GENIUS FORUMS

Steve: What'd you major in?

Milli: Psychology. But I work in I.T. Psychology has the easiest classes.

I gotta write a midterm real soon and could use some tips from someone who majored in psyche, or even from someone who knows this stuff.

Hey Mill, do you remember much about 'action potential/depolarization' in neurons? It's my first year at Uni and right now we're learning about this stuff and I just think my prof is out to lunch when it comes to understanding what she seems to have not much passion for teaching. We've recently been hit with a Quiz to prepare us for a midterm, and just the way she words her questions are kind of, well, they don't seem to jive very well with how my mind wants to approach the subject.

Maybe if you read this particular question I was hit with, you'll know whether or not her approach is wise.

Here it is:

Pottasium is added to the outside of a neuron, increasing the external concentration of pottasium. What effect will this have on the equilibrium potential of potassium?

a) the equilibrium potential will decrease in size (e.g. from -90mv to -75mv)

b) the EP will increase in size (from -90 mv to -100mv)

c) The equilibrium potential for potassium will remain unchanged

d) None of the above

----------------------------------------------------------

Is it just me, or wouldnt it make sense for a question like this to inform you what the stage is of the particular action potential that we are dealing with? If we are not informed in such a way, should we even regard the question as sensible or fair?

Just a refresher on action potential: An action potential(the firing of a neuron) has stages.

1) A Neurotransmitter is received and attatches itself to a receptor of a particular neuron, and a reaction takes place in this receptor, and this reaction opens up chemically gated channels that are built into the membrane wall of the neuron.

2) A mass of 'relatively' positively charged ions flow into the cell

3) The sudden pressence of of these positive ions........you see this is where I'm confused. I realize that there is a difference between mere depolarizaton and a full-blown action potential.

The sudden pressence of these positive ions is either going to be a weak pulse (that has no refractory period? Why?) or a full blown action potential which sends an electric pulse down the length of the axon. This electric pulse is a current that carries Neurotransmitters down the length of the axon and into the axon terminals where they eventual pass through the membrane wall and diffuse accross the synapse and get sucked up by the next neuron.

At this point, the votage of the neuron drops into a refractory period where it is unstimulatable.

It is at this stage that the neuron regains it's 'resting potential' of -70mv. (is it always approximately -70mv?)

Anyone care to take this a bit further?

Actually, Ryan you might now this maybe I should call you.

Someone, by all means, take the reigns.

uhmmm. yeah, ummmm. Hey, look at the pony!

According to Wikipedia:

“For a single-ion system only, the term reversal potential is synonymous with equilibrium potential. For example, the resting potential of most cells is close to the potassium reversal potential because at rest, potassium conductance dominates. During a stereotypical action potential, the small resting conductance mediated by potassium channels is overwhelmed by the opening of a large number of sodium channels, which brings the membrane potential close to the reversal potential of sodium.

So according to wikipedia, all three terms are synonymous: resting, reversal and equilibrium.”

So therefore the equilbrium potential or potassium should be close the to resting potential: -70MV

Here are a couple visible videos that helped me perceive the process as a whole:

http://www.blackwellpublishing.com/matt ... annel.html

http://www.maxanim.com/biochemistry/Act ... ential.htm

--------------------------------------------------------------------------------------


Her question:

Pottasium is added to the outside of a neuron, increasing the external concentration of pottasium. What effect will this have on the equilibrium potential of potassium?

a) the equilibrium potential will decrease in size (e.g. from -90mv to -75mv)

b) the EP will increase in size (from -90 mv to -100mv)

c) The equilibrium potential for potassium will remain unchanged

d) None of the above


I picked A.) because if you refer to the first video, when potassium is added to the outside of the cell membrane then the MV value always decreases if you watch the graph.

---------------------------------------------------------------------------

Your Questions:

The sudden pressence of these positive ions is either going to be a weak pulse (that has no refractory period? Why?)

