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 CHANNELS It is an opening so that ions move inwards and outwards -70 mv-55 mv

SPECIFIC CHANNELS INVOLVED Type of channel Na + weak Fast Ca 2++ Autoryh Thmic K + Voltage Depende nt Na + Slow Ca 2++ openedcontinous ly -40mv 0mv -55mv +30mv Result on ions Na + enters in Ca 2++ Enters in K + outNa + enters in Ca 2++ out Effect on Vm Raise in Vm Raise in Vm Lower in Vm Raise in Vm Cardiac Muscle K + +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+ weak Fast Ca2+ AR k+ Vm Time o

PHASE I Na+ enters through leak channel and raises Vm. PHASE II When Vm reaches -40mv, Fast ca 2+ channels open and ca 2+ 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 VD Na + Slow Ca 2+ CM K + Intercalated disc Gap junctions

PHASE I Na + and Ca 2+ 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 Ca 2+ and k + opens and k + exits, while Vm remains the same. PHASE IV Calcium causes muscle contraction PHASE V Ca 2+ 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.