8. Control of Ventilation Flashcards
What does ventilator control require?
Stimulation of the skeletal muscles of inspiration.
How does stimulation of the muscles of inspiration occur?
Via the phrenic nerve and intercostal nerves
Where does ventilator control reside?
Within ill defined centres located in the pons and medulla
What is ventilator control entirely dependent on?
Signalling from the brain
When will breathing cease?
If the spinal cord I severed above the origin of the phrenic nerve C3-5
What is breathing normally?
Subconscious
Although normally subconscious, what can breathing be subject to?
Voluntary modulation
What are the 2 groups of neurons?
- Dorsal respiratory group
- Ventral respiratory group
Respiratory centre have their rhythm modulated by…
- Emotion ( via limbic system in the brain)
- Voluntary over-ride (via higher centres in the brain)
- Mechano-sensory input from the thorax (e.g stretch reflex)
- Chemical composition of the blood (PCO2, PO2 and pH) detected by chemoreceptors
What is the most significant stimulant affecting respiratory centre rhythm?
Chemoreceptor input
What are the 2 types of chemoreceptors??
- Central
- Peripheral
Where are central chemoreceptors located?
Medulla
What do central chemoreceptors respond to?
Respond directly to H+
directly reflects PCO2
What are the central chemoreceptors responsible for?
Primary ventilator drive
Where are peripheral chemoreceptors located?
Carotid and aortic bodies
What do peripheral chemoreceptors respond to?
Respond primarily to plasma [H+] and PO2
less so to PCO2
What are the peripheral chemoreceptors responsible for?
Secondary ventilator drive
What crosses the blood-brain barrier when arterial PCO2 increases?
Carbon dioxide
What muscles does the dorsal respiratory group of neurons innervate?
Muscles of inspiration
What muscles does the ventral respiratory group of neurones innervate?
Muscles of expiration
What do the respiratory centres do?
- Set an automatic rhythm of breathing through co-ordinating the firing of smooth and repetitive bursts of action potentials in DRG- travel to inspiratory muscles.
- Adjust this rhythm in response to stimuli
What do the central chemoreceptors in the medulla do?
- Detect changes in [H+] in CSF around brain
- Cause reflex stimulation of ventilation following rise in [H+] which is driven by hypercapnia (raise PCO2)
What is ventilation reflexly inhibited by?
A decrease in arterial PCO2 (reduced CSF [H+]) (hyperventilation)
What do the central chemoreceptors not respond to?
Do not respond to direct changes in plasma [H+]
