The Cardiac Cycle

Question 1

THE HEART CYCLE: Stage 1.

Answer 1

Electrical impulses from SAN spread across the artia walls, causing the left and right atria to contract at the same time (systole).

Question 2

THE HEART CYCLE: Stage 2.

Answer 2

Impulses pass to the ventricles via the AVN after a short delay to allow time for the atria to finish systole and that the ventricles contract after this.

Question 3

THE HEART CYCLE: Stage 3.

Answer 3

Impulses pass down the Purkyne fibres to the heart apex.

Question 4

THE HEART CYCLE: Stage 4.

Answer 4

The impulses spread through the ventricle walls causing contraction from the apex upwards. Blood is squeezed into the arteries. This is ventricular systole.

Question 5

What is the purpose of the band of non-conducting collagen tissue in the heart?

Answer 5

It prevents the wave of electrical activity from being passed directly from the atria to the ventricles.

Question 6

What is it meant by when the heart is described as myogenic?

Answer 6

Heart muscle can contract and relax without receiving signals from neurones, the impulse originates from within the heart itself from the SAN.

Question 7

What does it all mean??

Answer 7

• P wave - contractions (depolarisation) of atria/time of atrial systole
• QRS complex - Time of ventricular systole
• T wave - repolarisation of the ventricles during diastole