control of the heartbeat

• What type of muscle is cardiac muscle?

  Myogenic
• How does cardiac muscle contraction occur?

  It is stimulated from within the cardiac muscle
• Why can't individual heart cells beat randomly?

  The heart wouldn't function as a pump
• What initiates the cardiac cycle?

  The sino-atrial node (SAN)
• What role does the sino-atrial node (SAN) play?

  It acts like a pacemaker for the heart
• How does the SAN affect other cardiac muscle cells?

  It sets the rhythm for all other cells
• How does the SAN contract compared to the rest of the heart muscle?

  It contracts slightly faster
• What happens when the SAN contracts?

  A wave of electrical activity spreads rapidly
• What is the effect of the electrical activity from the SAN?

  It causes simultaneous contraction of atrial walls
• What is the role of the atrio-ventricular node (AVN)?


  It causes a delay before ventricles contract
• How long is the delay caused by the AVN?

  0.1 seconds
• What does the AVN do after receiving the impulse?

  It passes the impulse down the bundle of His
• What does the bundle of His branch into?

  Purkinje tissue
• Where does the electrical impulse spread after the apex?

  Outwards and upwards through the ventricle walls
• What is the result of the ventricles contracting from the base upwards?

  All blood is pumped out into the arteries
• What is an electrocardiogram (ECG) used for?

  To measure electrical activity of the heart
• How is an ECG recorded?

  Electrodes are attached to the chest
• What does the ECG trace show?

  The electrical activity during heartbeats
• How do you calculate the average resting heart rate?

  Count spikes in 4 seconds, multiply by 15
• What happens to the ECG spikes during exercise?

  They become more frequent but same shape
• what does P show on ECG?

  -SAN generates wave of excitation

  -Causes depolarisation of atria

  -Causes contraction of atria
• what does Q,R,S show on ECG?

  -AVN relays waves of excitation

  -Passes through Bundle of His

  -Depolarisation of ventricles

  -Causes contraction of ventricles
• what does T show on ECG?

  -repolarisation of ventricles

  -causes ventricular disatole (relaxation of ventricles)