Lecture 7

• amount breathing vary according to need:

  1. activity v rest: oxygen consumption can increase > 10-fold
  2. altitude: less oxygen in air so need work harder maintain oxygen supply
  3. disease: compromising gas exchange or delivery
• factors/sensors providing information to resp. centre —> respiratory centre —> target muscles controlling ventilation

  
• The respiratory centre involves the medulla oblongata and Pons

  
• Pons: regulates medulla

  Medulla: primary centre
• Ventral respiratory group contains mixed neurons, some fire during inspiration, some during expiration

  Dorsal repsiratory group contains neurons which fire during inspiration

  
• recipriocal inhibition of VRG and DRG during exercise

  
• receptors providing info to resp centre

  A) stretch

  B) respiratory

  C) irritant

  D) central

  
• central chemoreceptors specialised regions close to medulla resp. centres, but also close to rich blood supply.

  sensitive to CO2 & H+

  H+ cannot cross blood-brain barrier but CO2 can
• A rise of CO2 or a rise of [H+]

  (= fall of pH, or acidosis)

  stimulates the central 

  chemoreceptors and 

  increases ventilation
• Carotid and aortic bodies, sensitive to hypoxia, hypercapnia and acidosis

  
• glomus cell is the primary sensor of hypoxia
• hypoxia triggers calcium influx into glomus cells via depolarisation, which triggers release of transmitters which initate action potentials in afferent nerve.
• summary overall