How does electricity flow through the body?

[sameeralord]

Hello everyone,

Ok so electricty must flow through ions in the body right, I have some questions about this.
From what I researched this is my understanding of it, please correct me if I'm wrong.

When electricity passes to your body, the positive ions migrate towards the negative charged area and gains electrons while negative ions migrate towards positively charged area and releases them. Now I have some questions about that.

1.Can't the positive ions gain electrons and completely neutralize the current?
2. If the positive ions move towards the negative side and balance the charges at both ends, wouldn't that neutralize the current, why do redox reactions occur to keep a current going?
3. Electricity is movement of electrons, here the ions are moving so can we really say the electricity is conducted in the ionic solution?
4. I also like to know when a hair fryer is placed on water (obviously not for real), how does water conduct the electricity, using my logic where do the negative ions release electrons, I mean what is their to gain them?

Thank you

 

[Andy Resnick]

The currents are generally low because the resistance is high. For example, the current through renal epithelial tissue is around a micro-amp/cm^2. I don't know what the current is for an action potential, though.

As for your last question, pure water is not conductive at all- it's around 13 MOhms/cm. Dissolved *salts* increase the conductivity, because those charges are very mobile in the presence of a voltage- lots of current is generated.

 

[sameeralord]

The currents are generally low because the resistance is high. For example, the current through renal epithelial tissue is around a micro-amp/cm^2. I don't know what the current is for an action potential, though.

As for your last question, pure water is not conductive at all- it's around 13 MOhms/cm. Dissolved *salts* increase the conductivity, because those charges are very mobile in the presence of a voltage- lots of current is generated.

Thanks for the response Since electricity if flow of electrons. Do we take movement of negative ions as electricty. Also when salt water gets electricity, do the ions eventually become deionized?

 

[Borek]

pure water is not conductive at all- it's around 13 MOhms/cm.

18 MΩ/cm

 

[Borek]

1.Can't the positive ions gain electrons and completely neutralize the current?

I would love to know what you mean...

2. If the positive ions move towards the negative side and balance the charges at both ends, wouldn't that neutralize the current, why do redox reactions occur to keep a current going?

You have two reactions taking place, at two ends. In one electrons go into the body, at the other they are leaving. So you can't think about one end only.

3. Electricity is movement of electrons

No, it is transfer of charge.

4. I also like to know when a hair fryer is placed on water (obviously not for real), how does water conduct the electricity, using my logic where do the negative ions release electrons, I mean what is their to gain them?

Again, two reactions at two electrodes - one being something inside the hair drier, other something on the way to ground. In this case it is more complicated, as you are dealing with an active current, so reduction/oxidation are switched twice in each cycle.

 

[aryan_605]

Hello everyone,

Ok so electricty must flow through ions in the body right, I have some questions about this.
From what I researched this is my understanding of it, please correct me if I'm wrong.

When electricity passes to your body, the positive ions migrate towards the negative charged area and gains electrons while negative ions migrate towards positively charged area and releases them. Now I have some questions about that.

1.Can't the positive ions gain electrons and completely neutralize the current?


2. If the positive ions move towards the negative side and balance the charges at both ends, wouldn't that neutralize the current, why do redox reactions occur to keep a current going?


3. Electricity is movement of electrons, here the ions are moving so can we really say the electricity is conducted in the ionic solution?4. I also like to know when a hair fryer is placed on water (obviously not for real), how does water conduct the electricity, using my logic where do the negative ions release electrons, I mean what is their to gain them?



Thank you

1) yes they can, but what about the place where positive charges are leaving from. if positive charge leave that space, then it will essenstially make that place more negative, in other words its just a different way of thinking the traveling current.

