Neural Control Ventilation (M2)

Question 1

LO’s

Answer 1

1. Describe the location and names of centres in the brain stem controlling ventilation
2. Describe how brain stem centres interact to control activity of the respiratory muscles
3. Describe how respiratory centre activity is modulated by chemical and neurogenic input
4. Describe the integration of neural and chemical control systems
5. Describe the importance of reflexes that protect and/or clear the airways

Question 2

Describe output to respiratory muscles

Answer 2

• The respiratory groups/centres receive chemical input (messages from chemoreceptors to increase the ventilation rate) and neurogenic input.
• Output happens to the external and internal intercostal muscles and the diaphragm, making them expand/contract
• The phrenic nerve (from cervical vertebrae C3, C4, C5) makes the diaphragm contract.
• The nerves from the thoracic vertebrae T5 and T6 make the external intercostals contract.
• The nerves from the T11 and T12 make the internal intercostals expand.

Question 3

Where are the respiratory groups/centres?

Answer 3

• At the top of the brainstem is the PONS (pontine respiratory group). This doesn’t initiate breathing, but regulates it.
• Underneath the PONS, in the medulla oblongata is the Ventral Respiratory Group (to the sides of the medulla.) In the middle of the medulla is the Dorsal Respiratory Group.

Question 4

What does the pontine (PONS) region do?

Answer 4

• Influence pattern ventilation
• “Phase switching”
• JUST LEARN: I CAN’T FIND WHAT THIS MEANS*

Question 5

Why is nerves output to internal/external intercostals and the diaphragm ramp like, ratehr than on/off?

Answer 5

• Ramp like, slow build up, to reflect how we slowly inspire.
• If it was on/off, then we would inspire all at once, forcefully, so couldn’t speak.

Question 6

What does the Ventral Respiratory Group (VRG) do?

Answer 6

• Contains Inspiratory & Expiratory neurons
• Amplitude (depth)
• Rhythm generation (pre-Bӧtzinger complex)

JUST LEARN

Question 7

What does the Dorsal Respiratory Group (DRG) do?

Answer 7

• Inspiratory (I) neurons
• Integrate sensory information (solitary tract)

Question 8

How does the VRG generate rhythym in exhaling and inhaling?

Answer 8

• Two theories
• Pacemaker theory: When inspiratory neurones stimulated, expiratory neurones are silenced, so an output to inspire only is sent. And vica versa.
• However pacemaker theory doesn’t explain how we can also consciously change our breathing.

Question 9

How is respiratory centre activity modulated by neurogenic input/ reflexes?

Answer 9

1. We have conscious control over breathing = cortical factors.
2. We have reflexes from lung receptors:
   
   • Irritant receptors
   • C-fibre receptors
   • Hering-Breuer inflation reflex (Stretch receptors)
   • J-receptor reflexes
3. Baroreceptor reflex: low arterial BP causes increased ventilation.
4. Reflexes from muscles/ joints: increase ventilation.
5. Reflexes from the periphery: (pain and heat cause increased ventilation).
6. Protective reflexes:​
   • Laryngeal (protect lungs)
   • Cough (protect lower airways)
   • Sneeze (protect upper airways)
7. Co-ordination with other functions:
   
   • ​​Speech (prolong expiration)
   • Defaecation (expiration against a closed glottis = increased abdominal pressure)
   • Sigh, Hiccup, Yawn

Question 10

What is the J-receptor reflex in the lungs?

Answer 10

• Juxtapulmonary capillary receptor
• Simulated by pulmonary capillary hypertension and oedema in the alveolar walls
• Causes impulses to shoot up vagus nerve, causing the pattern of breathing seen in left heart failure = rapid, shallow breathing.

Question 11

Describe the Hering-Breuer inflation reflex (stretch receptor in the lungs)

Answer 11

• Prevents overinflation of the lungs
• Info transmitted to pneumotaxic centre- upper pons
• “Phase switching” by inhibiting apneustic centre- lower pons
• Stimulates expiration

Question 12

Why are neural and chemical reflexes important?

Answer 12

1. Chemical reflexes are of primary importance in adjusting ventilation to body’s metabolic needs
2. Neural reflexes are of secondary importance and tend to modify the pattern of ventilation rather than regulate the overall level of ventilation