Week 21: (C.3) Neuroanatomy & Neurophysiology of breathing

Question 1

What is the pathway of regulation of involuntary breathing rhythm?

Answer 1

sensors —> controller —> effectors

Question 2

What are the sensors for the involuntary breathing rhythm?

Answer 2

Central chemoR
Peripheral chemoR
stretch R
allergen and irritant R

Question 3

What innervates the peripheral chemoR?

Answer 3

increased PCO2

decreased PO2 & pH

Question 4

What is the function of the central chemoR?

Answer 4

Monitor pCO2 in

cerebral spinal fluid (CSF).

Question 5

What is the function of the peripheral chemoR?

Answer 5

Monitor PO2, PCO2 and pH in blood and mixed lung gases.

Carotid Body (blood) Neuroepithelial Bodies (airway)

Question 6

What are the other receptor inputs?

Answer 6

stretch R

allergens and irritant Receptors

Question 7

What is the function of the stretch R?

Answer 7

> Hering-Breuer reflex:
Inhibition of lung over-inflation (>50% resting tidal)
Increased breathing frequency following rapid lung deflation (exhalation→ pant).

Question 8

What is the function of allergens and irritant Receptors?

Answer 8

Feed into Vagus

Cough, sneeze and bronchoconstriction reflex

Question 9

What does the central chemoR detect?

Answer 9

pH changes caused by increased PaCO2 in CSF

Question 10

What does the peripheral cemoR detect?

Answer 10

decreased PaCO2 in the blood and airway. (less responsive to increased PaCO2 and decreased pH)

Question 11

What receptor has a linear response mode?

Answer 11

central chemoR

Question 12

What is the location of the central chemoR?

Answer 12

medulla (surafce)

Question 13

What is the location of the peripheral chemoR?

Answer 13

arteial vasculature & airway

Question 14

What contributes more to normal control of breathing?

Answer 14

central chemoR 80%

Question 15

What has the faster response time?

Answer 15

Peripheral chemoR

seconds

Question 16

Can the peripheral chemoR be altered by training?

Answer 16

NO

Question 17

What does the central chemoR control?

Answer 17

system for normal breathing

Question 18

What does the central chemoR respond to?

Answer 18

CO2 driven pH changes in Cerebral Spinal Fluid (CSF)

Changing Alveolar pCO2 (pACO2)

Question 19

How does CO2 travel from the blood to the CSF (cerebral spinal fluid)?

Answer 19

1) CO2 carried as HCO3- in blood
2) Blood HCO3- & H+ cannot cross blood brain
barrier
3) High HCO3- → reaction reversal
4) Dissolved CO2 crosses blood brain barrier

Question 20

What happens to CO2 in the CSF?

Answer 20

Change to carbonic acid then to H+ and bicarbonate

Question 21

What happens to H+ in the central chemoR pathway?

Answer 21

decrease pH in the central chemoR on medulla surface

Question 22

Why is H2CO3 to HCO3- + H+ a slow reaction in the CSF?

Answer 22

no carbonic anhydrase in brain is reaction is slow

mediated by a chemical reaction

Question 23

When does CO2 diffuse across the blood-brain barrier?

Answer 23

when an accumulation of CO2 in blood drives reverse anhydrase reaction

Question 24

Why are central chemoR slow?

Answer 24

they are not mediated by carbonic anhydrase

Question 25

What is the efect of H+ in the CSF?

Answer 25

detected by and responded to by the medulla | Causes a decrease in pH in the central chemoR on the medulla surface

Question 26

What is the effect of decreased pH in the central chemoR on the medulla surface?

Answer 26

increase firing rate of DRG | increase frequency

Question 27

What is the effect of increased DRG and F?

Answer 27

increased VE | ventilation

Question 28

How do you increase the sensitivity of central chemoR to PACO2?

Answer 28

decrease alveolar PO2 levels e.g. top of everest haldane effect

Question 29

What happens to PO2 as we increase PACO2?

Answer 29

increase

Question 30

Why does the increase in PACO2 increase PO2 levels?

Answer 30

it increase the firing of the central chemoR.

Question 31

What is the effect of hypoxia on ventilation?

Answer 31

Hypoxia makes the response steeper | bigger change in VE per pACO2

Question 32

What is the effect of anaesthesia?

Answer 32

decrease sensitivity of central chemoR to PACO2

Question 33

Where are peripheral the chemoR located?

Answer 33

``` carotid body (carotid sinus) aortic body (aortic arch) ```

Question 34

What are the type 1 glomus cell?

Answer 34

- neurotransmitters rich cells which detect changes in oxygen ph and pp of CO2 in arterial blood as its perfusing through the carotid body

Question 35

What drives the changes in breathing? (peripheral chemoR)

Answer 35

glomus cells sit in close proximity to the capillaries afferent neurones which terminate on the type 1 glomus cell which relay info as neurotransmission is released from the type 1 glomus cell in the centre of the brain and the dorsal respiratory which drives changes in breathing.

Question 36

What do peripheral chemoR respond to?

Answer 36

hypoxia and hypercapnia and acidosis

Question 37

what is hypercapnia?

Answer 37

increased paCO2

Question 38

What happens to Peripheral chemoR sensitivity as we decrease PAO2?

Answer 38

blood becomes increasingly hypercapnic | increase peripheral chemoR sensitivity to CO2

Question 39

When is hypoxia response not linear?

Answer 39

pAO2=60mmHg

Question 40

What drives the peripheral chemoR response?

Answer 40

Response is driven by low partial pressure of O2 and not O2 concentration or HbO2 saturation. Does not occur with anaemia.

Question 41

What raises the sensitivity of the peripheral chemoR? (increase ventilation)

Answer 41

Hypercapnia or acidosis raises the sensitivity of chemoreceptor to pAO2.

Question 42

What causes depolarisation of the peripheral chemoR?

Answer 42

depolarisation of the cell by decreased O2, decreased | pH increased CO2

Question 43

What does the depolarisation of the glomus cell cause? (peripheral chemoR)

Answer 43

opening of the voltage gated calcium channels (Ca2+ entry into cell) Neurotransmitter release

Question 44

What does the glomus cell innervate with its neurotransmitter release?

Answer 44

Glossopharyngeal Nerve | innervates the brain stem (DRG & RRG)

Question 45

What does the Brain stem (DRG & RRG) innervate? (peripheral chemoR)

Answer 45

1) Hypoxic Ventilatory Response (↑F, ↑TV) | 2) Hypoxic pulmonary vasoconstrictor response ↑Pulmonary Artery Pressure

Question 46

How is hypoxia detected?

Answer 46

oxygen not abundant -Hypoxia is sensed, inhibition on K+ channel depolarisation from K and Ca2+ channels open and neurotransmitter release