2)
everything that happens inside the body has a purpose it just don't happens to neutralize, if everything was neutralized then your change in free-energy is 0, which means everything has reached its equilibrium. if all the reactions in the body reach equilibrium point then no reactions would beable to occur and body or cell would not exist. so in other words, the thing you are saying in 2 does occur, but you don't see it because it goes as non-existence.

for example, take cellular respiration. if all the glucose and purvate goes on equilibrium, then velocity of forward and backward reactions are the same, sooo...essentially no reaction, you wouldn't see any change. so, this is the reason for us to have enzymes. electronic nature can also reach equilibrium, but our enzyme chemically control it so it would not reach equilibrium. body use compounds to create current, which come from movement of charges.

when i say movement of charges, negative charge does not necessarly travel. you could also say that positive charged particles moved toward some direction, leaving the initial place as negatively charge...and it keeps on going...soo you have a current!3)
of course!, what is electrochemical bettery my friend!. its simply oxidation-reduction reactions ------------which is?...transfer of electrons!

4.
water is not a good conductor of electricity. salt water is!. not good conductor doesn't mean it don't conduct electricity, there is always some amount of uncertainty in everything. nothing is 100% perfect!

 

[aryan_605]

remember, the books of classical physics are still written in a way that positive charges are moving in electricity.

this is early years of electromagnetics, physicist thought positiver charges were moving instead of neg. charges. it was later understood that there are 3 parts of atom: electrons, protons, and nutrons. later found that electrons are outside, which are freely moving around in electron clouds (quantum levels).

so overall, just explaining that you could also think of electricity as moving of positive charges. just depends on you perspective of thinking.

 

[Deoxyribose]

I don't know what the current is for an action potential, though.

Well, the usual example of an action potential shows the voltage of the inner membrane moving from -70mV to ~40mV and back to -70mV in about 5ms, http://1.bp.blogspot.com/_4Oy_7FFvA...doutpsyde.com+300px-Action-potential.jpg.png".

Using the formula i= C*(dv/dt):
C= 2 µF/cm² = 2x10^-6
dv= 40mV-(-70mV)=.110V
dt= .005 sec

So if my calculations are correct (I love saying that ) i = 2x10^-6* (.110V/.005sec) = 4.4x10^-5A/cm². So about 44microamps per square centimeter. Multiply that by the area of the membrane to find the total current.

If I made a mistake anywhere please don't hesitate to correct me.

 

[Gokul43201]

As for your last question, pure water is not conductive at all- it's around 13 MOhms/cm.

18 MΩ/cm

<cough>18 MOhm*cm</cough>

 

[aryan_605]

Well, the usual example of an action potential shows the voltage of the inner membrane moving from -70mV to ~40mV and back to -70mV in about 5ms, http://1.bp.blogspot.com/_4Oy_7FFvA...doutpsyde.com+300px-Action-potential.jpg.png".

Using the formula i= C*(dv/dt):
C= 2 µF/cm² = 2x10^-6
dv= 40mV-(-70mV)=.110V
dt= .005 sec

So if my calculations are correct (I love saying that ) i = 2x10^-6* (.110V/.005sec) = 4.4x10^-5A/cm². So about 44microamps per square centimeter. Multiply that by the area of the membrane to find the total current.

If I made a mistake anywhere please don't hesitate to correct me.

good job my friend...

 

[Moonbear]

I don't have anything to add to this thread. I just had to stop into comment that I LOVE reading threads like this. When I first joined this forum many moons ago, I used to feel I had to constantly explain to physics students that biology DOES involve physics. It's nice coming in now and seeing physicists and chemists responding to a biology (physiology) question with physics and equations!

 

[somasimple]

It's nice coming in now and seeing physicists and chemists responding to a biology (physiology) question with physics and equations!

Since K⁺ gradient makes the outer cell positive how is it posible to find :
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1396124/?tool=pubmed

It is proposed that the most satisfactory way to account for the present observations is by a membrane carrying negative fixed charge of the order of 2·5 × 10³ e.s.u./cm2.

By the way the notion of membrane capacitor is subject to discussion: It is possible to prove it doesn't work/exist.

 

[alxm]

Since nobody pointed this out:
A large enough voltage can and will ionize things. This is called the 'breakdown voltage' of an insulator. A big enough voltage will pass through anything, even vacuum.

In this context, water is actually relatively easy to ionize. So while pure water is a pure conductor, it's still a very good one compared to most (if not all) oils, which are difficult to ionize. (In fact, when insulating oils become conductive in practice it's usually due to contamination with water or other things.)

