Action Potential COPY Flashcards
Action potential in axon values
RMP: -70mV
Depolarisation peak: +30mV
Action potential skeletal muscle values
RMP: -90mV
Depolarisation peak: +40mV
SA node action potential values
RMP: -60mV
Depolarisation peak: +30mV
Cardiac ventricle action potential values
RMP: -90mV
Depolarisation peak: +30
How long does action potential last in axon/skeletal muscle?
0.5ms
How long does action potential last in SA node/cardiac ventricle?
100ms
What is conductance dependent on?
number of ion channels open
higher conductance = more channels open
What happens if you increase conductance of an ion?
Membrane potential moves towards the equilibrium potential for that ion
How much ion change is needed for large changes in membrane potential?
only small amounts (larger axons need less)
Membrane potential during action potential
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
What occurs when V gated channels of Na+ open?
Membrane gets depolarised as Na+ enters cells
How are V gated Na+ channels reactivated?
After membrane gets hyperpolarised
How can we show experimentally that Na+ is responsible for AP depolarisation?
If you decrease extracellular Na+ action potentials get smaller
How can currents be measured over time at a set membrane potetnial?
Voltage clamp
K+ causes hyperpolarisation, Na+ causes depolarisation
How does conductance change over action potential?
Na+ channels conductance changes rapidly - quickly inactivate in response to depolarisation
K+ channels are slower at closing so have a shallower curve
How does hyperpolarisation occur?
Non voltage gated K+ channels are naturally open
When you pair this with open v gated k+ channels membrane gets more negative than RMP
What causes membrane to go back RMP after hyperpolarisation?
Closure of V gated K+ channels
What triggers an action potential?
Depolarisation to threshold at axon hillock
What does depolarisation to threshold trigger?
Positive feedback to open Na+ channels and allow influx of Na+
What does depolarisation trigger?
Inactivation of V gated Na+ channels
Voltage gated K+ channels open
Is the Na+K+ATPase involved in repolarisation?
NOOOOOOOOO (just sets up gradients)
What is absolute refractory period (ARP)?
Na+ channels are inactivated
Depolarisation cannot re-occur no matter stimulus
No other action potential can occur during this
What is relative refractory period?
Na+ channels are closed (not inactivated)
If stimulus is strong, can cause opening of channels and depolarisation
V gated K+ channels are closing
structure of V gated Na+ channel
1 alpha subunit
four similar sections
voltage sensor (in S4)
pore region (P)
what is important about the S4 voltage sensor?
Contains positively charged amino acid residues
senses changes
conformational change
What is located between 3rd and 4th sections of alpha subunit on Na+ channel?
Inactivation particle
Enters pore when membrane is depolarised
Inactivates channel so no Na+ can enter
structure of v gated K+ channels
4 individual a subunits
voltage sensor (s4)
Pore region
NO INACTIVATION
What does pore region contribute to?
Selectibility - only tries to allow K+ ions through
differences V gated K+ channel and V gated Na+ channel
No inactivation in K+ channel
K+ is made of 4 subunits, Na+ only 1
Phases of V gated Na+ channel
Closed, Open, Inactivated
What form of anesthetic is permeable to the membrane?
Unprotonated
hydrophobic/lipophilic
example of anaesthetic
Lidocaine
How does lidocaine work?
Hydrophilic pathway (open channel block) Hydrophobic pathway (inactivated)
(block Na+ channels)
Hydrophilic/open channel pathway
Channel must be open Drug crosses membrane (uncharged hydrophobic) Gets protonated inside cell Enters Na+ channel Blocks
Hydrophobic pathway
Drug crosses membrane (uncharged hydrophobic)
Moves into Na+ channel within membrane (across)
Gets protonated
Blocks Na+ channel
STRONGEST
When is block in strongest form?
When the Na+ channel is in inactivated state
How is unblocking occur?
Channel must be closed
Drug gets deprotonated
Local anaethetics blocking order
small myelinated axons
unmyelinated axons
large myelinated axons
why is important Na+ channels become inactivated?
So action potentials occur in one direction
What is the consequence of delayed closing of V gated K+ channels?
Membrane gets hyperpolarised
Na+ channels can be reactivated
