Neural control of breathing Flashcards
Which muscle involved in inspiration?
diaphragm
Which muscles are involved in forced inspiration?
Respiratory : external intercotsals
Accessory : pectroals, sternomastoid, scalene
Which muscle involved in expiration?
elastic recoil of lung
Which muscles involved in forced expiration?
Respiratory : elastic recoil, internal intercostals
Accessory : abdominals
What causes respiratory muscles to contract?
- Contractile signals initiated within medulla upper motor neurons
- descend via spinal tracts
- synapses w lower motor neurons that innervate the respiratory muscle tissue
What’s the basic pattern of ventilation determined by?
complex system of neurons within brainstem : medulla+ pons -central pattern generator (CPG) /respiratory pattern generator (RPG)
What innervates the diaphragm?
C3-5 via phrenic nerve
What innervates the intercostal muscles?
T1-12
Role of ventral respiratory group (VRG)?
expiratory output + innervation of URT (in medulla)
Role of dorsal respiratory group (DRG)?
inspiratory output (in medulla) receives input from chemoreceptors + sensory
What’s pre-Bötzinger complex?
cluster of interneurons in VRG (in medulla)
What’s the higher centre in pons?
pontine respiratory group (PRG)
Why’s breathing a subject to voluntary control + emotional states
inputs from higher somatic + emotional centres feed into CPG
Why’s it impossible to voluntarily self asphyxiate?
urge to breath due to excess CO2
acute hypoxaemia –>unconsciousness
What’s reciprocal inhibition?
inspiratory neuronal activation signals via interneurons to inhibit expiratory neurons
What initiates compensatory changes in ventilation?
CPG receives inputs from central + peripheral chemoreceptors
How does the central respiratory chemoreceptors (CRC) monitor changes in PaCO2 eg increase?
responding to changes in pH of the CSF
- arterial CO2 passes via BBB into CSF
- reacts ->carbonic acid
- H+ activates CRCs
Why doesn’t CRC respond to blood pH directly?
- increase PaCO2 decreases pH
- H+ in arterial blood cannot pass via BBB
What’s the predominant signal regulating ventilation?
CRC response to PaCO2
70%
What do peripheral chemoreceptors consist of + location?
type-I glomus cells in carotid +aortic bodies
Role of peripheral chemoreceptors
activated by low O2, high CO2,low pH,
signal to medullar centres to increase ventilation
Eg of CPG integrating info from other inputs
stretch receptors within lungs that prevent damage due to over-inflation
irritant receptors within airways that initiate cough
Define hypercapnic drive
ventilation proportional to PaCO2 due to dominant CRC
Define hypoxic drive
low PaO2 stimulates increased ventlation
Define type II respiratory failure
COPD - chronic hypercapnia + hypoxia
Why are CRC responses reduced when chronic hypercapnia?
due to homeostatic mechanisms that compensate for chronic acidification of CSF + increase CSF pH back to normal levels, even in high PaCO2
If chronic hypercapnia how to initiate ventilation?
PO2
Define sleep apnoea + durations?
temporary cessation of breathing during sleep
>5 episodes per hour lasting >10 s
may be as long as 90s and 160 episodes per hour
Effects of sleep apnoea on health?
Tiredness Cardiovascular complications (stress + ↑SNS tone) Obesity/Diabetes (inflammation + metabolic dysfunction)
Define obstructive sleep apnoea
temporary blockade of URT
What causes obstructive sleep apnoea?
-Increased p on the neck =obesity, fat deposition
-Variation in facial structures= displacing genioglossus (tongue muscle) into airway
-Fluid moving legs to head + neck =recumbent position
during sleep, swelling pharyngeal tissues
-Relaxation of pharyngeal dilator muscles
Risk factors of obstructive sleep apnea?
- obesity- fat deposition/neck circumference
- alcohol/sedatives -decrease in muscle tone
- smoking -irritation/inflammation
Define central sleep apnoea
dysfunction in CNS processes that initiate breathing
What causes central sleep apnoea?
- opioids + barbiturates = inhibiton of brainstem
- stroke/trauma = injury to brainstem
- central hypoventilation syndrome = congenital defects in brainstem signalling processes
- insufficient development of respiratory centres in neonates (infantile central sleep apnoea)
- hypocapnia = altitude, hypobaric oxygen p, Cheyne-Stokes respiration
How to differentiate obstructive + central sleep apnoeas?
polysomnography -whether diaphragmatic contractions continue during apnoea
Diff between obstructive vs central diaphragmatic contractions?
Obstructive = increasing diaphragmatic effort as it tries to overcome URT blockage Central = no diaphragm response as temporary cessation of the CNS respiratory muscle pathway that initiates breathing
Define Cheyne-Stokes respiration
oscillating apnoea + hyperpnoea
Describe Cheyne-Stokes respiration
- apnoea –>hypercapnia + hypoxaemia
- stimulate compensatory hyperventilation
- However due to pathology (heart failure, brain injury, chemoreceptor dysfunction) –>
- compensatory hyperventilation –>
- hypocapnia, respiratory alkalosis
- loss of respiratory drive
- subsequent period of apnoea