So you often have a situation where the more ions you have, the more current passes, generating even more ions, lower resistance and even more current (Known as http://en.wikipedia.org/wiki/Negative_resistance" ). This is what happens when electricity arcs through a gas for instance. This is why fluorescent lights take a second to light up: They have to build up sufficient voltage to make the initial arc. Or for instance, if you move a grounded object towards a charged wire so that it starts arcing, you have to move it farther away than the initial distance to stop the arcing.

(Or if your transformer oil gets dirty, it could start arcing from the transformer to the surrounding casing, causing the oil to gasify and the arcing to increase further until the temperature and pressure build up and the thing explodes! Or would, if they didn't have safety valves to stop this from happening)

 

[Deoxyribose]

I screwed up. The http://1.bp.blogspot.com/_4Oy_7FFvA...doutpsyde.com+300px-Action-potential.jpg.png" shows the maximum voltage at roughly t=2.4msec and the initial voltage at roughly t=1.2msec, so that would make dt=.0012sec. So the average current per square centimeter during the rising phase would be closer to (5/1.2) the value I posted, so closer to 180 microamps per square centimeter. I'm surprised no one called me out on that.

 

[somasimple]

I don't have anything to add to this thread. I just had to stop into comment that I LOVE reading threads like this. When I first joined this forum many moons ago, I used to feel I had to constantly explain to physics students that biology DOES involve physics. It's nice coming in now and seeing physicists and chemists responding to a biology (physiology) question with physics and equations!

Biology says that ions are in equal quantity inside and oustide before the difusion process takes place, so :
If P stands for positive and N for negative ions, a, b are integer o=outside and i= inside.
the solutes are electroneutral =>
a(P_o+N_o)=0 and b(P_i+N_i)=0
If a membrane is semipermable to one ion, P and if the concentration is greater inside then you find a potential that is something like that:
V=k Log(P_o/P_i).
It is clearly a difference from two concentrations of the form : V= k2*(P_o-P_i)

How does biology removes the N_o and N_i terms?
In fact, how biology is able to stop the electrostatic/electric forces that come from negative charges?

 

[Borek]

N terms are not removed and they should be included. If they are not that's probably because in the cells they are not actively transported so their concentrations remain constant, and as such can be ignored to make calculations easier.

Such simplified models are used very often and they prove to be useful. Problems arise when people start to think that these simplified models are the real ones. Unfortunately, that happens quite often when scientists from different branches speak about chemistry - they have no idea laws they are using are special cases, "dumbed down" to describe some part of the reality, but not applicable outside.

My guess is that chemists are guilty as well, just in different areas.

 

[somasimple]

Borek,
I agree but how is it possible at a moment to say :
The solution is electroneutral because all charges are taken in account.
And a second after, we may forget one of the species.

If you try to make a simple drawing showing the electrochemical diffusion process, you will face to an/several impossibility.
The system will be divergent and self stopping: it doesn't work.

A model may be described from its start (IC) to the end, without any hole.

 

[Borek]

The solution is electroneutral because all charges are taken in account.
And a second after, we may forget one of the species.

We do it all the time. It is called approximation.

 

[somasimple]

A severe approximation may create a model that does not reflect the reality of facts.

 

[somasimple]

We do it all the time. It is called approximation.

How far an approximation is scientifically acceptable?
5%? 10%? 50%? Less? More?
If a solute contains k negative charges and k positive charges homogeneously distributed and all charges having the same valence,

Is it fair to say :
1/ The solute is neutral.
2/ The solute is positive by approximation.

Biology stands in the second allegation in the present case.

 

[Deoxyribose]

Has the http://upload.wikimedia.org/math/d/f/c/dfcc65e44e966776276226a7c637751e.png" been mentioned here? It considers the concentration and permeability of sodium, potassium, and chloride and is used to calculate the resting membrane potential. Granted, it neglects the presence of calcium and assumes that all neurons have the same permeability to a specific ion when the permeability is more likely a function of the number of Na/K pumps or chloride pumps, but it does give a good idea of how the resting membrane potential is generated.

If these equations produce values that conflict with experimental observation, then it means that the equations are wrong and need to be improved. Hopefully we will one day have an expression that models how neurons change receptor density in response to the magnitude and duration of ion flux over time, but that model would be quite tricky to express.

