7 Control & Ventilation Flashcards
Why is Ventilatory control reliant on signalling from the brain?
Diaphragm and intercostal muscles are skeletal muscle
Therefore they need stimulation by alpha-motor neurons to act unlike smooth/cardiac.
What innervates the diaphragm?
Phrenic nerve
Where does the phrenic nerve origniate?
C3, C4, C5
Where are the respiratory centres found?
In the pons and medulla
/What are the respiratory centres in the medulla called?
The ventral Respiratory group (VRG)
The dorsal respiratory group (DRG)
How doe respiratory centres set an automatic breathing rhythm?
Co-ordinating & firing smooth and repetitive bursts of APs in the DRG.
Where does the DRG output go?
Mainly to inspiratory muscles
Why does the DRG still fire during expiration?
The DRG fires at a background level during expiration to give a slow controlled expiration
Where does the VRG output go?
To inspiratory muscles
Pharynx muscle
Larynx muscle
Tongue muscles
Why does the VRG also fire during expiration?
To maintain patency of the airway
Which cranial nerves enter the respiratory centres?
Cranial Nerve 9 & 10 bring mechanical and chemosensory data
What 4 things can modulate rhythm?
- Emotion via the limbic system
- Voluntary over ride from higher brain centres
- Mechano-Sensory input from the thoracic wall
- Chemical composition of blood (PCO2, PO2, pH)
Whats the use of mechano-sensory input from the thoracic wall?
Its a safety mechanism preventing over inflation (i.e. a stretch reflex)
Which input has the largest effect on breathing rhythm?
Chemoreceptors, i.e. chemical composition of blood
What do central chemoreceptors respond to?
[H+] changes in the CSF around the brain which reflect PCO2 levels
They are the primary drive for ventilation
Where are central chemoreceptors found?
In the medulla
Where are peripheral chemoreceptors found?
In Carotid & Aortic Bodies
Where are carotid bodies found?
In teh neck where the carotid divides into the internal/external artery
Where are aortic bodies found?
On the aortic arch
What do peripheral chemoreceptors respond to?
[H+] in the plasma & Po2
Why do central chemoreceptors only detect H+ reflecting CO2 levels?
Because H+ cant cross the blood brain barier but CO2 can so it crosses then forms carbonic acid which dissociates into H+ in the CSF
What is a raised PCO2 called?
Hyercapnia
How does the body repsond to ypercapnia?
Reflex ventilation
When does a raised PCO2 often occur?
During hypoventilation
