Read the summary and the most important questions on Human Anatomy and Physiology

• 1. Physiology heart

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• How is the membrane potential determined?

  • Concentration differences
    
  • Permeability to ions

• If you look at this graph, what happens at which points?

  0: Na+ channels open, this starts depolarisation (inside of the membrane gets positive)
  2: Ca2+ channels open, this starts repolarisation (inside of the membrane gets more positive)
  3:  K+ channels open (inside of the membrane gets negative)
  4: Na+ and Ca2+ come to the inside of the membrane from adjacent cells

• By what is the heart rate determined?

  • Resting membrane potential of SA node cell
    
  • Velocity of depolarisation: slope of the prepotential

• What determines the slope of the prepotential?

  Na+

• What happens to the prepotential slope if you increase the heart rate? And how can the heart rate be increased?

  (Nor)adrenaline activates the sympathetic NS and causes more Na+/Ca2+ to move into the cell, giving a smaller prepotential slope.

• What happens to the prepotential slope if you decrease the heart rate? And how can the heart rate be decreased?

  Acetylcholine activates the parasympathetic NS and caused the K+ channels to remain open, this results in a bigger prepotential slope.

• What is the refractory period? Why do you need this?

  The period in which cells are inexcitable (Na+ channels are not reset). You need this in order for cells not to be overstimulated.

• What is the difference in absolute and relative refractory period?

  During the absolute refractory period it is ABSOLUTELY impossible to have a new action potential. During the relative refractory period a new action potential is inhibited but not impossible.

• What initiates contraction?

  Ca2+ binding to myofilament

• Describe a single heart beat at cellular level.

  • Electrical signal from neighbouring cell (CM, SA node, conduction system)
    
  • Action potential
  • • Na+ influx
    • Ca+ influx
    • K+ influx
  • Ca2+ induced Ca2+ release (CICR)
  • Ca2+ binding to myofilaments
  • Power stroke --> cell shortening
  • Ca2+ release from myofilaments
  • Reuptake in SR --> relaxation