The cardiac cycle - heart beat
When the heart muscles are relaxed the heart is in diastole.
When the ventricles are contracted the heart is in systole.
What causes this?
When the heart is in diastole, the atria at the top are relaxed and blood can flow into the atria freely from the vena cavae and the pulmonary vein. The AV valves prevent the blood from flowing into the ventricle.
The atria will not contract (systole) to force blood through the AV valves and into the ventricles.
The atria will then relax and go back into diastole and the ventricles contract to go into systole.
Contraction of the ventricles forces blood out of the heart and into the relevant artery.
The ventricles will diastole. The entire heart is relaxed.
The atria prepare for systole again.
Noise of heart
Lubb/ Dupp/ no noise / Lubb Dupp/ no noise / Lubb Dubb
Lubb noise
Dupp noise- made by movement of semi-lunar valves.
No noise - everything is relaxed.
Atrial systole
ventricle systole
complete diastole
One full cardiac cycle - one heart beat.
A message is sent from the cardiovascular centre in our brain - the medulla oblongata - to tell us to continue triggering our heart to contract.
To begin atrial systole, cells in the sinoatrial node (SA) creates an ACTION POTENTIAL. This ACTION POTENTIAL is pulled down through the nerves and into the sinoatrial node(SA). The surrounding cells depolorise and the atria contract.
This action potential moves through the heart.
Every so often the cardiovascular centre will send another ACTION POTENTIAL down.
Current moves down from the SA node to the AV node then from the AV node to the septum/ bundle of His then divides into left and right branches into something called purkinje fibres in the ventricular muscle.
This process triggers ventricular systole/ contraction.