How membrane potential of a cell is reached, we discuss about nernst equation. goldman equation and pumps that are involved in the working of cell membrane. Concentration and working of ions across cell membrane

1. MEMBRANE POTENTIAL
A VOLTAGE DIFFERENCE ACROSS CELL MEMBRANE
Dr. Nitin Khajotia

2. THIS SEMINAR’S
LEARNING OBJECTIVES
• WHAT IS A MEMBRANE POTENTIAL.
• UNDERSTANDING RESTING MEMBRANE
POTENTIAL
• GIBBS DONNAN EQUILIBRIUM
• FACTORS CONTRIBUTING TO RMP
• NERNST EQUATION
• GOLDMAN EQUATION

3. WHAT IS A MEMBRANE
POTENTIAL.?
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4. WHAT IS MEMBRANE POTENTIAL..?
• An electrical potential which exist across a
semi-permeable membranes
• Virtually present across all cells of the body
• In general negative ions are accumulated
inside of the cell while positive ions are on the
outside of the membrane.

5. WHAT IS MEMBRANE POTENTIAL..?
• When a cell is at rest or not excited, this
potential is called resting membrane potential.
• Which is usually around negative 90mv.

6. MEASURING MEMBRANE POTENTIAL
• Step 1 - The pipette is impaled through the
cell membrane to the interior of the fiber

7. MEASURING MEMBRANE POTENTIAL
• Step 2 - Another electrode, called the “indifferent
electrode,” is then placed in the extracellular fluid
• Potential difference between
the inside and outside of the
fiber is measured using an
appropriate
voltmeter(OSCILLOSCOPE).

8. MEASURING MEMBRANE POTENTIAL
• As long as the electrode Is outside the nerve
membrane, the recorded potential is Zero,
which is the potential of the extracellular fluid.
• Then, As the recording electrode passes
through the voltage change area at the cell
membrane the potential decreases to
−90 Mv.

9. RESTING MEMBRANE POTENTIAL
• Difference in ion permeability and
concentration establish the resting membrane
potential.
• Ions higher outside of the cell membrane Na+,
Ca2+, Cl-
• Ions that are higher inside are K+ and Anions
Anions include – Amino acids and Proteins

10. GIBBS DONNAN EQUILIBIRIUM

11. GIBBS DONNAN EQUILIBIRIUM
• When 2 solutions containing ions are separated
by membrane, that is only permeable to some
of the ion and not all. An electrochemical
equilibrium is established.
• Electrical and chemical energies on the either
side of the membrane are equal and opposite
to each other

12. GIBBS DONNAN EQUILIBIRIUM
• This accounts for small
differences in the ionic
compositions of the
plasma vs interstitial
fluid.

13. GIBBS DONNAN EQUILIBRIUM
• As seen in the diagram, presence of
impermeable ion in a compartment can
increase the presence of permeable ion in
the same compartment.
• It causes the increase in osmotic active
particles
• Increases the osmotic pressure and water
enters the compartment.

14. DIFFERENT IONS INVOLVED IN RMP
VIA OSMOSIS VIDEOS

15. FACTORS CONTRIBUTING TO
THE RESTING MEMBRANE POTENTIAL
1. Na+ K+ Pump (ACTIVE TRANSPORT MECHANISM)
2. Potassium Leak Channels / inward rectifier
channels

17. Na+ K+ Pump
(ACTIVE TRANSPORT MECHANISM)

18. WHAT CONTRIBUTES TO RMP
1. Na+ K+ Pump (ACTIVE TRANSPORT MECHANISM)
For every ATP molecule, it exports 3 Na+ ions and imports 2 K+ ions

19. WHAT ARE THE FACTORS
CONTRIBUTING TO RMP
1. Na+ K+ Pump (ACTIVE TRANSPORT MECHANISM)
Concentration gradients for sodium and potassium across
the resting nerve membrane because of this pump.

20. Potassium Leak Channels
or inward rectifier channels

21. WHAT CONTRIBUTES TO RMP
2. Potassium Leak Channels / inward rectifier channels
As K+ leaves the cell from this channel it leaves
behind a negatively charged anion
This Makes the inside environment more negative
This attract K+ ions back into the cell
Its called Electrostatic Gradient

22. WHAT CONTRIBUTES TO RMP
2. Potassium Leak Channels / inward rectifier channels
- K+ leak channels may also leak
sodium ions slightly
- But K+ is 100 times more permeable then Na+

23. NERNST POTENTIAL
(EQUILIBRIUM POTENTIAL)

24. NERNST POTENTIAL
(EQUILIBRIUM POTENTIAL)
• The Diffusion potential level across a membrane that
exactly opposes the net diffusion of a Particular ion
through the membrane is called the Nernst Potential.
• If a membrane is permeable to only one ion
then EQUILIBRIUM POTENTIAL is equal to
RMP.

25. NERNST EQUATION
• Since there are multiple ions involved in building up of RMP. The
EQUILIBRIUM POTENTIAL for individual ion is calculated by Nernst
Equation.
• Nernst equation, can be used to calculate the nernst potential for any
univalent ion at the normal body temperature of 98.6°f (37°c)
EMF – Electromotive force
Z is the electrical charge of the ion
• While calculating we assume potential outside the membrane
remains at zero potential

26. HOW THE RMP IS REACHED
CONTRIBUTION OF THE POTASSIUM
DIFFUSION POTENTIAL
• Ratio of Potassium ions inside to outside 35 : 1
• Logarithm of 35 is 1.54
• 1.54 X 61Mv = -94Mv
• NERNST POTENTIAL OF K+ = −94 MV
• Similarly for Na+ Nernst potential is = +61 MV

27. HOW THE RMP IS REACHED
CONTRIBUTION OF THE NA+ K+ PUMP
ABOUT − 4 MV ON THE INSIDE
• BEYOND THAT WHICH CAN BE ACCOUNTED FOR BY
DIFFUSION ALONE.

28. GOLDMAN EQUATION

29. GOLDMAN EQUATION
• ALSO KNOWN AS
GOLDMAN-HODGKIN-KATZ EQUATION
• Used to calculate the diffusion potential when
the membrane is permeable to several
different ions

30. GOLDMAN EQUATION
• Using this value in the Goldman equation
gives a potential inside the Membrane of −90
millivolts

31. Thank you !!