Where does ventilation control reside?
Within ill-defined centres located in the pons and medulla (respiratory centres)
What muscles are stimulated on inspiration?
Diaphragm and intercostal muscles
What stimulates the diaphragm?
What stimulates the intercostal muscles?
What can you say about the conscious level required to breath?
In subconscious but can be voluntaraly modulated
What levels of the spinal cord does the phrenic nerve originate?
C3 - C5
Where must the spinal cord be severed for breathing to stop?
Above the origin of the phrenic nerve (C3 - C5)
What are the functions of the respiratory centres?
Set an automatic rhythm of breathing through co-ordinating the firing of smooth and repetative bursts of action potentials in dorsal respiratory groups (DRG) which travel to inspiratory muscles
Adjust the rhythm in response to stimuli
What do respiratory centres have their rhythm modulated by?
Emotion (via limbic system of the brain)
Volunrary over ride (via higher centres in the brain)
Mechani-sensory input from thorax (such as stretch reflex)
Chemical composition of the blood detect by chemoreceptors (PCO2, PO2 and ph)
What input has the most inpact on modulation of the respiratory centres rhythm?
What does DRG stand for?
Dorsal respiratory group of neurons
What is VRG stand for?
Ventral respiratory group of neurons
What do the dorsal respiratory group of neurons innervate?
Inspiratory muscles via the phrenic and intercostal nerves
What does the ventral respiratory group of neurons innervate?
What are the 2 kinds of chemoreceptors?
Where are central chemoreceptors?
What do central chemoreceptors respond to?
Directly to H+ (directly reflects PCO2)
Where are peripheral chemoreceptors?
Carotid and aortic bodies
What do peripheral chemoreceptors respond to?
Plasma [H+] (less so to PCO2)
What is the primary ventilation drive?
What is the secondary ventilation drive?
What do central chemoreceptors detect?
Changes in [H+] in the CSF around the brain
How do central chemoreceptors respond to changes in [H+] in the CSF around the brain?
Reflex stimulation of ventilation is increase in [H+)
When do central chemoreceptors cause ventilation as a reflex?
When they detect an increase in [H+]
When do central chemoreceptors inhibit ventilation?
When [H+] drops
What is hypercapnia?
Abnormally elevated levels of carbon dioxide in the blood
What is abnormally elevated levels of carbon dioxide in the blood called?
What is the process of central chemoreceptor altering ventilation?
1) Arterial PCO2 increases and carbon dioxide crosses the blood brain barrier (not H+)
2) Bicarbonate and H+ are formed and receptors respond to H+
3) Feedback via the respiratory centres increases ventilation in response to increased arterial PCO2
4) Decreased arterial PCO2 slows ventilation rate
5) This means that the central chemoreceptors monitor the PCO2 indirectly in the cerebrospinal fluid
What cross the blood brain barrier before acting of central receptors?
Carbon dioxide, not H+, which is formed once carbon dioxide is broken down in the CSF
What do peripheral chemoreceptors detect changes in?
PO2 and [H+]