SM 157a - Control of Breathing

Question 1

The PreBötC signals to the _________________, in order to generate [inspiration/expiration]

Answer 1

The PreBötC signals to the inspiratory bulbospinal neurons in the rostral ventral respiratory column** , in order to generate **inspiration

Question 2

What is the difference between the Breur-Hering inspiratory terminating reflex and the Breur-Hering expieratory facilitating reflex?

Answer 2

They are two parts of the same reflex

• Inspiratory terminating reflex
  
  • Activated when lung inflation is 3*V_T
  • Terminates current inspiration and initiates expiration
• Expiratory facilitating reflex
  
  • Activated when lung inflation is prolonged
  • Slows breathing
  • Prolongs expiration
  • Activates abdominal expiratory muscles

Question 3

If the body’s response to increases in P_aCO2 is to hyperventilate, why do patients with chronic respiratory insufficiency hypoventilate?

Answer 3

The body adapts to chronically elevated P_aCO2

• Compensatory increases in arterial [HCO₃^-] lead to increased [HCO₃^-​] in the brain
• This resets medullary (central) chemoreceptors, leading to decreased respiratory drive
• The body basicallly becomes more okay with chronic high levels of P_aCO2

Question 4

The parafacial respiratory group signals to the _________________, in order to generate [inspiration/expiration]

Answer 4

The parfacial respiratory group signals to the expiratory bulbospinal neurons in the caudal ventral respiratory column** , in order to generate **expiration

Question 5

A sigh or augmented breath is a reflex caused by activation of the ____________ pulmonary stretch receptors

Answer 5

A sigh or augmented breath is a reflex caused by activation of the rapidly adapting pulmonary stretch receptors

Question 6

Peripheral chemoreceptors begin to really respond to hypoxemia when P_aO2 decreases below _____ mmHg

Answer 6

Peripheral chemoreceptors begin to really respond to hypoxemia when P_aO2​ decreases below 60 mmHg

Question 7

What stimulus activates the slowly adapting pulmonary stretch receptors?

What is their response?

Answer 7

The slowly adapting pulmonary stretch receptors are activated by lung inflation or bronchoconstriction

They will continue rapid firing as long as inflation is maintained

They function to terminate the current inspiration and initiate expiration

Question 8

Which pathophysiologic stimulus will most strongly activate the body’s ventilatory response?

1. Increased P_aCO2
2. Decreased pH
3. Decreased P_aO2

Answer 8

a. Increased P_aCO2

Question 9

What does the pre Bötzinger complex (preBötC) do?

Where is it located?

Answer 9

The preBötC is responsible for generating inspiratory breathing rhythm

It is located in the rostral ventral respiratory column (VRC), which is located in the ventrolateral medulla

Question 10

Describe the ventilatory response to increased P_aCO2

Answer 10

Increased P_aCO2 causes…

• Central and peripheral chemoreceptor activation
  
  • Central chemoreceptors have the strongest response
• Increase alveolar ventilation by increasing minute ventilation (V̇_E)
  
  • There is a linear increase in V̇_E as P_aCO2 increases
  • Steeper slope = more sensitive chemoreceptor

Question 11

Most of the response to short-term decreases in pH_a can be attributed to which receptors?

Answer 11

Peripheral chemoreceptors

Question 12

Describe the body’s compensatory response to chronically elevated P_aCO2

Answer 12

Chronically elevated P_aCO2 causes…

• Compensatory increase in arterial [HCO₃^-] over days
  
  • Due to increase in kidney retention of HCO₃^-
• Eventually, the brain [HCO₃^-] will increase
  
  • This resets medullary (central) chemoreceptors
    
    • Increased [HCO₃^-] in the brain decreases respiratory drive
  • CO₂ sensitivity is reduced
  • The slope of the V̇_E/P_aCO2 curve decreases

Question 13

Describe the central chemoreceptor response to lactic acidosis

Answer 13

The central chemoreceptors are not very good at responding to changes in pH; H+ ions don’t typically cross the blood-brain barrier

However, the central chemoreceptors are very responsive to high P_aCO2 - they trigger a ventilatory response

Question 14

Activation of c-fibers + rapidly adapting receptors results in a [cough/sneeze]

Answer 14

Activation of c-fibers + rapidly adapting receptors results in a cough

Question 15

Why is V̇_A/Q̇ higher in the apical regions of the lung than the basal regions (in an upright person)?

Answer 15

The apex of the lung has a lower compliance (-> lower V̇) and lower blood flow (Q̇) than the base.

However, the decreased compliance, and therefore decreased V̇, is less than the decrease in blood flow.

This means that V̇_A/Q̇ will be higher in the apex of the lung than the base, if a person is sitting upright

Question 16

Where are the slowly adapting pulmonary stretch receptors located?

Answer 16

Airway smooth muscle

Question 17

Which pontomedullary cardiorespiratory cell group contains teh central pattern generator for expiration?

Answer 17

The parafacial respiratory group

Question 18

Irritation above the oropharynx results in a [cough/sneeze]

Answer 18

Irritation above the oropharynx results in a sneeze

Question 19

What stimulus activates the rapidly adapting pulmonary stretch receptors? (RARs)

What is the effect?

Answer 19

The RARs are also known as irritant receptors

They are activated by irritation to the airways

Activation ->

• Facilitates inspiratory efforts
• Contributes to airway protective reflexes
  
  • Cough, sneeze
• Increases mucus production
• Bronchoconstriction

Question 20

What does the ventral respiratory column (VRC) do?

Where is it located?

Answer 20

The VRC is the dominant site of nerual circuitry that generates breathing rhythm.

It is located in the ventrolateral medulla.

It contains the PreBötC which generates inspiratory rhythm, and the pFRG which generates expiratory rhythm.

