physiology of Membrane potentials & Resting Membrane Potential (RMP). Nernst Equation. Goldman Equation. Definitions of Excitation, action Potential, Stimulus; Types of Channels involved in Various Excitable Tissues

1. Membrane Potentials and RMP (Resting Membrane Potential)
Prof. Dr. Rashid Mahmood

2. © Dr. Rashid Mahmood 2
Membrane potentials
and
Resting Membrane
Potential
Preamble:
Video of
Potassium
channel
Prof. Dr. Rashid Mahmood
Courtesy: prof. Dr. Ihtesham-Ul-Haq

3. © Dr. Rashid Mahmood 3

4. Objectives
♦Goal /Aim
By the end of this session students should be able to
understand the Physiology of Membrane potentials and
Resting Membrane Potential
Student should be able to
 Define the electrochemical potential difference (Δμ)
 Use the Nernst equation to determine whether an ion is in
equilibrium across a membrane.
 Compute the equilibrium transmembrane electrical potential
difference across a membrane that is permeable to only one
ionic species.
 Estimate a cell’s resting membrane potential by the Nernst
equation & Goldman equation
© Dr. Rashid Mahmood
4

5. Lesson contents
• Membrane potentials
• DEFINITIONS
Excitation
Action Potential
Stimulus
 Excitable Tissues
• Types of Channels involved in Various Excitable Tissues
• Basic Physics of Membrane Potentials
• Nernst potential
• Distribution of Ions across the membrane
• Goldman Equation
• Resting Membrane Potential (RMP)
• Origin of RMP © Dr. Rashid Mahmood 5

6. © Dr. Rashid Mahmood 6
DEFINITIONS
• Excitation:
• the process of eliciting the Action Potential (Rapid changes in the
membrane potential that spread rapidly along cell membrane of
excitable tissues)
• Stimulus:
• Anything that excites
“Any Change in the environment”
TYPES: a. Electrical
b. Mechanical &
c. Chemical

7. © Dr. Rashid Mahmood 7
DEFINITIONS
•Excitable Tissues:
•Any tissue that can be excited.
•Any tissue that is capable of generating rapidly
changing electrochemical impulses at their
membranes (Action Potential)
• These include
• Nerve &
• Muscle

8. © Dr. Rashid Mahmood 8
Types of Channels involved in Various Excitable
Tissues
Na+
• Voltage gated channels (fast)
K+
• Slow Ca++- Na+ Channels
• Ligand Gated Channels
• Na+ - K+ Pump
• Na+ Leak Channels
• K+ Leak Channels

9. Assessment Q.1
• What is meant by Action Potential?
© Dr. Rashid Mahmood 9

10. © Dr. Rashid Mahmood 10
Basic
Physics of
Membrane
Potentials
Electrical potentials exist across
the membranes of virtually all
cells of the body

11. © Dr. Rashid Mahmood 11
Basic Physics of Membrane Potentials
• Membrane Potentials Caused by Diffusion
• "Diffusion Potential" Caused by an Ion Concentration
Difference on the Two Sides of the Membrane
• Nernst Potential:
• Relation of the Diffusion Potential to the Concentration
Difference

12. © Dr. Rashid Mahmood 12
Nernst potential
• Definition: The diffusion potential level across a
membrane that exactly opposes the net diffusion
of a particular ion through the membrane is
called the Nernst potential for that ion
• Magnitude of Nernst potential:
• determined by
• ratio of the concentrations of that specific ion on the two sides
of the membrane.
• Directly proportional

13. © Dr. Rashid Mahmood 13
Distribution of Ions across the membrane
• Na+ mainly extracellular---
142 mEq/L (ICF: 14 mEq/L)
• K+ mainly intracellular-----
140 mEq/L (ECF: 4 mEq/L)
• Cl- mainly extra cellular–
103 mEq/L(ICF: 4 mEq/L)
• Non-diffusible intracellular anions.
-- HPO4 –
-- SO4--
• ---Intracellular proteins
• (4 times as in the plasma)

14. © Dr. Rashid Mahmood 14
Nernst Potential
• EMF=± 61log
Z
• EMF is electromotive force
• at normal body temperature of 98.6°F (37°C):
• Z= valency
• +ve for –ve ion
• Conc. Inside= Ci
• Conc. Outside= Co
Conc. inside
Conc. outside

15. Contribution of K+ Diffusion Channel
© Dr. Rashid Mahmood
15-94 mV
-94 mV

16. Assessment Q.2
• Calculate Nernst Potential for Potassium ions.
(Log of 35=1.544)
© Dr. Rashid Mahmood 16

17. © Dr. Rashid Mahmood 17
Calculation of Nernst Potential for K+
• EMF=± 61log
• Conc. Inside= Ci=
140 mEq/L
• Conc. Outside= Co=
4 mEq/L
• EMF= -61 log (140/4)
• EMF= -61 log (35)
• EMF= -61 (1.544)
• EMF= -94 mv
Conc. inside
Conc. outside
Log of 35=
1.544

