1. Changes in electrical gradients
Electrical disequilibrium
Consequences of electrical disequilibrium
Resting membrane potential
Equilibrium potential
Membrane depolarization and hyperpolarization

2. Cell in the body are: In chemical disequilibrium
In osmotic equilibrium
In electrical disequilibrium – few extra negative ions inside cells and their matching positive ions are outside

3. Distribution of main ions
Na+
Cl-
Organic
Anions K+
Na+
Cl-
Organic anions K+
Distribution of main ions

4. 3 Na+ 2 K+ Na+ Cl- Na+ Cl- Organic anions K+ Organic Anions K+
ATPase
2 K+
Anionic proteins
are trapped
Inside the
cell
Electrical disequilibrium across the cell membrane
 membrane potential difference

5. How does electrical charge separation occur?

6. The cell membrane
Is an insulator
There are more positive charges outside and more negative charges inside

7. Na+ Cl- Na+ Cl- Organic anions K+ Organic Anions K+
Electrochemical gradient
is a combination of the electrical and chemical gradients

8. Electrochemical gradient
Electrical gradients and chemical gradients across the cell membrane
Electrical force moves K+ into the cell (cell has more neg. charges)
Chemical gradient favors K+ to leave the cell (K+ concentration is low outside)
These forces reach a steady state

9. Membrane Resting Potential
The voltage difference across the cell membrane when there is an electrochemical gradient at a steady state
There is a voltage difference between the inside and the outside (potential difference)

10. The value for the resting membrane potential

11. Membrane Potential Vm is the membrane potential (millivolts)
Resting membrane potential for nerves and muscles is -40 mV to -90 mV
The resting membrane potential is determined by K+

12. K+ channels are open during the resting membrane potential.

13. If K+ channels are open.

14. Equilibrium Potential
The membrane potential when the channels for a particular ion are open is called the equilibrium potential for that particular ion.
At EK+ the rate of ions moving in due to the electrical gradient equals the rate of ions leaving because of the concentration gradient.
EK+ is close to the resting membrane potential

15. Factors that are important for the equilibrium potential for an ion:
Only channels for that ion are open
The charge of the ion
Concentration of the ion inside the cell
Concentration of the ion outside the cell

16. At the equilibrium potential for Na+
Artificial cell, Na+ is leaving because the inside became + after the inward
Movement of Na+

17. Currents during resting membrane potential
K+ outward current is much stronger than Na+ inward current.
Lots of K+ channels are open, few Na+ channels are open at rest.

18. Currents during resting membrane potential
K+ outward current is much stronger than Na+ inward current.
Lots of K+ channels are open, few Na+ channels are open at rest.

19. The value for the resting membrane potential

20. Membrane potential changes when channels open or close.

21. Changes in membrane potential
Resting membrane is polarized
Depolarization positive charges move in membrane potential moves toward 0 mV
-70
time

22. Membrane potential changes when channels open or close.

23. Changes in membrane potential
Repolarization membrane potential returns to polarized state (+ charges leave cell)
Hyperpolarizationmembrane potential becomes more negative than at rest (extra + charges leave the cell)

24. During changes in membrane potential
Very few ions move to cause changes in membrane potential.

25. Large molecules can cross in vesicles.
Cell expends metabolic energy

26. Phagocytosis – cell engulfs a
particle into a vesicle

27. Vesicular traffic across cell membranes
Endocytosis
Pinocytosis, cell engulfs extracellular fluid
Receptor-mediated endocytosis

28. Receptor mediated endocytosis
LDL (which is a cholesterol carrier) is a ligand that enters by
receptor mediated endocytosis

29. Exocytosis Some molecules leave a cell by exocytosis
E.g. proteins leave cells by exocytosis

30. Integrated membrane activity during insulin secretion
Resting membrane potential

31. Integrated membrane activity during insulin secretion