Coordination of Heart Action
Applied Science: BTEC Level 3 National Extended Diploma, topic 4.5.7
The Heartbeat
With every heartbeat, the cardiac muscle contracts and relaxes without stimulation by nerves. Cardiac muscle is myogenic: it is self-stimulating. The processes involved in one heartbeat are:
Sinoatrial node (SAN)
- The SAN is located in the wall of the right atrium.
- The SAN acts as a pacemaker by transmitting waves of electrical activity along the walls of the atria at regular intervals.
Contraction of the atria
- The electrical waves from the SAN cause the right and left atria to contract together.
- This forces blood in the right atrium into the right ventricle and blood in the left atrium into the left ventricle.
Atrioventricular node (AVN)
- The waves of electrical activity cannot pass from the atria to the ventricles due to a collection of non-conducting tissue.
- This creates a delay to ensure the atria are empty before the ventricles begin to contract.
- The electrical activity passes through the AVN to the bundle of His.
- The bundle of His is a collection of conducting tissue that transmits the electrical activity to the apex (bottom) of the heart and around the ventricle walls along fibres called the Purkyne fibres.
Contraction of the ventricles
- As the waves of electrical activity pass along the Purkyne fibres, the ventricles contract together.
- Blood is forced out of the ventricles and out of the heart.
Test yourself on Coordination of Heart Action
The Heartbeat
What is the purpose of the delay of transmission of electrical activity through the AVN?
Which of the following statements about the heart are true?