The electrical properties of the heart

Question 1

What is the role of the Sinoatrial Node (SA NODE)?

Answer 1

Fastest pacemaker cells are found here. They are the pacemakers for the rest of the heart. They depolaries to threshold first. This depolarisation spreads cell to cell via electrical connections known as gap junctions. There will be a wave of depolarisation spreading through the atria which leads to the atria contracting and when this happens blood will squeeze down into the ventricles.

Question 2

What is the role of annulus fibrosis?

Answer 2

Annulus fibrosis is a ring of non conducting tissue and it prevents the depolarisation from spreading immediately from the atria to the ventricles.

Question 3

What is the role of atrioventricular node (AV NODE)?

Answer 3

Depolarisation spreads from the atria to the ventricle through the atrioventricular node. Key feature of this node is that it conducts slowly. The significance of this is it acts as a delay box and it allows the atria time to depolarise, contract and squeeze the blood into the ventricles before the ventricles then contract.

Question 4

What is the role of bundle of His and purkinje fibres?

Answer 4

This special conducting system ensured there is a coordinated contraction of the heart.

Question 5

What does an action potential in a myocyte evoke?

Answer 5

An action potential in a single myocyte evokes a very small extracellular electrical potential

Question 6

Why is teh ECG a good diagnostic tool ?

Answer 6

• It is non invasive
• It is quick and easy to do
• Gives us useful information about the special conducting system of the heart