heartbeat

• heart muscle is myogenic - it can contract and relax without receiving signals from nerves
• SAN

  1. Sending out regular waves of electrical activity to the atria walls

  2. Causing right and left atria to contract together
• Non-conducting collagen tissue


  Prevents waves of electrical activity from being passed directly from atria to ventricles
• AVN

  1. Responsible for passing the wave to bundle of his

  2. Delay before AVN reacts to ensure ventricles contract after atria has emptied
• Bundle of his

  Muscle fibres responsible for conducting the waves to finer muscle fibres in the right and left ventricle walls
• Purkyne tissue


  Carries waves of electrical activity into muscular walls of right and left ventricles causing them to contract together from the bottom up
• Action of the heart initiation and coordination

  Heartbeat is initiated from within the heart itself, heart triggers its own beat, heart muscle is myogenic, sinoatrial node (SAN) depolarizes triggering electrical excitation, wave of electrical excitation spreads across the atria causing atrial systole, atrioventricular node (AVN) connected to perkin fibers, AVN transmits electrical excitation down perkin fibers causing ventricles to contract from apex upwards, slight delay in AVN ensures ventricles contract after atria have contracted
• The heart does not need an external signal to beat because it triggers its own beat
• Myogenic


  Heart muscle is able to trigger its own beat
• Sinoatrial node (SAN) is a group of specialized cells in the wall of the right atrium
• Sinoatrial node (SAN) is also called the pacemaker
• Cells in the sinoatrial node (SAN) depolarize, becoming electrically excited, triggering a wave of electrical excitation to spread across the atria causing atrial systole
• Wave of electrical excitation cannot pass directly from atria to ventricles due to a layer of non-conducting tissue separating them
• Atrioventricular node (AVN) is a group of specialized cells between the atria
• Atrioventricular node (AVN) is connected to perkin fibers
• Perkin fibers initially bundled together are called the bundle of His
• Perkin fibers branch with fibers running down to the apex or base of the heart and then up the walls of the ventricles
• Atrioventricular node (AVN) detects electrical excitation passing over the atria and transmits it down the perkin fibers causing the ventricles to contract
• Ventricles contract from the apex upwards to ensure maximum volume of blood is pumped out
• Slight delay in atrioventricular node (AVN) ensures ventricles contract after atria have contracted
• Events taking place in the heart during the heartbeat are called the cardiac cycle
• 1. wave of electrical excitation starts at SAN, causes atria to contract starting the heartbeat
  2. electrical activity from the SAN is picked up by AVN, and it creates a slight delay before stimulating the bundle of his
  3. bundle of his splits into 2 branches and conducts a wave of excitation to the apex of the heart
  4. at the apex purkyne fibres spread out through the ventricle walls and this triggers the contraction of the ventricles starting from the apex