It is at this stage that the neuron regains it's 'resting potential' of -70mv. (is it always approximately -70mv?) Yes, the resting potential is always -70MV, refer to the first video (graph)

If you think I am in error, which could be the case, let me know.

Potassium is added to the outside of a neuron, increasing the external concentration of potassium. What effect will this have on the equilibrium potential of potassium?

Cory,

To approach this question, I would first uncover the relationship [the principle] between potassium and equilibrium potential.

Pay close attention to the phrasing:

Potassium is added to the outside of a neuron, increasing the "external concentration of potassium." What effect will this have on the equilibrium potential of potassium?

By definition, equilibrium potential in a single-ion system (e.g. potassium) is the same as reversal potential. In this case, the reversal potential is the voltage of the neuron's membrane at which there is no net flow of ions (atoms of potassium) from one side of the membrane to the other.

Does potassium increase the voltage of a neuron? And if not, is the neuron, in this case, even pertinent?

(Source Wikipedia)

Ryan Rudolph wrote: the resting potential is always -70MV.

No, taken from my A&P book, -70 is a typical resting potential, but the ranges are from -40mV to -90mV. The negative sign indicates the degree of potential on the inside, so -90mV is of more potential than -40mV.

She's talking about the potassium equillibrium potential in the sodium pump. A main factor contributing to the resting potential is the relative permeability of Na+ and K+, where the membrane is more permeable to K+ than Na+, and why the K+ channel only goes out and the Na+ channel only goes in. K+ can eventually seep back in, which is how the tissue is "fed" and it recovers to its resting potential, but there would not be an immediate effect.

I believe the answer is C

Ryan Rudolph wrote:if you refer to the first video, when potassium is added to the outside of the cell membrane then the MV value always decreases if you watch the graph.

In the video you refer to, the bottom of the picture is the inside and the top is the outside. K+ is "added" to the outside by releasing it from the inside through the K+ channel, and it is a representation of the moment of action. Releasing the action potential by causing action is not the same as extraneously adding potassium.

Steven Coyle wrote:Does potassium increase the voltage of a neuron? And if not, is the neuron, in this case, even pertinent?

Steven, are you done editing your post yet?

Yes, potassium increases the voltage of a neuron when it is on the inside of the neuron - which does make the neuron pertinent as it is the vehicle of action potential.

Elizabeth Isabelle wrote:

Steven Coyle wrote:Does potassium increase the voltage of a neuron? And if not, is the neuron, in this case, even pertinent?

Steven, are you done editing your post yet?

Yes, potassium increases the voltage of a neuron when it is on the inside of the neuron - which does make the neuron pertinent as it is the vehicle of action potential.

But in Cory's case, the potassium ion is on the outside of the neuron...

(Yes, I'm through editing)

:)

Steven Coyle wrote:

Elizabeth Isabelle wrote:

Steven Coyle wrote:Does potassium increase the voltage of a neuron? And if not, is the neuron, in this case, even pertinent?

Steven, are you done editing your post yet?

Yes, potassium increases the voltage of a neuron when it is on the inside of the neuron - which does make the neuron pertinent as it is the vehicle of action potential.

But in Cory's case, the potassium ion is on the outside of the neuron...

In the question, it stated

Pottasium is added to the outside of a neuron,

added to - there is naturally already K+ on the inside (or the neuron would be dead). The pertinant part of the question is whether or not adding K+ to the outside makes any difference, and if so, what difference would it make? I say no immediate difference.

There could be an eventual later difference, as the amount of K+ inside the cell is somewhat dependent on how muck K+ is outside the cell over a period of time to reabsorb (and in that way it is not a really fair question as the question does not specify time frame), but what rescues the question back into "fairness" is that over time, more K+ could seep into the neuron (increasing, reather than decreasing the potential), but only to a maximum of -90mV, not -100mV as option B suggests.

Great insight.

I agree.

Elizabeth wrote,

No, taken from my A&P book, -70 is a typical resting potential, but the ranges are from -40mV to -90mV. The negative sign indicates the degree of potential on the inside, so -90mV is of more potential than -40mV.

