anatomy and physiology. neural control of respiration

1. CONTROL OF RESPIRATION
QAP20803
DR. MOHANAD

2. Neural Control of Ventilation
Goals of regulation of ventilation is to
keep arterial levels of O2 & CO2 constant
The nervous system adjusts the level of
ventilation (RR & TV) to match perfusion
of the lungs (pulmonary blood flow)
By matching ventilation with pulmonary
blood flow (CO) we also match ventilation
with overall metabolic demand

3. Neural
Control Of
Breathing
Voluntary
Cerebral
cortex
Autonomic
Medullary
Centers
Dorsal
Respiratory
Group
Ventral
Respiratory
Group
Pontine
Centers
Pneumotaxic
Center
Apneustic
Center

5. Control of Respiration
 Respiration is controlled by areas of the brain
that stimulate the contraction of the diaphragm
and the intercostal muscles.
 These areas, collectively called
RESPIRATORY CENTERS

6. Diagram showing the pons and medulla oblongata

7. Respiratory Center
The Respiratory Center is
composed of several groups
of neurons located bilaterally
in the medulla oblongata
and pons of the brain stem.
It is divided into :
1. Dorsal Respiratory Group
2. Ventral Respiratory Group
3. Pneumotaxic Center
4. Apneustic Center

8. 8
Respiratory Centers

9. To larynx and bronchi
To respiratory muscles
Pontine center
Dorsal Respiratory Group
Brainstem Respiratory Centres
Pons
Medulla
Ventral respiratory group
- Nucleus ambiguus
- Nucleus retroambigualis

10. Respiratory Center
 Medullary Respiratory Centers
 Dorsal respiratory group-DRG- Inspiratory area-
 Ventral respiratory group-VRG- Expiratory &
inspiratory area
 Pons Respiratory centers
 Pontine respiratory group – (Pneumotaxic area),
Apneustic Center

12. Neural control of ventilation
 Dorsal respiratory group
 located primarily in the nucleus tractus
solitarius in medulla
 Sets the basic drive of ventilation
 Termination of CN IX & X (G.ph, Vagus N.)
 Receives input from:
 Peripheral chemoreceptors
 Baroreceptors
 Receptors in the lungs
 Rhythmically self excitatory
 Ramp signal
 Excites muscles of inspiration

13. Dorsal respiratory group
 INSPIRATORY CENTER
 When fired they generates
rhythmic nerve impulses that travel
along the phrenic nerve to
diaphragm and intercostal nerves
to excite external intercostal
muscles
 As a result, these muscles will
contract and the thorax expand,
 Volume increase
 Pressure decrease
 Air pushes into lungs

14. Dorsal Respiratory
Group
 DRG then becomes dormant,
and expiration occurs passively
as the inspiratory muscle relax
and the lungs recoil.
 This cyclic activity of the
inspiratory neurons repeats and
produce respiratory rate of 12 –
15 breaths per minute

15. Ventral Respiratory
Group
 VRG contain mix of neurons
 Inspiratory
 Expiratory (mainly)
 The VRG is responsible for motor
control of inspiratory and expiratory
muscles during exercise.
 Inactive during normal respiration
 They are especially important in
providing the powerful expiratory
signals to the abdominal muscles
during very heavy expiration

16. Pontine Respiratory
Center
Pons contains 2 centres
for control of
respiration:
1.Pneumotaxic Center
2.Apneustic Center

17. Pontine respiratory
group
 A collection of neurons in the
reticular formation within the Pons
 Pneumotaxic center
 a network of neurons in the rostral
dorsal lateral Pons
 Effectively decreasing the tidal volume
and regulating the respiratory rate.
 Absence of the PRG results in an
increase in depth of respiration and a
decrease in respiratory rate

18. Neural control of ventilation
 Apneustic center (lower pons)
 Functions to prevent inhibition of DRG under some
circumstances
 This center increases depth of inspiration (tidal
volume ) by acting directly on the inspiratory
center.
 If damaged it will lead to arrest of
breathing in inspiration

19. The “apneustic centre”
Apneustic centre
Impulses from
these neurones
excite
inspiratory
area of
medulla
Prolong inspiration
Conclusion?
Rhythm generated in
medulla
Rhythm can be modified
by inputs from pons

20. Neural control
 Afferents from higher centers:
 1. Cerebral cortex: voluntary control of respiration.(
Ondine curse)
 2.Cerebellum: coordination with swallowing and talking
 3.Hypothalamus: increased resp, with high temp.
 4. Limbic system: pain and emotional stimuli affect resp.

