Membrane potential refers to the electric potential difference across a biological cell's membrane, created by the uneven distribution of ions such as sodium (Na+) and potassium (K+). The resting membrane potential (RMP) is typically around -70mV in neurons, maintained through the selective permeability of the membrane and the activity of the sodium-potassium pump. Key equations, including the Nernst and Goldman equations, describe the relations and calculations for diffusion potentials of these ions, which influence cellular excitability and function.

1. membrane potential

2. Membrane potential is the difference in electric
potential between the interior and the exterior of a
biological cell.
Membrane potentials are described by various
ionic concentration configurations outside and
inside the membrane of a cell.
Membrane potential is measured in millivolts.
1mv = 1/1000 volts

3. The membrane potential is due to the
sodium ions found in the extracellular
matrix and the potassium ions found in the
intracellular matrix
A cell is
“polarized”
because the
interior (ICF)
side of the
membrane
is relatively
more negative
than the
exterior (ECF).

4. Plasma membrane of all
living cells has a
membrane potential
(polarized electrically)
Due to differences in
concentration and
permeability of key ions
ie Na+ K+ and large
intracellular proteins
b/w ECF & ICF

5. These potentials are:
• Resting membrane potential
• Action potential
• Post-synaptic potentials

6. Resting Membrane
Potential

7. Resting Membrane Potential
 The potential difference across the cell
membrane when the cell is at rest.
 The relatively stable membrane potential
(inside the cell membrane) of a cell in a
quiescent (un stimulated) state.
 Constant membrane potential present in cells of
non excitable tissues and those of excitable tissues
when they are at rest

8. •inside
•outside
•Resting potential of neuron = -70mV
•+
•-
•+
•+
•+
•- •- •-
•+
•-
• There is an electrical charge across the
membrane.
• This is the membrane potential.
• The resting potential (when the cell is not
firing) is a -70mV difference between the
inside and the outside.

9. Resting Membrane Potential
 Is RMP exist in all the cells???
 Yes. Electrical potential exist across the
membranes of all the cells of the body.
 Some cells such as glandular cells, macrophages
and ciliated cells, local changes in the membrane
potentials also activate many of the cell functions.

10. Basic physics of membrane
potentials
 At rest, membrane is
1. Highly permeable to potassium
2. Slightly permeable to sodium
3. Impermeable to proteins

11. Generation and maintenance of RMP
• The unequal distribution of a few key ions b/w
the ICF and ECF and their selective movement
through the plasma membrane are responsible
for the electrical properties of the membrane
• In body electric charges are carried by ions . So
the ions primarily responsible for the generation
of resting membrane potential are Na+ , K+ ,
and A-
• The concentration difference of Na+ and K+ are
maintained by the Na+ K+ pump. Since the
plasma membrane is impermeable to proteins
so A- are inside the membrane

13. More permeability of K+ as compared to Na+ in
resting state
• The plasma membrane is more permeable to
K+ in resting state than Na+ because the
membrane has got more leak channels for K+
than for Na+
• Moreover the hydrated form of K+ is smaller
than the hydrated form of Na+

14. Role of potassium
 Potassium
membrane
concentration is higher inside the
 Potassium
membrane
concentration is lower outside the
 At rest, membrane is highly permeable to potassium
 Due to concentration gradient, potassium starts
moving from inside to outside

15. Role of potassium

16. Role of potassium
 Due to this movement, electro positivity is created
outside
 Electro negativity is created inside
 As the movement keep going,
electrical gradient
there exist an
 Due to electrical gradient, potassium starts moving
from outside to inside

17. Role of potassium
 At one point of time, there will be a potential difference
between inside and outside, called diffusion potential
 Diffusion potential blocks the net movement of
potassium to outside even though there is
concentration gradient
 In mammalian nerve fiber the diffusion potential is
94mv with negativity inside the membrane

