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cardiac action potential, action potential, membrane potential, cardiac muscle cell, autorhythmic cell, resting membrane potential, fast chloride ion channels, slow calcium ion channels, potassium ion channels, sodium and potassium leakage from neighbouring cells
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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.
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