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Bioelectricity is central key to nervous system's function.
1737 (in Bologna, Italy) - 1798 - Luigi Galvani, physician and philosopher.
Back then, we can be physician, physicist, and philosopher at once.
1771 - Galvani discovered that muscles of dead frogs twitched as it's struck by electric sparks when his assistant (maybe his wife; Lucia Galvani) touched its nerve with a metal scalpel that picked a static charge.
He thought he found the key to life, inherent electricity in animals leading to movement and posited the existence of animal electric fluid for the effect.
Luigi Galvani with the frog leg.
the voltaic pile
Physicist and Galvani's contemporary - Alessandro Volta, repeated his experiments, but doubted existence of such fluid intrinsic to animals.
Spurred by his theories, Volta made the "voltaic pile", the 1st electric battery, proving that akin to electricity is made outside of a creature. Like other past figures, he died depressed and impoverished due to cruel political fate. But his name lives on. Volta coined the term galvanism for electrical phenomena in creatures and his name is used as roots of modern terms like galvanic and galvanometer.
Overall, their discoveries led to electrochemistry and bioelectricity studies. His notion of intrinsic animal electricity wasn't 100% right.
contemporary: fellow, peer (or modern)
intrinsic: belonging to the essential nature
spurred: motivated (or make it happen faster)
notion: belief, idea
Alessandro Volta
Voltage
Voltage
Electrical potential = amount of electric energy per unit charge in an electric field
Current = rate of charge flow of a conductor (measured in amperes (A))
Voltage = 2 points' electrical potential difference (how much to move a unit charge).
Understand electrical potential by comparing it to other potentials in physics.
E.g. a ball's gravitational potential at a hill's top tells its energy released if it starts rolling down and that it rolls down not up. Its potential is made by gravitational force of the ball and the earth.
Akin, electrical potential helps show strength and direction of forces led to electrical charge flow, based on charged objects' electrostatic forces.
Electrostatic force shows charged particles' interactions.
Opposite charges (+ and –) attract each other and (- and - or + and +) same charges repel.
If there's difference in charge between 2 points,
A is more positive than B, an ion with potential to move towards depending on its charge.
Left: potential made by A and B cause a positive ion to move to B (more negative charge).
Negative ion moves to A (more positive charge. Voltage tells potential difference's strength , measured in volts (V).
In neuroscience,
Points = locations of a cell's in and outside, separated by an impermeable membrane to charged particles.
impermeable: stops fluid to pass
Ions cannot flow across the membrane without channels or pumps.
Some ions move through membrane channels and form a charge difference between the 2 compartments, making potential (or voltage) across the membrane and its impermeability maintain voltage, like the charge of an electric circuit capacitor.
compartment: section, part
By convention, neuroscientists use a cell's outside as the ‘ground’ (reference point) to measure a membrane's voltage.
by convention: general agreement
E.g. if a cell's inside = 50 mV more negative compared to outside, its voltage = –50 mV.
Resting potential introduction
Resting potential introduction
Resting potential = when neurons don't send/receive signals.
Neurons send signals by electricity due to being electrical charged.
Specifically, their lipid membrane separates solutions of charged particles (K+ and Na+ ions), which creates a potential energy difference across the membrane.
Many different neurons types, all have same basic electrical principles.
Cell body/soma contains nucleus and cellular machinery.
Axons: Long, slender projections transmitting electric impulses away.
Dendrites: Branch-like things receiving neurons' signals other.
Cell membrane = outer surface of these is made up of lipid molecules bilayer that partition its inside from outside.
partition: division
Even at rest, a cell isn't electrically neutral (Em).
Membrane potential = electric potential difference across its membrane between living neuron's in and outside measured by voltage.
E.g. A battery makes electical potential/voltage, between its positive and negative terminals, which cause electron to flow through wires if there are hooked across the terminals.
Use this flow of electrons work, like lighting a light bulb.
