Control of Breathing

Question 1

Which respiratory centers establish breathing rhythm?

Answer 1

The DRG (in medulla) automatically initiates breathing and establishes a breathing rhythm.

Question 2

Which respiratory centers maintain breathing rhythm?

Answer 2

?

Question 3

What are the main sensors in the respiratory control system?

Describe the main difference between central and peripheral.

Answer 3

Chemoreceptors - detect changes in O2, CO2, and H+

Central - detect [CO2] via [H+]
(Not responsive to O2)

Peripheral - detect [O2] or [H+] <– may be from lactic acid!
(Minimally responsive to CO2)

Question 4

What stimulates inspiration and expiration?

Answer 4

Inspiration - phrenic nerve to diaphragm
- external intercostal nerve/muscles

Expiration - internal intercostal nerve/muscles
(only in active breathing)

Question 5

What causes prolonged deep inspiration with limited expiration?

Answer 5

Hypoactivation of the pneumotaxic centre

Question 6

What regulates the magnitude (depth and rate) of ventilation?

Answer 6

Pneumotaxic centre in the bottom 2/3rds of pons

Question 7

What is responsible for initiating and regulating breathing?

Answer 7

In the Medulla…
DRG - acts on inspiration
- generate Ramp Signal (APs increase amplitude)
- stops discharging for expiration

VRG - acts during heavy breathing

    - inhibits inspiratory group
    - stimulates expiration

Question 8

What is considered the Respiratory Rhythm Generator?

Answer 8

DRG

Dorsal Respiratory Group

Question 9

What stimulates inspiratory neurons?

Answer 9

Apneustic centre in lower 1/3rd of pons

Question 10

What may cause shallow and irregular breathing?

Answer 10

Removal of stimulatory effect of Apneustic centre.

Shallow breathing may also be due to hyperstimulation of the pneumotaxic centre.

Question 11

What is the action of the pneumotaxic centre?

Answer 11

Starts expiration

Shuts off Apneustic centre and DRG

Question 12

What modifies respiratory activity for purposes such as cough, speech, or sneeze.

Answer 12

Irritant in upper airway stimulates receptors
–> Afferent signals via Vagus (larynx,cough)
via trigeminal/olfactory (nose,sneeze)
–> to Respiratory Centre
–> Deep inspiration/forced expiration against closed glottis
–> Glottis opens
–> Forceful outflow of air (helps remove irritants)

Question 13

What are some neurogenic/alternate methods that can change breathing patterns?

Answer 13

Temperature
Pain
Alcohol
Exercise (higher cortical centres)

Question 14

What are the Hering-Breuer Inflation and Deflation Reflexes?

Answer 14

Inflation Reflex - prevent over-inflation

                    - stimulate slow-adapting stretch receptors
                    - inhibit inspiration (via pons/medulla)
                    - important for neonates

Deflation Reflex - prevents deflation of lungs

                      - dec activity of slow-adapting stretch R's
                      - dec afferent vagal activity
                      - inc activity of inspiratory neurons

Question 15

What is responsible for the sensation of “air hunger”?

What causes this reflex?
How does it work?

Answer 15

J-receptor reflex

Caused by PE or Pulm Edema

• -> stimulates juxtapulm capillary receptors
• -> stimulates Vagal afferent
• -> Respiratory Centre
• -> Rapid Shallow Breathing

Question 16

How is voluntary breathing controlled?

Answer 16

Cerebral cortex
--> Descending tracts
--> Motor neurons of Resp Muscles
         (dorsolateral corticospinal tracts)
--> Overrides automatic regulation

Question 17

Location of central chemoreceptors?

           ... peripheral chemoreceptors?

Answer 17

Central - Just beneath the ventral surface of the medulla

Peripheral - in direct contact with arterial blood at aortic body and carotid body

Question 18

Which chemoreceptors most affect respiratory drive under normal conditions?

Answer 18

Central - account for ~75-85% of respiratory drive

Question 19

At what [O2] will the peripheral chemoreceptors stimulate a significant drive to breathe.

Answer 19

PaCO2 < 60mmHg

Question 20

In Emphysema, what happens to the blood gas levels?

                 ... what stimulates the drive to breathe?

Answer 20

Chronic Hypercapnea (PaCO2 = 50-55mmHg)
          & Hypoxemia (PaO2 = 45-50 mmHg)

Low PaO2 stimulates breathing
(Because central chemoR’s adapt to the elevated PaCO2)

Question 21

What nerve controls closure of the glottis?

Answer 21

Recurrent laryngeal nerve