PHYSIOLOGY BASICS IN RESPIRATION TRYING TO MAKE A MILE STONE IN SIMPLIFIED WAY FOR MEDICAL STUDENTS

1. DR MAGDI SASI
MBBS,MD
DEPT. OF PHYSIOLOGY
REGULATION
OF
RESPIRATION.

2. OBJECTIVES
 Define respiratory centers regarding : location ,role in respiration
,afferent and efferent connections and lesions.
 Define the mechanism of gensis of normal rhythamic breathing
 Define central & peripheral chemoreceptors regarding location ,their
adequate stimuli and role in respiration.
 Illustrate the integrated response to oxygen ,carbon dioxide
Wednesday, April 15, 2020

3.  The motor neurons that stimulate the respiratory
muscles are controlled by two major descending
pathways: one that controls voluntary breathing
and another that controls involuntary breathing.
 The unconscious rhythmic control of breathing is
influenced by sensory feedback from receptors
sensitive to the PCO2, pH, and PO2 of arterial blood.

5. • Inspiration and expiration are produced by the
contraction and relaxation of skeletal muscles
in response to activity in somatic motor
neurons in the spinal cord.
• The activity of these motor neurons is
controlled, in turn, by descending tracts from
neurons in the respiratory control centers in
the medulla oblongata and from neurons in
the cerebral cortex.

6. • The normal rate of respiration in adults is 12-
18/min,
• Tidal volume of approx. 500 ml.
• Adjusted to the requirements of the body.
• Spontaneous respiration - rhythmic
discharge of motor neurons that innervate
the respiratory muscles.
Wednesday, April 15,
2020

8. Control of Breathing
• Normal breathing is a rhythmic, involuntary
act even though the muscles are under
voluntary control.
• Respiratory Center:
– Controls breathing by causing inspiration
and expiration and by adjusting the rate
and depth of breathing.

9. • Normal respiratory movement are involuntary.
• They are carried out autonomically through the
rhythmical discharge of nerve impulses from
controlling centers in the medulla oblongata
and pons.
• Respiratory neurons in the brainstem are of two
types:
I neurons discharge during inspiration;
E neurons discharge during expiration.

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

11. THE RESPIRATORY CENTRES
• Respiratory centres
are groups of
neurons.
• These are paired .
• These are
interconnected.

12. Neural Regulation of Respiration
• Activity of respiratory muscles is transmitted to and from
the brain by phrenic and intercostal nerves
• Neural centers that control rate and depth are
located in the medulla and pons
– Medulla—sets basic rhythm of breathing and
contains a pacemaker called the self-exciting
inspiratory center
– Pons—appears to smooth out respiratory rate
Medulla (inspiratory and expiratory centers) and
pons (apneustic and pneumotaxic centers).

13. I neurons send out streams
of impulses which travel down
to the ANTERIOR HORN CELLS
of the SPINAL CORD on the opposite
site and are relayed from
CERVICAL SEGMENTS
By the PHRENIC NERVES
to the DIAPHRAGM and from
THORACIC SEGMENTS
By the INTERCOSTAL NERVES
to the INTERCOSTAL MUSCLES
These nerve impulses cause
the muscle of inspiration to contract
In the nucleus retroambiguus (NRA)
E neurons in the upper end Inhibit
the I neurons during expiration

14. Respiratory Center
It is divided into :
1. Dorsal Respiratory Group
2. Ventral Respiratory Group
3. Pneumotaxic Center
4. Apneustic Center

15. Wednesday, April 15,
2020

16. – Expiratory center
( VRG)
•involved in
forced
expiration
Wednesday, April 15,
2020
Two respiratory nuclei in medulla oblongata
• Inspiratory center
(DRG)
• more frequently
they fire, more
deeply you
inhale
• longer duration
they fire, breath
is prolonged,
slow rate

17. VENTRAL RESPIRATORY
GROUP OF NEURONS.
• Caudal part or nucleus
Retroambigualis (NRA)
– E neurons
– Bulbospinal expiratory
Premotor neurons.
• Intermediate part.
– I neurons.
– N. Parambigualis
• Most Rostral part.
– Botzinger complex (E
neurons)
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2020

