MEMBRANE POTENTIAL DR. ZAHOOR ALI SHAIKH Lecture ---7 1.

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MEMBRANE POTENTIALDR. 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

•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 Stimulation2. 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

time2. 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