Electrical Signals in Neurons Flashcards
Voltage
Difference in electrical potential between 2 points
Voltage requires 2 _____ separated by a _____, such as a ____ in a neuron.
Compartments
Barrier
Membrane
Voltage will occur only if there are ____ ____ on at least 1 side of the barrier.
Charged molecules
If there is an equal charge on both sides, the net charge will be ____.
0
Permeability
Ability of molecules to move from one side to another
In the absence of permeability, is it possible to have voltage?
Yes
Current
Flow of electrical charge from one side to another
Net movement of ion
Is permeability required for current? If so, how many ions?
Yes
One or more
If the barrier is equally permeable to all ions, there will be current until when?
Ion concentrations and/or charge are equal on both sides of barrier
Molecules move along a chemical gradient from ___ to ___ concentration.
High
Low
Charged molecules move toward the ___ charge.
Opposite
Electrical gradient
Difference in total charge between one side and the other
Driving force is also called what?
Electrochemical gradient
How is driving force calculated?
DF= CG (chemical gradient) + EG (electrical gradient)
Conductance
How well an ion can pass through a membrane
What does driving force measure?
How much an ion wants to pass through the membrane
How is current calculated?
I (current) = DF x g (conductance)
What are 2 conditions in which current is 0?
g=0: no permeability
DF=0: ion doesn’t want to move
Is direction of chemical gradient determined as a sum or individually for each ion?
Individually for each ion
Is electrical gradient determined as a sum or individually for each ion? Direction an ion moves?
Electrical gradient is determined by sum of all charges on each side of the barrier
Direction ion moves depends on its charge relative to the electrical gradient
In most neurons, which is more negative, the outside or the inside? Difference in charge between inside and outside means that the neuron is ___.
Inside is more negative than the outside
Neuron is polarized
Membrane potential (Vm)
Charge inside vs outside
Resting membrane potential is recorded when?
When neuron is not firing
Most neurons have a resting membrane potential of ___ to ___ mV.
-40 to -80 mV
A stimulus causes the ____ _____ of the neuron to open. What is happening to the membrane?
Ion channels
Membrane becomes permeable/conductive to ion
Flow of ions in neuronal response causes change in ___ ___.
Membrane potential (Vm)
How much current will flow during a neuronal response depends on what 3 factors?
Concentration gradient of ion
Voltage across membrane
Whether or not membrane is permeable
Can you have voltage without current? Current without voltage?
Yes
No
Receptor potential: when is it created, how much depolarization?
Activation of sensory receptor neuron
Causes a small amount of depolarization
Synaptic potential: when is it created, how much depolarization
Single neuron synapses
Causes a medium amount of depolarization
Action potential: when is it created, how much depolarization?
Signal sent down axon to another neuron
Causes the biggest amount of depolarization
When potential is measured on a graph, what is the x axis measuring? Y axis?
X axis: time in ms
Y axis: membrane potential in mV
Equilibrium potential
Membrane potential at which there is no net movement of the ion
Ions move only if there is ____ ____.
Driving force
If concentration gradient is equal and opposite to electrical gradient, then DF=__ and there will be no ___ ___ of ___, even if there is ____.
0
Net movement of ions
Permeability
Equilibrium potential of an ion occurs at a ____ or ___ ___ at which concentration gradient and electrical gradient for the ion are ____ and _____.
Voltage or membrane potential
Equal and opposite
How can driving force be calculated using membrane potential and equilibrium potential?
DF= Vm (membrane potential) - Ex (equilibrium potential)
If an ion is at equilibrium, what is the value for its current? Why?
0 (ions are no longer moving)
If an ion is at equilibrium, what is its driving force? Why?
0 (concentration gradient and electrical gradient are equal and opposite, so ion doesn’t want to move)
When ions move, the direction and magnitude of the current are always determined by what 2 factors?
Driving force
Conductance/permeability
How can current be calculated from conductance, membrane potential, and equilibrium potential?
I = g x DF
Since DF = Vm-Ex, I = g x (Vm-Ex)
To get current, the barrier must be ____ ____. Why is this?
Selectively permeable
If the barrier is completely permeable, the situation goes to equilibrium
At equilibrium, is there current? Is the potential stable or fluctuating?
No net current
Potential remains stable (at rest)
In a situation where an ion can pass through a barrier permeable to it, when does it stop moving?
When its electrical gradient is equal and opposite to its concentration gradient
The Nernst equation calculates what?
Ion equilibrium potential
What is the formula for the Nernst equation?
Ex= [(RT)/(zF)]*log([X0]/[Xi]) Ex= equilibrium potential in mV R= gas constant T= absolute temperature in K F= Faraday constant z= valence of ion, including sign [X0]= concentration of ion X outside [Xi]= concentration of ion X inside
RT/F in the Nernst equation equals what?
58 mV
At what temperature is RT/F in the Nernst equation measured?
19 degrees C
LogX = Y can be written what other way?
