Gbcc

1. By:
Dr.Samraa Abd alwhab Khider

2. Living cell

4.  The Membrane potential:
 It is the electrical potential difference that
exist between the inside and the outside of
the cell membrane
 It is reported as the inside potential relative
to the outside

5.  The Membrane potential:
Ex:
 -90 mV membrane potential means the
inside of the membrane is 90 mV more
negative than the outside of the membrane
 +60 mV membrane potential means that the
inside of the membrane is 60 mV more
positive than the outside

6.  The origin of membrane potentials
 Diffusion potential

7. Direction of
concentration
gradient
Direction of
electrical
gradient

8. Direction of
concentration
gradient
Direction of
electrical
gradient

9.  Different types of Membrane potentials:
 Resting membrane potential
 Action potential
 Local potential
 Endplate potential .......

10.  The Resting membrane potential (RMP):
It is the constant potential difference that
exist between the inside and the outside of
the cell membrane in a resting un stimulated
cell.
-ve
-ve
-ve -ve -ve
-ve
+v
e
+v
e
+v
e
+ve +v
e +v
e

11.  All living cells have RMP
 The RMP is always negative :
in a resting cell, the inside of the membrane
is more negative than the outside
 The cell membrane is
polarized
-ve
-ve
-ve -ve -ve
-ve
+v
e
+v
e
+v
e
+ve +v
e +v
e

12.  The magnitude of the RMP differs in different
types of cells, for example:
 In a skeletal muscle cell = - 90 mv
 In a cardiac muscle cell = - 90 mv
 In a nerve cell = - 70 mv

13.  Factors that generated the negative RMP :
1. The different concentration of ions (Na+ and
K+) between the ICF and the ECF
2. Permeability of the cell membrane to K+ is more
than its permeability to Na+ during rest
3. The action of Na+/K+ ATPase pump
4. The effect of intracellular nondiffusible anions
(proteins and phosphates)

14. 1. The different concentration of ions (Na+ and
K+) in the ICF and the ECF:
 K+ is the main ICF cation and will diffuse out off
the cell following the concentration gradient
 When K+ diffuse out of the cell, the inside of the
cell loses a positive charge (become more
negative)

15. Direction of
concentration
gradient
Direction of
electrical
gradient

16.  Na+ is the main ECF cation and it can diffuse
into the cell following the concentration gradient
 When Na+ diffuses into the cell, the inside of
the membrane gains a positive charge (becomes
less negative)

17. Direction of
concentration
gradient
Direction of
electrical
gradient

18. 2. The permeability of the cell membrane to K+ is
far more than its permeability to Na+:
 All cell membranes in living cells have cation
channels that allow some diffusion of Na+ and
K+
 They are called Leak channels

19. Na+
Na+
K+
K+
-
ve
-
ve
k+
K+
Na+
K+
-ve
The resting membrane potential
Na+
Na+
-
ve
K+
-
ve

20.  The leak channels are far more permeable to
K+ than to Na+ (100 times more) that they are
called K+ leak channels or K+ channels
 Much more K+ ions can diffuse out off the cell (
making the inside negative) than Na+ ions
diffusing in (making the inside positive
 Because hydrated atom of potassium is smaller
than the hydrated atom of sodium).

21. 3. The action of Na+/K+ ATPase pump
 The function of this pump is to maintain the low
ECF K+ and low ICF Na+
 Na+, K+ ATPase pump transport 3 Na+ ions out
of the cell and 2K+ ions into the cell

22. Na+
Na+
K+
K+
-
ve
-
ve
k+
K+
Na+
K+
-ve
The resting membrane potential
Na+
Na+
ATP
ase

23.  An electrogenic pump that pumps 3 sodium ions
to outside and 2 potassium ions to inside,
 thus generating negative charges within the cell.

24. 4. The effect of nondiffusible anions (proteins and
phosphates):
 Because proteins and phosphates are negatively
charged and can not diffuse out of the
membrane
 Presence of non diffusible anions inside the cell
contributes to the genesis of RMP by increasing
the number of negative charges inside the cell
 *(Gibbs-Donnan effect)

25.  The more dominant in determining the value of
the normal RMP :
1. Permeability of the cell membrane to K+ is more
than its permeability to Na+ during rest