Heartbeat

• What is the sino-atrial (SAN) node often called?

  Pacemaker of the heart
• What is the function of the SAN in the heart?

  It initiates and regulates the heart beat
• What do the specialized cardiac cells in the SAN do?

  They depolarize and generate action potentials
• What happens when the SAN generates an impulse?

  It causes simultaneous contraction of atrial walls
• Why does the SAN contract faster than other heart cells?

  It has an unstable resting potential
• How does the SAN ensure the heart squeezes from top down?

  By contracting slightly faster than other cells
• What does the wave of electrical activity from the SAN cause?

  Both right and left atrial walls to contract
• What occurs during atrial systole?

  The SAN sends an electrical impulse to both atria
• What is the role of the atrio-ventricular node (AVN)?

  It delays the impulse from the SAN
• How long does the AVN delay the impulse?

  About 0.1 seconds
• Why does the AVN delay the impulse?

  To allow atria to fully contract and empty
• Where is the bundle of His located?

  In the septum between the ventricles
• What does the bundle of His form?

  Two branches leading to Purkinje fibres
• What do Purkinje fibres do?

  Carry the electrical impulse through ventricular walls
• How do Purkinje fibres affect the ventricles?

  They cause the ventricles to contract simultaneously
• From where do the ventricles contract?

  From the apex upwards
• What type of stimulation does the heart require to beat?

  Myogenic stimulation from within its muscle walls
• What happens to the heart if it is isolated from its nerve supplies?

  It continues to beat, but irregularly
• Which part of the brain regulates heart rate?

  Medulla oblongata
• What is the function of the sinoatrial node (SAN)?

  It sends a wave of excitation across the atria
• What is the term for the contraction of the atria?

  Atrial systole
• What occurs during the wave of depolarization in muscle cells?

  The cells contract when they depolarize
• How does the wave of excitation travel from the atria to the ventricles?

  It is prevented by fibrous tissues between them
• Where is the atrioventricular node (AVN) located?

  In the septum at the atrioventricular junction
• What is the purpose of the AVN delaying the wave of excitation?

  To allow atria to complete contraction and ventricles to fill
• How does the wave of excitation travel after the AVN?

  It passes to the bundle of His in the septum
• Why is it important for the wave of excitation to pass through the apex of the heart?

  So the ventricles contract from apex upwards
• What are Purkinje fibres responsible for?

  Spreading excitation through the ventricular walls
• What does an electrocardiogram (ECG) measure?

  Electrical changes in the heart during the cardiac cycle
• What does the P wave in an ECG represent?

  Depolarization of the atrial walls
• What does the QRS complex indicate in an ECG?

  Depolarization of the ventricular walls
• What does the T wave in an ECG signify?

  Repolarization of the ventricular walls
• How can heart rate be calculated using an ECG?

  By measuring the time on the x-axis
• What does a trace showing no pattern in an ECG indicate?

  Ventricular fibrillation, indicating a heart attack
• What does atrial fibrillation look like on an ECG?

  P waves show random electrical activity across atria
• What does heart block indicate on an ECG?

  Some P waves are not followed by QRS complexes
• What is a common treatment for heart block?

  Installing a pacemaker in the AVN
• What can longer than usual P-Q intervals indicate?

  Possible heart block in the ECG trace
• What is bradycardia?

  Slow heart rate below 50 bpm
• What is tachycardia?

  Rapid heart rate above 100 bpm