1. Heart Conduction and Contraction

2. Blood travels through the heart twice before returning to the body
The double circulatory system

3. External view of the heart
superior
vena cava
pulmonary
artery
aorta
pulmonary
vein
pulmonary
vein
coronary
artery
right atrium
left
ventricle
inferior
vena cava
right ventricle

4. Heart Section

5. The heart contains autorhythmic cells because they are self-excitable
The heart contains autorhythmic cells because they are self-excitable. They generate spontaneous electrical impulses. These cells act as a pacemaker, setting the rhythm for the heart.

6. 1. Cardiac excitation begins at the sinoatrial node
1. Cardiac excitation begins at the sinoatrial node. This caused the atria muscles to contract.

7. 2. This electrical signal propogates through the atria to the atrioventricular node.

8. 3. From the AV node, the electrical signal is carries along the Atrioventricular bundle (bundle of His.)

9. 4. The signal goes through the bundle of His through the septum to the apex.

10. 5. Finally, the signal makes it to the Purkinje fibres which causes the ventricles to contract. The time between contraction of the atria and ventricles is 0.20 seconds!

11. Finish