Cardiac ActionPotential

Presenter: Parichay S R

CONTENTS

• INTRODUCTION• RESTING MEMBRANE POTENTIAL• ACTION POTENTIAL• ION DISTRIBUTION• CHARGE DISTRIGUTION• VOLTAGE GATED CHANNELS• SPECIFIC CHANNELS INVOLVED• CARDIAC ACTION POTENTIAL• SUMMARY• REFERENCES

INTRODUCTION

What is membrane potential?

Resting membrane potential

Action potential

ION DISTRIBUTION

CHARGE DISRIBUTION

++++++++

++++++++

+ + + + + + + + + +

+ + + + + + + + + +

Vm= -70mv

VOLTAGE GATED CHANNELSIt is an opening so that ions move inwards and outwards

-70 mv -55 mv

+++

+++

SPECIFIC CHANNELS INVOLVEDType of channel

Na+

weakFast Ca2++ Autoryh

ThmicK+

Voltage Dependent Na+

Slow Ca2+

+

opened continously

Opens @-40mv

Opens@ 0mv

Opens @-55mv

Opens @+30mv

Result on ions

Na+ entersin

Ca2++

Enters inK+ out Na+

enters inCa2++ out

Effect onVm

Raise in Vm

Raise inVm

Lower inVm

Raise in Vm

Raise in Vm

CardiacMuscle K+

Opens @+30mv

Lets K+

out

Lower in Vm

CARDIAC ACTION POTENTIAL

SA (Sinoatrial) node

AV(Atrioventricular)node

Autorhythmic cells

Explaination

Time

Vm

Time

Vm

-By these two graphs

IN AUTORHYTHMIC CELLS

Na+ weakFastCa2+ AR k+

Vm

Time-60-40

o

PHASE I Na+ enters through leak channel and raises Vm.

PHASE II When Vm reaches -40mv, Fast ca2+ channels open and ca2+ enters, this raises Vm further.

PHASE III At 0mv k+ channel opens, k+ excite cell and returns Vm to rest (-60mv).

PHASE IV Start over.

IN CARDIAC MUSCLE

Time

Vm

Time

Vm

-70-55

30

VD Na+SlowCa2+

CMK+

Intercalated disc

----------------------------------------------------------

Gap junctions

PHASE I Na+ and Ca2+ leaks from neighbouring cells and raise Vm from -70mv to -55mv.

PHASE II At –55mv voltage dependent Na+ channel opens enters to raise Vm.

PHASE III At +30mv both slow Ca2+ and k+ opens and k+ exits, while Vm remains the same.

PHASE IV Calcium causes muscle contraction

PHASE V Ca2+ closes, K+ remains open, K+ exits and Vm returns to rest and continues for next set

SUMMARY

REFERENCES

Textbook of cell and molecular biology- 2nd ed– Ajoy Paul

Textbook of Medical physiology- Tenth edition – Arthur C.Guyton, M.D & John E.Hall, Ph.D.