2.3 Cardiac cycle

Question 1

What does myogenic mean?

Answer 1

Beats on its own.

Question 2

What is the cardiac cycle initiated by?

Answer 2

The sino-atrial node(SAN).

Question 3

What is step 1 in the cardiac cycle?

Answer 3

• The sinoatrial node (SAN) sends out a wave of excitation across the muscle of the atria.
• The muscle responds by contracting (atrial systole).
• The wave of excitation is prevented from passing to the ventricles by fibrous tissue

Question 4

What is a wave of excitation?

Answer 4

The wave of excitation is a wave of depolarisation of muscle cells. When the cells depolarize, they contract.

Question 5

What is step 2 in the cardiac cycle?

Answer 5

• Wave of excitation passes to the
  atrioventricular node (AVN) in the septum at the atrioventricular junction.
• AVN delays the wave of excitation
  so the atria completes contraction and the ventricles fill, ensuring that the ventricles contract after the atria.

Question 6

What is step 3 in the cardiac cycle?

Answer 6

• The AVN passes the wave of excitation to the bundle of His in the septum. The wave of excitation is passed through the bundle of His to the apex of the heart.
• From the bundle of His, the wave of excitation passes through Purkinje fibres in the muscle of the ventricles. The spread is upwards through the ventricle walls, so the contraction begins at the apex.