MEMBRANE POTENTIAL
Prepared by
Dr.Mohammed Sharique Ahmed Quadri
Assistant prof. Physiology
Al Maarefa College
Objectives
• Define Membrane Potential?
• Describe the electrical potential across the cell
membrane.
• Explain the Resting Membrane and its cause
(Concentration of ions, permeability of ions)
• Emphasize Role of Na+ - K+ pump
• Define the term excitable tissue .
• Outline the Types of Channels present in cell
membrane – Stimuli which can open the Gated
Channels – Electrical , chemical
• Define terms Depolarization, Repolarization,
Hyperpolarization.
Membrane Potential
• Plasma membrane of all living cells has a
membrane potential (polarized electrically)
• Separation of opposite charges across plasma
membrane
• Due to differences in concentration and
permeability of key ions
Membrane Potential
 What is Membrane Potential ?
• It is the electrical potential across the cell
membrane.
• It is due to the separation of opposite charges across
the Membrane.
• It is due to the number of Cations(+) charged
particles and Anions(-) charged particles in
intracellular fluid and extracellular fluid.
Membrane Potential
Molecular Gradients
inside
outside
(in mM)
(in mM)
Na+
K+
Mg2+
Ca2+
H+
HCO3ClSO42PO3-
14
140
0.5
10-4
(pH 7.2)
10
5-15
2
75
142
4
1-2
1-2
(pH 7.4)
28
110
1
4
protein
40
5
Active Transport
inside
outside
+
K
Na+
+
Na
ATP
K+
3 Na+
2 K+
ADP
Remember: sodium is
pumped out of the cell,
potassium is pumped
in...
Simple Diffusion
inside
+
K
Na+
outside
K+
+
Na
Membrane Potential (Vm) (
- charge difference across the membrane -
inside
+
K
Na+
outside
K+
+
Na
…how can passive
diffusion of potassium
and sodium lead to
development of
negative membrane
potential?
Simplest Case
Scenario:
inside
outside
If a membrane were permeable
to only K+ then…
K+ would diffuse down its
concentration gradient until the
electrical potential across the
membrane countered diffusion.
The electrical potential that
counters net diffusion of K+ is
called the K+ EQUILIBRIUM
POTENTIAL (EK).
+
K
K+
Simplest Case
Scenario:
inside
outside
If a membrane were permeable to only
Na+ then…
Na+ would diffuse down its
concentration gradient until
potential across the membrane
countered diffusion.
The electrical potential that
counters net diffusion of Na+ is
called the Na+ equilibrium
potential (ENa).
Na+
+
Na
• In living cell effect of both Na+ and K+ must be
taken into account
• Greater the permeability of plasma membrane for
the given ion , the greater is the tendency for that
ion to drive the membrane potential towards the
ion’s own equilibrium potential.
• At rest membrane is 25 to 30 times more permeable
to K+ than Na+, thus K+ influence the membrane
potential at rest to much greater extent.
Resting Membrane
Potential
Vm -90 to -70
0 mV
ENa +61
EK -94
Why is Vm so close to EK?
Ans. The membrane is far more
permeable to K than Na..
The resting membrane potential is closest to the equilibrium
potential for the ion with the highest permeability!
RESTING MEMBRANE POTENTIAL
• Resting Membrane Potential (RMP) – is the
potential across the cell membrane at rest.
(unstimulated cell)
Usually used to refer to the intracellular potential
when compared to the extracellular potential.
• Normal value of excitable cells -70 to -80mV
 Presence of negatively charged proteins inside the
cells
( impermeable )
RESTING MEMBRANE POTENTIAL
• RMP established by –
 concentration difference of different ions between
ICF & ECF
 Relative permeability of the cell membrane to the
different ions. (more permeable to K)
 The Na-K ATPase pump which is electrogenic in
nature
Membrane Potential
• Effect of sodium-potassium pump on
membrane potential
– Makes only a small direct contribution to
membrane potential through its unequal
transport of positive ions
Membrane Potential
• Nerve and muscle cells
– Excitable cells
– Have ability to produce rapid, transient changes in
their membrane potential when excited
• Resting membrane potential
– Constant membrane potential present in cells of
nonexcitable tissues and those of excitable tissues
when they are at rest
19
Specialized Use Of Membrane Potential In
Nerve & Muscle Cells
• Nerve and Muscle can rapidly change their
membrane permeabilities to the ions, when
stimulated.
• Therefore, bring changes in membrane potentials.
• These rapid changes in membrane potential are
responsible for producing nerve impulses in nerves
and contraction in muscle cells.
SUMMARY
•
•
•
•
•
All living cells have membrane potential.
Cell is negative inside.
Nerve and Muscle are excitable tissues.
Nerves send electrical signal or nerve impulses.
Rapid changes in membrane potential in muscle cell
cause muscle contraction.
• Resting membrane potential in Neuron (nerve cell) is
-70 mv.
Neural Communication
• Membrane electrical states
– Polarization
• Any state when the membrane potential is other than
0mV
– Depolarization
• Membrane becomes less polarized(less negative) than
at resting potential
– Repolarization
• Membrane returns to resting potential after having
been depolarized
– Hyperpolarization
• Membrane becomes more polarized(membrane
becomes more negative) than at resting potential
Types of Changes in Membrane
Potential
Resting and action potentials
• There are some terms that need
to be understood & remembered:
–
–
–
–
excitability
depolarization
hyperpolarization
overshoot
• means positive to 0 mV
– repolarization
• towards resting potential
– threshold (for action potential
generation)
overshoot
0 mV
repolarization
-90 mV
threshold
depolarization
hyperpolarization
excitability
+
resting
potential
Neural Communication
• Two kinds of potential change
– Graded potentials
• Serve as short-distance signals
– Action potentials
• Serve as long-distance signals
Channels & local potentials
• The ionic basis of the action potential
membrane permeability
ion channels
types of channels
voltage-dependent channels
receptor operated (ligand-gated) channels.
References
• Human physiology by Lauralee Sherwood,
seventh edition
• Text book physiology by Guyton &Hall,11th
edition
• Text book of physiology by Linda .s
contanzo,third edition
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