ICPP - Action Potential Flashcards Preview

CJ: UoL Medicine Semester One (ESA1) > ICPP - Action Potential > Flashcards

Flashcards in ICPP - Action Potential Deck (24):

Which type of action potential can be observed to have a plateau in the middle?

Cardiac ventricle


What happens if a cell is depolarised to a level higher than the threshold value?

An action potential occurs


What does the level of conductance of a membrane to a particular ion depend on?

The number of channels for the ion that are open.


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

Plot a graph of predicted change in [Na+] against peak of action potential as external [Na+] is reduced.


How is change in concentration calculated in an axon of 1 micrometer in diameter?

Change in concentration = mol/volume


Which rises first during an action potential, Na+ conductance or K+ conductance?

Na+ conductance rises first, then K+ rises slightly later (and doesn't rise as high).


What sort of mechanism allows the sodium channels to open more and more during the action potential?

Positive feedback


Is the Na+K+ATPase pump involved in the repolarisation of the action potential?

Nope. It just returns the concentrations to normal afterwards.


What is the difference between the ARP and the RRP?

ARP (absolute refractory period) - nearly all Na+ channels inactivated, shorter, cannot be overcome

RRP (relative refractory period) - Na+ channels recovering from inactivation, excitability returning towards normal, can be overcome by strong enough action potential


What is the function of the S4 region in a voltage-gated Na+ or K+ channel?

It has positive amino acid residues, which contribute to voltage sensitivity.


What is the function of the P region in a voltage gated Na+ or K+ channel?

Contributes to pore selectivity


How many subunits is a functional K+ channel formed from?

Four separate alpha subunits


How many subunits is a voltage gated Na+ channel formed from?

One alpha subunit


Which type of axons are blocked first by local anaesthetics?

Blocked in following order:

- small myelinated axons
- un-myelinated axons
- large myelinated axons


Which type of channels do local anaesthetics block?

Na+ channels


What is the "length constant" of the action potential?

The distance it takes for the potential to fall to 37% of its original value.


What is "capacitance"?

Ability to store charge, which is a property of the lipid bilayer.


What does it mean when a membrane has high capacitance?

Voltage changes more slowly in response to current injection


What does it mean when an axon has high resistance?

Change in voltage spreads further along the axon


What do the nodes of Ranvier have lots of?

High density of Na+ channels (around 10,000 per node)


How are the Na+ channels distributed on an unmyelinated axon?

Evenly across its surface


What is saltatory conduction?

Action potential "jumps" from node to node, allowing a much faster conduction velocity.


In what ways does the myelin sheath improve conduction?

- large increase in membrane resistance
- large decrease in membrane capacitance
- this means length constant is increased
- slight decrease in time constant


Give some examples of disease states affecting conduction of the action potential.

- multiple sclerosis (CNS)
- Devic's disease (CNS)

- Landry-Guillain-Barre syndrome (PNS)
- Charcot-Marie-Tooth disease (PNS)

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