Neurones Flashcards
What is resting potential?
When the membraae is not stimulated as it is polarised: the outside of the membrane is more positive than the inside
What value is resting potential at?
-70mv
What does mV stand for?
Milivolts
What 3 things in the neurone membrane work towards maintaining resting potential?
- Sodium-potassium pump
- Voltage gated sodium ion channels
- Voltage gated potassium ion channels
In the maintenance of resting potential, what does the sodium potassium pump do? 3
- Uses active transport and ATP
- Pumps 3x Na+ out
- Pumps 2x K+ ions in
In the maintenance of resting potential, is the voltage gated sodium ion channel open/closed?
Closed
Why are the voltage gated sodium ion channels closed in maintaining resting potential?
- Membrane not permeable to sodium ions
- Can’t diffuse back in
Are the voltage gated potassium ion channels open/closed in maintaining resting potential?
Open
Why are the voltage gated potassium ion channels open in maintaining resting potential? 2
- Allows facilitated diffusion of K+s out of membrane down the concentration gradient
- Doesn’t reach equilibrium because of the positive charge outside
What do the sodium-potassium pumps, voltage gated sodium ion channels and voltage gated potassium ion channels all ensure in resting potential?
That there is an electrochemical gradient and therefore resting potential maintained by more positive ions being on the outside than inside
What are the steps in generating action potential?
- Resting potential
- Depolarisation
- Repolarisation
- Hyperpolarisation
Summarise resting potential 3
- Sodium Potassium pumps Na+ out and K+ in
- Using active transport with ATP against concentration gradient
- Some K+ diffuses out the K+ channel
What happens in depolarisation? 4
- Potential difference reaches threshold [-55mv]
- More voltage gated Na+ channels open
- More Na+ diffuse into axon
- More positive on the inside
What is depolarisation an example of?
Positive feedback
What occurs in repolarisation? 4
- Voltage gated K+ channels open
- Membrane more permeable to K+
- K+ diffuse out down concentration gradient
- Voltage gated Na+ channels close
What occurs in hyperpolarisation? 4
- Potential difference becomes more negative than resting potential
- K+ channels are too slow to close
- Too many potassium ions diffuse out of neurone
- Too positive outside of membrane
Label the stages of action potential on a graph
See notes
When drawing action potential on a graph, what are the labels for the x and y axis?
x axis: time [per ms]
y axis: potential difference across membrane [mV]
What happens if there is a weak stimulus?
- Some Na+ channels open
- Some Na+ diffuses in
- Does not reach threshold
- Sodium potassium pump restores resting potential
What value is threshold?
-55mV
What is the refractory period?
Period of time when another action potential cannot be generated
What 2 things does the refractory period ensure?
- Action potentials are discrete [don’t overlap]
- Action potentials are unidirectional [one way] - can’t go backwards because neurone being in refractory period prevents action potential being triggered behind initial action potential
How does the refractory period occur?
Ion channels are closed
Na+ channel was closed in repolarisation
K+ channel closed in hyperpolarisation
What 2 stages of generating action potential make up the refractory period?
- Repolarisation
- Hyperpolarisation