By measuring potential difference between a neuron at rest's in and outside, voltage = roughly -70 millivolts (mV).
Saying that a voltage at a circuit's point is a certain amount millivolts, first define what point is the "zero".
A cell's voltage is measured with respect to extracellular "ground" from earlier.
extracellular: outside/occurrs outside a cell
By reference, double-A batteries have electrical potentials of 1.5 volts, so a cell's resting potential at -70 millivolts = about 20x smaller in magnitude.
So neurons have small, unimportant voltage at its cell membrane.
As double-A batteries make voltage, electrochemical reactions release electrons on its positive and negative side.
Unlike batteries use chemical reactions to make voltage by make and consume electrons, neurons' resting membrane potential is kept by membrane's ions movements.
Cells' in and outside is made of water with proteins, ions, and sugars, with charged ions and molecules floating nearby (magnesium, bicarbonate, phosphate, sulfate, etc).
Membrane potential = a membrane's voltage at all point in time; a neuron's membrane potential vary widely, e.g. -90 mV to +60 mV
Resting potential = a neuron's membrane potential "at rest" - it isn't sending/receiving signals, often roughly -60 mV to -70 mV
Diffusion and electrostatics
Diffusion and electrostatics
Neurons' in and outside, ions (K+, Na+), etc are in aqueous forms.
aqueous: made of/containing water
Many forces guide them to move around: 2 key forces: diffusive and electrostatic forces—drive their movements across the neuron's membrane, directly influencing its membrane potential.
Both forces crucial to understand resting potential.
Diffusion's dye (colored substance) movements are caused by thermal motion/due to heat.
E.g. jiggling, bumping into each other, random walks, across biology and life.
In aggregate, diffusion causes particles to move high to low concentration.
aggregate: collection, mass, cluster, lump
Electrostatic force's particles have charges associated: positive or negative, serving as electricity basis.
The 2 different force attract and repel each other.
Question 1
Question 1
At rest, in a neuron is said as more negative than outside (resting potential ~ -75 mV).
Given a K+ ion (potassium) and only on electrostatic forces, except:
K+ ions move from inside to outside.
K+ ions move from outside to inside.
Answer:
2. K+ ions move from neuron's out to inside.
Explanation: A neuron's inside is more negative, so K+ (a positive ion), is attracted to its inside and moves inside.
Note that diffusion and electrostatic forces oppose each other based on concentration gradients.
concentration gradients: measure of how something's concentration changes
Potentials and equilibrium
Potentials and equilibrium
Ion movement in membrane channels is guided by diffusive and electrostatic forces and changes membrane potential.
The voltmeter has a ground electrode outside the cell and another in the neuron's intracellular side, measuring the voltage difference between the 2 points.
Suppose a cell has negative ions with a potential difference of 60 millivolts across its membrane.
Measuring outside the cell, the membrane potential of often -60 millivolts.
At rest, most human body cells have negative membrane potentials roughly -5 to -100 millivolts.
In neurons, the resting potential is often -40 to -90 millivolts.
See the neuron's intracellular part and extracellular.
intracellular: is/occuring in cells
A membrane's each side is almost electroneutral - there's roughly no electric charge, as in the bulk solution for all positive charge, there's a negative charge to balance it out.
Note: For clarity, from here, positive and negative charges won't be shown, but it's still there.
for clarity: quality of being easily understood
But the membrane potential is from tiny imbalance increasing near a membrane, making an electric field across the membrane, resulting in electrical potential.
This arrangement is like a capacitor (center of image).
The membrane shown is a lipid bilayer without openings, so ions can't pass.
There are a whole host of positively and negatively charged species in solution on both sides of the membrane.
Now, for an equal concentration of potassium on both sides. If the voltage across this impermeable membrane is measured, what will be shown on a volt meter?
Think what happens when there's imbalance of ion concentrations. Focus on the ion potassium.
