Baroreceptors

• Baroreceptors:

  • free nerve endings
  • detect stretch
  • situated within the carotid sinus of the carotid artery and also the aortic arch

  A) baroreceptors

  B) carotid artery

  C) carotid sinus

  D) baroreceptors

  E) aortic arch

  
• Baroreceptors:

  • excitation is caused by high pressure (increase in blood pressure) causing stretching of arteriole walls
  • excitation will therefore decrease blood pressure
  • activation of baroreceptors will decrease activity of the vasomotor centre via action potentials i.e. baroreceptors inhibit the vasomotor centre
  • so there is a decrease in sympathetic activity to arterioles, causing vasodilation
  • smooth muscle relaxes, lumen opens up, reduced resistance to blood flow -> decreased total peripheral resistance-> decreased blood pressure

  
• Baroreceptors:

  • remember
  • input from baroreceptors inhibit the vasomotor centre - so when there's increased blood pressure -> more stimulation of baroreceptors -> more traffic to vasomotor centre -> more inhibition -> more vasodilation
  • output from the vasomotor centre is only via sympathetic nerves to the arterioles - so when baroreceptors cause more inhibition of vasomotor centre -> decreased action potentials through sympathetic nerves to arterioles -> vasodilation

  
• Baroreceptors:

  • since the vasomotor centre communicates with the cardioinhibitory and cardioexcitatory centres, the baroreceptors directly affect the vasomotor centre and indirectly affect the heart
  • so when reducing blood pressure, we want to cause vasodilation via the vasomotor centre and decrease cardiac output of the heart via excitation of the cardioinhibitory centre via the vagus nerve, decreasing action potentials, so decrease heart rate
• when VMC activity is decreased:

  • vasodilation of arterioles
  • decreased TPR
  • decreased BP
  • vasodilation of veins, making them act as capacitors instead of returners
  • decreased venous return
  • decreased CO
• Cross-chat/communication between VMC & cardiac centres means baroreceptors also causes:

  • inhibition of the cardioexcitatory centre
  • excitation of the cardioinhibitory centre
• What happens to baroreceptors when BP is low:

  • baroreceptors dont get stimulated, so the number of action potentials they convey is lower than normal
  • so theres less sympathetic traffic from BR to the vasomotor centre -> less inhibition of vasomotor centre -> increased action potentials to arterioles down sympathetic nerves -> increase vasoconstriction of arterioles -> increase resistance to blood flow -> increase total peripheral resistance -> increase blood pressure
• What happens to baroreceptors when BP is low:

  • baroreceptors dont get stimulated, so the number of action potentials they convey is lower than normal
  • also causes inhibition of cardioinhibitory centre and excitation of cardioexcitatory centre -> increase sympathetic activity to heart -> increase heart rate (via pacemaker cells) + inotropy (via ventricular muscle mass) -> increase stroke volume
  • increase of stroke volume + heart rate = increase CO -> increase blood pressure
• • baroreceptors allow for a buffer control, allowing for a steady range of blood pressure
  • someone with normal BR would have steady blood pressure, whereas someone with abnormal BR would have a fluctuating blood pressure