Communication between heart and brain

• Myogenic


  The heart is able to initiate its own contraction within muscle cells. This allows it to maintain a consistent and regular rhythm of beating, ensuring continuous blood flow.
• the sinoatrial node connects to two nerves located in the medulla:

  • the accelerator nerve
  • the inhibitory nerve
• Acceleratory nerve

  • part of the sympathetic nervous system
  • higher frequency of impulses to SAN, to increase heart rate
• Inhibitory nerve

  • part of parasympathetic nerve and decreases heart rate by delivering a lower frequency of impulses to SAN
• Parasympathetic (resting)

  parasympathetic neurones secrete acetylcholine (neurotransmitter) which decreases heart rate.
• Sympathetic neurones

  Secrete noradrenaline (neurotransmitter) which increases heart rate.
• Types of receptors

  • chemoreceptors
  • baroreceptors
• Chemoreceptors

  Detect chemical changes such as CO2 concentration and blood pH. they are found in medulla
• Baroreceptors

  Detect changes in blood pressure and are found in carotid arteries and aorta
• Chemoreceptors at high blood oxygen, pH, or low CO2

  1. impulses sent from chemoreceptors to medulla, sending an impulse down parasympathetic neurones.
  2. this causes acetylcholine to be releases in the cardiac cycle, binding to receptors on SAN
  3. heart rate will slow to return levels to normal
• Chemoreceptors at low blood oxygen, pH or high CO2

  1. when these changes are detected, impulses are sent down the sympathetic neurones by medulla
  2. this causes noradrenaline to be released in the cardiac muscle, binding to receptors on the SAN
  3. heart rate will speed up to return to normal levels
• Steps that occur when heart rate increases:

  1. Receptors send an impulse to the cardioregulatory centre, located in medulla
  2. the impulse gets sent to sinoatrial node along sympathetic neurone where depolarisation occurs. The SAN releases noradrenaline which results in an increased heart rate.
• cardiac output

  the volume of blood pumped by the heart per minute
• role of thyroxine

  Boosts metabolism and increases heart rate by enhancing sensitivity of the heart to adrenaline and noradrenaline.
• role of adrenaline

  Released during stressful situations, triggering fight or flight response. this enhances blood flow to the medulla, providing more oxygen and glucose for aerobic respiration.