Neural Regulation of Respiration

1. Neural Regulation of
Respiration
Dr. Sai Sailesh Kumar G
Assistant Professor
Department of Physiology
RDGMC

2. Learning objectives
 List the respiratory centers
 Describe organization of respiratory centers
 Enumerate the peripheral inputs affecting
respiration including peripheral receptors
 Describe the Hering - Breuer reflex

3. Introduction
The nervous system adjusts rate of alveolar
ventilation almost exactly to the demands of the body
so that PO2 and PCO2 in the blood are hardly
altered, even during heavy exercise and most other
type of respiratory stress

4. Regulation of respiration
 Voluntary regulation
(Cerebral cortex)
 Involuntary regulation
1. Neural regulation
2. Chemical regulation

5. Advantage of voluntary control
 Facilitates activities like talking, swimming,
singing, laughing, breath holding and hyper
ventilation

6. Voluntary control

7. Advantage of involuntary control
Can breath even during sleep

8. RESPIRATORY CONTROL SYSTEM

9. Why Respiratory centre
1. To generate respiratory rhythm
2. To control rate and depth of respiration

10. Respiratory centre
 Composed of several groups of neurons located
bilaterally in the medulla and pons (brain stem)
1. Dorsal Respiratory Group – mainly for inspiration
2. Ventral Respiratory Group – inspiration and expiration
3. Pneumotaxic Center – Causes transition of inspiration
to expiration (controls rate and depth of breathing)
4. Apneustic center – Causes prolonged inspiration

11. Respiratory center

12. Dorsal Respiratory Group (DRG)
 Plays fundamental role in control of respiration
 Located in the dorsal portions of medulla
 Most of its neurons located in the nucleus of tractus
solitarius (NTS)
 NTS is the sensory termination of both the vagal and
glossopharyngeal nerves that transmits sensory
signals into respiratory system

13. Dorsal Respiratory Group (DRG)

14. Rhythmical inspiratory discharges
 DRG generates basic rhythm of respiration
 Cause for this basic rhythm is unknown
 In primitive animals a neural network was found
 One set of neurons (self excitatory) excites second set of
neurons
 This second set of neurons inhibits the first
 After a period, the mechanism repeats itself and continues
through out the life
 Similar mechanism was expected to present in humans

15. Inspiratory ramp signal
 Nervous signal transmitted to the inspiratory muscles are not
instantaneous burst of action potentials
 Signals begins weakly and increase steadily in a ramp
manner for abut 2 seconds in normal respiration
 Contraction of inspiratory muscles- inspiration
 It then stops for approximately next 3 seconds
 Turn off excitation of inspiratory muscles
 Elastic recoil of lungs and chest wall - expiration
 Inspiratory signals begin for another cycle
 This cycle repeats again and again

16. INSPIRATORY RAMP
2 Sec
2 Sec
3 Sec
ALLOWS SLOW FILLING OF LUNGS

17. Advantage of ramp signal
 Causes steady increase in the volume of the lungs
during inspiration
 Prevents inspiratory gasps

18. Respiratory cycle
DRG
inspiratory
ramp signals
Sensory neurons
(mainly to diaphragm)
Contraction of
inspiratory
muscles-
Inspiration occurs
Switch off – ramp
signal
Elastic recoil of
lungs and chest wall
Expiration take
place

19. Ventral Respiratory Group (VRG)
 Located on each side of medulla
 5 mm anterior and lateral to DRG
 Consists of four main nuclei
1. Botzinger complex- Controls expiration
2. Pre-Botzinger complex- sets pace of respiration
3. Nucleus ambiguus – Inspiratory neurons
4. Nucleus retro ambiguus – Inspiratory and expiratory neurons

20. Ventral Respiratory Group (DRG)

21. Functions of Ventral Respiratory
Group (VRG)
 Remains inactive during normal quiet inspiration
 Consists both inspiratory and expiratory neurons
 Active during forceful respiration
 Example – During exercise
 Electric stimulation of few neurons of VRG- inspiration
 Electric stimulation of few neurons of VRG- expiration
 VRG contributes for both inspiration and expiration

22. Apneustic Centre
 Located in the lower pons
 Stimulates DRG
 Increases inspiration
 Gets feedback from vagi and other centres

