Neural control of breathing

Question 1

Which muscle involved in inspiration?

Answer 1

diaphragm

Question 2

Which muscles are involved in forced inspiration?

Answer 2

Respiratory : external intercotsals

Accessory : pectroals, sternomastoid, scalene

Question 3

Which muscle involved in expiration?

Answer 3

elastic recoil of lung

Question 4

Which muscles involved in forced expiration?

Answer 4

Respiratory : elastic recoil, internal intercostals

Accessory : abdominals

Question 5

What causes respiratory muscles to contract?

Answer 5

• Contractile signals initiated within medulla upper motor neurons
• descend via spinal tracts
• synapses w lower motor neurons that innervate the respiratory muscle tissue

Question 6

What’s the basic pattern of ventilation determined by?

Answer 6

complex system of neurons within brainstem : medulla+ pons -central pattern generator (CPG) /respiratory pattern generator (RPG)

Question 7

What innervates the diaphragm?

Answer 7

C3-5 via phrenic nerve

Question 8

What innervates the intercostal muscles?

Answer 8

T1-12

Question 9

Role of ventral respiratory group (VRG)?

Answer 9

expiratory output + innervation of URT (in medulla)

Question 10

Role of dorsal respiratory group (DRG)?

Answer 10

inspiratory output (in medulla)
receives input from chemoreceptors + sensory

Question 11

What’s pre-Bötzinger complex?

Answer 11

cluster of interneurons in VRG (in medulla)

Question 12

What’s the higher centre in pons?

Answer 12

pontine respiratory group (PRG)

Question 13

Why’s breathing a subject to voluntary control + emotional states

Answer 13

inputs from higher somatic + emotional centres feed into CPG

Question 14

Why’s it impossible to voluntarily self asphyxiate?

Answer 14

urge to breath due to excess CO2

acute hypoxaemia –>unconsciousness

Question 15

What’s reciprocal inhibition?

Answer 15

inspiratory neuronal activation signals via interneurons to inhibit expiratory neurons

Question 16

What initiates compensatory changes in ventilation?

Answer 16

CPG receives inputs from central + peripheral chemoreceptors

Question 17

How does the central respiratory chemoreceptors (CRC) monitor changes in PaCO2 eg increase?

Answer 17

responding to changes in pH of the CSF

• arterial CO2 passes via BBB into CSF
• reacts ->carbonic acid
• H+ activates CRCs

Question 18

Why doesn’t CRC respond to blood pH directly?

Answer 18

• increase PaCO2 decreases pH

- H+ in arterial blood cannot pass via BBB

Question 19

What’s the predominant signal regulating ventilation?

Answer 19

CRC response to PaCO2

70%

Question 20

What do peripheral chemoreceptors consist of + location?

Answer 20

type-I glomus cells in carotid +aortic bodies

Question 21

Role of peripheral chemoreceptors

Answer 21

activated by low O2, high CO2,low pH,

signal to medullar centres to increase ventilation

Question 22

Eg of CPG integrating info from other inputs

Answer 22

stretch receptors within lungs that prevent damage due to over-inflation
irritant receptors within airways that initiate cough

Question 23

Define hypercapnic drive

Answer 23

ventilation proportional to PaCO2 due to dominant CRC

Question 24

Define hypoxic drive

Answer 24

low PaO2 stimulates increased ventlation

Question 25

Define type II respiratory failure

Answer 25

COPD - chronic hypercapnia + hypoxia

Question 26

Why are CRC responses reduced when chronic hypercapnia?

Answer 26

due to homeostatic mechanisms that compensate for chronic acidification of CSF + increase CSF pH back to normal levels, even in high PaCO2

Question 27

If chronic hypercapnia how to initiate ventilation?

Answer 27

PO2

Question 28

Define sleep apnoea + durations?

Answer 28

temporary cessation of breathing during sleep >5 episodes per hour lasting >10 s may be as long as 90s and 160 episodes per hour

Question 29

Effects of sleep apnoea on health?

Answer 29

``` Tiredness Cardiovascular complications (stress + ↑SNS tone) Obesity/Diabetes (inflammation + metabolic dysfunction) ```

Question 30

Define obstructive sleep apnoea

Answer 30

temporary blockade of URT

Question 31

What causes obstructive sleep apnoea?

Answer 31

-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

Question 32

Risk factors of obstructive sleep apnea?

Answer 32

- obesity- fat deposition/neck circumference - alcohol/sedatives -decrease in muscle tone - smoking -irritation/inflammation

Question 33

Define central sleep apnoea

Answer 33

dysfunction in CNS processes that initiate breathing

Question 34

What causes central sleep apnoea?

Answer 34

- 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

Question 35

How to differentiate obstructive + central sleep apnoeas?

Answer 35

polysomnography -whether diaphragmatic contractions continue during apnoea

Question 36

Diff between obstructive vs central diaphragmatic contractions?

Answer 36

``` 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 ```

Question 37

Define Cheyne-Stokes respiration

Answer 37

oscillating apnoea + hyperpnoea

Question 38

Describe Cheyne-Stokes respiration

Answer 38

- 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