control of ventilation Flashcards
what does ventilatory control require
stimulation of the skeletal muscles of inspiration which occurs via the phrenic and intercostal nerves
where does ventilatory control reside
centres in the pons and medulla
entirely dependent on signalling from the brain
is ventilatory control conscious or subconscious
subconscious
can be subject to voluntary modulation
what happens if the spinal cord is severed above C3-5
this is above the origin of the phrenic nerve
breathing ceases
what do the respiratory centres do
- set an automatic rhythm of breathing through co-ordinating the firing of smooth muscle and repetitive bursts of action potentials in the dorsal respiratory group - travel to inspiratory muscles
- adjust this rhythm in response to stimuli
what modulates the rhythm of the respiratory centres
- emotion (via limbic system)
- voluntary over-ride (higher centres)
- mechano-sensory input from the thorax (prevents alveolar damage)
- chemical composition of the blood (detected by chemoreceptors)
central chemoreceptors
located in medulla
respond directly to [H+] (directly reflects PCO2)
1y ventilatory drive
how to central chemoreceptors respond to increase in PaCO2 (hypercapnea)
CO2 crosses blood brain barrier (not H+)
central chemoreceptors monitor PCO2 indirectly from CSF
HCO3- and H+ are formed, receptors respond to H+
feeback via resp centres, increased ventilation
reduced PaCO2, reduced ventilation rate
10% PaCO2 increase = 100% increase in ventilation
peripheral chemoreceptors
carotid and aortic bodies
respond to plasma [H+] (any source, not just CO2) and PO2 (arterial)
2y ventilatory drive
cause reflex stimulation of ventilation following significant change
ventilation is reflexly inhibited by…
reduced arterial PCO2
(reduced CSF [H+]
hyperventilation
ventilatory drive in chronic lung disease
most people rely on CO2 levels for stimulation of ventilation
in chronic lung disease PCO2 is chronically elevated
patients become desensitised to PCO2
rely on changes in PO2 to drive ventilation
HYPOXIC DRIVE
what happens when PO2 falls below 60mmHg
we are much more sensitive to changes in PO2
peripheral chemoreceptors significantly increase ventilation
changes in plasma pH and their effects on ventilation
reduced plasma pH - stimulates ventilation
increased plasma pH - inhibits ventilation (retain CO2 to increase [H+]
descending neural pathways and control of breathing
descending neural pathways from the cerebral cortex to respiratory motor neurons allow a large degree of voluntary control over breathing
can involuntary stimuli be over-ridden
e.g. arterial PCO2, [H+]
NO, they cannot be overidden
