heart action

• Control of the basic heartbeat is myogenic, what does this mean?

  the heart will beat without any external stimulus

  this intrinsic rhythm means the heart beats at around 60 times per minute
• What is the sinoatrial node (SAN)?

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


  to send out regular waves of electrical activity/depolarisation that causes the atria to contract
• What is the annulus fibrosus, what is it's role?

  a band of non-conducting collagen which prevents the waves of electrical activity from being passed directly from the atria to the ventricles

  instead, these waves of electrical activity are transferred from the SAN to the atrioventricular node (AVN)
• What is the atrioventricular node (AVN) responsible for?

  passing the waves of electrical activity on to the bundle of His

  but there's a slight delay before the AVN reacts, to make sure the ventricles contract after the atria have emptied
• What is the bundle of His?

  a group of muscle fibres responsible for conducting the waves of electrical activity to the finer muscle fibres in the right and left ventricle walls : Purkyne tissue
• What is the role of the purkyne tissue?

  to carry the waves of electrical activity into the muscular walls of the right and left ventricles, causing them to contract simultaneously, from the bottom up
• What are the events in sequence?

  sinoatrial node sends out regular waves of electrical activity (or wave of excitation)

  atria contract

  atrioventricular node passes the waves of electrical activity onto the bundle of His, after a slight delay

  purkyne tissue conducts the waves of electrical activity

  ventricles contract
• • The SAN sends out a wave of excitation and this spreads across both atria, causing atrial systole.
  • Non-conducting tissue called the Annulus fibrosus prevents the excitation from spreading to the ventricles and so this ensures that atria and ventricles don’t contract at the same time.
  • The AVN then sends the wave of excitation to the ventricles after a short delay, ensuring that the atria have time to empty their blood into the ventricles.
  • The Purkyne fibres conduct the excitation down the septum of the heart, before the excitation is carried upwards in the walls of the ventricles.
• 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.
• What is special about cardiac muscle?

  it is myogenic, meaning it contracts on its own accord/automatically

  but the rate of contraction is controlled by a wave of electrical activity
• Where is the sinoatrial node (SAN) located?

  in the right atrium

  it's known as the pacemaker
• Where is the atrioventricular node (AVN) located?

  near the border of the right and left ventricle within the atria still
• Where is the bundle of His located?

  it runs through the septum
• where are the Purkyne fibres located?

  in the walls of the ventricles
• control of the cardiac cycle:

  • SAN releases a wave of depolarisation across the atria, causing it to contract
  • AVN releases another wave of depolarisation once that first wave reaches it, there's a non-conductive layer between the atria and ventricles preventing the wave of depolarisation travelling down to the ventricles
  • instead it forces the wave to move down the bundle of His, which conducts the wave of depolarisation down the septum and the Purkyne fibres
  • as a result it causes the apex (bottom) of the heart and then walls of the ventricles to contract
  • there is a short delay before this
• last step

  • avn transmits the second wave of depolaristaion thus there's a short delay before the walls of the ventricles contract
  • this allows enough time for the atria to pump all the blood into the ventricles
  • the cells repolarise and the cardiac muscle relaxes