Normal heart beat

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  • Created by: katie
  • Created on: 23-03-13 15:01
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  • Normal heart beat 
    • Heart muscle is myogenic 
      • It can contract without any nerve stimulation. 
    • The stimulus to contract originates in the sinoatrial node (SAN) 
      • Which controls the rate of beating / acts as pacemaker 
      • It is situated in the wall of the right auricle / atrium 
      • Electrical impulse from the SAN causes the two auricles / atria to contract 
        • Thin layer of connective tissue prevents the stimulus spreading to the ventricles 
          • At the bottom of the wall separating the two auricles / atria is the atrioventricular node AVN 
            • This delays the impulse (about 0.1 sec) before passing it on to the ventricles 
              • The impulse is sent to the tip/apex of the ventricles 
                • Along bundle branches (Bundle of His) 
                  • And is conveyed upwards along the branching Purkinje fibres 
                    • Causing a wave of ventricular contraction starting from the lowermost part of the ventricle 
    • The SAN may be stimulated by various factors to change its pacing 
      • One example – hormones (adrenalin), exercise, body temperature, etc. (allow: ref. autonomic nervous system) 


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