The document discusses membrane and action potentials, explaining how electrical potentials arise from ion concentration differences across cell membranes. It details the diffusion potential, equilibrium potential, and introduces the Nernst and Goldman equations used to calculate these potentials based on varying ion concentrations. The content focuses on the implications of these calculations for nerve and muscle cell signaling.

1. MEMBRANE POTENTIALS AND
ACTION POTENTIALS
BY
Prof. Dr. Nusrat Tariq

2. INTRODUCTION
Electrical potentials exist across the
membranes of virtually all cells of the body.
Some cells, such as nerve and muscle cells,
generate rapidly changing electrochemical
impulses at their membranes.
These impulses are used to transmit signals
along the nerve or muscle membranes.

3. BASIC PHYSICS OF
MEMBRANE POTENTIALS

4. Membrane potentials are caused
by ion concentration differences
across a selectively permeable
membrane

6. DIFFUSION POTENTIAL
A diffusion potential is the potential difference generated
across a membrane because of a concentration difference of
an ion.
• It can be generated only if the membrane is permeable to
the ion.
• The size of the diffusion potential depends on the size of
the concentration gradient.
• The sign of the diffusion potential depends on whether
the diffusing ion is positively or negatively charged.

7. EQUILIBRIUM POTENTIAL
The equilibrium potential is the diffusion
potential that exactly balances (opposes) the
tendency for diffusion caused by a
concentration difference.
At electrochemical equilibrium, the
chemical and electrical driving forces that
act on an ion are equal and opposite, and no
more net diffusion of the ion occurs.

8. Nernst equation
The Nernst equation is used to calculate the
equilibrium potential at a given concentration
difference of a permeable ion across a cell
membrane.
It tells us what potential would exactly balance the
tendency for diffusion down the concentration
gradient or at what potential would the ion be at
electrochemical equilibrium?

9. NERNST EQUATION
Used to calculate the Nernst potential for any
univalent ion at the normal body temperature
of 98.6°F (37°C).
where EMF is electromotive force and z is the
electrical charge of the ion (e.g., +1 for K+).

10. CALCULATION WITH THE NERNST
EQUATION
Sample:
If the intracellular Na+ is 15 mM and the
extracellular Na+ is 150 mM, what is the
equilibrium potential for Na+?

11. GOLDMAN-HODGKIN-KATZ
EQUATION

12. GOLDMAN-HODGKIN-KATZ
EQUATION
The Goldman Equation is used to calculate the diffusion
potential when the membrane is permeable to several
different ions.
When a membrane is permeable to several different
ions, the diffusion potential that develops depends on
three factors:
(1) the polarity of the electrical charge of each ion
(2) the permeability of the membrane (P) to each ion
(3) the concentrations (C) of the respective ions on the
inside (i) and outside (o) of the membrane.

13. GOLDMAN-HODGKIN-KATZ
EQUATION
Goldman equation gives the calculated membrane
potential on the inside of the membrane when two
univalent positive ions, sodium (Na+) and potassium
(K+), and one univalent negative ion, chloride (Cl−),
are involved.

14. GOLDMAN-HODGKIN-KATZ
EQUATION

15. TO BE
CONTINUED