18. VENTRAL RESPIRATORY GROUP
 The Ventral respiratory group of neurons is found in
the nucleus ambiguus rostrally and the nucleus
retroambiguus caudally.
 The VRG contains both inspiratory and expiratory
neurons.
 During normal quiet respiration,They remain almost
totally inactive.
 The VRG is responsible for motor control of inspiratory
and expiratory muscles during exercise.
 They are especially important in providing the
powerful expiratory signals to the abdominal muscles
during very heavy expiration

19. Medullary respiratory centres:
dorsal respiratory group (DRG)
• The centres have two types of activities - inspiratory
and expiratory .
• It is a group of inspiratory neurones, which is
diffusely situated on the dorsal aspect of medulla in
and around the nucleus of tractus solitarius.
• It is responsible for generation of the inspiratory
ramps (the type of electrical activity which
gradually increases and then stops suddenly).

20. Medullary respiratory centres:
dorsal respiratory group (DRG)
• The DRG is autorhythmic and can
maintain somewhat rhythmic
respiration in absence of all other
inputs.
• For normal rhythmic respiration
it is helped by feedback
information from peripheral
chemoreceptors, vagal inputs,
central chemoreceptors and
inputs from other centres.

21. CENTRAL INSPIRATORY ACTIVITY NEURONS.(RΑ)
• Central inspiratory
activity neurons.(Rα)
– Inspiratory pump.
– Ramp signal.
• Inspiratory off-switch
(IOS) neurons.
– Terminate inspiratory
Ramp.
• Integrator neurons.
(Rβ)
• Other neurons.(P cells)

22. INTEGRATOR NEURONS.
(RΒ)
• Excitatory inputs.
– Cerebral cortex.
– Pneumotaxic
centre.
– Vagal afferents
from stretch
receptors.
• Inhibitory inputs.
– Apneustic
centre.
Wednesday, April 15,
2020

23. 23
Rhythmic Ventilation (Inspiratory Off Switch)
• Starting inspiration
– Medullary respiratory center neurons are continuously
active (spontaneous)
– Center receives stimulation from
– Peripheral and central receptors
– brain concerned with voluntary respiratory movements
and emotion
– Combined input from all sources causes action potentials
to stimulate respiratory muscles

24. 24
•Increasing inspiration
–More and more neurons are activated
•Stopping inspiration
–Neurons receive input from pontine group and stretch receptors
in lungs.
–Inhibitory neurons activated and relaxation of respiratory muscles
results in expiration.
–Inspiratory off switch.

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

26. • Sends continual inhibitory
impulses to inspiratory
center of the medulla
oblongata,
• As impulse frequency
rises, breathe faster and
shallower
• Stimulation causes
apneusis
• Integrates inspiratory
cutoff information
Wednesday, April 15,
2020
Respiratory Centers in Pons
Pneumotaxic center (upper pons) Apneustic center (lower pons)

27. Pneumotaxic centre (PN)
• It is situated in the upper pons in the nucleus
parabrachialis medialis (NPBM) and in the Kolliker-Fuse
nucleus.
• Its absence causes apneustic type of breathing, i.e.,
breathing characterised by prolonged inspiration.
When the vagi are intact respiration becomes slow and
deep after damage of this centre.
• The pneumotaxic centres relay information from higher
centres.
• They normally cut down the activity of inspiration, so
that there is quick initiation of expiration, thus they
may help to increase the rate of respiration.

28. PONTINE RESPIRATORY
CENTRE.
• Pneumotaxic
centre.(PNC)
• In N. Parabrachialis in
upper pons.
• Excite integrator N &
inhibits Apneustic C.
• Increases rate of
breathing.
• So Rhythm by DRG, rate &
depth controlled by
APN,PNC.
Wednesday, April 15,
2020

29. SUMMARY-Control of Breathing
• The dorsal respiratory group is responsible for the basic
rhythm of breathing.
– Neurons in the pneumotaxic area control the rate of
breathing.
• The ventral respiratory group is active when more forceful
breathing is required.

