Neuro and chemical control of breathing Flashcards
Describe the involuntary and voluntary input of neural input in breathing
Tidal breathing- involuntary
IRV, ERV, breathing frequency- voluntary
What maintains ventilatory homeostasis?
Chemo-receptive inputs monitor plasma and cerebral spinal fluid composition
Where are the respiratory centres of the brain?
Brain stem under hypathalamus ; pons and medulla
What are the two centres of the control centres in the brains tem called?
Pons respiratory center
Medulla respiratory centre
What centres are within the pons respiratory?
Pneumotaxic center
Apneustic center
What centres are within the medulla respiratory?
Pre-Botzinger complex
Dorsal respiratory complex
Ventral respiratory complex
What groups do inspratory group require?
Dorsal and ventral respirator group
What groups do expiratory group require?
Mainly from Pre-botzinger complex in ventral respirator group
Describe the dorsal respiratory group (DRG)
- Inspiratory control
- Located within the nucleus tracts solitaires and is dorsal to VRG
- Site of sensory info input
- Site of central chemoreceptor input
- Some premotor neurons
Describe the ventral respiratory group (VRG) and what 3 regions it spans within the medulla
Rostral - Expiration control (Botzzinger complex)
Intermediate- Inspiration control mediated through Pre-botzinger complex - thought to be site of respiratory pattern generator
Caudal- Expiration control
Describe the innervation of the respiratory muscles-nerves
Hypoglossal nerve
Laryageal
Carotid sinus- Peripheral chemoreceptor feedback
Vagus nerve- Breathing frequency and volume
Intercostal nerve- Respiratory muscles
Phrenic nerve- Diaphragm inspiration control
Why are expiratory muscles passive during quiet breathing?
Elastic recoil pressure is sufficient
What muscles are required during forced expiration?
Abdominal wall
Internal intercostals
What is a respiratory rhythm generator?
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 are properties of RRG?
- Always active even in the absence of concious input (endogenous cyclical oscillation)
- Transmit in an orderly sequence to respiratory muscles
- Respond to inputs from other parts of the brain (eg limbic system-emotions as well as sensory afferents(eg pulmonary stretch receptors, peripheral chemoreceptors))
What are the three recognised phases of breathing?
Inspiration
Post-inspiration
Late expiration
What are the 6 types of neuronal discharge released from phases of breathing?
I (inspiration)
E (expiration)
Pre-I Early-I I Late-I Early-I E
What happens in Phase 1?
Neurons inhibit expiratory neural circuit
Expiratory muscles relax
What happens during Early-I?
Early-I neurons inhibit output from entire RRG
Refractory period. No breathing movements
What happens during I?
Neurons ramp fire. As frequency increases so more I neurons contribute. Activate motorneuron circuit to inspiratory muscles and inhibit E and Pre-I neural circuits
Inspiratory muscles contract as intensity of I firing increases Exp muscles relaxed
What happens during Late-I?
Neurons feedback 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 during Early-E?
Neurons repress all I and E neuronal firing. Creates refractory period at peak inhalation
Inspiratory muscles relax and lung begins to deflate by elastic recoil
What happens during E?
Neurons ramp fire. Activate motoneuron circuit to expiratory muscles. Major point of conscious inout into breathing (eg during exercise)
Expiratory muscles contract as e firing intensity increases Insp muscles relaxed
What nerve innervtaes diaphragm?
Phrenic nerve
What happens if there is an increase in tidal volume?
Breathing frequency remains same
Stronger diaphragm contraction and deeper breathing
What is involved in the regualtion of involuntary breathing?
Controller which recieves sensors that turn into effectors
What are central chemoreceptors?
Monotor pCO2 in cerebral spinal fluid
What are peripheral chemoreceptors?
Carotid body (blood) Neuroepithelial bodies (airways)
Where are central chemoreceptors located and what is their contribution to normal control of breathing?
Medulla (surface)
80%
Where are peripheral chemoreceptors located and what is their contribution to normal breathing?
Arterial vasculature and airway
20%
How is CO2 carried in blood?
HCO3 bicarbonate
What are very sensitive to changing pCO2?
And what makes the response even steeper?
Central chemoreceptors
Hypoxia allows for a bigger change in Ve per pACO2-brings cells closer to firing threshold
What does hyperventilation do to pACO2? Explain a shallow water blackout
Drives it down
Then O2 is consumed during breath hold dive
Low central chemoreceptor sensitivity (caused by breath-holding training) fails to trigger breathing response in time to prevent severe hypoaemia
This causes a loss of consciousness and drowning
Peripheral chemoreceptors are located where?
Carotid body- carotid sinus
Aortic body- aortic arch
What is a peripheral chemoreceptor’s primary response to?
Hypoxia
Also hypercapnia and acidosis
Is the response to hypoxia linear?
No - driven by low low partial pressure of O2
Describe the basics of the cellular mechanism of chemoreception
O2 DECREASE, pH DECREASE, CO2 INCREASE-Causes depolarisation of O2 or pH sensor
This causes an opening of voltage gated calcium channels where Ca2+ enters the cell
There is then a release of neurotransmitters into the glossopharyngeal nerve and into the brain stem or either DRG or RRG
Brain stem- Hypoxic ventilatory response
DRG RRG- Hypoxic pulmonary vasoconstrictor response (rise in pulmonary artery pressure)
What channels regulate chemoreceptor membrane potential?
K+ channels