As I understand it, a resting potential is kind of like a black hole. Any thing close to a black hole, gets pulled, depending on how close it is. You can have strong black holes (-90mv), or you can have weak black holes (-30mv) .

The neuron is the black hole. Ah, but a better analogy is a planet.

Some planets have stronger gravity depending on their size.

Small neurons have smaller resting potentials (weaker gravity)(-30mv). Bigger neurons have bigger resting potentials (stronger gravity) (-90mv).

The gravity is caused by the size of the planet. Therefore, the resting potential is caused by the size of the neuron.

The neuron is just this negative force encapsulated in a little bubble membrane, much like a planet.

Now, unlike a planet, a neuron is not just a sphere, but it is a sphere that has a trunk extending out of it like an elephant.

Here is a picture:

http://www.usm.maine.edu/psy/broida/101/neuron.JPG

The ‘trunk’ is depicted as kind of like a string of sausages. It is called ‘the axon’. Think of the axon as kind of like the barrel of a gun.

Elizabeth: She's talking about the potassium equillibrium potential in the sodium pump.

No, I don’t think that is right at all. Why do you think this?


I'd like to hear some good questions from whomever wants to understand neurons.

I want to talk with someone who is puzzled by the same things that I am.

Eliz: A main factor contributing to the resting potential is the relative permeability of Na+ and K+ where the membrane is more permeable to K+ than Na+, and why the K+ channel only goes out and the Na+ channel only goes in.

Ok, lets take a closer look at this. What is causing the neuron to be a negative sphere?

Did you know that positively charged sodium ions gather around a resting neuron, clinging to it, trying to get it? Do you know that positively charged potassium does the same?

The outside of a neuron is just dancing with positive ions trying to get into the neuron. Why do they want to get in so bad? It’s because they can’t stand each other. They are repelled by each other. They are too much alike. Positivity is repelled by positivity.

The positive wants to go where it is negative, where there is less of itself. It hates itself and its kind!

And so the positive ions outside of the neuron cling to the membrane, waiting for their chance to get in.

But still, why is the inside of the neuron a negative force? The reason why is because there are negatively charged proteins inside the neuron, and these proteins are too large to ever leave the neuron.

The membrane wall creates what we call “a separation of charge”.

It’s just like if you had a small glass sphere that was filled with salty water and you submerged the sphere in a fresh water lake. If you could measure the difference between the water in the sphere compared to the water in the lake, you might measure some sort of number to signify the difference, like 70. If you broke the glass sphere, the concentration would diffuse, and there would thus be no difference to measure. It would almost instantaneously go down to a value of 0. Differentiation would cease to exist.

It’s also helpful to consider how the water in the glass sphere is only ‘relatively’ salty.

For instance, if you dipped the glass sphere into ocean water that was more salty, then you would perhaps measure the sphere at -70. The presence of the sphere would almost be like a depression in contrast to the general concentration of the ocean. Break the sphere and the differentiation becomes wiped out almost instantaneously.

And that is what a neuron is like.

A neuron is like a globe of depression, an spherical undulation, in sea of positive charge.

If the neuron were to open up a tiny window in itself, then positive ions would leak in.

I question whether or not my prof would agree to all of this.

However, despite all I've said, I've only illustrated the most basic, fundamental, ground state of a neuron.

As for explaining how an action potential works, I havent even come close.

Does anyone want to take it from here? Or does anyone have any questions?

Nope, no questions. Now I fully understand why your professor could not explain action potential to you in a way that would "jive" with your mind.

When you get your quiz back, please us which was the correct answer.

Cory Duchesne wrote:Pottasium is added to the outside of a neuron, increasing the external concentration of pottasium. What effect will this have on the equilibrium potential of potassium?

a) the equilibrium potential will decrease in size (e.g. from -90mv to -75mv)

b) the EP will increase in size (from -90 mv to -100mv)

c) The equilibrium potential for potassium will remain unchanged

d) None of the above

----------------------------------------------------------

Is it just me, or wouldnt it make sense for a question like this to inform you what the stage is of the particular action potential that we are dealing with? If we are not informed in such a way, should we even regard the question as sensible or fair?

answers a & b did tell you what stage the action potential is in. it is at -90mV

Cory Duchesne wrote: (at the start of the thread) I gotta write a midterm real soon and could use some tips from someone who majored in psyche, or even from someone who knows this stuff.

