4.2 Control of breathing: chemical and neural

Question 1

which chemoreceptors are responsible for most ventilatory response in normal conditions?

Answer 1

central

Question 2

where are central chemoreceptors located?

Answer 2

under ventral surface of medulla

Question 3

pulmonary mechanoreceptors

Answer 3

stretch receptors in lungs

Question 4

what is sensed by peripheral chemoreceptors?

Answer 4

-decreased pO2
-low pH
- high CO2

Question 5

what is sensed by central chemoreceptors?

Answer 5

-low pH
-high CO2

Question 6

where are carotid bodies?

Answer 6

bifurcation of common carotid arteries

Question 7

where are aortic bodies?

Answer 7

aortic arch of thorax

Question 8

major function of peripheral chemorecrptors?

Answer 8

sense hyperaemia and signal cells in medulla to increase ventilation

Question 9

type 1 glomus cells
-derivation
-function

Answer 9

-ectoderm (like neurones)
-membrane depolarises when O2 low, c cause release of intracellular vesicles neurotransmitters, triggers action potential in carotid body nerve afferent fibres, signals low pO2 to medulla

Question 10

sensory innervation to
-carotid body
-aortic body

Answer 10

-branch of CNIX (glossopharyngeal)
-branch of CNX (vagus)

Question 11

how does hyperaemia change peripheral chemoreceptors sensitivity?

Answer 11

increased to acidosis and hypercapnia

Question 12

first chemorectpro to respond

Answer 12

peripheral

Question 13

what forms blood brain barrier?

Answer 13

endothelial cells of blood vessels in brain surrounded by peidcytis and foot processes of astrocytes = highly selective permeability barrier

Question 14

explain how central chemoreceptors sense changes in pCO2 and pH

Answer 14

-BBB separates central chemoreceptors in medulla from arterial blood
-BBB low permeability to H+ AND HCO3- but high to CO2
-co2 diffuses into CSF and central chemoreceptor neuron cells
-CNS has limited buffering from HCO3 so acidosis develops
-pH change raises chemoreceptor firing rate so hyperventilation

Question 15

explain the effect of chronic hypercapnia on central chemoreceptors

Answer 15

-pH slowly recovers 8-24 hrs as choroid plexus increases active transport of HCO3 into CSF (metabolic compensation)
-now higher CO2 needed to cause acidosis and increase ventilation so level ‘reset’
-metabolic comp in body 3-5 days

Question 16

which chemoreceptors respond to low pO2?

Answer 16

peripheral

Question 17

describe the neural control of breathing

Answer 17

respiratory pattern generators in medulla receives inputs from pO2, pCO2, pH, lung stretch, cerebral cortex (emotional state).

Stimulates inspiratory centres which synapses on either phrenic nerve (diaphragm) or intercostal nerve (intercostal muscles)

or could stimulate expiratory centres to act on intercostal muscles via intercostal nerve

Question 18

describe the voluntary control of breathing

Answer 18

pathways from cerebral cortex, impinge on respiratory centre connections to nerves and voluntarily switch h on phrenic/intercostal nerves

Question 19

what’s Ondines curse?

Answer 19

stroke which destroys autonomic system but leaves respiratory system intact, so patient must always be thinking about breathing.
need ventilator at night

Question 20

how can we only ever breathe in OR out?

Answer 20

reciprocal inhibition so inspiratory ad expiratory centres can’t be stimulated at same time

Question 21

is expiratory centres used much? when’s it used?

Answer 21

no silent most of the time, allowing lung elasticity to exhale, just turn inspiratory centre on/off
used in exercise