18. Plasma membrane
ECF ICF
Concentration
gradient for K+
Electrical
gradient for K+
EK+ = –94mV

19. Role of sodium
 Sodium concentration is higher outside the membrane
 Sodium concentration is lower inside the membrane
 At rest, membrane is moderately permeable to sodium
 Dueto concentration gradient, sodium starts
moving from outside to inside
 As the movement goes on, electro negativity
is created outside
 Electro positivity is created inside

20. Role of sodium
 Due to electrical gradient, sodium starts moving
from inside to outside
 Again the membrane potential raises with in a
millisecond and blocks the net diffusion of sodium
ions to the inside
 Diffusion potential of sodium is +61mv inside the
nerve fiber

21. Plasma membrane
ECF ICF
Concentration gradient for Na+
Electrical gradient for Na+
ENa+ = +61 mV

22. Nernst equation
 Describes the relation between diffusion potential of the ion
with the ion concentration difference across the membrane
 The diffusion potential level across the membrane exactly
opposes the net diffusion of a particular ion through the
membrane is called “Nernst potential” for that ion.
 Nernst equation is used to calculate Nernst potential for any
univalent ion at the normal body temperature (37 degree
centigrade)

23. Nernst equation
 EMF= electro motive force

24. •. Therefore : for K+ ion
•EMF= ± 61 log conc. Of K+
Outside
conc. Of K+ inside
EMF = ± 61 log 4
140
= 61 log1
35
= - 61 × (-1.54) because log of 1/35 is -1.54
= - 94 mvs

25. •Similarly for Na ions
•EMF = ± 61 log conc. Outside
conc. Inside
= +61 log 150/15
= +61 × 1 (log of 10=1)
= +61 mvs

26. Table 3-3, p. 75

27. Nernst equation
 It is assumed that the potential in the ECF outside the
membrane is zero, and the Nernst potential is the
potential inside the membrane.
 The sign of the potential is positive if the ion diffusing
from inside to outside is negative ion and vice versa.

28. Goldman equation
 Used to calculate diffusion potential when the membrane is
permeable to several different ions
 When the membrane permeable to several different ions, the
diffusion potential that develops depends on three factors
1. Polarity of electrical charge of each ion
2. Permeability of membrane to each ion
3. Concentrations of respective ions inside and
outside the
membrane

29. Goldman equation

30. Goldman equation demonstrates
 Sodium, potassium and chloride ions are the most
important ions involved in the development of membrane
potentials in nerve and muscle fibers as well as in the
neuronal cells in the nervous system.
 Membrane permeability to the respective ion determines the
quantitative importance of each of the ions.
 Positive ion concentration gradient from inside the
membrane to outside causes electronegativity inside the
membrane.

31. Normal value of RMP in different cells
●Resting membrane potentials for cells generally
range: -20 mV to -200mV
●
TYPE OF CELL RMP
SKELETAL MUSCLE - 90 mvs
SMOOTH MUSCLE - 60mvs
CARDIAC MUSCLE - 85 to - 90 mvs
NERVE CELL - 70 mvs

32. Maintaining the Resting Potential by
Na+ K+ pump
● Na+ ions are actively transported (this uses
energy) to maintain the resting potential.
● The sodium-potassium pump (a membrane
protein) exchanges three Na+ ions for two K+ ions.
since more +ve ions move outside so causes
negativity of -4 mvs on inside
outside
Na+
Na+
inside
K+
K+
Na+

33. Sodium-Potassium pump

34. Contribution of sodium
potassium pump
 Provides additional contribution to RMP
 Pumps three sodium ion to outside
 Pumps two potassium ions inside
 More positive ions pumped to outside
 Loss of positive charges from inside
 Creates negativity -4mv inside

35. Impermeable anions
 Inside the cell, there are many negatively charges
ions that can not pass through the membrane.
 Anions of protein molecules and of many
organic phosphate compounds and sulfate
compounds
 Contribute to negative charge inside the cell when
there is a net deficit of positively charged ions

36. Summary
 Potassium and sodium diffusion contributes -
86mv of RMP
 Sodium-potassium pump contributes
an additional -4mv
 Net membrane potential is -90mv

37. THANK YOU