Lecture 18: Neural control of ventilation in health and disease

Question 1

Describe the origin of respiratory motor nerves:

Answer 1

C3-5 Phrenic nerves -> Diaphragm
T1-L1 -> Intercostal motor neurons -> Internal and external intercostals
T7-L1 -> Abdominal motor neurons -> Abdominal nerve (Rectus abdominus)

Question 2

How do they know respiratory rhythm is CNS in origin?

Answer 2

High spinal cord injury stops breathing, indicating respiratory rhythm is driven from the CNS

Question 3

Where is the respiratory network located in the brain?

Answer 3

• Pons
• Medulla oblongata
• Spinal cord

Question 4

Why do we need respiratory rhythm?

Answer 4

Need breathing rhythm because dont want inspiration and expiration drive to occur together

Question 5

What are the essential locations of our respiratory network?

Answer 5

Pontine respiratory group (in pons)
Dorsal respiratory group (has NTS) (medulla)
Ventral respiratory group (has AMB) (medulla)

Question 6

What did lumsdens research demonstrate with brainstem regions?

Answer 6

They sliced sequentially through the brainstem region

Vagus cut:

• Slice One: Above the pons did not impact the respiratory rhythm generation
• Slice Two: Below the pneumotaxic centre; Results in apneustic breathing (APC still in tract)(long inspiration, cant expire)
• Slice Three: Pons/Medulla transition, below APC (apneustic centre) -> Results in gasping
• Slice four: Below VRG/DRG = No respiratory rhythm generation

Question 7

What happened to lumsdens observations when the vagus remained in tact?

Answer 7

• Breathing is initially shallower and more frequent and once slice two occurs, apneustic breathing does not occur, just slower bigger breaths

Question 8

What is apneusis?

Answer 8

Breathing generation cant switch to exhalation

Question 9

What is the hering-bruer reflex also known as?

Answer 9

Pulmonary stretch reflex

Question 10

Describe the hering-bruer reflex:

Answer 10

Switches off inspiration by inhibiting inspiratory neurons

i.e

Pulmonary mechanosensory stretch receptors in airway smooth muscle sense inspiration (stretch/inflated lungs)

• > Vagus nerve activated, communicates to NTS->PONS -> VRG and inhibits the inspiratory neurons here
  i. e terminates inspiration

Question 11

What takes over if the vagus is cut?

Answer 11

The pons (PWC)

Question 12

Describe the cough reflex:

Answer 12

Stimulant: Particulates, Inflammation, Gastric reflux, Larynx
Location: Trachea, bronchi
Receptors: Mechanosensory, Chemosensory
Afferents: Vagal fibres
CNS: DRG, VRG
Afferents: Cranial and spinal motor neurons

Question 13

Describe the stages of the cough reflex:

Answer 13

Irritation
Inspiration
Compression
Expulsion (Sphincters close)

Question 14

What is the idea about the VRG respiratory rhythm generation:

Answer 14

Respiratory rhythm generation by the VRG drives the phrenic motor neurons (Inhale) and switches to internal intercostals and abdominal motor neurons

Question 15

Describe the oscillator model of the VRG respiratory rhythm generation

Answer 15

Reciprocal inhibition rhythm = Oscillator model

Two groups of neurons:

Inspiratory neurones which provide inspiratory drive (Diaphragm and ext. intercostals) and inhibits (GABA and Glycine) the expiratory neurons

Expiratory neurons which provide expiratory drive (int. intercostals and abdominals) and can inhibit inspiratory nuerons

Feedback loops can inhibit each of the groups of neurons determining insp or exhal.

Question 16

How many breathing phases are there?

Answer 16

Lung volume suggests 2

but

Nerve recordings show three

Question 17

Describe the three phases of breathing:

Answer 17

Inspiration
Post inspiration
Expiration

Question 18

What suggests three phases of breathing:

Answer 18

There is activity in the diaphragm to prevent relaxing too quickly // allows gas exchange to occur (post insp. phase)
- Recurrent laryngeal also active during this time to adduct the glottis and prevent rapid exhalation for the same reasons above

Question 19

What are the many factors that control breathing?

Answer 19

• Emotion
• Temperature (fever = inc. breathing)
  = Feed into pneumotaxic centre
  = This feeds into apneustic centre
  = This feeds into rhythm generator and onto the lungs
• Voluntary control is direct to resp. muscle
• Peripheral receptors feed back to the rhythm generator

Question 20

What are some pathology and diseases that can trigger the peripheral chemoreceptors?

Answer 20

HF, Hypertension, COPD
= Tonically activated and highly sensitised
= Causes hypertension, overactive symp. activity, dyspnoea

Question 21

What are some pathology and diseases that can trigger laryngeal receptors:

Answer 21

Interstitial pulmonary fibrosis
= Tonically activated and highly sensitised
= Chronic cough