Control of Ventilation

Question 1

what actors control ventilation?

Answer 1

skeletal muscles of inspiration, via the phrenic nerve (diaphragm) and intercostal nerves (external intercostal muscles)

Question 2

where are the respiratory centres (responsible for control of ventilation) located?

Answer 2

in the pons and medulla

Question 3

is ventilatory control subconscious or not?

Answer 3

normally subconscious but can be subject to voluntary modulation

Question 4

what is ventilatory control entirely dependant on? what could be severed to stop breathing from happening?

Answer 4

signalling from the brain, severed spinal cord above origin of phrenic nerve (C3-5) makes breathing stop

Question 5

what do the respiratory centres do?

Answer 5

set an automatic rhythm of breathing through co-ordinating the firing of smooth and repetitive bursts of action potentials in DRG, adjust this rhythm in response to stimuli

Question 6

what does DRG stand for? where does it transmit information?

Answer 6

dorsal respiratory group (of neurones), transmits to phrenic and intercostal nerves (inspiratory muscles)

Question 7

what does PRG stand for?

Answer 7

pontine respiratory group

Question 8

what does VRG stand for? where does it transmit information?

Answer 8

ventral respiratory group (of neurones), transmits to tongue, pharynx, expiratory muscles

Question 9

what does NTS stand for?

Answer 9

nucleus tractus solitarius

Question 10

what modulates respiratory centre rhythm? and via which system?

Answer 10

emotion (via limbic system in the brain), voluntary over-ride (via higher centres in the brain), mechano-sensory input from thorax (e.g: stretch reflex), chemical composition of the blood (PCO2, PO2 and pH) (detected by chemoreceptors)

Question 11

which of these modulators is the most significant?

Answer 11

chemoreceptor input

Question 12

which is most superior along the brainstem? pons or medulla?

Answer 12

pons (medulla is just below)

Question 13

where are central chemoreceptors situated? what do they do?

Answer 13

situated in the medulla, they respond directly to (H+) change is CSF around the brain (which itself directly reflects PCO2), they are the primary ventilatory drive (cause reflex stimulation of ventilation following rise in (H+), reflex inhibition of ventilation if decrease in arterial PCO2 (in case of hyperventilation)

Question 14

where are peripheral chemoreceptors situated? what do they do?

Answer 14

situated in the carotid and aortic bodies, they respond primarily to plasma (H+) and PO2 (less so to PCO2), they are the secondary ventilatory drive

Question 15

what are central chemoreceptors driven by?

Answer 15

driven by raised PCO2 (=hypercapnea)

Question 16

do central chemoreceptors respond directly to (H+) change in the plasma?

Answer 16

no (CSF)

Question 17

TRUE/FALSE when arterial PCO2 increases, CO2 crosses the blood-brain barrier not H+

Answer 17

TRUE

Question 18

TRUE/FALSE central chemoreceptors monitor the PCO2 directly in the CSF

Answer 18

FALSE, Indirectly

Question 19

what two products are formed as a result of increased PCO2?

Answer 19

H+ and bicarbonate

Question 20

how does ventilation change in response to increased arterial PCO2? decreased arterial PCO2?

Answer 20

increases ventilation, decreases ventilation

Question 21

what do peripheral chemoreceptors do?

Answer 21

cause reflex stimulation of ventilation following significant fall in arterial PO2 (consider haemoglobin dissociation) or a rise in (H+)

Question 22

do peripheral chemoreceptors respond to arterial oxygen content?

Answer 22

no, just PO2

Question 23

is pH falls, ventilation will be stimulated/ inhibited?

Answer 23

stimulated (acidosis)

Question 24

is pH rises, ventilation will be stimulated/ inhibited?

Answer 24

inhibited (alkalosis)

Question 25

what does a descending neural pathway from cerebral cortex to respiratory motor neurone allow?

Answer 25

a large degree of voluntary control of breathing

Question 26

can you override involuntary stimuli such as arterial PCO2 or H+?

Answer 26

well, no of course not it’s “involuntary”

Question 27

when is ventilation inhibited? what happens chemically speaking?

Answer 27

hyperventilation, during which ventilation is reflexly inhibited by an increase in arterial PO2 or a decrease in arterial PCO2/(H+)

Question 28

what drugs often result in death as result of respiratory failure if overdosage? what do they do?

Answer 28

barbiturates and opioids depress respiratory centre

Question 29

what effects do gaseous anaesthetic agents have?

Answer 29

increased respiratory rate but decreased tidal volume so decreased AV (?)

Question 30

what is nitrous oxide used for? what does it do?

Answer 30

it is a common sedative/ light anaesthetic agent, blunts peripheral chemoreceptor response to falling PaO2

Question 31

is nitrous oxide safe? when can it cause problems?

Answer 31

for most individuals, yes, it causes problems in patients with chronic lung disease cases (patients often on “hypoxic drive”). Administrating nitrous oxide makes things worse

Question 32

what happens to respiration during swallowing? why?

Answer 32

it is inhibited to avoid aspiration of food or fluids into the airways

Question 33

what is swallowing followed by in terms of ventilation? why?

Answer 33

an expiration, to dislodge any particles outwards from the region of the glottis

Question 34

is the heart entirely dependent on signalling from the brain?

Answer 34

no, but ventilatory control is

Question 35

what role does stretch reflex have in protecting the respiratory system?

Answer 35

forces expiration to protect alveoli when too much inspiration (reaction to a mechano-sensory input)

Question 36

what is the blood brain barrier permeable to?

Answer 36

gas

Question 37

what is the blood brain barrier impermeable to?

Answer 37

ions