Control of ventilation Flashcards
How are skeletal muscles stimulated during inspiration?
Phrenic nerve to diaphragm
Intercostal nerves to external intercostal muscles
Entirely dependant on signalling from the brain
What part of the brain is responsible for ventilatory control?
Il defined centres located in the pons and the medulla (respiratory centres)
What is the activity of respiratory centres?
Fire repetitive short bursts of action potentials in DRG which travel to the inspiratory muscles
This sets an autonomic rhythm of breathing
They adjust their rhythm according to the stimuli
What does DRG stand for?
Dorsal respiratory group
What does PRG stand for?
Pontine respiratory group - pneumotaxic area
What does VRG stand for?
Ventral respiratory group
What does NTS stand for?
Nucleus tractis soolitaris
Which respiratory centre is located in the pons?
PRG
What modulates rhythm of respiratory centres?
- Emotion (limbic system of brain)
- Voluntary over-ride (higher centres in the brain)
- Mechano-sensory input from the thorax (stretch reflex)
- Chemical composition of the blood (PCO2, PO2 and pH) – detected by chemoreceptors.
What does the VRG supply?
Tongue, pharnyx, larynx, expiratory muscles
What does the DRG supply?
Inspiratory muscles via phrenic nerve and intercostal nerve.
What is the most significant input?
Chemoreceptor input
What are your central chemoreceptors?
Medulla
What chemical change does the medulla detect from the CSF?
Responds directly to H+, which directly reflects PCO2
Primary ventilatory drive
What are your peripheral chemoreceptors?
Carotid and aortic bodies
What chemical change do the peripheral chemoreceptors detect?
Primarily to plasma [H+] and PO2 (not oxygen content) (less so to PCO2)
Second ventilatory drive
What is hypercapnea?
Raised PCO2
What change in blood PCO2 does hyperventilation cause
Reduces PCO2 - reduces CSF H+
Inhibits ventilation
does the medulla respond to direct changes in the plasma H+?
No
What crosses the blood brain barrier, PCO2 or H+?
PCO2
What do the peripheral chemoreceptors cause?
Reflex stimulation of ventilation, following a SIGNIFICANT fall in arterial PO2 or rise in H+
Dissociation of CO2 in water is - CO2 + H2O H2CO3 HCO3- + H+
Which direction does increased ventilation shift the equilibrium?
Increased ventilation drives this equation to the left (by blowing off CO2) and lowers [H+]
Decreased ventilation drives this equation to the right (by retaining CO2) and increases [H+]
Which type of chemoreceptors afferent sensory neurones?
Carotid and aortic chemoreceptors
who is ‘da bomb’?
Kitty don O’Leary
What do the somatic motor neurones for inspiration and expiration innervate?
Inspiration - Scalene and sternocleidomastoid muscles, external intercostals, diaphragm
Expiration - Internal intercostals
Abdominal muscles
What allows us to have a large degree of voluntary control over breathing
Descending neural pathways from cerebral cortex to respiratory motor neurones..
Can cerebral coretex neural pathways override involuntary stimuli such as PCO2 or H+?
NO
What are examples of voluntary control of ventilation?
Breath-holding
Hyperventilation
What is the neurotransmitter that responds to low PO2 in the peripheral chemoreceptors?
DOPAMINE
What type of drugs repress respiratory centre?
Barbituates and opiods
What is the effect of anaesthetic agents?
Increases respiratory rate but decrease Tidal volume so decrease AV.
What is the effect of nitrous oxide?
Sedative/light anaesthetic agent
Blunts peripheral chemoreceptor response to falling PaO2.
When is nitrous oxide problematic?
Chronic lung disease cases where individuals often on hypoxic drive.
What happens when you administer oxygen to patients with chronic lung disease?
Aggravates the situation
Describe respiration during swallowing
Inhibited to avoid aspiration of food or fluids into the airways
Why is swallowing followed by an expiration?
In order that any particles are dislodged outwards from the region of the glottis.
