MEMBRANE POTENTIAL
PLASMA MEMBRANE
Plasma membrane of neurons is filled with channels
that allow specific ions to cross.
1. Passive or leakage channels –
usually open and allow specific ions to pass
(i.e., K+)
2. Gated channels
 only open when appropriate signal
received.
Chemically (ligand) gated channels –
only open when the appropriate chemical
or neurotransmitter present.
Voltage gated channels
only open when the membrane voltage
is at an appropriate level.
TYPES OF ION CHANNELS
4
4
140
 The concentration difference of ions
across a selectively permeable
membrane can , under appropriate
conditions cause a creation of a
membrane potential
NERNST EQUATION

MEMBRANE POTENTIAL TO BE
CALCULATED FOR A PARTICULAR ION.
– Membrane potential that would exactly balance the
diffusion gradient and prevent the net movement of a
particular ion.
– Value depends on the ratio of [ion] on the 2 sides of
the membrane.

 The potential level across the membrane
that prevents the net diffusion of an ion in
either direction through the membrane is
called “NERNST POTENTIAL FOR THAT
ION”
EMF(millivolts) = ± 61log Conc inside/Conc outside
Equilibrium potential for K+ = - 94 mV.
Equilibrium potential for Na+ = + 61 mV.
Goldman-Hodgkin-Katz
equation
0 mV
-90 mV
+
+ + +
- - -
+
+
-
+
-90 mV
+
 Potential difference exists across every cell’s plasma
membrane.
– cytoplasm side is negative pole, and extracellular fluid
side is positive pole
 Inside of cell negatively charged because:
– large, negatively charged molecules are more abundant inside the
cell
– sodium potassium pump
– voltage-gated ion channels
THE RESTING MEMBRANE POTENTIAL
• If we measure voltage between the inside of a
neuron and the outside we find that the neuron
is more negative inside than outside with a
potential of about –90 mV.
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Resting membrane potential:
AT REST
The differences in electrical
charges between
the inside of the cell and the
outside cell
How Do Neurons Operate?
• Neuron at Rest  Resting Potential
Occurs when the neuron is at rest.
A condition where the outside of the membrane is
positively(+) charged compared to the inside which is
negatively(-) charged.
Neuron is said to be polarized.
Neuron has a voltage difference of -90 mV
Active transport of sodium and
potassium ions through the membrane
outside)- 142 mEq/L
Na+( inside)14 mEq/L
Na+(
K+ ( outside)- 4 mEq/L
K+( inside)- 140mEq/L
• Na+ ions are actively transported (this uses
energy) to maintain the resting potential.
NOTE: Na+/K+ pump = PumpKin
(Pump K+ in)
Na
Na+
+
Na+
outside
K+
K+
inside
Leakage of potassium and sodium through
the nerve membrane
Origin of normal RMP
 Contribution of pottasium diffusion potential
 Contribution of sodium potassium pump
SUMMARY
1. A Nerve Cell has ELECTRICAL
POTENTIAL across its cell membrane
because of a difference in the number of
Positively and Negatively Charged IONS on
each side of the Cell Membrane.
 2. The Electrical Potential is due to
PROTEINS in the Neuron known as
Sodium-Potassium Pumps move Sodium
ions (Na+) OUT of the Cell and Actively
Pump Potassium ions (K+) INTO the Cell.
 3.The result of this Active Transport of ions
is the Cytoplasm of the neuron contains
MORE K+ IONS and LOWER Na+ IONS .
The Cytoplasm also contains Many
NEGATIVE CHARGES PROTEINS
Molecules and Ions.
 5. K+ ions can leak out across the
membrane more easily than Na+ ions
can leak in.
 4.
 6.
The Negatively charged protein
molecules and ions do not leak in or
out.
 7. The Net Result of the leakage of
positively charged ions out of the cell is
a Negative Charge on the INSIDE of
the neuron's Cell Membrane
 8. The Charge Difference is known as the
RESTING POTENTIAL of the Neuron's
Cell Membrane.
 9. As a result of its Resting Potential, the
Neuron is said to be POLARIZED.
 10. POLARIZED = Negatively
Charged on the inside of the Cell
Membrane, and Positively Charged
on the Outside.
 11. A Neuron maintains this polarization
until it is stimulated.
 12. A STIMULUS is a change in the
environment that may be of sufficient
strength to initiate an impulse.
Thank you………