action potential??

[Kaille]

Hey guys,

so school decided to make us learn homeostasis chapter over the holidays....

read the page on action potential 13975832758327523 times and i still have no understanding.

Q.

1. How does an action potential occur?

2. How does the first Na+ gates open? (Are there Na+ ions within the soma that diffuse into the axon to generate the first voltage gate to open? If so, what causes the Na+ ions to diffuse?-I don't even know if this is true....)

3. what is the refractory period and why can there be no impulse generated at this point?

Any help muchly appreciated.

 

[TrueLight]

http://vce.atarnotes.com/forum/index.php/topic,13672.msg150143.html

[Kaille]

thanks a gazzillion

[Edmund]

1. An action potential occurs when a stimulus causes the resting membrane potential (-70mV) to reach threshold (-55mV). When this threshold is reached, voltage gates Na channels open, causing a depolarising current (more positive), Na quickly comes into cell and an action potential can occur.

2. The depolarising stimulus that causes membrane resiting potential to reach threshold and these voltage gated Na channels then open. Since more Na is found outside the cell, Na will diffuse into the cell when the channels open, hence depolarising it.

3. The refractory period is when another action potential can't take place. In simple terms, the voltage gated channels has to reset before it can be activated again.

Aww... beaten, but this may address your question

[Kaille]

1. An action potential occurs when a stimulus causes the resting membrane potential (-70mV) to reach threshold (-55mV). When this threshold is reached, voltage gates Na channels open, causing a depolarising current (more positive), Na quickly comes into cell and an action potential can occur.

2. The depolarising stimulus that causes membrane resiting potential to reach threshold and these voltage gated Na channels then open. Since more Na is found outside the cell, Na will diffuse into the cell when the channels open, hence depolarising it.

3. The refractory period is when another action potential can't take place. In simple terms, the voltage gated channels has to reset before it can be activated again.

Aww... beaten, but this may address your question

so this reseting period is when the sodium and potassium pump thing happens? So the sodium must be outside and the potassium inside before another action potential can occur? <--- is that right?

[Edmund]

1. An action potential occurs when a stimulus causes the resting membrane potential (-70mV) to reach threshold (-55mV). When this threshold is reached, voltage gates Na channels open, causing a depolarising current (more positive), Na quickly comes into cell and an action potential can occur.

2. The depolarising stimulus that causes membrane resiting potential to reach threshold and these voltage gated Na channels then open. Since more Na is found outside the cell, Na will diffuse into the cell when the channels open, hence depolarising it.

3. The refractory period is when another action potential can't take place. In simple terms, the voltage gated channels has to reset before it can be activated again.

Aww... beaten, but this may address your question

so this reseting period is when the sodium and potassium pump thing happens? So the sodium must be outside and the potassium inside before another action potential can occur? <--- is that right?

The Na and K pumps are activated only when resting membrane pot reaches threshold. And yes, at resting membrane potential, there's more Na outside and more K inside.

[shinny]

A little diagram from my notes (drawing in Word ftw). I guess the important thing to understand is that Na+ channels have three states:
1. Closed
2. Open
3. Inactive

They go from closed to open when the membrane potential goes above the threshold. After a certain amount of sodium enters the cell, the channel becomes inactive. In this inactive state, the channel is closed but also inactive and cannot open at all regardless of any stimuli. It stays like this until the membrane potential returns to its resting value. At the RMP, it then turns into the closed form where the channel is closed, but can go back to being open if the membrane potential goes above the threshold once more. All of this is shown on the diagram below anyhow.

[IMG]http://img39.imageshack.us/img39/7411/unled2p.jpg[/img]

[Kaille]

A little diagram from my notes (drawing in Word ftw). I guess the important thing to understand is that Na+ channels have three states:
1. Closed
2. Open
3. Inactive

They go from closed to open when the membrane potential goes above the threshold. After a certain amount of sodium enters the cell, the channel becomes inactive. In this inactive state, the channel is closed but also inactive and cannot open at all regardless of any stimuli. It stays like this until the membrane potential returns to its resting value. At the RMP, it then turns into the closed form where the channel is closed, but can go back to being open if the membrane potential goes above the threshold once more. All of this is shown on the diagram below anyhow.

[IMG]http://img39.imageshack.us/img39/7411/unled2p.jpg[/img]

So the refractory period occurs when the Na+ channels become inactivated. So does that means that for another action potential cannot occur, there must be sodium outside the cell and potassium insude the cell?

[Russ]

There is always sodium outside and potassium inside, it's just the relative amounts that are important.
When Na+ channels become inactivated, you can't move sodium in, thus you can't accumulate positive charge inside the cell. Since you need to do that to trigger an AP, inactivating the Na+ gates will prevent APs being produced

[Kaille]

Ah i see. thanks for the help

[Souljette_93]

Watch some YouTube videos, they also help.

[Lesliel1]

can someone explain why the conduction of the action potentials only go in one direction? I get that it is because of the refractory period but i still dont understand whyy... like its because the Na+ channels are inactived but like i still dont know why it only goess in one direction...if that makes sense.. xD

[TrueLight]

well...actually the current does flow back into the area that just produced the AP but because the Na+ voltage gated channels inactivate (become refractory) very quickly after the AP is produced (ie: unavailable to open to create another AP until it moves back into a closed state), the current is unable to to produce another AP (ie: unable to reach threshold because the threshold is pretty much infinite) , so it will just 'leak' out.

[Inside Out]

you know that graph what direction would the impulse travel. in biozone it says it will travel from the right to left side.

[jasoN-]

you know that graph what direction would the impulse travel. in biozone it says it will travel from the right to left side.

I'm not sure what you mean by 'right to left side'
The graph (I assume you mean shinny's graph) resembles an action potential going from the cell body (soma), along the axon, to the axon terminals.