MEMBRANE POTENTIAL

بسم الله الرحمن الرحيم

Prepared byDr.Mohammed Sharique Ahmed Quadri

Assistant prof. PhysiologyAl 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

Na+

K+

Mg2+

Ca2+

H+

HCO3-

Cl-

SO42-

PO3-

protein

inside(in mM)

141400.510-4

(pH 7.2)10

5-152

75

40

outside(in mM)

14241-21-2(pH 7.4)2811014

5

ATP

3 Na+

2 K+

ADP

Active Transport

K+ Na+

Na+ K+

inside outside

Remember: sodium is pumped out of the cell, potassium is pumped in...

Simple Diffusioninside outside

K+ K+

Na+Na+

Membrane Potential (Vm) ( - charge difference across the membrane -

K+

Na+

K+

Na+

inside outside…how can passive diffusion of potassium and sodium lead to development of negative membrane potential?

If a membrane were permeable to only K+ then…

inside outside

K+ K+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).

Simplest Case Scenario:

Simplest Case Scenario:

Na+Na+

If a membrane were permeable to only Na+ then…

The electrical potential that counters net diffusion of Na+ is called the Na+ equilibrium potential (ENa).

inside outside

Na+ would diffuse down its concentration gradient until potential across the membrane countered diffusion.

• 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

0 mV

EK -94 ENa +61

Vm -90 to -70

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

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.

• 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

0 mV

hyperpolarization

depolarization

repolarization

overshoot

threshold

resting potential

-90 mV

+

-

excitability

• 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)

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 potentialmembrane permeability ion channels

types of channelsvoltage-dependent channelsreceptor 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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