30. REGULATION.
• Neural
– Automatic control.
– Afferent impulses to respiratory center.
• Chemical.
– Chemoreceptors
– Effect of Po2, Pco2 &pH.
Wednesday, April 15,
2020

31. CONTROL MECHANISMS.
• Voluntary control.
• Located in cerebral cortex.
• Functional significance –
facilitate acts like talking,
singing, swimming,
laughing, breath holding &
hyperventilation.
Wednesday, April 15,
2020

32. FROM HIGHER CENTRE.
• Voluntary control
system.
– Controlled by
Neocortex
– Bypasses medullary
respiratory centres
& project directly to
spinal respiratory
neurons.
– For talking, singing,
swimming & breath
holding.
• Limbic control
system.
– Limbic system –
pontomedullary
respiratory
neurons.
– So alter during pain
& emotional
stimuli.
Wednesday, April 15,
2020

33. II Pulmonary Reflex
1.Chemoreceptor Reflex

34. CENTRAL CHEMORECEPTORS.
• Location – beneath
ventral surface of
medulla.
• Innervations –
project directly to
respiratory centres
deeper to central
chemoreceptors.
• Mechanism:
• Co2 crosses BBB
– in CSF
• co2 + H2O –
H2CO3
• H2CO3 ------H+
HCO3
• H+ ion stimulate
central
chemoreceptors.
Wednesday, April 15,
2020

35. 35
Two Sets of Chemoreceptors Exist
• Central Chemoreceptors
– Responsive to increased arterial PCO2
– Act by way of CSF [H+] .
• Peripheral Chemoreceptors
– Responsive to decreased arterial PO2
– Responsive to increased arterial PCO2
– Responsive to increased H+ ion concentration.

36. EFFECT OF ARTERIAL pH
• Increase H+ ion
conc.(metabolic
acidosis)- leads
to
hyperventilation.
In DKA, renal
failure, severe
exercise.
• Decrease H+ ion
conc.(metabolic
alkalosis)
• Primary pulmonary
hypoventilation causes
respiratory acidosis.
• Primary pulmonary
Hyperventilation
causes respiratory
alkalosis.
Wednesday, April 15,
2020

37. 37
Central Chemoreceptor
Location
Rostral
Medulla
Caudal
Medulla
Ventral Surface

38. PERIPHERAL CHEMORECEPTORS.
• Location - carotid
bodies & aortic bodies.
• Structure.
– Capsule – surrounding
bodies.
– Sinusoidal large
capillaries below capsule
– Epithelial cells – type I
(Glomus cells) like
chromaffin cells contains
catecholamine.
– Type II (Glial cells).
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2020

39. FACTORS STIMULATING
• O2 tension V o2
content.
• Elevated Pco2
• H+ conc.
• Hyperkalemia.
• Asphyxia.
• Functions
• Carotid bodies
increases both rate
& depth, aortic
bodies only rate of
respiration.
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2020

40. 40
Peripheral Chemoreceptors
• Carotid bodies
– Sensitive to: PaO2, PaCO2, and pH
– Afferents in glossopharyngeal nerve.
• Aortic bodies
– Sensitive to: PaO2, PaCO2, but not pH
– Afferents in vagus

41. EFFECT OF HYPOXIA
• Normal arterial Po2 is
100 mm Hg. Decrease
in Po2 causes Hypoxic
Hypoxia.
• A decrease in arterial
Po2
• Po2 100-60mm Hg. –
breaking effect of CO2.
• Po2 below 60 mm Hg.
Wednesday, April 15,
2020

42. 42
Carbon Dioxide
• Indirect effects
– through H+ in CNS
• Direct effects
–  CO2 may directly stimulate peripheral
chemoreceptors and trigger  ventilation more
quickly than central chemoreceptors
• Receptor adaption
• If the PCO2 is too high, the respiratory center
will be inhibited.

43. 43
Oxygen
• Direct inhibitory effect of hypoxemia on the
respiratory center
• Chronic hypoxemia, PO2 < 60 mmHg, can
significantly stimulate ventilation
– Emphysema , pneumonia
– high altitudes after several days
• Receptor: Slow Adaption
• More important in chronic hypoxemia

44. 44

45. Wednesday, April 15,
2020

46. Thank
You