There's still an impermeable membrane - but the relative potassium concentrations changes.
Question 1
Question 1
Potassium's concentration ions = 5 mM outside and 100 mM inside, but the membrane is impermeable to potassium ions. Keep the intracellular and extracellular fluids electroneutral by making sure that there's an appropriate number of matching negative ions (‘A-’) on membrane's both sides.
If we measure Em in this new situation, it will be?:
0 mV.
positive.
negative.
Answer:
1# 0mV
Since the membrane is impermeable to potassium and there’s no ions movement, the membrane potential (Em) is 0 mV.
There's no potential difference made as the membrane doesn't let potassium ions contribute to potential difference.
What happens if a channel like potassium (in purple) is added to the membrane, on the left.
Channels = passages where ions go
Think what happens to potassium ions now that potassium channel is added.
Question 3
Question 3
If we there's 100 millimolar K+ (potassium) in the cell and 5 millimolar K+ outside, which direction will K+ ions flow after the potassium channel is added?:
It moves out of the cell
It won't move
It moves into the cell
Answer:
1# It moves out of the cell
Explanation:
K+ ions are more concentrated in the cell, so they flow from its inside to outside down their concentration gradient.
concentration gradient or solutes: process of particles going through solution or gas from area of higher to area of lower number of particles
millimolar (mM): measurement unit of amount of substance in liquid
Question 4
Question 4
Now, one may may have know that positive ions migration creates an electric field.
As K+ ions move across a membrane, out of a cell, what will the membrane potential become?
0 mV
A positive voltage
A negative voltage
Answer:
2# A negative voltage
Explanation:
As K+ ions move out, this build negative charge in the cell and positive charge outside of the cell.
By taking away positive ions inside, left with excess of negative ones.
But, early electro neutral solution outside gained positive charges via potassium.
Excess of positive charge = inside is more negative than outside.
Since the convention is to defined the extracellular voltage as the zero reference point, membrane potential is negative.
But the excess charge just float around in the bulk solution,.
Laws of physics says that these extra charges move to the membrane.
Question 5
Question 5
With current info, what happens to intracellular and extracellular K+ concentrations at equilibrium?
[K+]in = [K+]out (concentrations are equal)
[K+]in < [K+]out (most K+ ions leave cell)
[K+]in > [K+]out (most K+ ions stay in cell)
Answer:
3# [K+]in > [K+]out (most of the K+ ions stay inside the cell)
Explanation:
As K+ ions exit, it leaves excess of negative charges near the cell's membrane, causing electrostatic force pulling K+ ions back into the cell, causing more K+ ions to stay in once an equilibrium is reached.
equilibrium: state of rest or where opposing forces are balanced
A small amount diffuses through, but concentration is still greater inside, as it's charged ions.
If there are just uncharged particles flowing through, they'd diffuse to the same concentration on membrane's both sides.
This doesn't happen to potassium as there's additional electrostatic force.
As more potassium moves down concentration gradient from in to outside, the additional net positive charge creates an electrostatic force repelling additional positive charges from diffusing out.
But all forces aren't equal.
What 1 in 100,000 ions looks actually like:
The circled particle is surrounded by a sea of particles.
Moving just 1 in 100,000 ions across a membrane is enough to create a negative 80 millivolt membrane potential.
Biology constantly involves with very such small and big numbers.
Real cells and neurons have trillions of ions. So even moving one in 100,000 ions moves millions of ions outside to create this equilibrium. To understand this is by electrostatic force for moving just a tiny fraction of charged particles to the membrane's other side can balance out huge numbers of particles' diffusion, showing how much stronger electrostatic force is compared to diffusion, meaning that regardless ions do move across the membrane to make membrane potentials, so few ions need to move that the concentrations in and outside are effectively unchanged.
Only a tiny ion proportions move relative to the total number of ions in and outside a cell.
Ions moving across the membrane can basically be ignored when it's about the intracellular and extracellular concentrations.