18. Contribution of Na+ Diffusion Channel
© Dr. Rashid Mahmood 18
+61 mV
+61 mV

19. © Dr. Rashid Mahmood 19
Calculation of Nernst Potential for Na+
• EMF=± 61log
• Conc. Inside= Ci= 14 mEq/L
• Conc. Outside= Co= 142 mEq/L
• EMF= -61 log (14/ 142)
• EMF= -61 log (0.0986)
• EMF= -61 (-1.00616031)
• EMF= 61.366 mv
Conc. inside
Conc. outside
Log of 0.0986=
-1.006

20. © Dr. Rashid Mahmood 20
Diffusion Potential of Na+ and K+
• POTASSIUM :94
millivolts, with negativity
inside the fiber
membrane.
• SODIUM: 61 millivolts
positive inside the fiber.

21. © Dr. Rashid Mahmood 21
Goldman Equation
(Goldman-Hodgkin-Katz equation)
• EMF=-61log
• P= Permeability (depends Lipid solubility, Mol. weight, &
Thickness of membrane)
• More than one ion
• Potential in ECF outside cell membrane= zero
(CNa+i PNa+) + (CK+iPk+) + (CCl-o PCl-)
(CNa+o PNa+) + (CK+oPk+) + (CCl-i PCl-)

22. Assessment Q.3
• Calculate Nernst Potential for Sodium ions.
© Dr. Rashid Mahmood 22

23. © Dr. Rashid Mahmood 23

24. Resting Membrane Potential
(RMP)
Definition:
The resting membrane potential is the electrical potential
difference across the plasma membrane of a normal living cell in its
unstimulated state.
In most cells RMP is close to Nernst
Potential for K+

25. 25
Channels involved in origin of RMP
© Dr. Rashid Mahmood

26. Potassium leak channel
© Dr. Rashid Mahmood 26

27. 27
Contribution to RMP
• Contributed by
1. K+ Diffusion Potential = -94 mv
2. Na+ Diffusion Potential = +61mv
3. Na+ K+ Pump = -4mv
Net RMP?
Large nerve fibers= -90 mv
© Dr. Rashid Mahmood

28. 28
Origin
of RMP
Contribution by
K+ Diffusion Potential
Contribution by
Na+ K+ Pump
-4 mv
Contribution by
Na+ and K+
Diffusion Potential
(Goldman Equation)
Contribution by
Na+ Diffusion Potential
Net RMP
© Dr. Rashid Mahmood

29. 29
Types of Disturbances across the Cell Membrane
• TWO Types:
• Non-Propagated Potentials:
• Synaptic
• Generator
• Propagated
• Action Potential
Next Lecture: Action Potential© Dr. Rashid Mahmood

30. Summary (Take Home Points)
• Electrical potentials exist across the membranes of virtually all cells of the body
• The diffusion potential level across a membrane that exactly opposes the net
diffusion of a particular ion through the membrane is called the Nernst potential
for that ion
• Diffusion Potential of POTASSIUM is -94 millivolts, and of SODIUM is +61
millivolts
• Goldman Equation is used to calculate diffusion potential if more than one ions
are taken into consideration
• Resting Membrane Potential (RMP) is defined as the electrical potential
difference across the plasma membrane of a normal living cell in its unstimulated
state.
• In case of large myelinated nerve fibers Contribution to RMP by K+ Diffusion
Potential is -94 mv, by Na+ Diffusion Potential is +61mv; and Na+ K+ Pump© Dr. Rashid Mahmood 30

31. Assessment Q.4
• In case of large myelinated nerve fibers how much is the
Contribution to RMP by
1. K+ Diffusion Potential
2.Na+ Diffusion Potential, and
3.Na+ K+ Pump
© Dr. Rashid Mahmood 31

32. Learning Resources
• Guyton and Hall (Text book of physiology), 13th
Edition
• Ganong (Text book of physiology), 25th Edition
• Berne & Levy Principles of Physiology (Koeppen BM),
6th Edition
• Human Physiology Stuart Ira Fox, 13th Edition
• Human Physiology : from cells to system Lauralee
Sherwood,9th Edition
• Internet
© Dr. Rashid Mahmood 32

33. Next topic
• Action potential & its propagation
• Prior knowledge required for next lecture
• Membrane potentials and Resting Membrane Potential
• Types of Channels involved in Various Excitable Tissues
© Dr. Rashid Mahmood 33

34. Word derivatives
commonly used
in Physiology
© Dr. Rashid Mahmood 34
Human
Physiology : from
cells to system
Lauralee
Sherwood, 9th
Edition

35. The End
Questions ?
Comments ?
drrashid62@gmail.com
rashid.mahmood@rmi.edu.pk
ppt also available at
https://www.slideshare.net
© Prof. Dr. Rashid Mahmood

36. Thank You
© Dr. Rashid Mahmood 36