Typical values These differences result 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 difference across here is membrane potential More negative charges here More positive charges here

X+ is present at 1 M in chamber A and at 0. 1 M in chamber B 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 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 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 فيبر عصبی به صورت شماتيک

Where EX is the chemical potential and z is the charge of ion X THE NERNST EQUATION The cytoplasmic and extracellular concentrations of an ion determine the chemical driving force for that ion and the equilibrium membrane potential if this is the ONLY ion that is permeable through the membrane EX = 58 mV z log [X]out [X]in Nernst Equation Where EX is the chemical potential and z is the charge of ion X z = +1 [K+]in = 130 mM [K+]out = 5 mM For potassium: 58 mV 5 EK+ = log = - 82 mV 1 130

RESTING POTENTIAL SET BY RELATIVE PERMEABILITIES OF K+, Na+, & Cl- IONS Nernst Potential Relative Permeability (P) EK = - 82.1 mV 1.0 ENa = + 84.8 mV 0.05 ECl = - 63.6 mV 0.2 Resting membrane potential reflects the relative permeabilities of each ion and the Nernst potential of each ion PK EK + PNa ENa + PCl ECl PK + PNa + PCl Vm = When the resting membrane potential is achieved, there is ongoing influx of sodium and a matching efflux of potassium. Na/K ATPase is continually needed to keep the ion gradients from running down over time

PK[K+]o + PNa[Na+]o + PCl[Cl-]i PK[K+]i + PNa[Na+]i + PCl[Cl-]o THE GOLDMAN EQUATION PK EK + PNa ENa + PCl ECl PK + PNa + PCl Vm = from before EX = 58 mV z log [X]out [X]in Nernst equatiion Vm = 58 mV log10 PK[K+]o + PNa[Na+]o + PCl[Cl-]i PK[K+]i + PNa[Na+]i + PCl[Cl-]o ( ) Goldman equation The greater an ion’s concentration and permeability, the more it contributes to the resting membrane potential When one ion is by far the most permeable, Goldman eq. reduces to Nernst eq.

PK[K+]o + PNa[Na+]o + PCl[Cl-]i PK[K+]i + PNa[Na+]i + PCl[Cl-]o THE GOLDMAN EQUATION & THE RESTING POTENTIAL ) ( PK[K+]o + PNa[Na+]o + PCl[Cl-]i Vm = 58 mV log10 PK[K+]i + PNa[Na+]i + PCl[Cl-]o [K+]o = 5 mM [Na+]o = 145 mM [Cl-]o = 100 mM [K+]i = 130 mM [Na+]i = 5 mM [Cl-]i = 8 mM PK = 1 PNa = 0.05 PCl = 0.2 Vm = - 69.6 mV

Rest During Action Potential INCREASING SODIUM PERMEABILITY UNDERLIES SODIUM INFLUX AND 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 5.0 ECl = - 64 mV 0.2 0.2 Nernst Potential Prest Paction-potential Rest During Action Potential - 70 mV + 36 mV GOLDMAN EQUATION-PREDICTED Vm 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 عصبی با کمک ميکروالکترود

پمپ سديم پتاسيم و کانالهای نشتی سديم، پتاسيم

برقراری پتانسيل استراحت در سه حالت: A) زمانی که پتانسيل غشاء صرفا“ ناشی از انتشار K+ باشد. B) ناشی از Na+ و K+ باشد. C) ناشی از Na+، K+ و پمپ سديم پتاسيم باشد.

پتانسيل عمل ثبت شده (به صورت شماتيک)

ويژگی کانالهای سديمی و پتاسيمی (وابسته به ولتاژ بودن)

Na Selectivity Filter

روش voltage clamp برای مطالعه جريان يون از کانال های خاص

تغيير هدايت کانالهای سديمی و پتاسيمی در زمان ايجاد پتانسيل عمل

تغييرات هدايت سديم و پتاسيم در طی پتانسيل عمل نسبت هدايت سديم به پتاسيم

روش Patch clamp برای مطالعه کانالهای يونی غشاء سلول در حالتهای مختلف

Action Potential (HyperPhysics, Georgia State University)

گسترش پتانسيل عمل در هر دو جهت طول يک فيبر هدايتی

Action Potential Propagation (BiologyMad.com)

Action Potential Propagation (BiologyMad.com)

Action Potential Propagation (BiologyMad.com)

Action Potential Propagation myelin stealth Ranvier nodes (ion channels only) axon nerve cell

توليد حرارت در فيبر عصبی در حالت استراحت و حالت تحريک

پتاسيل عمل کفه دار

پتانسيل عمل ريتميک

آکسون، سلول شوان و غلاف ميلين

هدايت جهشی در طول آکسون ميلين دار

Transmission of a nerve impulse

The passive spread of an electrical signal

Conduction down the axon is fundamentally different It proceeds by saltatory jumps

SODIUM CHANNELS ONLY AT NODES ROLE OF MYELIN IN FAST ELECTRICAL TRANSMISSION Unmyelinated Axon (SLOW CONDUCTION) Myelinated Axon (FAST CONDUCTION) SODIUM CHANNELS ONLY AT NODES AT VERY HIGH DENSITY Action potential at one point along unmyelinated axon produces current that only propagates short distance along axon, since current is diverted through channels in axon membrane. So action potential can only next occur short distance away Myelin reduces effective conductance and capacitance of internodal axon membrane. (how???) Action potential at node of Ranvier produces current that propagates 0.5-5 mm to next node of Ranvier, generating next action potential

اثر محرکها بر پتانسيلهای غشاء تحريک پذير

اسيلوسکوپ اشعه کاتدی برای ثبت پتانسيلهای 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 پتانسيل 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

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