Membrane potential (also transmembrane potential or membrane voltage) is the difference in electric potential between the interior and the exterior of a biological cell. ... Almost all plasma membranes have an electrical potential across them, with the inside usually negative with respect to the outside.

1. MEMBRANE POTENTIAL

3. definition
■ It is the difference in electrical potential between the two sides
of the membrane surface under resting conditions.
■ The inside is negative relative to the outside of the membrane
(polarized state).

4. Measuring cell membrane
potential

5. Excitable Tissue
■ Nerve cell and Muscle are excitable tissue, they
produce rapid, transient changes, in their membrane
potential when stimulated
■ These changes in potential cause Electrical signals.

6. Resting membrane potential
(RMP)
■ When cells are at rest (not stimulated) – there is Resting
Membrane Potential.
■ myelinated nerve& skeletal muscle is -90 mV.
■ The RMP in Medium-sized neuron is -70 mV.
■ The RMP of the cardiac muscle is -60 Mv.

7. Causes of RMP
■ Diffusion Potential caused by an ion concentration difference on the
two sides of the membrane.
■ The Na+ - K+ PUMP transports THREE Na+ out, for TWO K+ it
transports inside the cell.
■ As both are positive ions, unequal transport causes more positive
charge outside negative charge inside.
Selective permeability for: Na +K Na-K ATP pump
Diffusion potential

8. Selective permeability
Inside of the cell:
K+. is the main cation &proteins are the main anions.
The cell membrane is :
■ It is more permeable to K+, less permeable to
Na+,freely permeable to Cl- & impermeable to
proteins.

10. Cont” selective permeability
K+ ions:
Although K+ is more concentrated inside the cell , it tends to diffuse
outside the cell according to
1-The concentration gradient
2- the high permeability of the cell membrane.
However the K+ outflux is limited by :
1-Attraction between K+ &intracellular proteins.
2-Repulsion between K+ & Na+ outside cell membrane.
3- K+ -Na+ pump which derive K+ inside the cell

11. Na+ ions:
Although Na+ is more concentrated outside the cell , it tends to diffuse
inside the cell according to:
1-The concentration gradient.
2-Electrical gradient.
However the Na+ influx is limited by :
1-the low permeability of the cell membrane to Na+ .
2.Na+ -K pump which pump Na outside the cell.
Cont” selective permeability

12. Na-K ATP pump
•Pumps 3 Na+ outside the cell for every 2 K+
•Electrogenic pump

13. Action potential
A short-term change in the electrical potential on
the surface of a cell (e.g. a nerve cell or muscle
cell) in response to stimulation, and spread
rapidly along the nerve fiber membrane.

15. The
Nobel
Prize
in
Physiology
or
Medicine
(1963)
“for their discoveries concerning the
ionic mechanisms involved in excitation
and inhibition in the peripheral and
central portions of the nerve cell
membrane”
Alan Lloyd Hodgkin Andrew Fielding
Huxley

16. Basic Electrophysiological Terms
o Stimulus: a sudden change of the (internal or external)
environmental condition of the cell.
o includes physical and chemical stimulus.
o Threshold (intensity): the lowest or minimal intensity of
stimulus to elicit an action potential

17. Basic Electrophysiological Terms :
 Polarization: a state in which membrane is polarized at
rest, negative inside and positive outside.
 Depolarization: the membrane potential becomes less
negative than the resting potential (close to zero).
 Hyperpolarization: the membrane potential is more
negative than the resting level.
 Repolarization: restoration of normal polarization state of
membrane.

19. Phases of action potential
1.resting stage
2 depolarization stage
3.repolarization stage

20. Resting stage
■ The membrane is polarized.
■ all Na+ and K+ gated channels are closed.

21. depolarization stage
Depolarization phase
the voltage gated fast Na+ channels open partially & when it reaches -
55mV :Na+ channels are fully open and the Na+ moves inside the cell.

22. Activation gate
Inactivation gate

23. "for their discoveries concerning
the function of single ion channels
in cells"
The
Nobel
Prize
in
Physiology
or
Medicine
(1991)
Erwin Neher Bert Sakmann

24. Repolarization stage
■ Repolarization
■ hyperpolarization

25. Properties of the Action Potential
 “All or none” phenomenon
A threshold or suprathreshold stimulus applied to a single nerve fiber
always initiate the same action potential with constant amplitude,
time course and propagation velocity.
 Propagation
 Transmitted in both direction in a
nerve fiber

26. Inhibition of action potential
Local anesthetics:
■ Proacaine and Tetracaine.
■ Work on gate of Na channels: difficult to open.

27. Refractory periods
1. relative
2. Absolute.

29. Slide 3 of 28

30. Thank You