Question 6
Question 6
What would happen to the K+ ions when more negative ions are added extracellularly?
Less K+ flows out
More K+ flows out
No K+ flows
2# More K+ flows out
Explanation:
Given more negative charge outside the membrane, more positive K+ ions will be attracted to flow to the outside of the cell.
Question 7
Question 7
Consider a neuron in which Cl- concentration in a cell = 15 mM and outside = 140 mM.
Once ions flow and reach equilibrium, what will be the Cl- concentration in it roughly (a number)?
Answer: 15
Explanation:
It only takes the movement of a few ions to reach equilibrium.
So the concentrations is about the same in and outside the neuron.
Can you see now how this concentration gradient is kind of like a little engine that drives the electrical potential? How many ions on both sides doesn't matter, it's the relative concentration gradient that indicates the equilibrium potential.
This relationship can be formalized via the Nernst equation, to calculate potential across a membrane given the concentrations of a particular ion in and outside a cell. Previously, with a membrane that was only permeable to potassium, the cell's equilibrium membrane potential is calculated based on potassium's concentration in and outside the cell. But neurons have many ions contributing to the resting potential, so the membrane potential of an actual cell can't be found just by looking at potassium.
Click here ↑
Question 1
Question 1
Consider again a K+ ion, with higher concentration inside. By diffusion, it moves from in a neuron to outside down its concentration gradient.
How doethis affect membrane potential?
The membrane potential becomes more positive.
The membrane potential becomes more negative.
2. The membrane potential will become more negative.
Explanation
If K+ ions moves from inside to the cell's outside, then its inside becomes more negative (since positive charges leave), so does the potential.
Question 2
Question 2
The previous question shows that K+ ions move out of the cell down their concentration gradient, the membrane potential changes in a certain way.
For this potential change (previous question), this then causes... (diffusive forces or electrostatic forces?) to move K+ ions... (into or out of?) the cell.
Answer:
For this potential change (previous question), this then causes... electrostatic forces to move K+ ions... into the cell.
Question 3
Question 3
From past 2 questions, see that diffusive and electrostatic forces acting on K+ ions oppose each other.
At some point, diffusive and electrostatic forces balance out, and at this point the neuron will have a certain potential (voltage), called the:
Equilibrium Potential
Membrane Potential
Steady Potential
Answer: Equilibrium potential
Explanation:
Again, K+ ions first move out of cell down concentration gradient, but start to be pulled back into the cell as its inside becomes more negative. For one ion (here K+), the 2 forces balance out at equilibrium potential.
E.g. under normal conditions for a neuron, equilibrium potential of K+ = about -90mV.
Nernst Potential
Nernst Potential
Nernst Potential calculates the membrane potential when diffusion and electrostatic forces for an ion balance out, given particular concentrations in and outside a cell.
It helps summarize ion's behavior at times, a lipid bilayer membrane, and some ion selective leakage channels.
By measuring a neuron's resting potential, it's for the electrical gradient or difference in potential energy between in and outside a cell.
Electrical gradient forms across a membrane due to ions leakage down their concentration gradient.
Fluid in and outside a cell are basically net electro neutral and few ions like potassium moving across a membrane cause big changes in a membrane's potential.
Equilibrium is reached by concentration gradient and electrical gradient are equal and opposite.
Membrane potential is also calculated if ion concentrations and its few properties are known.
With 1 ion type, Nernst equation can also calculate electrical potential (Nernst potential) at which electrical force precisely balances the ion's concentration gradient. At this equilibrium, there's no net movement of the ion across the membrane.
The equilibrium potential tells at what membrane potential electrical forces and diffusion balance each other out.
'E' (on left) = dependent variable solved for, referred by many names in neuroscience courses.
Either means:
Nernst potential
Eeversal potential
Equilibrium potential
When solving Nernst equation for given ion and its concentration in and outside a cell, it's for when electrostatic force exactly balances out the diffusional force.
