Resting membrane potential. Large Nerve. Na -K ATPase. Guyton and Hall. Medical Physiology. Dr. Nusrat Tariq. Professor Of Physiology. M.I.M.D.C.

1. RESTING MEMBRANE POTENTIAL
BY
Prof. Dr. Nusrat Tariq
M.I.M.D.C

2. LEARNING OBJECTIVES
By the end of this lecture you should be able to:
• Describe the transport properties of the Resting
Nerve Membrane.
• Describe the Origin of Normal Resting Membrane
Potential
• Describe the factors that determine the level of
Resting Membrane Potential.

3. RESTING MEMBRANE POTENTIAL
The resting membrane potential of large nerve
fibers when they are not transmitting nerve
signals is about −90 millivolts.
The potential inside the fiber is 90 millivolts
more negative than the potential in the ECF on
the outside of the fiber.

4. ORIGIN OF THE NORMAL RESTING
MEMBRANE POTENTIAL
• Contribution of the Potassium Diffusion
Potential.
• Contribution of Sodium Diffusion Through
the Nerve Membrane.
• Contribution of the Na + -K+ Pump

7. Contribution of the Potassium And
Sodium Diffusion Potential
The resting membrane potential is established
by diffusion potentials that result from
concentration differences of permeant ions.

8. Each permeable ion attempts to drive the
membrane potential toward its equilibrium
potential.
• Ions with the highest permeabilities, or
conductances, will make the greatest
contributions to the resting membrane potential.
• those with the lowest permeabilities will make
little or no contribution.

9. EXAMPLE
The resting membrane potential of nerve is –90 mV,
which is close to the calculated K+ equilibrium
potential of –94 mV, but far from the calculated Na+
equilibrium potential of +65 mV.
At rest, the nerve membrane is far more
permeable to K+ than to Na+.

10. Contribution of the Na + -K+ Pump
Active transport of Sodium and
Potassium ions through the
membrane takes place by the sodium-
potassium (Na+-K+) Pump.

12. The Na+-K+ pump also causes large concentration
gradients for sodium and potassium across the resting
nerve
membrane. These gradients are as follows:
Na+ (outside):142mEq/L
Na+ (inside):14mEq/L
K+ (outside): 4mEq/L
K+ (inside):140mEq/L
The ratios of these two respective ions from the inside to
the outside are:
Na inside /Na outside + + = 0.1
K inside /K outside + + = 35.0

13. The Na+–K+ pump contributes only
indirectly
• The Na+–K+ pump contributes only indirectly
to the resting membrane potential by
maintaining, across the cell membrane, the
Na+ and K+ concentration gradients that then
produce diffusion potentials.
• The direct electrogenic contribution of the
pump (3 Na+ pumped out of the cell for every
2 K+ pumped into the cell) is small.