1. Resting (membrane) Potential
DENT/OBHS 131 Neuroscience
2009

2. Electrical signaling in neurons
dendritic synaptic inputs
transfer to the soma
generate APs
axonal propagation
ionic basis of RMP
AP initiation & propagation

3. Learning Objectives
Explain how the concentration gradient of potassium ions across the membrane gives rise to the resting membrane potential
Compute the equilibrium potential of an ion using the Nernst equation
Predict the effect of changing the concentration of an ion (or it’s relative permeability) on the membrane potential

4. How familiar are you with resting and active properties of membranes?
Not at all
Somewhat
Very
Intimately

5. The major ion involved in setting the resting membrane potential is...
Sodium
Calcium
Chloride
Potassium
Bicarbonate
Hydrogen 10

6. Learning Objective #1
Explain how the concentration gradient of potassium ions across the membrane gives rise to the resting membrane potential

7. The RMP

8. 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…

9. initial conditions: at equilibrium: different distribution of a K-salt
membrane is only permeable to K
there is no potential difference across the membrane
at equilibrium:
K ions diffuse down concentration gradient
anions are left behind: net negativity develops inside the cell
further movement of ions is opposed by the potential difference

10. Electrical difference….. IN vs. OUT+ -
0 mV
DS Weiss

11. Electrical difference….. IN vs. OUT+ -
0 mV
-70 mV
DS Weiss

12. Can we calculate the potential?
Ex = ln
[x]outside
[x]inside RT zF
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.

13. Learning Objective #2
Compute the equilibrium potential of an ion using the Nernst equation

14. The Nernst potential for K+
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 RT zF
= log 10
100 60 z =
-60 mV

15. If we lowered the [K+]OUT 10-fold to 1 mM, the RMP would…..
Not change
Hyperpolarize
Depolarize 10

16. The Nernst potential for K+
What about hyperkalemia?
Ex = ln
[K]OUT
[K]IN RT zF
= log 1
100 60 z =
-120 mV

17. Learning Objective #3
Predict the effect of changing the concentration of an ion (or it’s relative permeability) on the membrane potential

18. 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

19. Concentrations of other ions…..
[X]in
[X]out
Eq. (mV) K
155 4
-98 Na 12
145
+67 Cl
4.2
123
-90

20. General rule(s) relationship between:
membrane
potential (mV) EK
ENa
RMP
+67
-90
-98
ECl
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)

21. 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)