action potential??

[shinny]

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.

The graph is only indicative of the membrane potential at one particular point in the axon over time. The axis isn't showing what happens along the length of the axon itself. So yeh, not sure what you mean by left to right.

[jasoN-]

Yeah sorry that's what I meant lol,
on that note 1 AP between two nodes of ranvier, or at any point a new AP is generated?

[Inside Out]

yea that means it goes from the left to the right, as in the never impulse start at resting period then moves ont o depolarisation and so on. WHats the difference btwm a refractory period and hyperpolarisation

[jasoN-]

There's two different 'types' of refractory periods;
Absolute refractory period: No matter how strong a stimulus, another action potential cannot be generated during this time
Relative refractory period: A strong enough stimulus CAN generate a new action potential

During the relative refractory period, K+ channels are still closing, to return to the resting membrane potential.

Hyperpolarisation is when the membrane potential goes under the resting membrane potential (is more negative)

[shinny]

Yeah sorry that's what I meant lol,
on that note 1 AP between two nodes of ranvier, or at any point a new AP is generated?

Was considering more in the case of unmyelinated neurons. Saltatory conduction which occurs in myelinated neurons is a bit more complex. Studied it 2 years ago and forgot the major details of it, but for a VCE level, you can pretty much assume that graph to be at each node of Ranvier.

yea that means it goes from the left to the right, as in the never impulse start at resting period then moves ont o depolarisation and so on. WHats the difference btwm a refractory period and hyperpolarisation

Oh right. Figured that was obvious with the numbering and just typical convention going from left to right. Thought you meant in terms of the axon itself.

Regarding the refractory period, there's two parts to it. The first is the absolute refractory period where another AP cannot be generated during this time no matter what occurs. This is because all the voltage-gated sodium channels are either already currently open, or are in their inactivated state. They remain like this until they return to resting membrane potential.

At which point they do, this ends the absolute refractory period and begins the relative refractory period. Since the membrane potential is below the resting membrane potential, the sodium channels now switch back to their active state and can possibly be activated. The relative refractory period is due to the phenomenon of hyperpolarisation which you mentioned, where due to the lag in potassium channels closing, the membrane potential actually goes below the resting membrane potential. As said before, the sodium channels can potentially be activated. However, since hyperpolarisation makes the membrane potential more negative, you will need a greater stimulus to bring the membrane potential above threshold. Thus, it's possible in the relative refractory period to generate APs, but due to hyperpolarisation, you need an above-normal stimulus to be able to do so.

I don't remember understanding much of this at all during VCE Bio and I don't think such details are tested. But yeh, if just for interest's sake, read through this a few times accompanied by the graph and it should start to make sense.

EDIT: For more details on the channel states, go back to the original post here.

[Inside Out]

Why do the cells let Na+ in and K+ out instead of Na+ in and Na+ out

[jasoN-]

Why do the cells let Na+ in and K+ out instead of Na+ in and Na+ out

"Na+ in and Na+ out" I assume you mean Na+ out and K+ in?

This is purely due to the concentration gradients between the extracellular and intracellular environment.
At the resting state, there's a higher concentration of Na+ outside of the neuron (~150mM) than the inside (~5mM)
Similarly to K+, there's a higher concentration inside (~10-15mM) than outside (~140mM).

When the channels are open, the ions will diffuse accordingly to reduce the concentration gradient.

[Inside Out]

are you sure that 6. is where the NA+ channel closes cause i thought it closed immediately when repolarization starts

[jasoN-]

At 4. (when repolarisation starts), the Na+ channels are INACTIVATED (subtle difference), this is during the Absolute refractory period where an action potential cannot be generated no matter the stimulus.
The Na+ channels close (ie. reset) when the membrane potential hits the starting resting membrane potential (as demonstrated in shinny's graph).
From 4. to 6. no Na+ enters the neuron if that's what you're thinking. When the Na+ channels are closed (and not inactivated), an action potential can be generated if the stimulus is strong enough.

[shinny]

are you sure that 6. is where the NA+ channel closes cause i thought it closed immediately when repolarization starts

Re-read the part above the graph regarding the different channel states if you need more elaboration on what jasoN- has already said.

[Inside Out]

i dont get this   i have a sac in two days glucose regulation should i be bothered knowing all these terms?

[HERculina]

i dont get why its that way in the book too - this is the graph she is talking about:

[shinny]

Not sure what that arrow regarding direction of impulse travel is referring to. Can't see the whole graph so it's hard to judge, but you probably don't need to worry about it.

i dont get this   i have a sac in two days glucose regulation should i be bothered knowing all these terms?

Well if it's on the endocrine system, then no, not really for your SAC. For the exam though, I doubt you'll need to either. They generally tend to test more about the general principles of endocrine vs neural control rather than specifics of the AP itself. Go through trial exams and you'll see what's expected of you.

[Kaille]

i dont get why its that way in the book too - this is the graph she is talking about:

is it because the refractory period (time when no action potential can occur) forces the impulse to travel in one direction (away from soma)? also, if you notice the direction of the arrow is in the same direction as the arrow on the nerve impulse diagram. so maybe during this refractory period the impulse can only travel away from the nerve body?

iuno. this diagram is really confusing.

[Russ]

The refractory period means that even though charge spreads in both directions, it can only trigger more channels opening in the forward direction. That means it can only propogate along the axon and can't reverse