Respiratory Physiology Part E + F: Control of Respiration

Question 1

2 groups of neurons in respiratory centre in Medulla

Answer 1

1. ventral (VRG) generates rate = expiratory and inspiratory neurons
2. dorsal (DRG) received chemoreceptors input and modifies VRG output

Question 2

Inspiratory Neurons send impulses down spinal cord to which nerves?

Answer 2

1. Phrenic nerve (innervates diaphragm)

2. Thoracic nerves (innervate ext. intercostals)

Question 3

What do expiratory neurons do?

Answer 3

fire to inhibit inspiratory neurons and expiration occurs passively

Question 4

Quiet breathing

Answer 4

• Inspiratory neurons active ∼ 2 seconds = inspiration
• Expiratory neurons inhibit inspiratory neurons’ output ∼3 sec = expiration
• VRG also active for forced insp. and exp. to recruit more muscles
• Respiration may cease if VRG damaged or suppressed e.g. alcohol, morphine

Question 5

What controls respiration?

Answer 5

1. Respiratory Centres in Medulla
2. Pontine respiratory centres
3. Other factors affecting breathing

Question 6

What do pontine respiratory centres do?

-if theres damage?

Answer 6

• work with medullary centers to make breathing smooth

- damage = gasping, irregular

Question 7

How do lung stretch receptors affect breathing?

Answer 7

• in smooth muscle of bronchi + bronchioles
  Hering-Breuer Reflex:
  1. receptors overstretched on insp. ->
  (impulses via vagus nerve)
  2. inhibit insp. neurons ->
  3. relaxes muscles (expiration - prevents overinflation)

Question 8

How does voluntary control affect breathing?

Answer 8

• 1° motor cortex to skeletal muscle (corticospinal pathway) - bypass medulla
• if medulla damaged must remember to breathe
• Hold breath - ⇑ PCO2 - medulla overrides voluntary control ⇒ breathe

Question 9

How do peripheral chemoreceptors (carotid and aortic bodies) affect breathing?

Answer 9

• weakly sensitive to PCO2
• very sensitive to H+
  
  • If blood H+ ⇑ (⇓ pH) ⇒ vent rate ⇑ (+ vice versa)
  • Recall: blood is buffered ∴ takes large change in H+ to change pH
• PO2 – stimulates receptors when PO2 reaches ∼ 50-60 mmHg (end of plateau of Hb-O2 curve) - emergency situation
• PO2 ⇓ due to lung disease, low atm PO2

Question 10

How do central chemoreceptors (medulla oblongata) affect breathing?

Answer 10

• respond indirectly to arterial PCO2
  -resting arterial PCO2 = 40 mm Hg (set point = 37 – 43 mmHg)
  -CO2 crosses blood-brain barrier easily; H+, HCO3- do not
  In CSF:
  CO2 + H2O H2CO3 -> H+ + HCO3-
  carbonic anhydrase
  -CSF poorly buffered ⇒ small change stim. response

Question 11

Increase and decrease in temp has what effect on ventilation?

Answer 11

1. increased
2. decreased
   temp is directly correlated

Question 12

Increase in emotion has what effect on ventilation?

Answer 12

increased

Question 13

Increase in proprioceptor discharge (exercise before change in blood gases occur) has what effect on ventilation?

Answer 13

increased

Question 14

Sudden increase or decrease in blood pressure has what effect on ventilation?

Answer 14

1. increased
2. decreased
   directly correlated

Question 15

sudden pain has what effect on ventilation?

Answer 15

stops ventilation

Question 16

chronic pain has what effect on ventilation?

Answer 16

increased

Question 17

sudden cold has what effect on ventilation?

Answer 17

stops temporarily

Question 18

stretching anal sphincter has what effect on ventilation?

Answer 18

increased

Question 19

Hyperventilation

Answer 19

⇓ arterial PCO2 ⇒ cerebral vasocon. (intrinsic metabolic response) ∴ ⇓ PO2 to brain ⇒ dizziness

Question 20

Hypoventilation

Answer 20

⇑ arterial PCO2, ⇑ H+ = acidosis

Question 21

CO poisoning

Answer 21

• CO - incomplete burning of gas (cars, furnaces)
• CO binds 210x more strongly to Fe than O2 = carboxyHb (HbCO)
• result: total ⇓ O2
• no change in PO2 or PCO2 (dissolved gases)
  ∴ ventilation rate doesn’t change