(most recently)I want to talk with someone who is puzzled by the same things that I am.

So you no longer want to actually understand it, but want to debate it with someone equally puzzled? Hey millipodium, I think Cory's calling you again. Nice pony.

I just posted something over on the other side that connects with this [the post above] in a Totality kind of way.

We got some strange telepathic thing goin' on here :)

I just saw that and came over here - I thought you might be referencing this thread when you posted that. LOL.

It seems we also were LOLing at about the same time... spooky.

Yes, it is interesting how duality is written into nature's design at all levels of existence. And for you kid's at home you can also see duality operating in all of the other natural sciences as well.

Let me take a rough quick stab at action potential - Time is of the essence:

It seems that as the postively charged ions enter the pumps and penetrate the negatively charged neuron, it causes the immediate area inside the neuron and outside to temporary change polarity. In essence this burst of change is the action potential - it is the firing of the neuron in a small section.

This activity also causing the areas left and right to it to change polarity as well-

We could think of the action potential section as a polarized hole that creates currents that inevitably send ions to both the inside and outside of the cell and to the left and to the right sections of the action potential area. When this reaches its threshold then the action potential logically moves down to the next section of the neuron.

However the area to the left is in refractory period meaning it cannot go through another action potential because it already has gone through one - it must be a protective mechanism created by the cell to protect firing in both directions. So the area to the right changes in polarity due to the polarity change that has occured in the prior section.

It's like the domino effect only with more dimension. I know there are many unadressed questions and mysteries in there, but I dont have time to address them - other work.

Elizabeth Isabelle wrote:

Cory Duchesne wrote: (at the start of the thread) I gotta write a midterm real soon and could use some tips from someone who majored in psyche, or even from someone who knows this stuff.

(most recently)I want to talk with someone who is puzzled by the same things that I am.

So you no longer want to actually understand it, but want to debate it with someone equally puzzled? Hey millipodium, I think Cory's calling you again. Nice pony.

Look over there, there's a funny clown with balloons!

Elizabeth Isabelle wrote:It seems we also were LOLing at about the same time... spooky.

Yeah, yeah . . .

Cory wrote:

The positive wants to go where it is negative, where there is less of itself. It hates itself and its kind!

Hey, you dont have to play stupid Milli, you can relate to this one, a good metaphor for what Cory is saying here is that digesting feeling you get (Milli) when your friends pull you from your local gay bar hangout and push you into a straight bar where you must dance with women.

Ryan Rudolph wrote:Cory wrote:

The positive wants to go where it is negative, where there is less of itself. It hates itself and its kind!

Hey, you dont have to play stupid Milli, you can relate to this one, a good metaphor for what Cory is saying here is that digesting feeling you get (Milli) when your friends pull you from your local gay bar hangout and push you into a straight bar where you must dance with women.

Cory wrote:

The ‘trunk’ is depicted as kind of like a string of sausages. It is called ‘the axon’. Think of the axon as kind of like the barrel of a gun.

Trunks, sausages, guns, and a gay bar? Hey Cory, this psychology class you're taking - did they cover Freud yet?

Elizabeth Isabelle wrote:I just saw that and came over here - I thought you might be referencing this thread when you posted that. LOL.

I hadn't even read your post when I wrote it.

Totality...

Ryan Rudolph wrote:Cory wrote:

The positive wants to go where it is negative, where there is less of itself. It hates itself and its kind!

Hey, you dont have to play stupid Milli, you can relate to this one, a good metaphor for what Cory is saying here is that digesting feeling you get (Milli) when your friends pull you from your local gay bar hangout and push you into a straight bar where you must dance with women.

I never counted on being called Milli, for the record. :)