Control of ventilation Flashcards
Ventilatory control requires the stimulation of…
Skeletal muscles of inspiration
What stimulates the skeletal muscles of inspiration?
Phrenic nerve (to diaphrgam)
Intercostal nerves (to external intercostal muscles)
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
Ventilatory control resides within ill-defined centres located in the…
Pons and medulla (respiratory centes)
Is ventilatory control normally conscious or subconscious?
Normally subconscious but can be subject to voluntary modulation
If the spinal cord was severed above the origin of the phrenic nerve, what would happen to breathing?
Breathing would cease
Where is the origin of the phrenic nerve?
C3-5
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 the dorsal respiratory group (DRG) which supply the inspiratory muscles via the phrenic and intercostal nerves
What modulates 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 by what system?
The limbic system in the brain
Voluntary over-ride of the rhythm of respiratory centres requires input from…
The higher centres in the brain
Out of the 4 things that modulate the rhythm of respiratory centres, which is most significant?
The chemo-receptor input
What does the ventral respiratory group (VRG) of neurons supply?
Tongue
Pharynx
Larynx
Expiratory muscles
Where are central chemoreceptors located?
Medulla
Central chemoreceptors detect changes in the concentration of what ions in the CSF around the brain?
H+ ions
Why do the central chemoreceptors detect changes in the concentration of H+?
As it directly reflects the PCO2 which is the primary ventilation drive
Where are the peripheral chemoreceptors found?
Carotid and aortic bodies
What do the peripheral chemoreceptors respond to?
Mainly to plasma H+ conc and PO2
Less so to PCO2
What do central chemoreceptors cause following a rise in [H+]?
Reflex stimulation of ventilation
What is the term that refers to raised PCO2
Hypercapnea
What effect will a decrease in arterial PCO2 have on ventilation?
Ventilation is reflexly inhibited therefore ventilation rate is slowed
What do central chemoreceptors NOT respond to?
Direct changes in plasma H+ conc.
What changes do peripheral chemoreceptors detect?
Changes in arterial PO2 and [H+]
Peripheral chemoreceptors cause reflex stimulation of ventilation when…
There is a 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+ conc.
Changes in plasma pH will alter ventilation through what pathways?
Peripheral chemoreceptor pathways
If plasma pH falls, ventilation will be…
Stimulated
What effect does alkalosis have on ventilation?
Inhibits it
A large degree of voluntary control over breathing is allowed by…
Descending neural pathways from cerebral cortex to respiratory motor neurons
Can we override involuntary stimuli like arterial PCO2 or H+ conc?
No, we can’t
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 gaseous anesthetic agents have?
Increase RR, but decrease Tidal Volume so decrease Alveolar Ventilation
What effect does nitrous oxide have on peripheral chemoreceptor response to falling PaO2? Is this safe or dangerous?
It blunts the response
Safe in most patients, problematic in chronic lung disease cases where individual often on “hypoxic drive”
Respiration is inhibited during swallowing to avoid what?
Aspiration of food or fluids into the airways
Swallowing is followed by an expiration because?
So that any particles are dislodged outwards from the region of the glottis.
