Heart Action (Cambridge (CIE) A Level Biology): Revision Note

Heart action: initiation & control

• Control of the basic heartbeat is myogenic, which means the heart will beat without any external stimulus

• This intrinsic rhythm means the heart beats at around 60 times per minute

• The sinoatrial node (SAN) is a group of cells in the wall of the right atrium

  • The SAN initiates a wave of depolarisation that causes the atria to contract

• The Annulus fibrosus is a region of non-conducting tissue which prevents the depolarisation spreading straight to the ventricles

  • Instead, the depolarisation is carried to the atrioventricular node (AVN)

  • This is a region of conducting tissue between atria and ventricles

• After a slight delay, the AVN is stimulated and passes the stimulation along the bundle of His

  • This delay means that the ventricles contract after the atria

• The bundle of His is a collection of conducting tissue in the septum (middle) of the heart

  • The bundle of His divides into two conducting fibres, called Purkyne tissue, and carries the wave of excitation along them

• The Purkyne fibres spread around the ventricles and initiate the depolarization of the ventricles from the apex (bottom) of the heart

  • This makes the ventricles contract and blood is forced out of the pulmonary artery and aorta