Week 21: (C.2) Neuroanatomy & Neurophysiology of breathing Flashcards
What is a respiratory rhythm generator? (RRG)
A network of interneurons that produce a predictable and repetitive motor pattern.
In the case of breathing, inspiratory neurons must be activated before expiratory Neurons
What must be activated first inspiratory of expiratory neurones?
RRG must generate inspiratory neurones first
Does the RRG need conscious input?
No, it is always active even in the absence of conscious input.
What is the name of circuit generating regular and repeated sequences of neural activity?
endogenous
cyclical oscillation
(body’s natural clock)
What does the RRG innervate?
respiratory muscles in an orderly sequence
What does the RRG respond to inputs from?
parts of the brain
(eg limbic system – emotions)
as well as sensory afferents (eg pulmonary stretch receptors, peripheral
chemoreceptors)
What are the 3 phases of breathing cycle?
inspiration
post-inspiration
late expiration
What are the 6 types of neural discharge from the RRG?
Pre-I early-I I late-I early-E E
What happens in phase pre-I?
neurons inhibit expiratory neural circuit
Expiratory muscles relax
What happens in phase Early-I?
neurons inhibit output from entire RRG
Refractory period. No breathing movements
What happens in I phase?
> Neurons ramp fire. As frequency increases so more I neurons contribute. Activate motorneuron circuit to inspiratory muscles & inhibit E and Pre-I neural circuits
Inspiratory muscles contract as intensity of I firing increases. Exp muscles relaxed
What happens in Late-I phase?
> I neurons feed back to suppress I neuronal firing when at peak intensity. May involve stretch receptor input (eg from Vagus)
> Inspiratory muscles relax and lung begins to deflate due to elastic recoil
What happens in early-E phase?
> neurons repress all I & E neuronal firing. Creates refractory period at peak inhalation
> Inspiratory muscles relax and lung begins to deflate by elastic recoil
What happens in E phase?
> neurons ramp fire. Activate motorneuron circuit to expiratory muscles. Major point of conscious input into breathing (eg during exercise).
> Expiratory muscles contract as E firing intensity increases. Insp muscles relaxed.
What can change breathing patterns?
DRG
in the medullary respiratory centre
What innervates the DRG?
1) Central Chemoreceptors:
Medulla Surface
2) Peripheral Chemoreceptors:
> Carotid Body (blood)
> Aortic Bodies (blood)
> Neuroepithelial Bodies (airway)
What are the peripheral chemoreceptors?
> Carotid Body (blood)
Aortic Bodies (blood)
Neuroepithelial Bodies (airway)
What does the input on the DRG modulate?
RRG rhythm
What does the DRG innervate?
VRG–> Pre-Bötzinger Complex
What is the Pre-Bötzinger Complex?
is a bilateral and symmetrical neural network located in the brainstem which is essential for the generation and modulation of respiratory rhythm.
What are phrenic nerves?
contain motor, sensory, and sympathetic nerve fibres. These nerves provide the only motor supply to the diaphragm as well as sensation to the central tendon. In the thorax, each phrenic nerve supplies the mediastinal pleura
What does the firing of phrenic nerves cause?
diaphragm contraction and inhalation
What does an increased tital vol do to AP and breathing?
Increased action potentials per burst gives
stronger diaphragm contraction & deeper breathing
What is the effect of increased total ventilation volume?
increased tital vol increased frequency (bursts per minute)
What is the tital vol? (in terms of AP)
AP per min
How does Vt and frequency effect total ventilation volume?
Increased burst per minute gives Increased breathing frequency (↑f).
When combined with increased action potentials per burst (↑VT) then VE increases.
