Electrical Activity in the Heart (Edexcel A (SNAB) A Level Biology)

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Electrical Activity in the Heart

  • 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
  • There 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
  • Purkyne fibres spread around the ventricles and initiate the depolarisation of the ventricles from the apex (bottom) of the heart
  • This makes the ventricles contract from the bottom upward and blood is forced out of the ventricles into the pulmonary artery and aorta

Stages in the Cardiac Cycle Table

Stages in the Cardiac Cycle Table

Electrical Activity of the Heart_1

The wave of depolarisation spreads across the heart in a co-ordinated manner

Examiner Tip

Remember that the heart is myogenic, which means that the heart will generate a heartbeat by itself and without any other stimulation. Instead, the electrical activity of the heart regulates the heart rate. Be aware that you may sometimes see an alternative spelling of "Purkyne" as "Purkinje" they mean the exact same thing!

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Marlene

Author: Marlene

Expertise: Biology

Marlene graduated from Stellenbosch University, South Africa, in 2002 with a degree in Biodiversity and Ecology. After completing a PGCE (Postgraduate certificate in education) in 2003 she taught high school Biology for over 10 years at various schools across South Africa before returning to Stellenbosch University in 2014 to obtain an Honours degree in Biological Sciences. With over 16 years of teaching experience, of which the past 3 years were spent teaching IGCSE and A level Biology, Marlene is passionate about Biology and making it more approachable to her students.