Respiratory center
summary
midbrain
(upper pons) – inhibits inspiration
pneumotaxic center
Apneustic center (lower pons) – to promote
inspiration
pons
medulla
Cause the basic respirarory
rhythm
Spinal cord
transfer for brain and
respiratory muscle
hypothesis of three –lever of
respiratory center
PBKF neurons
dorsal respiratory group
ventral respiratory group
Two respiratory nuclei in medulla oblongata
Inspiratory center (dorsal respiratory group, DRG)
• inspiratory neuron
•more frequently they fire, more deeply you
inhale，longer duration they fire, breath is
prolonged, slow rate
Expiratory center (ventral respiratory
group, VRG)
expiratory neuron, inspiratory neuron
involved in forced expiration mainly
pond
PBKF neurons
dorsal respiratory group
ventral respiratory group
Spinal
cord
hypothesis of basic rhythm——
pacesetter cell theory
pneumotaxic center
Central inspiratory
activity generator
inspiratory nueron
Inspiratory muscle
motor nueron
PBKF neurons
Inspiratory
off swithch
mechanism
Rhythmic Ventilation (Inspiratory Off Switch)
• Starting inspiration
– Medullary respiratory center neurons are
continuously active (spontaneous)
– Center receives stimulation from receptors and
brain concerned with voluntary respiratory
movements and emotion
– Combined input from all sources causes action
potentials to stimulate respiratory muscles
•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 swithch.
3. Higher Respiratory Centers
regulate the activity of the more primitive control
centers in the medulla and pons.
Allow the rate and depth of respiration to be
controlled voluntarily.
During speaking, laughing, crying, eating,
defecating, coughing, and sneezing. ….
deflation
Hering-Breuer Reflex or Pulmonary Stretch Reflex
• Including pulmonary inflation reflex and
pulmonary deflation reflex
• Receptor: Slowly adapting stretch receptors
(SARs) in bronchial airways.
• Afferent: vagus nerve
Significance of Hering-Breuer reflex
– Terminate inspiration timely.
– enhance inspiration/expiration
transition， increase respiratory
frequency.
• Normal adults. Receptors are not activated at end
normal tidal volumes.
– Become Important in Chronic obstructive lung
diseases when lungs are more distended.
• Infants. Probably help terminate normal inspiration.
– Become Important during exercise when tidal volume
is increased.
Chemoreceptor Reflex
Two Kinds of Chemoreceptors
• Central Chemoreceptors
– Responsive to increased H+ in
CSF(cerebrospinal fluid) or local extracellular
fluid
• Peripheral Chemoreceptors
– Responsive to decreased arterial PO2
– Responsive to increased arterial PCO2
– Responsive to increased H+ ion concentration.
Peripheral Chemoreceptors
R：Carotid bodies
•
Aortic bodies
adequate stimulus:PO2
PCO2
H+
exciting of breath
depth and frequency Of breath
pulmonary ventilation
–glossopharyn
–vagus
Carbon Dioxide, Oxygen and pH Influence
Ventilation (through peripheral receptor)
• Peripheral chemoreceptors sensitive to PO2, PCO2
and pH
• Receptors are activated by increase in PCO2 or
decrease in PO2 and pH
• Send APs through sensory neurons to the brain
• Sensory info is integrated within the medulla
• Respiratory centers respond by sending efferent
signals through somatic motor neurons to the
skeletal muscles
• Ventilation is increased (decreased)
Central Chemoreceptor Location
Rostral
Medulla
Caudal
Medulla
Ventral Surface of
the medulla
The sensor neurons are especially excited by H+
H+ are the only direct stimulus for these sensor neurons .
Carbon Dioxide
• Indirect effects
– through pH as seen previously
• Direct effects
– CO2 may directly stimulate peripheral
chemoreceptors and trigger  ventilation
more quickly than central chemoreceptors
• If the PCO2 is too high, the respiratory center
will be inhibited.
•CO2 easily crosses blood-brain barrier
•, in CSF the CO2 reacts with water and releases H+,
• central chemoreceptors strongly stimulate inspiratory center
arterial
Blood –brain
barrier
Central
Chemoreceptor
Carbonic
anhydrase
arterial
Central
Chemoreceptor
peripheral
Chemoreceptor
arterial
Central
Chemoreceptor
peripheral
Chemoreceptor
arterial
Central
Chemoreceptor
peripheral
Chemoreceptor
80%
20%
Effects of Hydrogen Ions
Increasing H+ or decreasing PH can faster
respiration. It is the effective stimulator to
chemoreceptor.
Pathway of H+ regulating respiration
a. H+ in blood increases—excites peripheral
chemoreceptor mainly
b. H+ in cerebrospinal Fluid increases-excites central chemoreceptor
Oxygen
• character
• 1)Hypoxia stimulation act through peripheral
chemoreceptor.
If the inputing of peripheral chemoreceptor
is cut, the stimulation effect disappear.
• 2)The direct effect of hypoxia to center is
inhibition.
• 3)hypoxia ：PO2< 80mmHg
ventilation volume increase is been awareness.
• The pathway of hypoxia regulating
respiration:
• The main pathway is acting directly on
peripheral chemoreceptor and inputting
impulse. Respiration center is excited.
• Chronic hypoxemia, PO2 < 60 mmHg, can
significantly stimulate ventilation
– emphysema, pneumonia
– high altitudes after several days
Brief summary
Central
Chemoreceptor
peripheral
Chemoreceptor
Overall Response toPco2, Po2 and pH