Physio - Neural & Chemical Control Breathing

Question 1

Where is the location of α‐motoneurons responsible for contraction of the diaphragm, internal and external intercostal muscles?

Answer 1

Spinal Respiratory α‐motoneurons

• Phrenic motoneurons
  
  • C3-C5
  • input from contralateral inspiratory neurons of caudal medulla oblongata
• External intercostal motoneurons
  
  • thoracic segments
  • input from contralateral inspiratory neurons of caudal medulla oblongata
• Internal intercostal motoneurons
  
  • thoracic segments
  • input from contralateral expiratory neurons of caudal medulla oblongata

Question 2

What is the collections of neurons in the brainstem (medulla oblongata and pons) responsible cyclical inspiratory and expiratory neural activity?

Answer 2

Inspiratory neurons:

• Discharge during inspiration
  
  • Dorsal respiratory group (DRG)
  • Ventral respiratory group (VRG)

Expiratory neurons:

• Discharge during expiration
  
  • Ventral respiratory group (VRG) ONLY!

Note:

• If you have a stroke in this region, know what would get messed up if DRG/VRG or both get messed up.

Question 3

What are the types of central or peripheral inputs that modulate the activities of brainstem respiratory neurons?

Answer 3

Active during inspiration:

• Pre‐Bötzinger complex
  
  • Rostral VG
  • respiratory patter generator
• DRG
• Diaphragm
• Thoracic inspiratory muscles

Active during expiration:

• Bötzinger complex
• Caudal VRG
• Thoracic expiratory muscles

Modulate respiratory pattern:

Pneumotaxic center

• same as medial parabrachial nucleus (Kölliker‐Fuse)
  
  • pons
• Influences transition btw inspiration & expiration

Nucleus Solitarus

• Dorsal medulla

Note:

• Cyclic firing of medulla oblongotta

Question 4

What are the different types of pulmonary receptors?

Answer 4

Pulmonary stretch receptors (PSRs)

• slowly adapting PSRs
  
  • lung parenchyma
  • myelinated fibers
• increase discharge (as lungs inflate)
• contribute to cessation of inspiration
• negative feedback control
• may not play a large role during quiet eupneic breathing

Rapidly adapting PSRs

• irritant receptors
  
  • stimulated by noxius chemicals, smoke, dust
• myelinated fibers
• larger airways

J-receptors

• respond to abnormal stretch of lung tissue + chemicals
• unmyelinated fibers (c-fibers)
• responsible for sensation of dyspnea
  
  • shortness of breath during inflammation

Note:

• Vagal afferent = senses stretch
• Phrenic efferent = does something about it
  
  • slow PSR provide neg feedback to terminate inspiration

Question 5

Where are the sites which have chemoreceptors sensitive to arterial
concentration of oxygen, carbon dioxide, and H+, and cerebrospinal fluid concentration of carbon dioxide and H+?

Answer 5

Peripheral Chemoreceptors

• Detect changes in arterial P_O2 & P_CO2 & pH
  
  • Carotid bodies
    
    • afferent fibers in glossopharyngeal nerve (CN IX)
    • project to NTS (next to DRG)
  • Aortic bodies
    
    • afferent fibers in vagus nerve (CN X)
    • project to NTS

Note:

• If you increase PCO2 –> pH will increase!

Question 6

What is the chemical control of breathing related to Hypoxia?

Answer 6

Peripheral chemoreceptors

• respond to ↓ in arterial P_O2 (below 60 mmHg)
• leads to ↑ in minute ventilation​
  
  • response enhanced by ↑ arterial P_CO2

Note:

• we need to decrease pp of O2 significantly to see increase in chemoreceptors
  
  • greater pp of CO2 –> activate chemoreceptors

Question 7

What is the chemical control of breathing related to Hypercapnia?

Answer 7

Peripheral chemoreceptors:

• respond to ↑ in arterial P_CO2
  
  • elicits ↑ in minute ventilation
  • response enhances by ↓ in arterial P_O2

Notes:

• What happens when CO changes…
  
  • if we ↓ in PP of CO2, we see a ↓in minute ventilation in alveoli
• Respiratory sys needs to respond to pp of CO2
  
  • b/c can lead to vary deg of hypoxia
  • ↑ P_CO2 –> ↓ventilation

Question 8

What happens to chemical control of breathing during Acidemia?

Answer 8

Peripheral chemoreceptors:

• responds to ↓ in arterial pH ( ↑ H+)
  
  • linked w/ changes in CO2, hydration of CO2 by carbonic anhydrase
• leads to ↑ minute ventilation

Note:

• as we increase [H+] –> to ↑ in minute ventilation;
  
  • chemical control of breathing!

Question 9

What are central chemoreceptors?

Answer 9

Central chemoreceptors:

• Ventral aspect of medulla oblongata
• Detects changes in cerebrospinal fluid (CSF), CO2, pH​

Stimulation:

• ↑ PCO2 –> ↑ minute ventilation
• ↓ pH –> ↑ minute ventilation

Note:

• NOT stimulated by hypoxia

Question 10

How can we illustrate the neural control of ventilation via concept map?

Answer 10

Question 11

What are the contributions of peripheral and central chemoreceptors to an abrupt increase in carbon dioxide?

Answer 11

Response to abrupt ↑ in CO2:

• Immediate:
  
  • peripheral chemoreceptor stimulation
  • ↑ in minute ventilation
• Delayed response:
  
  • central chemoreceptor stimulation
  • maintain ↑ in ventilation

Question 12

What are the factors that contribute to the marked increase in ventilation occurring during exercise?

Answer 12

Ventilation during exercise:

• exercise = powerful stimulus to breathing
• breathing (minute ventilation) will ↑ (proportion to intensity)
  
  • P_O2 stays constant
  • strenuous exercise leads to ↓ P_CO2
    • _​↑ [H+]

Regulation:

• Feed-forward & feed-back pathways –>
  
  • regulate arterial P_O2 (and lesser extent P_CO2)

Question 13

What are the ventilatory adjustments to high altitude?

Answer 13

Decrease barometric pressure!

Immediate:

• Stimulation of peripheral chemoreceptors by ↓PO2
• ↑Minute ventilation
• ↓ Arterial PCO2 and partial return of arterial PO2
• Hyperventilation

Midterm adjustment (days)

• Initial ↑ in CSF pH (basic)
• ↓ central respiratory drive
  
  • due to ↓ stimulation of central chemoreceptors
• ↓ bicarb in CSF
  
  • due to active transport of bicard from CSF
• ↑ renal excretion of bicarb
  
  • so blood gets more acidic
• meanwhile…continued stimulate of peripheral chemoreceptors = ↑ minute ventilation

Long term adjustment

• ↑ synthesis of Hb –> polycythemia