Somasimple, I'm not sure that it's simple diffusion that produces the concentration gradients seen in neural models. Concentration gradients are produced by ion channels and pumps. By converting the electrochemical energy stored in the bonds of ATP into changes in protein conformation, ion pumps move ions into or out of the cell and create a gradient. Na/K pumps, for example, move 3 sodium ions out of the cell and 2 potassium ions into the cell with each hydrolysis of ATP. Even if a cell starts in a homogeneous solution of NaCl and KCl to begin with, with every cycle of Na/K pumps more positive charge ends up outside the cell than inside. Thus, the negative membrane potential with respect to the outside of the cell.

 

[somasimple]

1/ No: The resting potential exists because there is a charge difference between the two sides.
Permeability introduces the notion that a ion becomes ineffective/neutral on one side (or two). How a ion is able to become neutral and loses its charge?
2/ No: The facilitated diffusion involves k+ and Na+ voltage gated channels in the case of action potential. Action potential is generated, almost a thousand time, even if ATP is removed. BTW, the NaK pump is not playing a major role in the resting potential.

 

[Deoxyribose]

The resting potential exists because there is a charge difference between the two sides.

And where does that charge difference come from? Na/K pumps.

Permeability introduces the notion that a ion becomes ineffective/neutral on one side (or two). How a ion is able to become neutral and loses its charge?

Do you mean that permeability causes ions to flow down their concentration gradient? Never in the neuroscience classes or books that I've been exposed to has it been stated that permeability causes an ion to become ineffective/neutral on one or both sides, unless you mean permeability causes an ion to flow down its concentration/electrical gradient. Where did you learn this?

The facilitated diffusion involves k+ and Na+ voltage gated channels in the case of action potential.

Agreed.

Action potential is generated, almost a thousand time, even if ATP is removed.

Interesting fact. However, since action potentials occur at a frequency up to 100Hz or more, this means that a cell could only propagate action potentials for about 10 seconds after ATP is removed. I'd like to see a gene-knockout experiment where neurons with ineffective Na/K pumps can still generate action potentials.

BTW, the NaK pump is not playing a major role in the resting potential.

The NaK pump establishes the high external Na⁺ concentration and high internal K⁺ concentration, which is crucial for generating the resting membrane potential.

http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=neurosci&part=A140
In summary, Hodgkin and Katz showed that the inside-negative resting potential arises because (1) the membrane of the resting neuron is more permeable to K+ than to any of the other ions present, and (2) there is more K+ inside the neuron than outside. The selective permeability to K+ is caused by K+-permeable membrane channels that are open in resting neurons, and the large K+ concentration gradient is, as noted, produced by membrane transporters that selectively accumulate K+ within neurons. Many subsequent studies have confirmed the general validity of these principles.

 

[somasimple]

And where does that charge difference come from? Na/K pumps.

http://en.wikipedia.org/wiki/Resting_potential

For most animal cells potassium ions (K+) are the most important for the resting potential[1]. Due to the active transport of potassium ions, the concentration of potassium is higher inside cells than outside. Most cells have potassium-selective ion channel proteins that remain open all the time. There will be net movement of positively-charged potassium ions through these potassium channels with a resulting accumulation of excess negative charge inside of the cell. The outward movement of positively-charged potassium ions is due to random molecular motion (diffusion) and continues until enough excess negative charge accumulates inside the cell to form a membrane potential which can balance the difference in concentration of potassium between inside and outside the cell. "Balance" means that the electrical force (potential) that results from the build-up of ionic charge, and which impedes outward diffusion, increases until it is equal in magnitude but opposite in direction to the tendency for outward diffusive movement of potassium. This balance point is an equilibrium potential as the net transmembrane flux (or current) of K+ is zero. The equilibrium potential for a given ion depends only upon the concentrations on either side of the membrane and the temperature. It can be calculated using the Nernst equation:

Where is ATP in these sentences?

 

[somasimple]

And where does that charge difference come from? Na/K pumps.

