1. Cardiovascular Physiology
Hana Hakami

2. Cardiac structure

5. Cardiac Muscle

6. Cardiac Muscle

8. Cardiac Muscle

9. Cardiac Muscle

10. Cardiac Muscle

11. Cardiac Muscle

12. Cardiac Muscle striations Plasma membrane cytoplasm cytoplasm
Intercalated disc
Desmosome
Central nucleus
Gap junction channel

13. Spontaneous electrical activity (automaticity)
An isolated heart beats regularly without any extrinsic stimulation from nerves or hormones.
This mechanical automaticity reflects the fact that the action potentials which are conducted throughout the heart (the signals which lead to contraction) are generated spontaneously within the cardiac muscle itself.

14. Spontaneous electrical activity (automaticity)
Such activity is said to be myogenic (unlike action potentials in skeletal muscle which are neurogenic, i.e. they are only produced in response to nervous stimuli).

15. Spontaneous electrical activity (automaticity)
The cells responsible for spontaneous action potential production are often referred to as pacemaker cells because they determine the rate at which the heart beats.

16. Spontaneous electrical activity (automaticity)
Electrical recordings from such cells show that, instead of a constant resting membrane potential between action potentials, there is a steadily depolarizing potential known as a pacemaker potential , when threshold is reached an action potential fires.
And then the cycle of events is repeated.

17. Spontaneous electrical activity (automaticity)

18. Spontaneous electrical activity (automaticity)
Several cell types in the heart are capable of pacemaker activity, but in the intact organ it is the fastest pacemaker which drives the rest of the heart.
Once an action potential is generated at one site, it is rapidly conducted throughout the cardiac muscle and will trigger an action potential in slower pacemaker regions before they' can reach the threshold potential spontaneously.

19. Spontaneous electrical activity (automaticity)
Normally the pacemaking frequency is highest in a group of specialized cells called the sinoatrial node (SN\SAN) , which also have a different shape of action potential. These cells dictate the rate of electrical events in the rest of the heart.
This produces a resting heart rate of beats min-I, and the regular pattern of excitation and contraction which results is called sinus rhythm.

20. Spontaneous electrical activity (automaticity)

21. conducting pathways in the heart
Cardiac action potentials normally originate in the pacemaker cells of the sino-atrial node, which is located in the wall of the right atrium close to the superior vena cava .
Action potentials are conducted away from the sinoatrial node through the normal atrial fibres.

22. conducting pathways in the heart

23. conducting pathways in the heart
This is made possible by the interbranching structure of cardiac cells and the easy transmission of action potentials from one cell to another via the low-resistance gap junctions in the intercalated discs.
The conduction velocity through the atrial muscle is 0.3 ms-1

24. Electrocardiogram (ECG)
Because action potentials do not fire simultaneously in all cardiac cells but are conducted across the myocardium from one region to another, extracellular potential differences are generated between one area of the heart and the next.
These can be recorded from the skin as very small potential differences (approximately 1 mV) and such a record is known as an electrocardiogram (ECG).

25. Electrocardiogram (ECG)
An electrocardiogram (ECG) is an important clinical tool, used both in the diagnosis of abnormal cardiac rhythms (arrhythmias) or defects in the conduction pathways and when investigating possible damage to the bulk of the myocardium, e.g. caused by ischaemia.

26. Electrocardiogram (ECG)
To understand the principle underlying the ECG, let us consider an area of myocardium with two surface electrodes being used to record any potential differences from the overlying skin (next Fig. A).
At rest there will be zero potential difference between the electrodes, but as the depolarizing phase of an action potential spreads across the heart, the transmembrane potential will be reversed in one area while the other area remains polarized.

27. Electrocardiogram (ECG)

28. Electrocardiogram (ECG)
This generates a potential difference which is recorded as a positive deflection, assuming the electrodes are attached to the positive arid negative poles of the voltmeter as shown (reversing this connection would give a negative potential recording).
Eventually all the local myocardium will be depolarized, so the potentials at the two surface electrodes will be identical, giving zero potential difference again.

29. Electrocardiogram (ECG)
Once repolarization starts to spread, however, a negative potential will be recorded until the whole tissue returns to the resting potential again.
A typical ECG recording consists of three different waves (last Fig. B).
There is an initial positive deflection known as the P wave. This is generated by the spread of depolarization across the atria.

30. Electrocardiogram (ECG)

31. Electrocardiogram (ECG)
It is followed by the QRS complex, which is produced by the spread of depolarization across the ventricles.
These contain more muscle and so generate larger surface potentials.
The final T wave is the result of repolarization of the ventricles.
A wave caused by repolarization of the atria is not seen but is presumed to be obscured by the QRS complex.

32. Electrocardiogram (ECG)

33. Electrocardiogram (ECG)
The simplest piece of information which can be determined from the ECG is heart rate.
The beat to beat interval can be measured between equivalent points on consecutive waves, e.g. from the peak of one P wave to the next.
The total time for 10 beats is often measured from the ECG and divided to give an average beat to beat interval. This is then used to calculate an average heart rate.

34. Electrocardiogram (ECG)
Example to calculate an average heart rate:
Distance from first P wave to 11th P wave (10 X P-P intervals) = 208 mm
Average = 20.8 mm = 0.83 s (standard ECG chart speed = 25 mm s-1).
Heart rate = 60 ÷ 0.83 = 72 beats min-1.

35. Electrocardiogram (ECG)

36. Electrocardiogram (ECG)

37. the End Thank You
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