21. Chapter 22, Respiratory System 21
Medullary Respiratory Centers

22. Neural Control of Ventilation
 Herring-Breuer Inflation reflex
 stretch receptors located in wall of airways
 + when stretched at tidal volumes > 1500 ml
 Inhibits the DRG Increased or decrease
respiratory rate ?????
 Irritant receptors-among airway epithethium
+  sneezing & coughing & possibly airway
constriction
 J receptors - in alveoli next to pulmonary caps.
Stimulated by hyperinflation and chemicals (pulmonary
chemoreflex)
Mechanoreceptors

24.  1) Impulses from higher centers: impulses
from higher center can stimulate or inhibit
respiratory centers directly.
 2) Impulses from stretch receptors of lung

25. Factors influencing the Respiratory center
of the brain
 Pulmonary irritant reflexes
 Receptors in the lung that respond to irritants
Activation of irritant receptors
Send signals to respiratory centers through vagal nerve
Modify respiratory rate and depth

26.  Inflation of the lungs → +pulmonary stretch
receptor → +vagus nerve → -medually
inspiratory neurons → +eliciting expiration

27. Factors influencing the Respiratory center of
the brain
 Influence of higher brain centers
 Hypothalamic controls
Activation of sympathetic centers in hypothalamus
Send signals to respiratory centers
Modify respiratory rate and depth

28. Factors influencing the respiratory
center of the brain
 Influence of higher brain centers
 Cortical controls - Voluntary controls
Cerebral motor cortex
Send signals to motor neurons
Stimulate respiratory muscles
(Bypassing the medullary center)

29. CHEMORECEPTORS
 Central chemoreceptors
 Located in bilaterally in medulla
 Sensitive to the pH extracellular fluid (ECF):
Cerebrospinal fluid (CSF)
 Peripheral chemoreceptors
 Located in great vessels of neck
 Sensitive to PO2, PCO2 and pH

30. Chemical Control of Ventilation
Central chemoreceptors
 Chemosensitive area of respiratory center
 Hydrogen ions-primary stimulus but can’t
cross membranes (blood brain barrier-BBB)
 carbon dioxide-can cross BBB
 inside cell converted to H+
 rises of CO2 in CSF- effect on + ventilation faster
due to lack of buffers compared to plasma
 unresponsive to falls in oxygen-hypoxia
depresses neuronal activity
 70-80 % of CO2 induced increase in vent.

31. Chemical Control of Breathing
31

32. 32
 Changing PCO2 levels are monitored by
chemoreceptors of the brain stem
 Carbon dioxide in the blood diffuses into the
cerebrospinal fluid where it is hydrated
 Resulting carbonic acid dissociates, releasing
hydrogen ions
 PCO2 levels rise (hypercapnia) resulting in
increased depth and rate of breathing
Depth and Rate of Breathing: PCO2

34. Increase in CO2 increases
H+ concentration in CSF
(CO2 + H2O in CSF H2CO3 HCO3
– + H+)
Stimulates H+
receptors
Stimulates
RESPIRATORY
CENTERS
Increases rate and
depth of breathing
Fall in blood CO2 slightly depresses shallow breathing

35. Chemical Control of Ventilation
 Peripheral Chemoreceptors
 Aortic and Carotid bodies
 20-30% of CO2 induced increase in vent.
 Responsive to hypoxia
 response to hypoxia is blunted if CO2 falls as the
oxygen levels fall
 responsive to slight rises in CO2 (2-3 mmHg)
but not similar falls in O2
 sensitivity altered by CNS
 SNS decreasing flow-increased sensitivity to hypoxia

36.  Cells sensitive to arterial PO2
are found in:
Peripheral chemoreceptors:
 Aortic bodies
 In arch of aorta
 Carotid bodies
 In common carotid artery

37. Peripheral chemoreceptors
 Carotid chemoreceptors:
 Near carotid bifurcation. It has two types
of cells 1&11.
 Impulses carried by the glossopharyngeal
nerve & carotid sinus to the medulla.
 More sensitive to drop of O2 by type 1 cells.
 Type 1 cells contain dopamine which is released
in response to low O2.

39. Other receptors
1. Nose and upper airway
2. Joint and muscle
3. Gamma system
4. Arterial baroreceptors
5. Pain and temperature

40. Factors influencing the respiratory center of
the brain
 Chemical factors:
 Oxygen (O2)
 Carbon dioxide (CO2)
 Hydrogen ion (H+)
 Sensed by CHEMORECEPTORS

41. Influence of PCO2 and H+
 Most potent and most
closely controlled
 Sensed by central
chemoreceptors
35-45 mm Hg
The normal PaCO2 (arterial partial pressure
of carbon dioxide in the blood) is
40mmHg. There is a normal range, which
is 35-45mmHg.

42. Chapter 22, Respiratory System 42
Depth and Rate of Breathing: PCO2
Figure 22.26

43. 43
 Hypothalamic controls act through the limbic
system to modify rate and depth of
respiration
 Example: breath holding that occurs in anger
 A rise in body temperature acts to increase
respiratory rate
 Cortical controls are direct signals from the
cerebral motor cortex that bypass medullary
controls
 Examples: voluntary breath holding, taking a
deep breath
Depth and Rate of Breathing: Higher
Brain Centers

44. 44
 Hyperventilation – increased depth and rate
of breathing that:
 Quickly flushes carbon dioxide from the blood
 Occurs in response to hypercapnia
 Though a rise CO2 acts as the original
stimulus, control of breathing at rest is
regulated by the hydrogen ion concentration
in the brain
Depth and Rate of Breathing: PCO2

46. Summary