Topic 13: Respiratory System - Control of Respiration

Question 1

What is the function of the respiratory centres in Medulla?

Answer 1

• set rate, depth and rhythm of breathing

Question 2

What are the 2 groups of neurons in the respiratory centres of the medulla?

Answer 2

• ventral (VRG)
• dorsal (DRG) respiratory groups

Question 3

What are ventral respiratory groups? (2)

Answer 3

• generates rate
• expiratory and inspiratory neurons

Question 4

What do dorsal respiratory groups do? (2)

Answer 4

• receive chemoreceptor input
• modifies VRG output

Question 5

What do Inspiratory neurons do? (3)

Answer 5

• send impulses down spinal cord to:
• phrenic nerve (innervates diaphragm)
• thoracic nerve (innervates external intercostals)

Question 6

What do expiratory neurons do?

Answer 6

• fire to inhibit inspiratory neurons and expiration occurs passively

Question 7

What occurs in quiet breathing (4)

Answer 7

1) inspiratory neurons active for 2 seconds during inspiration
2) expiratory neurons inhibit inspiratory neurons’ output for 3 seconds for expiration
3) VRG active for forced inspiration and exp. to recruit more muscles
4) respiration may cease if VRG damaged or suppressed from alcohol, morphine, etc.

Question 8

What is the function of pontine respiratory centers?

Answer 8

• work with medullary centers to make breathing smooth

Question 9

What happens if there is damage to pontine respiratory centers?

Answer 9

• gasping, irregular breathing

Question 10

What other factors affect breathing?

Answer 10

1) lung stretch receptors
2) Voluntary control
3) Chemical control (chemoreceptors)

Question 11

Where are lung stretch receptors found?

Answer 11

• in sm. muscle of bronchi and bronchioles

Question 12

The lung stretch receptors include the Hering-Breur reflex. Recite the diagram

Answer 12

Question 13

Why does voluntary control affect breathing? (3)

Answer 13

• primary motor cortex to skeletal muscle (corticospinal pathway) bypasses the medulla
• if medulla is damaged, you must remember to breathe
• when you hold your breath, it increases PCO2 so medulla overrides voluntary control to breathe

Question 14

What are peripheral chemoreceptors? (3)

Answer 14

• carotid and aortic bodies
• weakly sensitive to PCO2
• very sensitive to H+

Question 15

What do peripheral receptors do if there is an increase in blood H+ (decrease in pH)? (2)

Answer 15

• increases ventilation rate (vice versa)
• recall that if blood is buffered, it takes a large change in H+ to change pH

Question 16

What do peripheral receptors do in relation to PO2? (2)

Answer 16

• stimulates receptors when PO2 reaches around 50-60 mmHg (end of plateau of Hb-O2 curve) - emergency situation
• decreased PO2 due to lung disease, low atm PO2

Question 17

What are central chemoreceptors? (2)

Answer 17

• medulla oblongata
• DOMINANT CONTROL

Question 18

Central chemoreceptors respond ___ to P__. What number is the resting arterial PCO2?

Answer 18

• indirectly
• CO2
• resting arterial PCO2 = 40 mmHg (set point 37-43 mmHg)

Question 19

What process (reaction) involves central chemoreceptors? (3)

Answer 19

• CO2 crosses blood-brain barrier easily, H+ and HCO3- do not
  1) in CSF, CO2 + H2O -> H2CO3 -> H+ + HCO3-
• CSF is poorly buffered so there is a small change stimulus response

Question 20

Other factors controlling breathing diagram

Answer 20