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MEMBRANE POTENTIAL
DR. ZAHOOR ALI SHAIKH
Lecture ---7
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Membrane Potential
• Plasma membrane or cell membrane of all living
cells have a membrane potential or they are
polarized.
• Membrane potential is Negative inside.
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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.
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Membrane Potential (cont)
• When there is difference in the number of
positive and negative charges between the two
sides( inside and outside)of cell membrane, than
we say Membrane potential is present.
• Potential is measured is volts(as we do in
electricity) but as membrane potential is low, the
unit we use is millivolt (mv).
• 1mv = 1/1000 volt
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Membrane Potential (cont)
What is the cause of Membrane Potential ?
• It is due to the differences in the concentration
and permeability of ions across the cell
membrane.
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Excitable Tissue
• Nerve cell and Muscle are excitable tissue, they
produce rapid, transient changes, in their
membrane potential when stimulated .
• These changes in potential cause Electrical
signals.
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Resting Membrane Potential
• When cells are at rest (not stimulated) – there is
Resting Membrane Potential.
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Resting Membrane Potential
Q- What is the cause of Resting Membrane
Potential (RMP)?
• Ans: RMP is due to
1) Concentration of ions(Na+& K+) across the
cell membrane.
2) Permeability of ions (Na+&K+) across the
cell membrane.
3) Na+ - K+ pump.
4) Protein inside the cell(A-), they are negatively
charged and plasma membrane is impermeable.
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Equilibrium Potential of K+
Calculation by Nernst Equation
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Na+ - K+ Pump
• The Na+ - K+ PUMP transports THREE Na+
out, for TWO K+ it transports inside the cell.
• As both are positive ions, unequal transport
causes more positive charge outside negative
charge inside.
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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.
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SUMMARY
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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.
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 REMEMBER
• Resting membrane potential in Neuron (nerve
cell) is -70 mv.
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Terms Used For Changes In
Membrane Potential
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Terms Used For Membrane Potential
•
Polarization
It means electrical changes are present on
both sides of membrane, therefore, membrane
has potential.
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Terms Used For Membrane Potential
(cont)
• Depolarization
During Depolarization, membrane
becomes less negative inside as Na+ enters the
cell therefore potential moves towards 0 mv (e.g.
change from -70 to +20).
• Repolarization
It is due to K+ efflux [going outside].
The membrane returns to resting membrane
potential i.e. -70 mv .
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Terms Used For Membrane Potential
(cont)
• Hyperpolarization
It is because of more K+ going outside.
Therefore, membrane becomes more negative
inside than resting membrane potential like
-80 mv now, instead of -70 mv.
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Changes in Membrane Permeability
• Changes in Membrane Permeability can be
brought by:
1. Electrical & Mechanical Stimulation
2. Changing channel permeability
3. Action of Chemicals
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Channels In Plasma Membrane
• There are
1. Leaky Channels – which are open all the time
2. Gated Channels – these channels work like gate
i.e. they open and close to the different stimuli.
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Channels In Plasma Membrane
Types of Gated Channels:
(i). Voltage Gated Channel – Open and close due to changes in charges on
membrane potential.
(ii). Chemically Gated Channel – Open and close due to effect of chemical
messenger.
(iii). Mechanically Gated Channel – Open and close due to mechanical
stimulus. E.g. Stretching
(iv). Thermal Gated Channel – respond to local changes in temperature.
These stimuli can change the permeability of cell membrane.
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Different Stimuli Cause
Electrical Signals
• Electrical Signals are produced due to changes in
ions movement across the membrane.
• Electrical Signals produce:
1. Graded Potential or Local Potential
2. Action Potential – It sends signal over long
distance.
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Graded Potential
• Graded Potential is local change in the
membrane potential.
E.g. RMP changes from -70 mv to -60 mv (a
10mv change).
• Graded Potential is due to Na+ entry at the small
region of plasma membrane.
• It is localized change in the membrane.
• Graded Potential can be summated by giving
stronger stimulus.
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GRADED POTENTIAL
‘Important Points’
• It is localized.
• It can be summated.
• Longer the stimulus – longer the duration of
graded potential.
• Graded Potential die down over short distance.
• Example of Graded Potential:
- Receptor Potential, Pace-maker Potential
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What You Should Know From This
Lecture
• What is Membrane Potential?
- The electrical potential across the cell membrane.
• Resting Membrane Potential in Nerve Cell – [-70 mv]
• What is the cause of Resting Membrane Potential?
- Concentration of ions, permeability of ions, Na+-K+ pump, protein
inside the cell.
• Na+ - K+ pump – it transports 3 Na+ out and 2 K+ inside the cell.
• Nerve cell and Muscle cell are excitable tissue.
• Channels present in cell membrane –
- Leaky Channels
- Gated Channels
• Stimuli which can open the Gated Channels – Electrical, Chemical,
Mechanical, and Thermal Stimuli.
• Depolarization, Repolarization, Hyperpolarization
• Graded Potential and its characteristics
- It is local potential, can be summated, does not propagate, dies down.
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Thank you