1/ And this response doesn't reply to my asking: why you do no take account of all other ionic species Ca, Mg, Cl..., Because you decide that their permeability is 0. But, in situ, how are you able to disable a single ion?
You must remember that Gauss'Law involves the sum of all species. "All" means every kind of ion.
2/ The GHK equation is derived from the Nernst equation
http://en.wikipedia.org/wiki/Nernst_equation
Where is now the "E" term? A membrane is not necessary, nor ATP.
3/Where are the redox terms? Which reaction gives an electron and which gets one?

 

[somasimple]

from this page :
http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=neurosci&part=A140

the resting membrane potential varied as predicted with the logarithm of the K+ concentration, with a slope that approached 58 mV per tenfold change in K+ concentration (Figure 2.6B).

A slope that approached 58 mV per tenfold !
What an approximation. This curve is all but linear, fortunately.
If the curve was linear as theorized, every time a cell encountered some quite pure water, it will be destructed by an intense electric field.
We are all able to drink low salt water (normal water) and nothing happens.

 

[Borek]

58 mV is just RT/F*ln(10), I guess they put it there to signal system is approaching the Nernstian behavior.

 

[somasimple]

58 mV is just RT/F*ln(10), I guess they put it there to signal system is approaching the Nernstian behavior.

the resting membrane potential varied as predicted with the logarithm of the K+ concentration, with a slope that approached 58 mV per tenfold change in K+ concentration

Maybe I'm unable to understand the red words in the sentence?
We are here speaking about an outside concentration of K+. The normal value for this concentration is 4 mmol. Problems appear when the concentration reaches the value of...5 mmol. Death is quite certain when the concentration is 50 mmol.
Here, we have a slope that is constructed with values > 200 mmol.
BTW, the cell model insists about the fact of iso-osmolarity. How is iso-osmolarity respected when you change a concentration known to act by diffusion?

see also this link and this virtual experiment and explanations.
http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=neurosci&part=A132&rendertype=figure&id=A134

 

[somasimple]

see also this link and this virtual experiment and explanations.
http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=neurosci&part=A132&rendertype=figure&id=A134

http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=neurosci&part=A132

This impediment results from the fact that the potential gradient across the membrane tends to repel the positive potassium ions that would otherwise move across the membrane. Thus, as compartment 2 becomes positive relative to compartment 1, the increasing positivity makes compartment 2 less attractive to the positively charged K+.

What process stops any action of chloride ions against these positive charges?
If negative charges (Cl^-) make a side more negative across the membrane, why positive ions from this side aren't attracted to these negative?
If positive charges (K⁺) make a side more positive across the membrane, why negative ions from this side aren't attracted to these positive?

 

[Deoxyribose]

As stated at wikipedia, ATP is needed to power ion pumps that are used to establish concentration gradients.

http://en.wikipedia.org/wiki/Resting_potential
Because the membrane permeability for potassium is much higher than that for other ions (disregarding voltage-gated channels at this stage), and because of the strong chemical gradient for potassium, potassium ions flow from the cytosol into the extracellular space carrying out positive charge, until their movement is balanced by build-up of negative charge on the inner surface of the membrane. Again, because of the high relative permeability for potassium, the resulting membrane potential is almost always close to the potassium reversal potential. But in order for this process to occur, a concentration gradient of potassium ions must first be set up. This work is done by the ion pumps/transporters and/or exchangers and generally is powered by ATP.

In the case of the resting membrane potential across an animal cell's plasma membrane, potassium (and sodium) gradients are established by the Na+/K+-ATPase (sodium-potassium pump) which transports 2 potassium ions inside and 3 sodium ions outside at the cost of 1 ATP molecule.

“Due to the active transport of potassium ions, the concentration of potassium is higher inside cells than outside.”
Where is ATP in these sentences?

It is implied that ATP is used in order to power the ion pumps that establish the concentration gradient. See quote above.

1/ And this response doesn't reply to my asking: why you do no take account of all other ionic species Ca, Mg, Cl..., Because you decide that their permeability is 0. But, in situ, how are you able to disable a single ion?

Cl is factored into the GHK equation. I honestly don't know why Ca and Mg aren't. I'm going to guess that P_Mg<<P_K, which would make the voltage contribution from Mg to be negligible. Any voltage due to Mg or other ions would be opposed by a change in flow of K⁺ through leak channels

2/ The GHK equation is derived from the Nernst equation
http://en.wikipedia.org/wiki/Nernst_equation
Where is now the "E" term? A membrane is not necessary, nor ATP.

