Cardiac conduction system

Question 1

What is the Cardiac conduction system?

Answer 1

• The cardiac conduction system is a group of cells located in the wall of the heart.
• These cells are responsible for the contraction of the heart.

Question 2

The heart (myogenic)

Answer 2

• The heart is a special muscle in that it generates its own impulses (they are not sent from the brain, it controls itself).
• The heart muscle is called myogenic (generates its own impulses).
• In order for the heart to work properly the blood needs to flow through in a controlled manner (in through atrium/ out through the ventricle).

Question 3

How does it work? pt.1

Answer 3

1) An electrical signal is sent from the sinoatrial node (SAN).
- This electrical impulse then spreads through the heart like a Mexican wave (wave of excitation).
2) This impulse first reaches the atriums, causing them to contract (atrial systole).
3) Blood flows into the ventricles.
4) The impulse passes through the atrioventricular node (AVN).

Question 4

How does it work? pt.2

Answer 4

5) The AVN delays the impulse for 0.1 seconds to enable the atria to fully contact.
6) The impulse then spreads down some specialised fibres called the Bundle of his (found in the septum).
7) The impulse continues through the smaller bundles called Purkinje fibres.
8) The ventricles now contract (ventricular systole).

Question 5

Cardiac conduction system (SIMPLIFIED)

Answer 5

1. SAN
2. Atrial systole
3. AVN (delay)
4. Bundle of his
5. Purkinje fibres
6. Ventricular systole

Question 6

During exercise

Answer 6

• The cardiac control centre ensures that heart rate increases during exercise.
• However, what causes the impulses to fire quicker or slower are controlled by 2 systems:
  1) Sympathetic nervous system- impulses fire quicker.
  2) Parasympathetic nervous system- impulses fire slower.