Question 38

Local anaethetics blocking order

Answer 38

small myelinated axons
unmyelinated axons
large myelinated axons

Question 39

why is important Na+ channels become inactivated?

Answer 39

So action potentials occur in one direction

Question 40

What is the consequence of delayed closing of V gated K+ channels?

Answer 40

Membrane gets hyperpolarised

Na+ channels can be reactivated