IB Cardiac Cycle 2

IB Cardiac Cycle 2

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  • gulps...
  • Now explain to me what I just told you... NOW.
  • Pacemaker cells generate their own action potentials. They are found in the sinoatrial node in the right atria. Therefore, the sinoatrial node is the natural pacemaker. Pacemaker cells spread their electrical impulses to cardiac muscle cells throughout the atria. Impulses leap across synapse-like connections between the cells called gap junctions and continue down the conduction system until they reach the atrioventricular node located just above the tricuspid valve.
  • Keep going...
  • Because gap junctions allow electric charges to flow freely between cells, the contraction which originated in the SA node spreads very rapidly across the entire atrium as if it were one cell. This causes the atria to undergo systole. From the AV node, the signal travels straight down to the inferior end of the heart. The path the electrical impulse takes to the bottom of the heart is called the atrioventricular bundle, where it branches out to the left and right ventricles.
  • Keep going...
  • Signals disperse out in the Purkinje fibres, which trigger depolarisation in all surrounding cells, causing the ventricles to contract from the bottom up (systole). This snaps the atrioventricular valves shut, and after the ventricles are emptied, the semilunar valves close. The ventricles begin diastole, and the atrioventricular valves open and the ventricles start filling with blood.
  • Keep going...
  • Finally, all four chambers are in diastole and filling. When the atria are filled and the ventricles are 70% filled, the cycle has ended.
  • ... and then... ?
  • Okay. Thank you sir. Goodbye.
  • Hmm... good job. You can go now.
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