Control of Ventilation Flashcards
Breathing depends on cyclical activation of what nerves?
Phrenic
Intercostals
The phrenic and intercostal nerves stimulate contraction of what muscles?
Inspiratory
The neural activity of rhythmic breathing is triggered by what neurones?
Medullary inspiratory neurones
Breathing is triggered by the medullary inspiratory neurones with
voluntary override
What muscle of inspiration does the phrenic nerve innervate?
The diaphragm
Ventilatory control resides within ill-defined centres located in the
pons and medulla
Is ventilatory control normally conscious or subconscious?
Subconscious
If the spinal cord was severed above the origin of the phrenic nerve, what would happen to breathing?
It would cease
At what vertebral level is the origin of the phrenic nerve?
C3-C5
What are the functions of respiratory systems
- to set an automatic rhythm of breathing
- to adjust this rhythm in response to stimuli
How do respiratory systems set an automatic rhythm of breathing?
Through co-ordinating the firing of smooth and repetitive bursts of action potentials in dorsal respiratory group (DRG)
What factors modulate the rhythm of respiratory centres?
- emotion
- voluntary override
- mechano-sensory input from the thorax (e.g. stretch reflex)
- chemical composition of the blood (PCO2, PO2 and pH, detected by chemoreceptors)
The rhythm of respiratory centres is modulated by emotional input via what system?
The limbic system
Input from higher brain centres changes the respiratory system rhythm via
voluntary override
Where are central chemoreceptors located?
Medulla
Central chemoreceptors detect changes in the concentration of what ions in the CSF around the brain?
H+
Where are peripheral chemoreceptors located?
Carotid and aortic bodies
What do central chemoreceptors cause following a rise in [H+]?
Reflex stimulation of ventilation
What effect will a decrease in arterial PCO2 have on ventilation?
Ventilation is reflexly inhibited - ventilation rate is slowed
Do central chemoreceptors respond to direct changes in plasma [H+]?
No
What changes do peripheral chemoreceptors detect?
Changes in arterial PO2 and [H+]
Peripheral Chemoreceptors cause reflex stimulation of ventilation following what?
A significant fall in arterial PO2 or a rise in [H+]
Do peripheral chemoreceptors respond to arterial PO2 or oxygen content?
Arterial PO2
What usually accompanies a rise in arterial PCO2?
Increased [H+]
Changes in plasma pH will alter ventilation via what pathways?
Peripheral Chemoreceptor Pathways
If plasma pH falls, ventilation will be
stimulated
What effect does alkalosis have on ventilation?
Ventilation will be inhibited
A large degree of voluntary control over breathing is allowed by what?
Descending neural pathways from cerebral cortex to respiratory motor neurons
What effect does hyperventilation have on ventilation?
Ventilation is reflexly inhibited by an increase in arterial PO2 or a decrease in arterial PCO2
What common drugs depress respiratory centre and can result in death following an overdose?
Barbiturates
Opioids
What effect does nitrous oxide have on peripheral chemoreceptor response to falling PaO2?
It blunts the response
Respiration is inhibited during swallowing to avoid what?
Aspiration of food or fluids into the airways
