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  1. 1. Dr Archna Ghildiyal Associate Professor Department of Physiology KGMU Respiratory System
  2. 2. LECTURE:8 Contents • Regulation of Respiration: Neural • Group of Neurons controlling Respiration • Breathing rhythm: Ramp Signals • Lung Receptors
  3. 3. Learning Objectives • NeuralControl of Respiration : - Automatic -Voluntary • I & E Neurones • Inspiratory “Ramp” Signal • Pre-Botzinger Complex • Lung Receptors
  4. 4. Neural Control of Respiration Breathing • Automatic/Spontaneous • Voluntary
  5. 5. Neural control of Respiration
  6. 6. Groups of Neurons in the Respiratory Center In medulla • Dorsal respiratory group • Ventral respiratory group In Pons • Pneumotaxic center • Apneustic Center?
  7. 7. Dorsal Respiratory Group(DRG) • Most neurons located within NTS, some in adjacent reticular substance of medulla • Normal quiet breathing: Repititive Inspiratory signals from DRG Controls • Inspiration • Respiratory rhythm
  8. 8. Inspiratory “Ramp” Signals • Rhythmical Inspiratory discharge from DRG • Nervous signal that is transmitted to the inspiratory muscles, mainly the diaphragm • Begins weakly & increases steadily for about 2 secs in normal respiration (inspiration) • Then ceases abruptly for approx next 3 secs (expiration)
  9. 9. Control of Inspiratory Ramp 1.Control of the rate of increase of the ramp signal rate of ramp signal - ramp increases rapidly - fills the lungs rapidly 2.Control of the limiting point at which the ramp suddenly ceases • Usual method for controlling the rate of respiration; shortens the duration of Inspiration & Expiration(frequency of respiration )
  10. 10. Contd… Stopping the Ramp  Shortens the rate of inspiration and expiration  Increasing the frequency of respiration
  11. 11. Pneumotaxic center (upper pons) • Located dorsally in upper pons,in N.parabrachialis • Sends continual inhibitory impulses to inspiratory center • Ramp controls stopping point of DRG • Inhibits I neurons • Switch breathing from inspiration to expiration
  12. 12. Contd… • As impulse frequency rises: Faster and Shallower Breathing • Damage to Pneumotaxic center : Results in increased depth of inspiration
  13. 13. Ventral respiratory group(VRG) • Located in ventrolateral part of medulla,in N.ambigues & N.retroambigues • Functions in both Inspiration & Expiration • Remain inactive during normal quite respiration
  14. 14. Contd… • Act as Overdrive mechanism (as in heavy exercise) • Powerful expiratory signals to internal intercostal & abdominal muscles
  15. 15. Pre-Bötzinger Complex • Cluster of interneurons in the ventrolateral medulla of the Brainstem • Contains Pace maker Cells- Spontaneous Breathing
  16. 16. Apneustic Center (Lower Pons) • Role not clear • Stimulation causes Apneusis( pause at full inspiration) • Integrates inspiratory cut-off information
  17. 17. Mechanism of Rhythmic Ventilation –Medullary respiratory center neurons are continuously active (spontaneous/automatic breathing) –Combined input from all sources (receptors,brain) causes action potentials to stimulate respiratory muscles
  18. 18. To Increase Inspiration More and more neurons get activated To Stop Inspiration Neurons receive input from pontine group and stretch receptors in lungs Inhibitory neurons activated , cause Inspiratory switch-off , Start of expiration Effect: Relaxation of Inspiratory muscles
  19. 19. Voluntary control • Provided via the Cerebral Cortex • Modulate the activity of controlling centers in the medulla and pons • Allow the rate and depth of respiration to be controlled • During speaking, laughing, crying, eating, defecating, coughing, and sneezing
  20. 20. Contd… • Chemoreceptor reflex is capable of overriding it. • Conscious control of respiratory neuronal networks in the reticular formation can effect other basic functions regulated by the brainstem(Yogic exercises)
  21. 21. Contd… • Stimulation of the reticular activating system of the brainstem (RAS):Stimulates Ventilation • Sleep: Ventilation
  22. 22. Peripheral receptors • Chemoreceptors • Pulmonary irritant receptors-on stimulation cause coughing,sneezing,bronchial constriction • Lung “J Receptors” • Hering-Breuer inflation reflex
  23. 23. Lung “J Receptors” • Indian Physiologist Prof A S Paintal • Location:Sensory nerve endings in alveolar walls in juxtaposition to pulmonary capillaries • Stimulus: Severe exercise, Engorged capillaries,Pulmonary oedema • Effect:Tachypnea,Hypotention,Bradycardia
  24. 24. J-Reflex • Stimulation (severe exercise)  • Inhibition of gama motor neurons supplying muscle spindle  • Muscle Tone  • Muscle Weakness & Stoppage of Exercise
  25. 25. Hering- Breuer Inflation Reflex • Protective reflex • Lung inflation signals limit inspiration • Stretch Receptors: In Muscular Walls Of Bronchi & Bronchioles • Active when Tidal volume > 1.5 liters/breath • Inspiratory ramp :“Switches off”
  26. 26. References • John E. Hall.Guyton & Hall Text book of Medical Physiology. A south Asian ed: New Delhi: Elsevier.2013.p. 364-373 • Kim E. Barrett, Heddwen L. Brooks, Scott Boitano, Susan M. Barman.ed:23rd Ganong’s Review of Medical Physiology:Mc Graw Hill • http://meded.ucsd.edu/ifp/jwest/resp_phys/ student_files.html
  27. 27. Question:1 Respiratory control centers are located in the : A) Midbrain and Medulla B) Medulla and Pons C) Pons and Midbrain D) Upper Spinal Cord and Medulla
  28. 28. Question:2 Damage to Pneumotaxic center results in: A) Decreased depth of Inspiration B) Increased depth of Inspiration C) Increased depth of Expiration D) Decreased depth of Expiration
  29. 29. Question:3 Stimulation of the reticular activating system of the brainstem (RAS) plays what role in ventilation? A) Stimulates ventilation B) Inhibits ventilation C) Stimulates inhalation but inhibits exhalation (apneustic breathing) D) Stimulates exhalation but inhibits inhalation
  30. 30. Question:4 Destruction of which part abolishes automatic respiration? A) Pre-Botzinger complex B) Ventral group of respiratory neurons C) Dorsal group of respiratory neurons D) Section at the inferior border of the pons
  31. 31. Question:5 Which of the following statement is true? A) Hering Breuer inflation reflex respond to lung distension by increasing frequency of respiration. B) Irritant receptors respond to noxious gases by reflex bronchodilatation C) J receptors respond to pulmonary capillary congestion by rapid shallow breathing D) DRG neurons initiate expiration
  32. 32. Answers 1-B 2-B 3- A 4- A 5-C