Respiration 1 Flashcards
What are 2 key facts about the respiratory rhythm?
- Respiratory rhythm (both inspiratory & expiratory) originates from the brainstem & is transmitted to the spinal cord
- Current view of the respiratory rhythmogenesis involves multiple rhythmogenic sites:
1. Pre-BotC (inspiration)
2. Post-inspiraory complex (Pico - postinspiration)
3. RTN/pFRG (expiration)
When are abdominal muscles stimulated during respiration?
during periods of quiescence in the diaphragm
when the laser turns on, the neurons within the lateral RTN/pFRG are excited and we get a rhythmic burst of abdominal muscle activity
what is causing this excitatory activity? probably the RTN/pFRG
What is the ventral respiratory group (VRG)?
The ventral respiratory group (VRG) is a column of neurons that fire action potentials in phase with respiration. It includes neurons depolarizing during inspiration (inspiratory, or I neurons) and expiration (expiratory, or E neurons). The pre-Bötzinger is in the rostral VRG.
What are the types of neurones within the VRG?
I neurone - fires at the same time as phrenic nerve
Post-I neurone - fires just after the phrenic nerve
E2 neurone - fires much after the phrenic nerve
Where does the respiratory neural netwrok start and end?
it is a continuous column of ‘respiratory neurns’ from the pontine tegmentum to the origin of the spinal cord (PRG + VRG)
PRG = potine respiratory group
VRG = ventral respiratory group
Where do the premotor neurons of the ventral respiratory group reside?
- In the prVRG –> sends axons o phrenic motor neurons –> then down the phrenic nerve –> diaphragm
- In the cVRG –> motor neurons that will control expiratory muscles
What is the effect of decreasing potassium conductance on neuronal membrane potential?
Less negative
Injection of substance P into the BotC. . .
will increase excitatory time / duration
activation of BotC via injection of DLH (glutamate receptor agonist) causes bradypnoea (reduction of breathing)
Injection of substance P into pre-BotC complex. . .
will increase respiratory frequency
exciting the pre-BotC causes faster breathing (trachypnoea)
Why is the hypoglossal nerve active just before the phrenic nerve?
Because it opens airways and innervates the tongue, so it ensures the airways are already ready to release air when the phrenic nerve fires
What happens to respiration if the pons are removed?
end up with only a 2-phase rhythm instead of a 3-phase rhythm
the post-inspiratory phase disappears
means something in the pons is importance for generating this post-inspiratory phase –> pontine respiratory
Which neurons in the pre-BotC are considered the rhythm generators?
the pre-I neurons
they ultimately tell inspiratory motor neurons like the phrenic nerve and recurrent pharyngeal nerve to fire
Explain the generation of 3-phase rhythm
- Pre-I neurons are firing at a constant rate (similar to pacemaker cells in heart) to determine when inspiration occurs
- These are the primary neurons active during the inspiratory phase
- After the inspiratory phase, we have post-inspiration & late expiration (expulsion of air from lungs)
- Post-inspiration basically temporarily closes the upper airways for a short period to trap oxygen in the lungs & increase gas exchange
- Both post-inspiration & late expiration require the phrneic nerve and other inspiratory motor neurons to be quiet so the thoracic cavity can decrease volume
What are the roles of post-I and aug-E in post-inspiration and late expiration?
- Post-I neurons (which receive excitatory input from the pons) are active when the inspiration phase ends and this functions to inhibit pre-I neurons (essentially inhibiting the next breath, i.e. inspiration) AND aug-E neurons
- The activity of post-I neurons eventually drops off (shows a decrementing pattern)
- This slowly removes the inhibition on aug-E neurons which gradually increase their firing (show an augmenting pattern)
- aug-E neurons also inhibit pre-I neurons so also function to prevent inspiration
- Eventually, activity in aug-E neurons stop & the cycle resets itself – pre-I neurons are no longer inhibited so can fire again and activate the phrenic nerve
Quick summary for the basic pattern of breathing
- Pre-I neurons fire & interact with inspiratory pre-motor neurons to stimulate contraction of inspiratory muscles (diaphragm, external intercostals, etc.)
- Post-I neurons are activated which turn off pre-I neurons and has secondary role in activating expiratory motor neurons (the recurrent laryngeal nerve is the most important in this phase) & show decrementing activity
- aug-E neurons begin to fire & continue to inhibit pre-I neurons (& can also activate expiratory neurons but this doesn’t occur in normal breathing, only active expiration)
- aug-E neurons stop firing and the cycle begins again