Solving the equation leads Nernst potential = balancing point, which is always calculated for one ion species and often denoted by a subscript to indicate which ion we refer.
The potential is reached when system is at equilibrium, so it's sometime known as equilibrium potential.
Reversal potential = when net flux ions change direction, often refer to reversal potentials when it's about ion channels.
Membrane potential = more general term refers to electric potential measured across a membrane.
Resting potential = measured membrane potential for a cell at rest that's not actively sending a signal.
For a neuron, the resting potential is close to the Nernst potential of potassium.
But it's key to know that the 2 are different.
The resting potential is made of flow of multiple ions, and work of active ion pumps.
While for the Nernst potential is just the passive equilibrium for a single ion. We'll talk more about this difference in greater detail later. But it's important for now to know your way around the terminology.
Nernst potential = universal gas constant times the absolute temperature measured in degrees Kelvin divided by valence of ion times Faraday's constant all multiplied by natural logarithm of concentration of ion outside the cell or concentration of ions inside.
Now, the universal gas constant and Faraday's constant
are numbers you may have encountered if you've taken chemistry or physics.
For our purposes today, you don't need to know anything about them
beyond the fact that you need to plug them in the right place.
Let's go through some questions to learn how this equation works.
Take temperature.
Most warm blooded mammals, such as ourselves,
have a body temperature of around 37 degrees Celsius.
Question 1
Question 1
What happens to Eion if 37˚C is down to 4˚C?
Eion decreases by 90%.
Eion decreases by 10%.
Eion will not change.
Answer: 2# Eion decreases by 10%.
Explanation:
The Nernst potential is directly proportional to temperature, so the Nernst potential decreases with temperature decrease.
proportional:
But recall, that temperature is measured in Kelvin, as to why the change is only 10%, since temperature is changed from 310 Kelvin to 277 Kelvin.
A neuron's potential doesn't change much over normal temperature ranges means that we don't have significant change in measurements on a neuron when in experiments at room temperature, instead of in an organism. Likewise, resting potential in neurons doesn't change much, even in a high fever. A neuron's potential is also inversely proportional to valence of z ion.
Here, valence can be thought of as the net charge of the ion and solution. For instance, both sodium and potassium are plus one. Chloride is minus one, and calcium is plus two. If the neuron's potential for sodium is around positive 60 millivolts, and I told you that chloride has about the same ion concentrations inside and outside as sodium, what would the neuron's potential for chloride be?
Question 2
Question 2
Since ENa = +60 mV, if Cl- has about same concentrations in and outside the cell as Na+, what's ECl?
+60 mV
-60 mV
0 mV
Cannot be determined
Answer: 2# - 60 mv
Explanation: Since Na+ and Cl- concentrations are about close in and outside a neuron, here, there's enough info to find ECl. Only difference is that Cl- has a valence of z = -1 (instead of 'z' of Na+ = +1), so ECl = - 60 mV.
Irl true chloride concentrations in and outside a neuron are a bit different from sodium. Chloride actually has a Nernst potential close to the resting potential (~ -70 mV).
Think about how Nernst potential depends on an ion's concentrations in and outside a cell.
Use true values to calculate Nernst potential below for potassium concentrations. It shows concentrations of K+ in and outside a cell and a voltmeter shows current Nernst potential for K+.
Now an experiment: in the interactive, analyze how changing concentrations of an ion (K+), affect its Nernst potential, or try to find at least 2 ways to create a Nernst potential of -50 mV for different sets of K+ concentrations in and outside the cell.
it's the relative concentration between in and outside that matters, not absolute values, which falls out of the equation, as this is the ratio of the out to inside concentration, which takes out all dependence on absolute concentration. E.g. in a squid's neurons has extracellular potassium concentration of 20 millimolar and an intracellular concentration of 400 millimolar, 4x higher than a human.
