cardiac conduction system

• Explain hormonal control


  Adrenaline is a stress hormone released by the sympathetic nervous system

  This stimulates the SA node to increase speed / force of contraction
• Explain neutral control


  - Sympathetic nervous system ( increases HR )

  - Parasympathetic nervous system ( decreases HR )
• Cardiac conduction system in order

  ( the heart is myogenic as it generates its own impulse )

  - The impulse starts at the SA node ( pacemaker )

  - The electrical impulse then spreads through the atria walls causing them to contract ( ATRIAL SYSTOLE )

  - The impulse then passes to the AV node, this delays the impulse for 0.1 seconds to allow atria to fully contract

  - The electrical impulse then passes down the BUNDLE OF HIS located in the septum which separates into 2 bundle branches

  - Finally the impulse spreads to PERKINJE FIBRES which cause ventricles to contract ( VENTRICULAR SYSTOLE )
• What do different receptors detect

  Chemoreceptors - change in CO2

  Baroreceptors - change in BP

  Proprioceptors - change in muscle movement
• How do receptors control HR during exercise

  - impulse sent to cardiac control centre in medulla in brain

  - SNS switched on and adrenaline released

  - Sympathetic nervous system sends impulse to SA node to increase HR
• How do you solve cardiovascular drift

  Hydration as increases venous return
• Explain cardiovascular drift


  Where stroke volume and venous return decreases when exercising for 10 minutes in warm environment

  - sweat is released from plasma in blood ( loss of fluid )

  - more viscous blood ( thicker ) means slower venous return

  - means less diastolic filling

  - no stretch of cardiac muscle therefore stroke volume is decreased

  - HR still increases to compensate for SV decrease