Question 21

What causes increased [HCO₃^-] in the brain?

What is the effect?

Answer 21

Increased [HCO₃^-] in the brain is caused by chronic hypercapnia (elevated P_aCO2)

The result is decreased respiratory drive, leading to retention of CO₂ in the blood

Question 22

What is Rett syndrome?

What causes it?

Answer 22

A developmental disorder of the CNS due to a mutation in the x-linked Mecp2 gene

• Severe neurological symptoms
• Speech and movement disorders
• Irregular breathing (Cheyne-stokes)
  
  • -> life-threatening apnea
• Onset 6-18 months

Question 23

Where are the rapidly adapting pulmonary stretch receptors located?

Answer 23

Between airway epithelial cells in the trachea and larger bronchi

• Near postcapillary venules
  
  • Activated by airway edema
• In epipharynx
  
  • Activation -> aspiration reflex (strong inspiratory efforts)

Question 24

Shallow, rapid breathing is a reflex caused by activation of the __________

Answer 24

Shallow, rapid breathing is a reflex caused by activation of the bronchopulmonary c-fibers

Question 25

What does the parafacial respiratory group (pFRG) do? Where is it located?

Answer 25

The pFRG is responsible for generating expiratory breathing rhythm It is located in the **caudal ventral respiratory column (VRC)**, which is located in the ventrolateral medulla

Question 26

Which gas is the most potent pathophysiologic stimulus for breathing?

Answer 26

CO2 Ventilation can double wtih a 2 mmHg increase in P_aCO2

Question 27

What stimulates teh central chemoreceptors?

Answer 27

* **High P_aCO2** * Low pH Central chemoreceptors are most responsive to **High P_aCO2** H+ ions don't typically cross the blood-brain barrier, so there is a limited acute response to lactic acidosis

Question 28

What stimulates the peripheral chemoreceptros in the carotid and aortic bodies?

Answer 28

* Low P_aO2 * Low pH_a * High P_aCO2

Question 29

Irritation in or below the oropharynx results in a [_cough/sneeze]_

Answer 29

Irritation in or below the oropharynx results in a **_cough_**

Question 30

The ventral respiratory column (VRC) is the dominant site for neural circuitry that generates breathing. Within the VRC, which region is responsible for inspiratory rhythm? Which region is responsible for expiratory rhythm?

Answer 30

**Inspiratory:** Pre Bötzinger complex (PreBötC) **Expiratory:** Parafacial respiratory group (pFRG)

Question 31

Activation of which receptors initiates the **Breur-Hering inspiratory terminating reflex?**

Answer 31

Slowly adapting pulmonary stretch receptors - when lung inflation is ~3\*V_T This reflex works to terminate the current inspiration and initiate expiration

Question 32

Activation receptors in the mucous membrane of the nose results in a [_cough/sneeze_]

Answer 32

Activation receptors in the mucous membrane of the nose results in a **_sneeze_**

Question 33

Activation of which pulmonary mechanoreceptors... Facilitates expiration? Facilitates inspiration?

Answer 33

**Expiration** is facilitated by activation of the **slowly adapting pulmonary stretch receptors** **Inspiration** is facilitated by activation of the **rapidly adapting pulmonary strech receptors**

Question 34

Describe the Breur-Hering inspiratory terminating reflex

Answer 34

This reflex is mediated by **slowly adapting pulmonary stretch receptors** that signal to the brainstem to **terminate the current inspiration and initiate expiration** It can also produce bronchodilation, prolong expiration, and activate abdominal expiraotry muscles

Question 35

Which pontomedullary cardiorespiratory cell group contains the central pattern generator for inspiration?

Answer 35

The PreBötzinger complex

Question 36

What causes Cheyne-stokes breathing? What is the effect?

Answer 36

Cheyne-stokes breathing is caused by **decreased sensitivity of central chemoreceptors due to decreased cardiac output** The effect is a delay between changes in P_ACO2 and detection by chemoreceptors. **This can lead to life-threatening apnea**

Question 37

Which pontomedullary cardiorespiratory cell groups is important for the coordination fo respiratory control with activity in other systems?

Answer 37

The pontine respiratory group

Question 38

Neurons involved in breathing are concentrated within which 3 regions of the medulla and the pons?

Answer 38

1. Dorsal respiratory group (DRG) 2. **Ventral respiratory column (VRC)** 3. Pontine respiratory group (PRG) Ventral respiratory column is the dominant site

Question 39

If lung inflation continues into the expiratory period, which receptors are activated? Which reflex is initiated?

Answer 39

**Slowly adapting pulmonary stretch receptors** initiate the **B****reuer-Hering expiratory facilitating reflex** * If lung inflation continues into the expiratory period, FRC increases and the slowly adapating pulmonary stretch receptors are activated * This slows down breathing * Expiration is prolonged * Abdominal expiratory muscles are activated

Question 40

What are C-fibers? What do they do?

Answer 40

C-fibers are **small, unmylinated nerve fibers near the alveoli** They are activated by the accumulation of pulmonary **fluid or inhaled irriatants** When activated, they induce a **rapid, shallow breathing pattern** and produce a sensation of **dyspnea**

Question 41

Where are central chemoreceptors located?

Answer 41

The retrotrapezoid nucleus (Ventral to the facial nucleus near the ventral surface of the medulla)

Question 42

Which receptors are the primary responders to hypoxia?

Answer 42

Peripheral chemoreceptors Located in the carotid and aortic bodies

Question 43

Activation of which pulmonary mechanoreceptors facilitates... Bronchodilation? Bronchoconstriction?

Answer 43

**Bronchodilation** is facilitated by activation of the **slowly adapting pulmonary stretch receptors** **Bronchoconstriction** is facilitated by activation of the **rapidly adapting pulmonary strech receptors**