This is about the membrane action potential.it involves the stages of action potential. there are also resting membrane potential. this ppt is for zoology 6 semester course code Z0L- 504 GCUF.

1. Membrane potential

2. 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).

3. Measuring cell membrane potential

4. Resting membrane potential (RMP)
• 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.

5. Causes of RMP
Selective permeability for:Na+K Na-K ATP pump
Diffusion potential

6. 1. 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.

8. 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

9. 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

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

11. 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.

13. 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

14. 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.

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

17. 1.resting stage
• The membrane is polarized.
• all Na+ and K+ gated channels are closed.

18. 2 .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.

19. Activation gate
Inactivation gate

20. 3.Repolarization stage
• Repolarization
• hyperpolarizati
on

21. 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

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

23. Refractory periods
1. relative
2. Absolute
.

25. Slide 3 of 28