The plasma membrane, ion channels, and ATP are all needed to establish the concentration gradients in the GHK equation. Without the membrane cells wouldn't be able to store charge inside or outside of the cell; without ion channels cells wouldn't be able to actively transport ions from one side of the membrane to the other, nor would they be able to have selective permeability for a specific ion; and without ATP the cells couldn't power the ion channels and pumps.

3/Where are the redox terms? Which reaction gives an electron and which gets one?

I wasn't aware that electrons were moving from one ion to another; I thought ions were flowing from one side of the membrane to the other.

You're on your own for the rest of your questions. You seem pretty smart, so you must be capable of researching and finding answers to your questions. My point is simply that without the plasma membrane, integral membrane proteins such as ion channels and pumps, and ATP, living cells could not establish a resting membrane potential.

 

[somasimple]

My point is simply that without the plasma membrane, integral membrane proteins such as ion channels and pumps, and ATP, living cells could not establish a resting membrane potential.

I gave this example that seems to function without any ATP !
http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=neurosci&part=A132&rendertype=figure&id=A134

 

[somasimple]

My point is simply that without the plasma membrane, integral membrane proteins such as ion channels and pumps, and ATP, living cells could not establish a resting membrane potential.

http://en.wikipedia.org/wiki/Action_potential

Ions cross the cell membrane under two influences: diffusion and electric fields. A simple example wherein two solutions - A and B - are separated by a porous barrier illustrates that diffusion will ensure that they will eventually mix into equal solutions. This mixing occurs because of the difference in their concentrations. The region with high concentration will diffuse out toward the region with low concentration. To extend the example, let solution A have 30 sodium ions and 30 chloride ions. Also, let solution B have only 20 sodium ions and 20 chloride ions. Assuming the barrier allows both types of ions to travel through it, then a steady state will be reached whereby both solutions have 25 sodium ions and 25 chloride ions. If, however, the porous barrier is selective to which ions are let through, then diffusion alone will not determine the resulting solution. Returning to the previous example, let's now construct a barrier that is permeable only to sodium ions. Since solution B has a lower concentration of both sodium and chloride, the barrier will attract both ions from solution A. However, only sodium will travel through the barrier. This will result in an accumulation of sodium in solution B. Since sodium has a positive charge, this accumulation will make solution B more positive relative to solution A. Positive sodium ions will be less likely to travel to the now-more-positive B solution. This constitutes the second factor controlling ion flow, namely electric fields. The point at which this electric field completely counteracts the force due to diffusion is called the equilibrium potential. At this point, the net flow of this specific ion (in this case sodium) is zero.

 

[Deoxyribose]

You are right in saying that when there is a concentration gradient between two solutes separated by a semi-permeable membrane, ions that are permeable to the membrane will move down their concentration gradient until the flow due to the electrical gradient equally opposes the flow due to the concentration gradient. In order for this to occur however, there must be an existing concentration gradient between the two solutes. In http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=neurosci&part=A132&rendertype=figure&id=A134" the concentration gradient is formed by pouring solutes of different concentrations into each chamber, and in the quoted paragraph the concentration gradient is formed by letting solution A have 30 Na⁺ and Cl^- ions and letting solution B have 20 Na⁺ and Cl^- ions, but in a living cell the concentration gradient is formed by ion pumps such as Na/K-ATPase moving ions against their concentration gradient.

 

[somasimple]

In fact, it doesn't matter (for me) if pumps exist or not. The only interresting thing is ions that are close to the membrane. If they are effectively at this place then pumps can't function and action potential can't occur.

 

[alxm]

Pumps do function. They're using energy, be it ATP (K/Na pumps) or some other reaction (COX).

You don't necessarily have a case where there's an equilibrium between electrical and concentration gradients, or any equilibrium at all. The inner mitrochondrial membrane, for instance, is not at equilibrium electrically or concentration-wise. (Although more so with respect to concentration because a certain amount of ion exchange occurs.)