Resting (membrane) Potential
DENT/OBHS 131Neuroscience 2009
dendritic synaptic inputstransfer to the somagenerate APsaxonal propagation
ionic basis of RMPAP initiation & propagation
Electrical signaling in neurons
Learning Objectives
1. Explain how the concentration gradient of potassium ions across the membrane gives rise to the resting membrane potential
2. Compute the equilibrium potential of an ion using the Nernst equation
3. Predict the effect of changing the concentration of an ion (or it’s relative permeability) on the membrane potential
How familiar are you with resting and active properties of membranes?1. Not at all
2. Somewhat
3. Very
4. Intimately
The major ion involved in setting the resting membrane potential is...
1. Sodium
2. Calcium
3. Chloride
4. Potassium
5. Bicarbonate
6. Hydrogen
Learning Objective #1
Explain how the concentration gradient of potassium ions across the membrane gives rise to the resting membrane potential
The membrane acts to……
separate and maintain (pumps) gradients of solutions with different concentrations of charged ions
selectively allow certain ionic species (K+) to cross the membrane…
initial conditions:different distribution of a K-saltmembrane is only permeable to Kthere is no potential difference across the membrane
at equilibrium:K ions diffuse down concentration gradientanions are left behind: net negativity develops inside the cellfurther movement of ions is opposed by the potential difference
Electrical difference….. IN vs. OUT
+- 0 mV
DS Weiss
Electrical difference….. IN vs. OUT
+-
-70 mV
0 mV
DS Weiss
Can we calculate the potential?
The Nernst equation determines the voltage at which the electrical and chemical forces for an ion (X) are balanced; there is NO net movement of ions.
Ex = ln [x]outside
[x]inside
RTzF
Learning Objective #2
Compute the equilibrium potential of an ion using the Nernst equation
if K is 10-fold higher on the inside
in excitable cells the RMP is primarily determined by K ions
Ex = ln [K]OUT
[K]IN
RTzF
= log 10100
60z =-60 mV
The Nernst potential for K+
If we lowered the [K+]OUT
10-fold to 1 mM, the RMP would…..1. Not change
2. Hyperpolarize
3. Depolarize
Ex = ln [K]OUT
[K]IN
RTzF
= log 1100
60z =-120 mV
The Nernst potential for K+
What about hyperkalemia?
Learning Objective #3
Predict the effect of changing the concentration of an ion (or it’s relative permeability) on the membrane potential
Other ions affect RMP
different ions have different distributions
cell membrane is not uniformly permeable (“leaky”) to all ions
relative permeability of an ion determines its contribution to the RMP
a small permeability to Na and Cl offsets some of the potential set up by K
in reality the cell membrane is < negative than EK
Concentrations of other ions…..
ion [X]in [X]out Eq. (mV)
K 155 4 -98
Na 12 145 +67
Cl 4.2 123 -90
relationship between: membrane potential ion equilibrium potentials
if the membrane becomes more permeable to one ion over other ions then the membrane potential will move towards the equilibrium potential for that ion (basis of AP) - DRIVING FORCE
artificial manipulation of MP - reverse direction of current flow (hence reversal or equilibrium potential)
membranepotential (mV)
EK
ENa
RMP
+67
-90-98
ECl
General rule(s)
ion flux explanation
driving force on an ion X will vary with MP = (Em - Ex)
Ohm’s law V = IR = I/g, or transformed I = gV Ix = gx (Em - Ex)
there will be no current if: no channels for ion X are open (no conductance, g)
no driving force (MP is at Ex)
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