Resting membrane potential

1. Resting membrane potential

2. Resting membrane potential (RMP) Unbalanced charges distributed across the plasma membrane that are responsible for membrane potential It is the difference in electrical potential between the inside &the outside membrane surface under resting conditions. The inside is negative relative to the outside of the membrane (polarized state). Extracellular fluid Closed Na+ channel Intracellular fluid Entire membrane at resting potential myelinated nerve& skeletal muscle is -90mV. The RMP in Medium-sized neuron is -70mV. The RMP of the cardiac muscle is -60Mv. excitable cell Portion of an

3. How to measurecell electrical potentials • RMP can be recorded when two microelectrodes ,one is placed outside the nerve fiber &the other is placed inside nerve fiber are connected to a cathode ray oscilloscope (CRO).

5. Causes of resting membrane potential The unequal distribution of ions on both sides of membrane is due to: 1-Selective permeability of the membrane for (Na+ &K+). 2- Na+ &K+ pump.

6. 1-Selective permeability of the membrane for (Na+ &K+). Outside the cell : Na+ is the main cation & Cl- is the main anion. Inside of the cell: K+. is the main cation &proteins are the main anions. The cell membrane Is semipermeable membrane. It is more permeable to K+, less permeable to Na+ ,freely permeable to Cl- & impermeable to proteins.

7. 1-Selective permeability of the membrane for (Na+ &K+) 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. 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- K+-Na+ pump which pumpsNa+ outside the cell.

8. 2- Na+ &K+ pump It is an electrogenic pump because it pumps3 Na+ outside the cell for every2 K+ inside the cell .This will add more positive charges outside the cell membrane producing the resting membrane potential. Na+ &K+ pump acts against the concentration gradient .So, it needs energy derived from hydrolysis of ATP

9. 2- Na+ &K+ pump

10. Basis and important of RMP The basis of RMP: 1- the existence of the Na+ &K+ pump. 2-The permeability of the membrane to the K + to the outside is a hundred times greater than that to the of Na+. 3-The large amount of protein anions within the cell. The cell membrane acts as a charged capacitor. At rest the outer surface carries positive charged with respect to inner surface.( polarized)

11. Action potential Action potential : Is the change in the membrane potential after application of an effective stimulus (threshold).

12. Phases of action potential 1-Stimulus artifact: A short irregular deflection of the base line at the time of stimulus application. 2-Latent period (isoelectric period) It is isoelectric period & indicates the Time taken by the current to travel from the stimulating to the recording electrode. It depend on: 1-The distance between site of application of the stimulus & the recording electrode. (direct proportional). 2-The velocity of nerve impulse. )indirect proportional).

13. Depolarization phase Depolarization phase Sudden shoots up (upstroke) from a potential -70mV to +35mV& it represents the reversal of polarity of the cell membranes .It is divided into:

14. Repolarization phase Downstroke ,the membrane potential return to the original polarity ,it is divided into: The peak value of the AP is known as Spike potential

15. component of AP Caused by Na+ influx Rpolarization is followed by After hyperpolarization: Prolonged period of mild hyperpolarization. Finally the RMP is restored. Caused by K+ efflux Rising phase Falling phase Threshold potential Resting potential

16. Ionic basis of action potential At resting potential all Na+ and K+ gated channels are closed At resting potential

17. As membrane potential decreases from -70mV,the voltage gated fast Na+ channels open partially & when it reaches -55mV Na+channels are fullyopen and the Na+ movement inside the cell The membrane potential Decreases to +35mV • As membrane potential decreases • from -70mV,the voltage gated • fast Na+ channels open partially • & when it reaches -55mV • Na+channels are fullyopen • and the Na+ movement • inside the cell • The membrane potential • Decreases to +35mV Explosive Na influx by both concentration and electrical gradient

18. Inward movement of Na+ makes the outside progressively less positive Explosive depolarization; potential reaches 0 mV Action potential begins Na influx produces Membrane depolarization until 0 mV is reached

19. Continued inward movement of Na+ reverses the potential with the inside becoming Positive and the outside becoming negative as the action potential Peaks Reversal of polarity or Overshoot K+ gate opens Na+ inactivation gate begins to close Peak of action potential; potential reversed

20. At the peak of action potential, the Na+gates close and the K+ gates open. Entry of Na+ ceases and K+ starts to leave the cell. Repolarization begins Outward movement of K+ (both by concentration and electrical gradient) makes the insideprogressively less positive and the outside less negative

21. Na+ inactivation gate opens; Na+ activation gate closes Continued outward movement of K+ (K EFFLUX) restores the resting membrane potential Action potential complete; after hyperpolarization begins Further outward movement of K+ through the still-open K+ gates transiently hyperpolarizes the membrane

22. then the K+ gates close, and the membrane returns to resting potential After hyperpolarization is complete; return to resting potential