In sodium, it's 12 millimolar inside concentration and for 440 outside, 3x higher than human neurons.
This difference may be linked to how that squids are always bathed in ocean salty water.
But if these values are pluged of the squid into the Nernst equation, the Nernst potentials of potassium and sodium are very similar of a human neuron despite big difference in environment, as the ratio of in to outside concentration is what matters.
Left table shows the physiologic concentrations of many ions and their respective Nernst potentials at 37 Celsius. See calcium has a tiny extracellular concentration of 2, millimolar but a big Nernst potential. It's only the intracellular to extracellular ion ratio that matters. Calcium is for big variety of signaling pathways in a cell, and thus, it's exquisitely regulated, as to why intracellular concentration is low, driving large extracellular intracellular ratio regardless there isn't much calcium outside, creating a big Nernst potential.
What do the numbers exactly mean?
What does it mean to have high Nernst potential in cell function?
Driving force = measure of how hard given ion is pushed across a membrane = difference between overall membrane potential at a certain moment and the Nernst potential for a particular ion of interest.
How hard iron is getting pushed is directly proportional to how far the current membrane potential is from Nernst equilibrium for the ion.
Ions always tend to wanting to approach Nernst potentials alone.
E.g. Compare calcium to potassium for a neuron at rest. A resting neuron has membrane potential of ~ -70 millivolts. Calcium has high positive Nernst potential (~ +120 millivolts), potassium has a Nernst potential of -80 millivolts.
Thus, calcium's driving force = ~ -200 millivolts and potassium = ~10 millivolts, so calcium wants to move down concentration gradient and enter the cell to reach equilibrium, which at rest is different from membrane potential. Thus, calcium ions rush in if there's an opening that they can enter in membrane.
Positive calcium ions try to make cell more positive inside to bring membrane potential closer to +120 millivolts. Calcium is used for many signaling cascades in true neurons.
High driving force ensure signals are sent robustly.
Via driving force concept, each ion are gauged by how far each it's from its Nernst potential and which direction it flows to move membrane potential closer to Nernst potential. For each ion's sole behavior their direction across the membrane is crucial as it's more realistic, same for the way by which neurons communicate among.
Nernst potential isn't fully useful to depict real neurons. True neurons have many ions moving across membrane both actively and passively - many contribute to membrane potential.
If a 2nd cation is added, sodium, like in nature, set it up that there's sodium high concentration outside the cell and low concentration inside. Intracellular and extracellular fluid is still net electro neutral due to the negative charges and there's more potassium inside than outside like earlier.
Question 3
Question 3
Assume both Na+ and K+ ions have channels and current membrane potential = -70 mV.
How will the each ions flow?
No ions flow
Na+ flows into the cell while K+ flows out
Only K+ flows into the cell
Only K+ flows out
Question
Question
Which below affects K+ Nernst potential?
Concentrations of K+ in and outside cell.
Concentrations of other ions (lke Na+) in and outside cell.
The temperature.
The GHK Equation
The GHK Equation
As said earlier, impermeability = ability to stop fluid from passing, so permeability = ease to let fluid pass
High permeability maybe caused by greater channel numbers like a door with a friendly bouncer in the Fleet Week metaphor.
GHK equation, named after scientists who derived it: David Goldman, Alan Hodgkin, and Bernard Katz, helps calculate realistic membrane potential by putting permeability's coefficients in front of major ions contributing to resting potential to weight relative effects.
Crucial subtle difference between Nernst and GHK equations:
Nernst describes equilibrium where net and ions flux are equal
GHK equation depicts a steady state, not equilibrium condition.
Why permeability matter:
As Nernst equation only indicates one ion's equilibrium state, resting potential is formed by many ions contributions.
So calculate a whole cell's resting potential is just to sum up contributions by each ion's Nernst potential.
Not all ions are equally permeable in a membrane.
