RESTING MEMBRANE POTENTIAL&

ACTION POTENTIAL

MR. Arjun MaitraAssistant ProfessorDept. of PhysiologyPCMS&RC

TO MY STUDENTS

HERE I HAVE TRIED TO SIMPLIFY THE HUGE SUBJECT WITH ANIMATIONS, DIAGRAMS, FLOW CHARTS & RELEVENT MCQs.DIFFERENT TEXT BOOKS AND REFERENCE BOOKS HAVE BEEN USED FORPREPARING THE CONTENTS. REMEMBERTHESE SLIDES ARE NOT THE SUBSTITUTE OF YOUR TEXT BOOKS

ANIMATIONS AND DIAGRAMS ARE COLLECTED FROM DIFFERENT WEBSITESOLELY FOR EDUCATION PURPOSE.

MEMBRANE POTENTIAL

Vm = Vin -- Vout

IONIC DISTRIBUTION

Ions Inside cell Outside cell EquilibriumPotential

Sodium 15.0 150.0 +55mV

Potassium 150.0 5.5 -75mV

Chloride 9.0 125.0 -69mV

OrganicAnions

385.0 ------- ------

Role of Ions

SODIUM Na

POTASSIUM K

CHLORIDE Cl

CALCIUM Ca

+

+

_

+ +

-

A

Resting Membrane Potential

Vr = Vin

[ Normal range -60mV ---- -70mV (Neurons)]

+

Na

+

K

No ionic movement across the cell membrane

1. How do ionic gradient contribute to RMP

2. How are they maintained

3. What prevents the ionic gradients from dissipating by diffusion of ions across the membrane through passive channels

PUZZLE SOLVERA simple GLIAL cell

Nernst Equation & Equilibrium Potential

• ELECTRICAL DRIVING FORCE = CHEMICAL DRIVING FORCE

EK = -75mV

(Nernst Potential)

Neurons are complicated as they have Resting channels

for

Different ion species

GOLDMAN’S EQUATION

A new approach to quantify the contribution of different ions

• Concentration gradient• Conductance/Permeability

PERMEABILITY RATIO (At Rest) PK : P Na : P Cl = 1.0: 0.04 : 0.45

(At peak of Action Potential) PK : P Na : P Cl = 1.0 : 20 : 0.45

ELECTRICAL EQUIVALENT CIRCUIT

Conductance = 1/ohm = 1 / g RUnit expressed as ‘S’ = Siemens

Ohm’s Law V=IR => I =V/R => I = gV

gNa= nNa X gNa

gK = nK X gK

gCl= nCl X gCl

INa I

K

Vr =

Role of Na – K ATPase in maintenance of Resting Membrane Potential + +

A Positive Controversy

Na – K ATPase+ +

ACTION POTENTIAL

Channels associated to Action potential

• VDSC – Voltage gated sodium channel

• VDKC – Voltage gated potassium channel

A type- Fast

Slow type

Inward Rectifier

IONIC MOVEMENT DURING ACTION POTENTIAL

Voltage Gated Sodium Channel

Voltage Gated Potassium Channel

Inward Rectifier Channel

Voltage Gated Fast

Voltage gated Slow

REFERENCES

• A.G.Brown – “Nerve Cells & Nerve Tissue”- 4th Edn.

• Carpentar – “Neurophysiology”

• Kandle & Schwartz – “Principles of Neural Sciences”

• Longstaff.A – “Instant notes on Neurosciences

• W. Ganong – “Review of Medical Physiology” 2005

• Corriteli – “Biophysics” 2003

• Devlyn – “Biochemistry”- 4th Edn