Action potential..

[Temperature101]

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What effect might the opening of K+ channels toward the end of the action potential (AP) have on the axonal membrane?

A. It could cause another AP.

B. It could make it difficult (but still possible) to elicit another AP immediately after the first one.

C. It could make it impossible to elicit another AP immediately after the first one.

D. It could make the threshold more negative..

I got the right answer for that question, which is B. But i was looking at D and i dont get why it is wrong... Because if K+ channels are open, there will be more getting out of the cell. The inside will be more negative. Consequently, the cell will be hyperpolarized. You will need more influx of Na+ to generate another AP...Wouldn't the threshold be more negative?

Edit: Got it... since you will need more Na+, in a sense, the threshold is more positive i.e less negative)

 

[FeinMS]

Threshold is the membrane potential where you can start the action potential. i.e. If you reach that membrane potential, action potential is fired. If not, action potential is not fired. It remains the same.

 

[MCATMountain]

What effect might the opening of K+ channels toward the end of the action potential (AP) have on the axonal membrane?

A. It could cause another AP.

B. It could make it difficult (but still possible) to elicit another AP immediately after the first one.

C. It could make it impossible to elicit another AP immediately after the first one.

D. It could make the threshold more negative..

I got the right answer for that question, which is B. But i was looking at D and i dont get why it is wrong... Because if K+ channels are open, there will be more getting out of the cell. The inside will be more negative. Consequently, the cell will be hyperpolarized. You will need more influx of Na+ to generate another AP...Wouldn't the threshold be more negative?

Edit: Got it... since you will need more Na+, in a sense, the threshold is more positive i.e less negative)

Isn't the threshold always the same regardless?

B says hyperpolarization. D says somethign nonsensical no?

 

[sakabato93]

What effect might the opening of K+ channels toward the end of the action potential (AP) have on the axonal membrane?

A. It could cause another AP.

B. It could make it difficult (but still possible) to elicit another AP immediately after the first one.

C. It could make it impossible to elicit another AP immediately after the first one.

D. It could make the threshold more negative..

I got the right answer for that question, which is B. But i was looking at D and i dont get why it is wrong... Because if K+ channels are open, there will be more getting out of the cell. The inside will be more negative. Consequently, the cell will be hyperpolarized. You will need more influx of Na+ to generate another AP...Wouldn't the threshold be more negative?

Edit: Got it... since you will need more Na+, in a sense, the threshold is more positive i.e less negative)

Quite simply, hyperpolarization occurs, and lessens the amplitude of subsequent APs. Theshold is simply the voltage at which the voltage-gated Na channels are activated in order to create the characteristic spike. Threshold is a feature of the channels and its unaffected by hyperpolarization. Threshold is a constant membrane phenomenon.

 

[Temperature101]

Threshold is the membrane potential where you can start the action potential. i.e. If you reach that membrane potential, action potential is fired. If not, action potential is not fired. It remains the same.

My God!... An AP is all-or-none phenomenon! I guess I am tired... Time to get some sleep... I have been studying for more than 6 hours...

 

[FeinMS]

Quite simply, hyperpolarization occurs, and lessens the amplitude of subsequent APs. Theshold is simply the voltage at which the voltage-gated Na channels are activated in order to create the characteristic spike. Threshold is a feature of the channels and its unaffected by hyperpolarization. Threshold is a constant membrane phenomenon.

Is this true? I thought APs are all-or-none where once it's fired, its magnitude is the same.

 

[MCATMountain]

Is this true? I thought APs are all-or-none where once it's fired, its magnitude is the same.

I agree. I thought AP's are all the same magnitude, there was no gradation.

Edit: I looked it up: https://www.boundless.com/psycholog...neurons-and-nerve-networks/action-potentials/

It's all or none and same strength.

 

[Intraleukin-6]

Is this true? I thought APs are all-or-none where once it's fired, its magnitude is the same.

I think he means inhibitory post synaptic potentials hyperpolarize the cell, and thus more excitatory (depolarizing) post synaptic potentials are required to reach threshold. So it seems like action potentials have less of an affect in depolarization of the subsequent cell.

 

[Mission Medical]

Is this true? I thought APs are all-or-none where once it's fired, its magnitude is the same.

Yes, in most of the situations encountered, APs do indeed have the same magnitude once fired. However, this is when we're talking about firing an AP after a previous one ended (When the membrane has returned all the way back to resting potential). It's important to realize that although you can't fire an AP during the absolute refractory period of a previous AP, you actually can indeed fire a second AP during the relative refractory period of the previous AP. If an AP is fired during the relative refractory period (The previous AP is not completely over yet; This period roughly coincides with the period of afterhyperpolarization), then the AP will be reduced in size. Why? Because at the previous AP site, some Na+ channels are still inactivated (They should be closed when an AP finishes), and some K+ channels are still open (These should also be closed when an AP finishes). As a result, when we generate our next AP, the depolarization won't occur to the same extent. Some Na+ channels are still inactivated and can't let Na+ in, and some K+ channels are still open and letting some K+ out. Both of these channels are thus making it more difficult for the inside of the cell to become as positive as it should during the depolarization that occurs during a normal action potential.

 

[sakabato93]

Hyperpolarization of the membrane simulates the relative refractory period. AP propagates, but at a lower amplitude. AP will always be all-or-nothing once membrane has reached threshold, but a hyperpolarized membrane has a pre-lowered max amplitude.

 

[MCATMountain]

Hyperpolarization of the membrane simulates the relative refractory period. AP propagates, but at a lower amplitude. AP will always be all-or-nothing once membrane has reached threshold, but a hyperpolarized membrane has a pre-lowered max amplitude.

Interesting. Will have to look this up.

 

[sakabato93]

Interesting. Will have to look this up.

Its literally the same as the relative refractory period. The relative refractory period is caused by increased K permeability, which is what the question stem is indicating. Increased K permeability induces hyperpolarization, which results in the diminished AP you see during the relative refractory period.

 

[rodmichael82]

Is this true? I thought APs are all-or-none where once it's fired, its magnitude is the same.

It is NOT true. Action potentials do not change in amplitude. The amount of depolarization to achieve enough to hit the "threshold" may change but not the action potential magnitude itself.

 

[rodmichael82]

Op the reason why D is wrong is because all the channels determine/effect the threshold during rest NOT during the action potential itself.

 

[mehc012]

Its literally the same as the relative refractory period. The relative refractory period is caused by increased K permeability, which is what the question stem is indicating. Increased K permeability induces hyperpolarization, which results in the diminished AP you see during the relative refractory period.

You don't see a diminished AP, though...you see a slower RATE of APs.

 

[sakabato93]

I apologize. Read my notes wrong. Diminished FREQUENCY, not amplitude.

 

[mehc012]

I apologize. Read my notes wrong. Diminished FREQUENCY, not amplitude.

👍👍👍🙂

 

[gettheleadout]

👍👍👍🙂

I was gonna say, I was reading through this thread thinking:

But I'm glad it's been resolved haha.

 

[FeinMS]

You don't see a diminished AP, though...you see a slower RATE of APs.

How does hyperpolarization lead to slower rate of APs? Is it because it takes more excitatory signals to reach the threshold?

 

[Temperature101]

How does hyperpolarization lead to slower rate of APs? Is it because it takes more excitatory signals to reach the threshold?

Yes

 

[gettheleadout]

How does hyperpolarization lead to slower rate of APs? Is it because it takes more excitatory signals to reach the threshold?

Assuming the rate of incoming EPSP's is constant before and through hyperpolarization, and those graded potentials are all of consistent intensity, yes.