23. Pneumotaxic centre (PC)
 Located in the upper pons (parabrachial nucleus)
 Transmit signals to inspiratory area
 Controls switch off point of inspiratory ramp ( transition
of inspiration to expiration)
 Control filling phase of lung cycle
 Strong PC signals decreases the duration of inspiration
to 0.5 sec ( short time for filling of lungs)
 Weak PC signals increases duration of inspiration
(more time for filling of lungs)

24. Strong Pneumotaxic centre
signals
 Strong PC signals
 Duration of inspiration decreases
 Less time for filling of lungs
 Also decreases duration of expiration
 Frequency of respiration increases

25. Weak Pneumotaxic centre
signals
 Weak PC signals
 Duration of inspiration increases
 More time for filling of lungs
 Also increases duration of expiration
 Frequency of respiration decreases

26. RESPIRATORY CONTROL
ORGANIZATION:MODERN CONCEPT
 All the respiratory centers are termed as the
BULBOPONTINE RESPIRATORY NEURONAL COMPLEX
 There is an inspiratory ramp generator called Respiratory
Control Pattern Generator: Pre Bottzinger Complex

27. Feedback regulation
central and peripheral receptors
 Central chemo receptors – Located with in the medulla
(sensitive to PH)
 Peripheral chemo receptors – located in carotid and aortic
bodies ( sensitive to PO2, PCO2 and PH)
 Lung receptors (stretch receptors, irritant receptors,
J receptors)
 Receptors in joints/ muscles

28. Hering Breuer(HB) Reflex
 It is a volume reflex
 Receptors located in the muscular portions of bronchi
and bronchioles
 These receptors are un-myelinated nerve endings
 Receptors are stimulated when the airways stretched

29. HB Inflation reflex
 When airways over stretch (inflation)
 Stimulation of stretch receptors
 Impulses to DRG
 Switch off inspiratory ramp
 Inspiration stops
 Expiration occurs

30. HB Inflation reflex
 In humans, this reflex is activated when the tidal
volume increases three times normal
 1500 ml
 This reflex is a protective mechanism that prevents
excess lung inflation

31. HB Deflation reflex
 Sustained lung deflation
 Decrease in tidal volume
 Impulses to DRG
 Switch on inspiratory ramp
 Inspiration occurs
 It is also protective reflex that prevents collapse of
lungs

32. Irritant receptors
 Located in the epithelium of trachea, bronchi and
bronchioles
 Supplied by sensory nerve endings
 Upon stimulation, they induces sneezing and coughing
 May also cause broncho constriction in persons with
diseases like asthma, emphysema

33. J receptors
 Sensory nerve endings
 Alveolar wall juxta position to pulmonary capillaries
 First discovered by Indian scientist Autar Singh
Paintal in 1955.

34. J receptors
 Stimulated during pulmonary edema or
engorgement of pulmonary capillaries
 Exact function is not clear
 When stimulated causes dyspnea

35. Complete transection of
brainstem
 Stops all respiration
 Apnea
 No change if vagi are intact or cut

36. Transection above pons
 Decerebration
 Regular breathing continues (eupnea)
 Respiratory centers are located in the medulla and
pons
 No change if vagi are intact or cut

37. Transection at mid-pons
 Pneumotaxic centre cutoff from apneustic centre
 No check over apneustic centre
 Apneustic centre over active
 If vagi intact, they inhibit apneustic centre and
respiration is regular and rhythmic but slower and
deeper.
 If vagi are cut, prolonged and sustained inspiration
(Apneusis)

38. Transection at junction of pons
and medulla
 Respiration continues
 It is rhythmic
 But irregular
 No change if vagi are intact or cut

39. Brain edema
 Head hit to solid object
 Damaged brain tissues will swell
 Compression of cerebral arteries
 Blockage of cerebral artery supply
 Depression/ inactivation of respiratory centre

40. Anesthesia
 Over dosage of anesthesia/ narcotics
 Respiratory Centre depression
 Respiratory arrest
 Respiratory Centre depressed more by sodium
pentobarbital

41. References
 Understanding Medical Physiology- R L Bijilani
 Textbook of Medical Physiology – Guyton and Hall
 Review of Medical Physiology- Ganong
 Internet sources

42. THANK YOU