| How is heart action initiated and coordinated | - process starts in the sino-atrial node (SAN), in the walls of the right atrium
- SAN sends out regular waves of electrical activity to the atrial walls
- this causes the right and left atrium to contract at the same time
- the waves of the electrical activity are transferred from the SAN to the atrioventricular node (AVN)
- AVN passes electrical activity to bundle of His, but there's a slight delay
- this ensures that ventricles contract after atria have emptied
- bundle of His conducts waves of electrical activity to Purkyne tissue
- Purkyne tissue carries waves of electrical activity to walls of right and left ventricles, causing them to contract simultaneously from bottom up |
| How can doctors check someone's heart function | using an electrocardiograph (ECGs), a machine that records the electrical activity of the heart |
| What happens to the heart muscle when is contracts | It depolarises, loses electrical charge |
| What happens to the heart muscle when is relaxes | It repolarises, regains charge |
| What is P wave caused by | The contraction of the atria |
| What is the QRS complex | The main peak of the heartbeat, together with the dips on either side. This is caused by the contraction of the ventricles. |
| What is the T wave caused by | The relaxation of the ventricles |
| How do you calculate heart rate | 60/time taken for one heartbeat |
| What is tachycardia | When the heartbeat is very fast. Problems include heart not pumping blood efficiently. |
| What is bradycardia | When the heartbeat is very slow. Problems include something may be preventing impulses from the SAN being passed on properly. |
| What is an ectopic heartbeat | When there is an extra heartbeat caused by earlier contraction of the atria or ventricle. |
| What is fibrillation | When the heartbeat is really irregular. The atria and ventricles have completely lost their rhythm and stop contracting properly, resulting in chest pain, fainting or death. |
