Control of ventilation

Question 1

Which nerves stimulate the muscles necessary for inhalation?

Answer 1

Phrenic nerve to diaphragm (C3-5)

Intercostal nerves to external intercostals

Question 2

What part of the brain regulates ventilation?

Answer 2

Ill defined respiratory centres in superior pons and inferior medulla oblongata

Dorsal respiratory group - medulla
Ventral respiratory group - medulla

Question 3

What happens if you sever the spinal cord above C3?

Answer 3

Breathing ceases

Question 4

What is the dorsal respiratory group, and what is it mainly responsible for?

Answer 4

Located in the dorsomedial region of the medulla, composed of cells in the solitary tract nucleus. One of the known two respiratory neuron localisations, mainly responsible for inhalation

Question 5

What is the ventral respiratory group, and what is it mainly responsible for?

Answer 5

located in the ventrolateral region of the medulla, containing both inspiratory and expiratory neurons

Question 6

What influences the respiratory centres to modulate breathing rhythm?

Answer 6

Emotion (via limbic system)
Voluntary override (via higher brain centres)
Mechanosensory input from thorax (stretch)
Chemical composition of blood

Question 7

Where are chemoreceptors found?

Answer 7

Central - in medulla (ventral resp. group)

Peripheral - carotid and aortic bodies

Question 8

What do central chemoreceptors respond to?

Answer 8

H+ (which directly reflects PCO2, through its reaction with H20 in the brain to form carbonic acid/H+); does not respond to O2 directly

Question 9

What do peripheral chemoreceptors respond to?

Answer 9

Plasma H+ and O2 (less so to CO2)

Question 10

What cranial nerves are found near the central chemoreceptors (and therefore the ventral respiratory group)?

Answer 10

Exit of 9th and 10th cranial nerves

Question 11

How do the respiratory centres respond to decreased PCO2?

Answer 11

Slows ventilation rate

Question 12

How do the respiratory centres respond to increased PCO2?

Answer 12

Increases ventilation rate

Question 13

What conditions can the peripheral chemoreceptors react to?

Answer 13

Hypoxia
Hypercapnia
Hypoglycaemia

Question 14

What conditions can the central chemoreceptors react to?

Answer 14

Hypercapnia/acidosis

Question 15

What happens if pH of blood falls (acidosis)?

Answer 15

Suggests hypercapnia, so ventilation is increased

Question 16

What happens if pH of blood increases (alkalosis)?

Answer 16

Ventilation will be decreased

Question 17

When is ventilation inhibited?

Answer 17

Hyperventilation = increased O2 or decreased H+

During swallowing

Question 18

Describe effect of swallowing on ventilation?

Answer 18

Ventilation is inhibited during swallowing, and swallowing is always followed by exhalation so any particles left can be dislodged outwards

Question 19

What drugs affect the respiratory centre?

Answer 19

Barbiturates and opioids - depress resp centres

Gaseous anaesthetics - increase RR but decrease TV to decrease respiration

NO - mild anaesthetic which blunts peripheral chemoreceptors to P02 and PCO2. Dangerous in those with hypoxic drive (chronic lung disease) as it leads to poor detection of PCO2, as they have a reduced central receptor response.

Question 20

What is hypoxic drive?

Answer 20

The hypoxic drive is a form of respiratory drive in which the body uses oxygen chemoreceptors instead of carbon dioxide receptors to regulate the respiratory cycle.

Question 21

What happens if you administer O2 to those with chronic lung disease who have been wrongly given NO as a sedative/anaesthetic?

Answer 21

Aggravates situation, as it masks increases in PCO2 even more