E.g. Sodium has positive Nernst potential, so it has strong inward driving force.
Regardless, it can't to rush across the membrane, as resting membrane has only few open sodium channels.
So, sodium has low permeability at rest.
Potassium has greater freedom to diffuse across a membrane at rest, so it has higher permeability at rest.
Greater permeability of membrane 2 potassium ions = potassium has higher influence on membrane potential.
So the resting potential is closer to potassium's Nernst potential than to sodium's.
Restricted movement across a membrane to one ion (like potassium) by making its permeability and chloride equal zero, the GHK equation becomes the Nernst equation.
left to right
Ion filters
Ion filters
If we put a positive charge in a pore, we could rely on electrostatic repulsion to keep the positive charges out.
Both potassium and sodium are positively charged they need to be sort them based on sizes, but they're very
tiny. Its ionic radius of sodium = 116 picometers - tenth of one billionth of a meter.
1/20 x 1,000,000,000 meters
A potassium ion = 152 picometers
if we have a positively charged ion diffusing around in water, it doesn't travel alone. You see, the water, H2O, while net neutral, has a polarity to it. The oxygen bit tends to be more negative, and the hydrogens tend to be a bit more positive.
If there's a cation in solution, water molecules are happiest when pointing negative ends to the cation and positive ends away.
The result is a sort of shell of water molecules surrounding the cation. We call this shell a solvation shell. Everything at a molecular level is about driving towards the lowest energy configuration, and the solvation shell for a particular cation is in its lowest energy configuration at a very particular spacing where the interactions between the negative ends of the oxygen and the cation and the interference and electrostatic interactions between the water molecules just balance out.
In solution, the water molecules are free to situate themselves wherever, so these solvation shells just form, and that's that. But nature has arrived at a very clever trick for leveraging this phenomenon to build selective ion channels. You see, the channel, which is made of protein, has a special mechanism in front of its pore called a selectivity filter. This molecular machine exists to do one thing-- simulate the spacing of the solvation shell in a fixed configuration for its ion of interest. So the protein includes carefully placed amino acids in its structure that reproduce a spacing and charge of the naturally occurring solvation shell.
Question 1
Question 1
Selective potassium leakage channel keeps out sodium on basis of difference between potassium and sodium's ...?
Charges
Driving forces
Sizes
3# Sizes
Explanation:
Different ionic radii cause K+ and Na+ ions to interact differently with residues in the leakage channel.
Question 2
Question 2
True or False: Bromide ions (Br-) are similar in size to K+ ions. So, Br- ions can flow through K+ leak channels.
True
False
3# False
Explanation:
Though the sizes are similar, the charges are different. Carboxyl groups in the K+ leak channel has negative dipole facing in the channel. This negative charge repels Br- ions.
Sodium/Potassium Pump
Sodium/Potassium Pump
Selective ions are crucial as they selectively allow ions to flow down their concentration gradients.
These are the most basic of the ion channels. We call them leakage channels because they passively allow certain ions to pass through.
Real neurons have lots of passive potassium selective channels and fewer passive sodium and chloride channels. Because the potassium permeability is much higher than other channels, potassium dominates the resting potential. But any ion that can pass through the membrane, even a little bit, will contribute to the overall membrane.
Earlier, it's shown that having a significant permeability to sodium would cause the resting potential to unravel. Because in that scenario, both potassium and sodium can travel down their concentration gradients without ever developing an electrical gradient. This is like having a separate door that lets the Americans get into the inside room. The sailors mix and the gender imbalance never gets out of hand.
K+ ions enter easily, but hard Na+ ions but not impossible. An Na+ ion may move enter once in a while, keep the balance and move down the electrical gradiant. Eventually Na+ ions will enter and everything is in equilibrium.
