2. Learning objectives
Describe the Nernst potential.
List the elements of the Goldman equation for
multiple ion movements.
Explain the contribution of different ion
movements to the development of the resting
membrane potential.
3. Resting Membrane Potential
The potential difference across the cell
membrane when the cell is at rest.
The relatively stable membrane potential
(inside the cell membrane) of a cell in a
quiescent (un stimulated) state.
5. Resting Membrane Potential
Is RMP exist in all the cells???
Yes. Electrical potential exist across the
membranes of all the cells of the body.
Some cells such as glandular cells, macrophages
and ciliated cells, local changes in the membrane
potentials also activate many of the cell functions.
6. Basic physics of membrane
potentials
At rest, membrane is
1. Highly permeable to potassium
2. Slightly permeable to sodium
3. Impermeable to proteins
7. Role of potassium
Potassium
membrane
concentration is higher inside the
Potassium
membrane
concentration is lower outside the
At rest, membrane is highly permeable to potassium
Due to concentration gradient, potassium starts
moving from inside to outside
9. Role of potassium
Due to this movement, electro positivity is created
outside
Electro negativity is created inside
As the movement keep going,
electrical gradient
there exist an
10. Role of sodium
Sodium concentration is higher outside the membrane
Sodium concentration is lower inside the membrane
At rest, membrane is moderately permeable to sodium
Due to concentration gradient, sodium starts moving from
outside to inside
As the movement goes on, electro negativity is created
outside
Electro positivity is created inside
12. Nernst equation
EMF= electro motive force
Z= electrical charge
It is assumed that the potential in the ECF outside the
membrane is zero, and the Nernst potential is the
potential inside the membrane.
The sign of the potential is positive if the ion diffusing
from inside to outside is negative ion and vice versa.
13. Goldman equation
Used to calculate diffusion potential when the membrane is
permeable to several different ions
When the membrane permeable to several different ions, the
diffusion potential that develops depends on three factors
1. Polarity of electrical charge of each ion
2. Permeability of membrane to each ion
3. Concentrations of respective ions inside and outside the
membrane
16. RMP of neurons
The resting membrane potential of large nerve
fiber when they are not transmitting nerve
signals is -90mv.
Potential inside is 90mv more negative than the
potential in the ECF on the outside of fiber.
17. Sodium-Potassium pump
Present in all the cell membranes of the body.
Electrogenic pump
Pumps three sodium
potassium ions inside
ions outside and two
More positive ions are pumped outside
Develops negative potential inside
membrane
the resting
19. Origin of normal RMP
Contribution of potassium diffusion potential
Contribution of sodium diffusion through the
nerve membrane
Contribution of sodium potassium pump
21. Who contributes more??
Membrane is highly permeable to potassium at rest
Membrane is slightly permeable to sodium at rest
In the nerve fiber, permeability of the membrane for
potassium is 100 times more than sodium
It is logical that the diffusion of potassium contributes far
more to the membrane potential than does the diffusion of
sodium
22. Contribution of sodium
potassium pump
Provides additional contribution to RMP
Pumps three sodium ion to outside
Pumps two potassium ions inside
More positive ions pumped to outside
Loss of positive charges from inside
Creates negativity -4mv inside
23. Impermeable anions
Inside the cell, there are many negatively charges
ions that can not pass through the membrane.
Anions of protein molecules and of many organic
phosphate compounds and sulfate compounds
Contribute to negative charge inside the cell when
there is a net deficit of positively charged ions
24. Summary
Potassium and sodium diffusion contributes -
86mv of RMP
Sodium-potassium pump contributes an
additional -4mv
Net membrane potential is -90mv
