Electrophysiology

• how do cardiac cells contract?


  spontaneously (myogenic) - beat by themselves
• how to co-ordinate cardiac muscle?

  use a pacemaker
• structure of cardiac cell:

  • mononucleated
  • striated
  • intercalated discs
• what is an intercalated disc?

  gap junctions, which allow the transmission of ions and action potential
• what is unusal about cardiac cells?

  they can be branched
• what holds intercalated discs together?

  desmosomes
• how is contraction stimulated?

  action potentials
• what is the the resting potential of cardiac muscle?


  -90mV
• why are cardiac action potential differ to the rest of the body?


  different action potential to stop spazming
• what occurs if some cardiac cells are hypoxic?

  Na channels are affected
• Describe the membrane potential of cardiac muscle after action potential:

  • initial intense peak
  • with slow refractory period - long time of depolarisation
• what is ca2+ used for in cardiac cell?

  contraction
• what does long refractory period mean?

  allows relaxtion, so ventricles can between fill
• which nervous system controls heart beat in synchrony?

  autonomic
• what may influence heart beat?

  caffeine or nicotine
• what is the regulation system in the heart called?

  nodal system
• what is the pacemaker?


  sinoatrial node
• what does the bundle of His do?

  branches into septum by the Purkinje fibres in ventriculars walls
• what are the stages of the cardiac conduction?

  1. SAN produce electrical impulses
  2. impluses spread through atria - contraction
  3. impluses moves through AV node towards ventricles - delays signal (allows time for atria to completely depolarise, contract and empty)
  4. impluse transmitted to ventricular muscle via Purkinje fibres to stimulate contraction
• what are the resting potential of the heart nodes?


  -60mV
• what leads to the depolarisation of SAN?

  funny channels
• how do SAN and AVN depolarise?


  spontaneously and slowly
• where does calcium go through?

  L-channels
• what is the pacemaker potential?

  Funny current (Na+) and T-channel (Ca2+) to allow threshold to be reached
• where is information from chemo/baro receptors processed?

  in medulla oblongata
• How to increase SA node firing?

  • muscarinic receptor antagonist
  • beta adrenergic receptor agonist
  • circulating catecholamine
  • hypokalemia
  • hyperthyroidism
  • hyperthermia
• how to decrease SA node firing?

  Parasympathetic stimulation
• what factors affect heart rate?

  • Hormones
  • age
  • fitness
  • sex
  • body temperature
• what does Parasympathetic stimulation, Muscarinic receptor agonist, β blockers, Ischaemia/hypoxia, Hyperkalemia, Sodium and calcium channel blockers, Hypothermia do?

  decrease SA node firing
• what are the three main issues with heart rate?


  Tachycardia, fibrillation, brachycardia
• what is tachycardia?


  >100bpm through stress, drugs, heart disease. May lead to death
• what is fibrillation?


  rapid, regular and unco-ordinated contraction
• what is brachycardia?


  <60bpm
• what may brachycardia imply?

  head trauma
• what are the waves of an ECG?

  P, QRS complex, T
• what is the P wave?

  atrial depolarisation
• what is QRS?

  onset of ventrciular depolarisation
• what is the T wave?

  ventricular repolarization
• when counting/measuring ECG where would you measure from?

  Tip of R
• why don't you see repolarisation of atria?

  masked by depolarisation of ventricles