But in nature, a solution to maintain this is sodium, potassium pump which moves 3 sodium ions out, each 2 potassium ions it pumps into a cell, by using ATP, a key energy carrying molecule in biology to drive its function and maintain electrical gradient in neurons. Transport of sodium out of a cell and potassium into it is so crucial to neuronal function it consumes 70% of required ATP for all brain function.
In perspective, about 1/3 of all we eat per day goes to power this.
Question 1
Question 1
A mutation is identified that disrupts the function of the Na+/K+ pump. What do you expect will happen to a neuron that possesses this mutation? (Select all that apply.)
Only K+ ion concentrations will be affected
Only Na+ ion concentrations will be affected
Both Na+ and K+ ion concentrations will be affected
correct
The resting potential of the neuron will change
correct
The neuron will no longer be able to function properly
Answer
1# Both Na+ and K+ ion concentrations will be affected
correct
2# The resting potential of the neuron will change
correct
3# The neuron will no longer be able to function properly
correct
Explanation
With the Na+/K+ pump not working properly, the concentrations of Na+ and K+ ions inside and outside of the neuron will begin to change. These changes can alter the resting potential of the neuron and disrupt a neuron’s electrical signalling.
Conclusion
Conclusion
So far the main goal is to understand how resting potential is done.
Neurons' defining feature is that they use electrical signalling, communicate, and allow nervous system to function. Neurons themselves have voltage in their membranes, a difference in electrical potential measured from inside with respect to outside.
These differences are result of ions movements. Neurons sit in a solution with particular concentrations of some ions, and these ions have particular concentrations in neurons themselves.
2 separate forces guide the ions' movements across a membrane: diffusion and electrostatic force.
Ions move through channels in membrane. Depending on proteins in neuronal membrane, different ions can pass through membrane easily or not, callde permeabilities.
Equations help calculate a membrane's electrical potential.
For one ion's movement, Nernst equation helps determine equilibrium potential in which diffusion and electrostatic force are balanced, and GHK equation is used to calculate resting potential when many ions are involved. The maintenance of the resting potential is very important for neurons - there are pumps such as the sodium/potassium ATPase consuming vast energy to keep ions at certain concentrations, ensuring that neurons can function.
Van de Graam generators
Van de Graam generators
"Van de Graaff" generator named after Robert Jemison Van de Graaff = mechanical charge pump ⦁ 1st done in 600 BC a Greek named Thales of Miletus. ⦁ Word "electricity" comes from Greek word for amber elektron ⦁ As when Thales rubbed amber with fur, he found a force between the 2 ⦁ Instead of an amber, you can use a plastic hoop with equal positive charge inside of all atoma nd negative charge outside. Both charge make electric force and each makes it opposite way. Often charges are equal amount. But when we put different material in contact, if the fur touches the hoop, the fur becomes positive charged and plastic negative charged. ⦁ Charges are invisible and silent ⦁ Unlike this, a Van de Graff generator uses a motor ⦁ Instead of accelerating atoms, you can accelerate cereals. ⦁ If one holds some cereals in their hand and the other hand touches the generator's sphere, the cereals is repelled away by the light charge once the generator is opened, demonstrating that like charges repel. ⦁ If another person's knuckle touches that person, there's invisible charge that will shock them So breakdown voltage in air at atmospheric pressure for very small gaps is about 30,000 volts per centimeter. And at that electric field strength, electrons acquire enough kinetic energy in between the space between molecules, the mean free path, that they obtain an ionizing potential amount of kinetic energy so that when they collide with a neutral atom, they liberate more electrons that then are accelerated to cause more ionization to cause more ionization and make an avalanche. And so for small gaps, when we achieve this, then it's enough to break the air down and make a spark. If the gap between the hand and the generator, the sparking accelerates, creating visible small lightnings
Human brain
Human brain
The skull has 3 layers of meninges that protect the brain from traumatic injury. A brain has a tought layer on top protects from trauma, made of 3 layers is the dura mater, means "tough mother".
Brain often consist of cerebrum, cerebellum, and brain stem.
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