Typical values These differences result in a resting potential.

Typical values

These differencesresult in a resting potential

Membrane potentials are based upon the unequal permeability of the membrane to different ions

Ions are not distributed equally across a membrane

Pumps maintain the membrane in a steady-state

This is NOT an equilibrium!

More positive charges here More negativecharges here

difference across here is membrane potential

X+ is present at 1 M in chamber A and at 0.1 M in chamber B. A concentration force for X+ tends to cause X+ to flow from A

to B. However, chamber A is electrically negative with respect to chamber B, so an electrical force tends to cause X+

to flow from B to A.

A membrane separates chambers containing different K+ concentrations. At an electrical potential difference (EA - EB)

of -60 mV, K+ is in electrochemical equilibrium across the membrane.

A membrane separates chambers that contain different HCO3-

concentrations. EA - EB = +100 mV.

HCO3- is not in electrochemical equilibrium. If EA - EB were +60 mV, HCO3

- would be in equilibrium. EA - EB (+100 mV) is stronger than it needs to be (+60 mV) to just balance the tendency for HCO3

- to move from A to B because of its concentration difference. Thus, net movement of HCO3

- from B to A will occur.

A, Before a Gibbs-Donnan equilibrium is established, a membrane separates two aqueous compartments. B, Ion concentrations after Gibbs-Donnan equilibrium has been attained.

A hydrostatic pressure of 2.99 atmospheres is required to prevent water from flowing from chamber B to chamber A in the Gibbs-Donnan equilibrium. This 2.99 atmosphere is equal to the osmotic pressure in chamber A minus that in chamber B.

A, A concentration cell. A membrane, separates KCl solutions of different concentrations. B, The concentration cell after

electrochemical equilibrium has been established. The flow of an infinitesimal amount of K+ generated an electrical potential

difference across the membrane that is equal to the equilibrium potential for K+.

برقراری پتانسيل انتشار در غشای برقراری پتانسيل انتشار در غشای فيبر عصبی به صورت شماتيکفيبر عصبی به صورت شماتيک

THE NERNST EQUATION

The cytoplasmic and extracellular concentrations of an iondetermine the chemical driving force for that ion andthe equilibrium membrane potential if this is the ONLY ionthat is permeable through the membrane

EK+ = 58 mV

1log 5

130

Nernst EquationNernst Equation

Where EX is the chemical potential and z is the charge of ion X

[K+]in = 130 mM [K+]out = 5 mM z = +1

EX = 58 mV

z log [X]out

[X]in

= - 82 mV

For potassium:

RESTING POTENTIAL SET BY RELATIVE PERMEABILITIES

OF K+, Na+, & Cl- IONS

EK = - 82.1 mV 1.0

ENa = + 84.8 mV 0.05

ECl = - 63.6 mV 0.2

Nernst Potential Relative Permeability (P)

Resting membrane potential reflects the relative permeabilitiesof each ion and the Nernst potential of each ion

When the resting membrane potential is achieved, there isongoing influx of sodium and a matching efflux of potassium.

Na/K ATPase is continually needed to keep the ion gradientsfrom running down over time

PK EK + PNa ENa + PCl ECl

PK + PNa + PClVm =

THE GOLDMAN EQUATION

PK EK + PNa ENa + PCl ECl

PK + PNa + PClVm =

from before

Nernst equatiion EX = 58 mV

z log [X]out

[X]in

Goldman equation Vm = 58 mV log10

PK[K+]o + PNa[Na+]o + PCl[Cl-]i PK[K+]i + PNa[Na+]i + PCl[Cl-]o

( )The greater an ion’s concentration and permeability, the more

it contributes to the resting membrane potentialWhen one ion is by far the most permeable, Goldman eq. reduces to Nernst eq.

THE GOLDMAN EQUATION & THE RESTING POTENTIAL

Vm = 58 mV log10

PK[K+]o + PNa[Na+]o + PCl[Cl-]i PK[K+]i + PNa[Na+]i + PCl[Cl-]o

( )[K+]o

[K+]i

PK

= 5 mM

= 130 mM

= 145 mM

= 5 mM = 8 mM

[Na+]o

[Na+]i

PNa

[Cl-]o = 100 mM

[Cl-]i

PCl= 0.2= 0.05= 1

VVmm = = - -69.669.6 mVmV

INCREASING SODIUM PERMEABILITY UNDERLIES SODIUM INFLUXAND MEMBRANE DEPOLARIZATION DURING ACTION POTENTIAL

During action potential, the number of open sodium channels increases dramatically

EK = - 82 mV 1.0 1.0

ENa = + 85 mV 0.05 5.05.0

ECl = - 64 mV 0.2 0.2

Nernst Potential Prest Paction-

potential

GOLDMAN EQUATION-PREDICTED Vm

Rest During Action Potential

- 70 mV ++ 36 mV 36 mV

When sodium channels open, sodium ions flow in rapidly because of the negative membrane potential and the strong inward sodium battery

Inward sodium current depolarizes membrane and moves it towards the positive potential predicted by Goldman’s equation

(this positive potential is never fully achieved due to additional channel dynamics)

اندازه گيری پتانسيل غشای فيبر اندازه گيری پتانسيل غشای فيبر عصبی با کمک ميکروالکترودعصبی با کمک ميکروالکترود

پمپ سديم پتاسيم و کانالهای نشتی پمپ سديم پتاسيم و کانالهای نشتی سديم، پتاسيمسديم، پتاسيم

برقراری پتانسيل برقراری پتانسيل استراحت در سه استراحت در سه

حالت:حالت:AA زمانی که پتانسيل ) زمانی که پتانسيل (

غشاء صرفا“ ناشی غشاء صرفا“ ناشی باشد. باشد.++KKاز انتشار از انتشار

BB ناشی از ) ناشی از (NaNa++ و و KK++ باشد.باشد.

