This document discusses the electrical activity and action potentials of cardiac muscle cells. It begins by defining excitability and describing the resting membrane potentials of different cardiac tissues. It then explains the phases of the cardiac action potential in detail, including initial depolarization, initial repolarization, plateau, and final repolarization. The document also discusses the ionic basis and rhythmicity of cardiac muscle, pacemaker cells in the sinoatrial node, and differences between cardiac and nerve cell action potentials.

1. ACTION
POTENTIAL
OF HEART..
BY: -ISHANI PUNJABI..

2. EXCITABILITY
▪ It is defined as the ability of a living tissue to give
response to a stimulus.
▪ In all the tissues, initial response to a stimulus is
electrical activity in the form of action potential.

3. Resting Membrane
Potential in:-
SINGLE CARDIAC MUSCLE FIBER: -85 TO -95
SINOATRIAL (SA) NODE: -55 TO -60
PURKINJE FIBERS: -90 TO -100

4. ACTION POTENTIAL..
Action potential in cardiac muscle is different from
that of other tissues such as skeletal muscles ,
muscle and nervous tissues.
Duration of action potential in cardiac muscle is 250
to 350ms (0.25 to 0.35)

5. Phases of Action Potential:-
▪INITIAL DEPOLARIZATION
▪INITIAL REPOLARIZATION
▪A PLATEAU OR FINAL
DEPOLARIZATION
▪FINAL REPOLARIZATION

6. 1)INITIAL DEPOLARIZATION:-is very rapid and it lasts for
about 2msec(0.002sec).
-amplitude of depolarization is +20mV.
2)INITIAL REPOLARIZATION:-immediately after
depolarization , there is an initial rapid repolarization for a
short period of time of about 2msec.
-the end of rapid repolarization is represented by a notch.
3)PLATEAU OR FINAL DEPOLARIZATION:-afterwards , the
muscle fiber remains in depolarized state for sometime
before further repolarization.
-it forms the plateau(stable period)in action potential curve.

7. -the plateau lasts for about 200msec in atrial
muscle fibers and for about 300msec in ventricular
muscle fibers.
-due to long plateau in action potential , the
contraction time is longer in cardiac muscles by 5 to
15 times than in skeletal muscles.
4)FINAL REPOLARIZATION:-it occurs after plateau.
-is a slow process and it lasts for about 50 to 80
msec before the re-establishment of RMP.

8. Add a Slide Title -
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9. 1)INITIAL DEPOLARIZATION:-is because of opening of
sodium channels and the rapid influx of sodium ions.
2)INITIAL REPOLARIZATION:-is due to the transient(short
duration)opening of potassium channels and efflux of a
small quantity of potassium ions from the muscle fiber.
-the fast sodium channels close suddenly and slow sodium
channels open , resulting in slow influx of low quantity of
sodium ions.
IONIC BASIS OF ACTION POTENTIAL..

10. 3)PLATEAU OR FINAL DEPOLARIZATION:-is due to
slow opening of calcium channels.
-these channels are kept open for a longer period
and cause influx of large number of calcium ions.
-because of the entry of calcium and sodium ions
into the muscle fiber , positivity is maintained
inside the muscle fiber producing prolonged
depolarization i.e., plateau.

11. 4)FINAL REPOLARIZATION:-is due to efflux of
potassium ions.
-number of potassium ions moving out of the muscle
fiber exceeds the number of calcium ions moving in.
-it makes negativity inside , resulting in final
repolarization.
-potassium efflux continues until the end of
repolarization.

13. •At the end of the repolarization , all sodium ions ,
which had entered the cell throughout the process of
action potential move out of the cell and potassium
ions move in to the cell , by activation of SODIUM-
POTASSIUM PUMP.
--Simultaneously , excess of calcium ions , which had
entered the muscle fiber also move out through
sodium-calcium pump.
Thus , the resting membrane potential is restored.
RESTORATION OF RESTING
MEMBRANE POTENTIAL..

14. --Is the ability of a tissue to produce its own
impulses regularly.
--also called as autorhythmicity or self-excitation.
--Heart has a specialized excitatory structure ,
from which the discharge of impulses is rapid.
--The specialized structure is called PACEMAKER.
RHYTHMICITY..

15. --is the structure of heart from which the
impulses for heartbeat are produced.
--it is formed by the pacemaker cells called
p cells.
--In mammalian heart , the pacemaker is
sinoatrial (SA) node.
PACEMAKER..

16. --is a small strip of modified cardiac muscle
, situated in the superior part of lateral wall
of right atrium , just below the opening of
superior vena cava.
--these fibers are continuous with fibers of
atrial muscle , so that the impulses from
the SA node spread rapidly through atria.
--Rate of production of impulses through Sa
node is about 70 to 80/min.
SINOATRIAL NODE ..

17. 1)SA node: 70 to 80/min
2)AV node: 40 to 60/min
3)Atrial muscle: 40 to 60/min
4)Purkinje fibers: 35 to 40/min
5)Ventricular muscle: 20 to 40/min
RHYTHMICITY OF DIFFERENT PARTS OF
HUMAN HEART..

18. --Pacemaker potential is the unstable RMP in SA
node.
--It is also called prepotential.
--In SA node , each impulse triggers the next
impulse.
--RMP in SA node has a negativity of -55 to -60
mV.
ELECTRICAL POTENTIAL IN SA
NODE..

19. --Depolarization starts very slowly and the
threshold level of -40mV is reached very slowly.
--After the threshold level , rapid depolarization
occurs upto +5mV.
--It is followed by rapid repolarization.
--Once again , the RMP becomes unstable and
reaches the threshold level slowly.
ACTION POTENTIAL IN SA NODE..

21. --The sodium ions leak into the pacemaker fibers
and cause slow depolarization.(initial part of
pacemaker potential).
--Then , the calcium channels start opening.
--At the beginning , there is a slow influx of
calcium ions causing further depolarization in the
same slower rate.(later part of the pacemaker
potential).
IONIC BASIS OF ELECTRICAL
ACTIVITY IN PACEMAKER..

22. --When the negativity is decreased to -
40mV , which is the THRESHOLD LEVEL ,
the action potential starts with rapid
depolarization.
--The depolarization occurs because of
influx of more calcium ions.
DEPOLARIZATION..

23. --After rapid depolarization , repolarization starts.
--It is due to the efflux of potassium ions from
pacemaker fibers.
--Potassium channels remain open for a longer
time , causing efflux of more potassium ions.
--It leads to the more negativity , beyond the level
of RMP.
--It exists only for short period.
--Then , the slow depolarization starts once again ,
leading to the development of pacemaker
potential , which triggers the next action potential.
REPOLARIZATION..

25. SLOW DEPOLARIZATION(SODIUM IONS INFLUX)
INFLUX OF CALCIUM IONS(SLOW DEPOLARIZATION)
RAPID DEPOLARIZATION(INFLUX OF MORE CALCIUM IONS)
EFFLUX OF POTASSIUM IONS(REPOLARIZATION STARTS)
SLOW DEPOLARIZATION STARTS
DEVELOPMENT OF PACEMAKER POTENTIAL.

27. DIFFERENCE BETWEEN ACTION POTENTIAL OF
CARDIAC MUSCLES AND NERVE CELLS..
CARDIAC MUSCLES..
▪ Duration: 250 to 350 ms.
▪ Depolarization: by calcium ions
influx.
▪ RMP: -90 mV
NERVE CELLS..
▪ Duration: 2 to 5 ms.
▪ Depolarization: by sodium ions
influx.
▪ RMP: -70mV