10^Y = X
At an equilibrium potential of 0, what is the magnitude of inside vs outside concentration relative to each other?
Inside and outside concentration are the same
At equal concentrations of an ion, what is the membrane potential for that ion?
0
The membrane potential is basically equal to the ___ ___.
Electrical gradient
The membrane potential at which equilibrium is reached is the same as the ___ ___.
Equilibrium potential
What does the “ten fold” rule for the Nernst equation state?
At 19 degrees C, every 10 fold change in ion concentration causes a change in equilibrium potential of 58/z
For a positively charged ion, increasing the ratio of outside to inside ion concentration does what to the equilibrium potential? Decreasing the ratio of outside to inside ion concentration?
Increases equilibrium potential
Decreases equilibrium potential
Does the “ten fold” rule apply to membrane potential?
No- applies only to equilibrium potential in Nernst equation
When a battery is inserted into a situation with ions and a selectively permeable barrier, how will its voltage affect the movement of the ions?
The voltage from the battery will drive the ions to move to the appropriate concentration gradient that is equal and opposite the imposed electrical gradient
For a positively charged ion, movement from outside the cell to inside the cell is called what?
Inward current
For a positively charged ion, movement from inside the cell to outside the cell is called what?
Outward current
An inward current will always ____ the membrane potential and an outward current will always ____ the membrane potential.
Increase
Decrease
The ion always moves to bring ____ potential toward ___ potential.
Membrane
Equilibrium
The equilibrium potential for an ion is also called the ____ ____ for the ion. Why?
Reversal potential
The direction of the ion’s current switches at the equilibrium potential
Assuming permeability, what will happen to membrane potential as ion concentration changes?
Membrane potential will change
As membrane potential changes, what will happen to ions?
Driving force on ions will change
If permeability is present, current will change
When the equilibrium potential equals the membrane potential, what is the magnitude of driving force and current?
Both driving force and current are 0
When equilibrium potential is greater than membrane potential, what kind of current results?
Inward current (ion moves to increase membrane potential)
When equilibrium potential is less than membrane potential, what kind of current results?
Outward current (ion moves to decrease membrane potential)
For a negative ion, inward current means moving from ___ to ___ the cell.
Inside to outside (bringing membrane potential up)
For a negative ion, outward current means moving from ___ to ___ the cell.
Outside to inside (bringing membrane potential down)
In biology, will plotting current vs membrane potential give you a linear graph? Why or why not?
No- linear graph assumes constant permeability, and permeability is determined by channels, which are gated and voltage-dependent, so they are not always open
In a single neuron with a voltage-gated ion channel, conductance can be approximated as __ when the channel is closed and ___ when the channel is open.
0
1
In a biological system, conductance of a value between 0 and 1 comes from what?
Multiple voltage-gated ion channels: some are open and some are closed
Plotting driving force on a graph will give you what kind of plot?
Linear
For a driving force of 1 and a driving force of -1, they both have the same ____ but different ____.
Magnitude
Directions
What are the 4 abundant ions in mammalian neurons for which channels exist?
Na+
K+
Ca+2
Cl-
Which of the 4 ions typically has a larger concentration inside the neuron than outside?
K+
Which ion doesn’t contribute much to the overall membrane potential, but has a large driving force due to its large concentration gradient?
Ca+2
At rest, the neuronal membrane is primarily permeable to what ion due to what channels?
K+
K+ leak channels
The resting membrane potential of the neuron is closest to the equilibrium potential of what ion? Why? What is that value?
K+
Because the membrane is primarily permeable to K+
Approximately -60 mV
Goldman equation
Vm = (RT)/F * log (PK [K0] + PNa [Na0] + PCl [Cli])/(PK [Ki] + PNa [Nai] + PCl [Cl0]) Vm = membrane potential RT/F = 58 mV P= permeability for an ion
In the Goldman equation, why is inside concentration of Cl over outside concentration of Cl?
There is no sign for valence, so o/i for negative ions like Cl are flipped
In the Goldman equation, which ion will have the highest permeability at rest?
K+
In the Goldman equation, the greater the permeability, the ___ the effect an ion will have on membrane potential
Greater
The Nernst equation predicts how ___ potential changes with ion concentration
Equilibrium
Driving force makes ions “want” to move until ____ equals ____.
Membrane potential
Equilibrium potential
When estimating how an ion’s concentration will affect membrane potential, use the ____ equation.
Goldman
Under normal biological conditions, will opening a specific ion’s channel move the membrane potential past its equilibrium potential? Why or why not?
No- ion moves to bring membrane potential toward equilibrium potential, so ion will reach equilibrium at equilibrium potential and won’t move past that voltage
What is a main difference in how equilibrium potential and membrane potential are determined?
Equilibrium potential is determined for a single ion, but membrane potential is determined through the summation of ions
The direction an ion moves depends on the relationship between what 2 factors?
Membrane potential and equilibrium potential
In a cell, changing permeability is caused by what?
Opening or closing ion channels