CC ناشی از ) ناشی از (NaNa++ ، ، KK++ و و پمپ سديم پتاسيم پمپ سديم پتاسيم

باشد.باشد.

پتانسيل عمل پتانسيل عمل ثبت شده (به ثبت شده (به

صورت صورت شماتيک)شماتيک)

ويژگی کانالهای سديمی و پتاسيمی ويژگی کانالهای سديمی و پتاسيمی (وابسته به ولتاژ بودن)(وابسته به ولتاژ بودن)

Na Selectivity Filter

برای مطالعه جريان يون voltage clampروش از کانال های خاص

تغيير هدايت کانالهای سديمی و تغيير هدايت کانالهای سديمی و پتاسيمی در زمان ايجاد پتانسيل پتاسيمی در زمان ايجاد پتانسيل

عملعمل

تغييرات تغييرات هدايت سديم هدايت سديم و پتاسيم در و پتاسيم در طی پتانسيل طی پتانسيل

عملعملنسبت هدايت سديم به نسبت هدايت سديم به

پتاسيمپتاسيم

Patch clampPatch clampروش روش

برای مطالعه برای مطالعه کانالهای يونی غشاء کانالهای يونی غشاء

سلول در حالتهای سلول در حالتهای مختلفمختلف

Action Potential(HyperPhysics, Georgia State University)

گسترش پتانسيل عمل در هر دو گسترش پتانسيل عمل در هر دو جهت طول يک فيبر هدايتیجهت طول يک فيبر هدايتی

Action Potential Propagation (BiologyMad.com)

Action Potential Propagation (BiologyMad.com)

Action Potential Propagation (BiologyMad.com)

myelinstealth

Ranvier nodes(ion channels only)

axonnerve cell

Action Potential Propagation

توليد حرارت در فيبر عصبی در توليد حرارت در فيبر عصبی در حالت استراحت و حالت تحريکحالت استراحت و حالت تحريک

پتاسيل عمل کفه دارپتاسيل عمل کفه دار

پتانسيل عمل ريتميکپتانسيل عمل ريتميک

آکسون، سلول شوان و غالف آکسون، سلول شوان و غالف ميلينميلين

هدايت جهشی در طول آکسون هدايت جهشی در طول آکسون ميلين دارميلين دار

Transmission of a nerve impulse

The passive spread ofan electrical signal

Conduction down the axon is fundamentally different

It proceeds by saltatory jumps

ROLE OF MYELIN IN FAST ELECTRICAL TRANSMISSIONROLE OF MYELIN IN FAST ELECTRICAL TRANSMISSION

UnmyelinatedUnmyelinatedAxonAxon

(SLOW CONDUCTION)(SLOW CONDUCTION)

MyelinatedMyelinatedAxonAxon

(FAST CONDUCTION)(FAST CONDUCTION)

Action potential at one point along unmyelinated axon produces current that only Action potential at one point along unmyelinated axon produces current that only propagates short distance along axon, since current is diverted through channels propagates short distance along axon, since current is diverted through channels in axon membrane. So action potential can only next occur short distance awayin axon membrane. So action potential can only next occur short distance away

Myelin reduces effective conductance and capacitance of Myelin reduces effective conductance and capacitance of internodal axon membrane. (how???)internodal axon membrane. (how???)

Action potential at node of Ranvier produces current that propagatesAction potential at node of Ranvier produces current that propagates0.5-5 mm to next node of Ranvier, generating next action potential0.5-5 mm to next node of Ranvier, generating next action potential

SODIUM CHANNELS ONLY AT NODESSODIUM CHANNELS ONLY AT NODESAT VERY HIGH DENSITYAT VERY HIGH DENSITY

اثر محرکها بر پتانسيلهای غشاء اثر محرکها بر پتانسيلهای غشاء تحريک پذيرتحريک پذير

اسيلوسکوپ اشعه کاتدی برای ثبت اسيلوسکوپ اشعه کاتدی برای ثبت پتانسيلهای عمل گذراپتانسيلهای عمل گذرا

Figure 3-11 The action potential of nerve and the associated absolute and relative refractory periods.

© 2005 Elsevier

تزريق جريان و ثبت تغييرات تزريق جريان و ثبت تغييرات پتانسيل غشاءپتانسيل غشاء

A, Responses of an axon of a shore crab to a subthreshold rectangular pulse of current

recorded extracellularly by an electrode located different distances from the current-passing electrode. As the

recording electrode is moved farther from the point of

stimulation, the response of the membrane potential is slower

and smaller.

© 2005 Elsevier

حافظ از باد خزان در چمن دهر مرنج فکر حافظ از باد خزان در چمن دهر مرنج فکر معقول بفرما گل بی خار کجاستمعقول بفرما گل بی خار کجاست