Lecture 15: Control of Ventilation Flashcards
what are the 4 components of neural control of ventilation?
- generation of rhythmic pattern of alt. insp and exp
- regulation of rate and depth of vent
- voluntary - speech, breath holding
- involuntary - coughing, sneezing
where is the respiratory centre located?
within the brainstem
what is the brainstem?
the rostral continuation of the spinal cord
the respiratory centre is composed of 5 aggregations of neuronal cell bodies, what are they and where are they?
within the:
Medulla oblongata - dorsal respiratory group (DRG), ventral respiratory group (VRG), pre-Botzinger complex
Pons - apneustic centre and the pneumotaxic centre
what do the efferent fibres from the DRG stimulate?
inspiratory spinal motor neurons innervating the diaphragm
rhythmic firing of the DRG is in response to what?
rhythmic action potentials originating in the pre-Botzinger complex
what does firing of the DRG neurone result in?
inspiration –> cessation of firing = expiration
axons from the VRG project to and stimulate what?
project to the spinal motor neurone of both expiratory and accessory inspiratory muscles
when is the VRG activated and how?
activated by the DRG when demands for ventilation increase
what two centres does the DRG receive input from?
the pneumotaxic and apneustic centres
what does the pneumotaxic centre do?
acts to terminate inspiration
what does the apneustic centre prevent?
switching off inspiratory neurons
stretch receptors in the smooth muscle of the airway prevent initiate what reflex? why?
the hering-breuer reflex
–> inhibition of firing of inspiratory neurons to prevent over-inflammation of lungs
mechanoreceptors in the airway initiate what reflex?
Why?
the coughing/sneezing
–> to remove unwanted material
what are the two locations of chemoreceptors
- peripheral - located in
- -> carotid bodies - located at origin of internal carotid artery
- -> aortic bodies - located in aortic arch - central chemoreceptors - located in ventral part of medulla oblongata
how is rate and depth of ventilation regulated?
carried out by the medullary centre - DRG and VRG in response to body’s need for gas exchange
what is another name for the regulation of rate and depth of ventilation by lowered arterial PO2?
hypoxic drive
how is arterial PO2 monitored?
by peripheral chemoreceptors
what kind of change in PO2 is needed to initiate the hypoxic drive? what is the response?
only sensitive to DRAMATIC change in arterial PO2
e. g <60mmHg = point where Hb saturation 90%
- -> detected by aortic and carotid chemoreceptors –> this stimulates medullary inspiratory neurone –> increases ventilation
why is the hypoxic drive a necessary life saving mechanism?
because low PO2 depresses all neural function except for chemoreceptors
what is another name for the regulation of rate and depth of ventilation by increased arterial PCO2?
hypercapnic drive
is arterial PO2 or PCO2 more important in regulating ventilation under normal conditions
PCO2
does stimulation of peripheral chemoreceptors produce a strong or weak response to increased PCO2?
weak response
does stimulation of central chemoreceptors produce a strong or weak response to increased PCO2?
strong response
–> most important regulation of ventilation in response to changing PCO2
in varying levels of PCO2 what do the central chemoreceptors actually measure and what is the response?
CO2 diffuse’s very rapidly across the blood brain barrier
CO2 levels in the medullary ECF = accurate level of CO2 in the peripheral fluid
the central chemoreceptors actually measure [H]+ derived from CO2 that crosses membrane
increase PCO2 –> Increase [H]+ Brain ECF
–> medullary chemoreceptor detect –> stem of medullary inspiratory neurone –> increase in ventilation
although you can measure hypoxic or hypercaprinic drive, what is another arterial regulatory measure rate and depth of ventilation?
arterial H+ concentration
what chemoreceptors are responsible for detecting arterial H+ concentration?
PERIPHERAL
increase In blood = acidosis = increase ventilation
decrease in blood = alkalosis = decrease ventilation
why is it that peripheral chemoreceptors are responsible for detecting arterial H+ receptors?
H+ cannot cross the blood brain barrier (where the central chemoreceptors are located)
what are some “conscious” higher controls of ventilation
- stopping breathing during swallowing
- vocalisation
- defection –> push down abdominal muscles
- parturition
- breath holding
- changes in gait in some species
higher control is overriden by chemotactic centres with extreme change in arterial PCO2
