YOUR AMAZING ELECTRICAL HEART
1 SPARK PLUG THAT GETS THE HEART PUMPING
WHAT makes your heart beat? The answer is simple: electricity.
The heart has an inbuilt electrical system that ensures the orderly contraction of the heart’s top two chambers, the atria, which then pump blood through into the lower chambers, the ventricles, which, in turn, contract and push out blood. This all takes less than a second.
The starting point for all of this is the master pacemaker, also known as the sinus node, a collection of cells 1cm to 3cm long, located in the upper right atrium (the green circle you can see, pictured right).
It acts like a spark plug, spontaneously producing an electrical signal which it sends through a network of ‘wires’ — modified nerve cells — down to the four chambers of the heart in 0.4 seconds.
‘The electrical charge generated is so tiny, you would need thousands of these charges to power a single fairy light,’ says Chris Gale, a professor of cardiovascular medicine at the University of Leeds.
2 THE BRAKE THAT STOPS THE PUMPING SO YOUR HEART FILLS WITH BLOOD
THE signal sent out by the sinus node ‘spark plug’ is like a match to the fire: all heart muscle cells are able to generate electricity, but not as fast as the specialised pacemaker cells.
Triggered by the sinus node, the muscle cells use the electricity they generate themselves to start the contraction process that creates the heartbeat, says Dr Chris Pepper, a consultant cardiologist at Leeds General Infirmary.
The signals then travel to the atrioventricular (AV) node — a small mass of muscular fibres between the two upper chambers of the heart, which forms the electrical link between the top and bottom chambers.
The AV node (seen in yellow, right) slows down the electrical signal — this allows the ventricles to fill with blood before the actual contraction occurs.
3 FINAL BURST OF POWER THAT SENDS BLOOD OUT TO THE BODY
THE current passes down into a bundle of cardiac muscle fibres (seen here in blue), then spreads rapidly through the muscles of the right and left ventricles, causing them to contract at the same time.
The whole process takes a break for about 0.5 seconds before it starts again, with the sinus node. This is how the normal resting heart rate is created.
Although pacemaker cells generate the electrical impulse that makes the heart beat, there are other nerves in the heart which can change the speed of the heart if required.
This can happen, for example, during periods of brisk exercise.