ANS + Pacemaker Cells

• • myogenic rates of depolarisation are modulated by the autonomic nervous system
  • so both the sympathetic and parasympathetic nervous systems innervate pacemaker cells within the sinoatrial and atrioventricular nodes
  • although both SNS and PNS synapse at the nodes, they dont work at the same time, one NS is supressed whilst one is dominant
  • sympathetic NS speeds up heart rate
  • parasympathetic NS slows down heart rate
• • PNS (e.g. vagus nerve) slows rate of sinoatrial node depolarisation -> decreased heart rate (negative chronotropy)
  • SNS speeds up sinoatrial depolarisation -> increased heart rate e.g. in exercise (positive chronotropy)
  • PNS and SNS nerves must synapse directly with pacemaker cells
  • but SNS hormones (catecholamines, especially epinephrine) make contact with pacemaker cells
  • catecholamines include epinephrine (adrenaline) and norepinephrine (noradrenaline)
• • pacemaker cells are affected by the SNS and PNS which is controlled by the ANS
  • the ANS is controlled by the medulla oblongata, which controls vital senses and contains your cardiac centres
  • there are 2 cardiac centres
  • cardioinhibitory centre for the PNS - information sent via the vagus nerve
  • cardioexcitatory centre for the SNS - information sent via the sympathetic cardiac nerve

  A) medulla oblongata

  B) cardioinhibitory centre

  C) parasympathetic

  D) cardioexcitatory centre

  E) sympathetic

  F) vagus nerve

  G) sympathetic cardiac nerve

  
• • the adrenal medulla is part of the adrenal gland
  • there is one adrenal gland on each kidney
  • when the SNS is activated, it will activate the sinoatrial node, but it will also send action potentials to the adrenal medulla, where the catecholamines (adrenaline and noradrenaline) are made and stored and then released into the blood stream