Control of breathing

Question 1

Neural control of inspiration

Answer 1

Phrenic nerve (diaphragm)
External intercostal nerve (external int. muscles)

Question 2

Neural control of expiration

Answer 2

internal intercostal nerves (internal int. muscles)

Question 3

Medullary respiratory neurons

Answer 3

Rhythmicity centre

Contains DRG and VRG

Question 4

Dorsal respiratory group (DRG)

Answer 4

Medullary
Inspiratory neurons, discharge during inspiration
generate the ramp signal
inspiratory signals that increase in amplitude, then stop for 3 sec
gradual increase in lung vol during inspiration

Question 5

Ventral respiratory group (VRG)

Answer 5

Medullary
Anterolateral to DRG
activated during heavy breathing --> increased activity of inspiratory neurons --> activation of VRG
Inhibits respiratory group
Stimulates mss of expiration

Question 6

Pontine respiratory centre

Answer 6

modify rate and pattern of respiration

contain apneustic + pneumotaxic centres

Question 7

Apneustic centres

Answer 7

Pontine
lower 1/3, close to medullary
stimulatory signals to inspiratory neurons
removal –> shallow/irregular inspiration

Question 8

Pneumotaxic centres

Answer 8

upper 2/3 of Pons
regulation of respiratory vol & rate
controls cessation of inspiratory ramp signals from DRG
switch off DRG & apneustic centre –> expiration

hypoactivation = prolonged deep inspiration with limited expiration
hyperactivation = shallow inspiration

Question 9

Peripheral input to respiratory centres

Answer 9

Chemoreceptors
Pulmonary stretch receptors (SARs)
Irritant receptors (RARs)
Mechanoreceptors
Muscle and joint proprioceptors

Question 10

Central chemoreceptor pathway

Answer 10

central chemosensitive area
just beneath ventral surface of medulla
relays sensory input
sensitive to changes in PaCO2, H+ conc, not to PaO2
normal cond’ns = 75-85% respiratory drive due to central chemorec. by PaCO2
Direct stimulant = H+, but cannot cross BBB (CO2 crosses, combines with H2O and dissociates to form H+ and bicarb, H+ stimulates)

Question 11

Peripheral chemoreceptors

Answer 11

at bifurcation of carotic artery
cells in direct contact with arterial blood
afferent neurons project to medullary control centres
respond to changes in PaO2 or pH (not much through PaCO2)

Question 12

Effects of PaO2 on ventilation

Answer 12

not much until <60 mmHg

response due to activation of peripheral chemoreceptors only

Question 13

Effects of PaCO2 on ventilation

Answer 13

Large effects
Mediated through central & peripheral chemoreceptors, but must be converted to H+ first
>90 mmHg = coma
>180 mmHg = death

Question 14

Hering-Breuer Inflation reflex

Answer 14

inhibito-inspiratory reflex
over-inflation of lungs –> stimulation of slowly adapting stretch receptors in smooth muscles of large & small airways –> afferent vagal signals –> inhibitory to medullary and pontine inspiratory network –> termination of inspiration

more important/powerful in neonates

Question 15

Hering-Breuer Deflation reflex

Answer 15

excito-inspiratory
deep expiration –> deflation of lungs -> decrease in activity of previous slowly adapting stretch receptors in smooth muscles –> decrease afferent vagal –> increase in activity of inspiratory neurons –> increased RR

Question 16

J-receptor reflex

Answer 16

PE or edema or congestion –> stimulation of juxtapulmonary capillaries receptors –> impulses along vagal afferent –> respiratory centre –> rapid shallow breathing

sensation of “air hunger”, dyspnea

Question 17

Cough & sneezing reflex

Answer 17

rapidly adapting reflexes
dust, smoking, irritant –> stimulation of irritant receptors in upper pathways (nose, larynx, bronchi) –> afferent vagal signals (larynx, cough) or trigeminal or olfactory (nose, sneezing) –> respiratory centre –> deep inspiration followed by forced expiration against closed glottis –> opening of glottis –> forceful outflow

Question 18

Other influences on respiration via hypothalamus

Answer 18

hot –> increase RR
pain –> sudden pain decreases RR, prolonged increases RR
alcohol –> decrease RR
exercise –> increase RR (higher cortical)

Question 19

Voluntary control

Answer 19

Cortical influence
descending tract from cerebral cortex to motor neurons of respiratory muscles (dorsolateral corticospoinal tracts)
allows CNS to override automatic regulation for a short time

Question 20

Emphysema

Answer 20

chronic hypercapnia (50-55 mmHg)
chronic hypoxemia (45-50 mmHg)
central chemoreceptors adapted to high level of PaCO2
most chemical stimulus to breathe comes from low PO2
(need to be careful about O2 administration, to sustain respiratory drive)