Control and regulation of the cardiac cycle LO1

Question 1

What is the cardiac cycle controlled by?

Answer 1

The cardiac cycle is controlled by the electrical activity that takes place in the heart

Question 2

What is the location and role of the sinoatrial (SA) node?

Answer 2

• the SA node is situated in the upper wall of the right atrium of the heart
• it is known as the ‘pacemaker’ and is responsible for setting the rhythm of the heart
• it ensures both atria contract simultaneously

Question 3

What is the location and role of the atrioventricular (AV) node in the heart?

Answer 3

• the AV node is situated at the bottom of the right atrium of the heart
• it is responsible for delaying the electrical impulses it receives from the SA node
• this delay allows time for blood to empty out the atria into the ventricles

Question 4

What are purkinje fibres? (also known as purkyne)

Answer 4

There are very fine specialised cardiac muscle fibres that rapidly transmit impulses from the atrioventricular node to the ventricles

Question 5

What does an electrocardiogram trace show?

Answer 5

An electrocardiogram (ECG) trace shows the spread of the electrical signal generated by the SA node as it travels through the atria, the AV node and the ventricles. A normal ECG trace shows 5 waves, named P, Q, R, S and T.

Question 6

What does the ECG trace tell us about what is happening in the heart?

Answer 6

• the waves represent the electrical activity in the heart.
• the different sections represent different activities within the heart
• the P wave at the beginning shows atrial contraction
• The QRS complex shows ventricular contraction (systole)
• the T wave shows ventricles relaxing (diastole)
• if the waves are disordered or out of rhythm, the ECG trace indicates which part of the heartbeat is problematic