1. Heart activity Modulation of autorhythmic cells
Electrical activity co-ordinates heart contraction
Pacemakers
Electrocardiogram shows heart electrical activity

2. close

4. Modulation of autorhythmic cells
NE (sympathetic) and E (adrenal hormone)
Autorhythmic cells have beta1 receptors
Cyclic AMP levels increase
Properties of If and Ca++ channels altered
More rapid Na+ and Ca++ entry
Rapid action potential
Rapid contractions

5. Modulation of autorhythmic cells
Parasympathetic, acetyl choline
Muscarinic receptors
K+ channels open mb hyperpolarizes cell less excitable
Ca++ channel less likely to open slower depolarization  cell is less excitable

6. Electrical activity in the heart
Begins with action potential in autorhythmic cells.
Gap junctions spread depolarization through intercalated discs

7. The heart’s main pacemaker is in the sinoatrial node (SA node)
where a group of autorhythmic cells are located at the junction of the
vena cava and the right atrium

8. The conductive
system of the heart
consists of noncontractile
autorhythmic cells

10. Action potentials spread across atria.

11. Action potentials encounter fibrous
Tissue at the junction of the atria and
Ventricles.

12. Action potential reach the ventricles
Through the AV node, then spread
Rapidly down the bundle of His.

13. Prukinje fibers rapidly transmit
Impulses up the ventricle
All contractile cells at apex
Contract simultaneously

14. Why does the AV node delay action potentials?
This allows the atria to complete contraction and allows the ventricles to fill before the ventricles contract

15. Autorhythmic cells All cells of the conducting fibers are autorhythmic
The cells of the SA node set the heart rate because their rhythm is fastest.
They set the pace.
If the SA node is damaged, the other pacemakers still function, the pace lowers.

16. The electrocardiogram shows the electrical activity of the heart.
ECG
Electrodes placed on the skin
On arms and leg
ECG shows summated electrical activity during heart activity
Indirectly shows contraction and relaxation of atria and ventricles

17. Einthoven’s triangle.
Location of electrode placement
For ECG

18. The electrocardiogram. Know the points.

19. ECG P wave, atria depolarize
QRS complex, wave of ventricular depolarization
T wave, ventricles repolarize

22. The heart cycle
Period from the beginning of one heart beat to the beginning of the next heart beat
Two phases:
Diastole, period of cardiac muscle relaxation
Systole, period of cardiac muscle contraction
The atria and ventricles do not contract and relax at the same time.

23. 5 phases of the heart cycle
Heart at rest (atrial and ventricular diastole)
Completion of ventricular filling (atrial systole)
Early ventricular contraction (first heart sound)
The heart pumps (ventricular ejection)
Ventricular relaxation (second heart sound)