3 Nervous control of ventilation

Question 1

Describe the location of neural regulation of ventilation

Answer 1

In the spinal cord and brain stem.

- It is made of the pons and medulla

Question 2

Describe the medullary groups of neural control of ventilation

Answer 2

In medulla:

• Dorsal respiratory group (inspiration)
• Ventral respiratory (not as clear - forced expiration)

Question 3

Describe the pons groups of neural control of ventilation

Answer 3

In pons:

• Pneumotaxic group (switch off inspiration)
• Apneustic centre (prolongs DRG stimulation)
• Vagus nerve (switch off inspiration)

Question 4

Describe the function of neural regulation of ventilation

Answer 4

• It sets the rhythm and pattern of ventilation

- It also controls the respiratory muscles

Question 5

Describe the differences in speed between neural and chemical regulation of ventilation

Answer 5

• Neural control - fast-acting impulses to and from CNS

- Chemical control - rely on changes in pCO2 and pO2 (must be detected by chemoreceptors first)

Question 6

Describe respiratory depression

Answer 6

The rate and/or depth of respiration is insufficient to maintain adequate gas exchange in the lungs
- Occurs as a result of effects on medullary and pons respiratory centers

Come drug side effects (benzodiazepines, opioids) can cause respiratory depression
- Respiratory depression reversed by analeptics e.g. doxapram hydrochlorides, (which work by reactivating the respiratory centers in the medulla and pons to encourage proper ventilation and breathing again)

Question 7

Describe the control mechanisms of the medulla -Dorsal Respiratory group (DRG)

Answer 7

DRG:
- Fibres from the DRG innervate the diaphragm and external intercostal muscles

Role in inspiration:
- Diaphragm contraction and thoracic cavity expansion causes inspiration

DRG neurons switch on for 2s and off for 3s, causing a respiratory pattern

Question 8

Describe the control mechanisms of the medulla - Ventral Respiratory Group (VRG)

Answer 8

VRG:

• Fibres from VRG innervate the abdominal muscles and internal intercostal muscles
• Activity enhanced during forced expiration
• Has some role in inspiration

Question 9

Describe the control mechanisms of the pons - Pneumotaxic center

Answer 9

• Transmits signal to the DRG
• Role is to limit inspiration
• ‘Fine-tunes’ breathing - sends inhibitory impulses to DRG
• Limit the period of inspiration by 2s
  Prevents over-inflation of the lungs

Question 10

Describe the control mechanisms of the pons - Apneustic center

Answer 10

• Responsible for prolonged inspiratory gasps (apenusis)
• Prolongs DRG stimulation
• Not clear on involvement in normal human respiratory
• Apneusis observed brain injury

Question 11

Describe the control mechanisms of the Vagus Nerve

Answer 11

• Sends afferent information from lungs > DRG

- Role is to prevent overinflation of the lungs by switching off inspiration (promotes a rhythmic pattern of breathing)

Question 12

Describe the role of higher brain centres on breathing

Answer 12

• Hypothalamus plays a role

- Cerebral cortex also plays a role in Voluntary breathing control

Question 13

Describe the control mechanisms of the cerebral cortex (in breathing)

Answer 13

• Stimulates motor neurons of the inspiratory muscles
• Bypasses the medullary respiratory centers when consciously controlling breathing
  e. g. breath-holding or changing the depth of breathing
• Limited ability to breath-hold
  > respiratory centers automatically initiate breathing when oxygen concentration in the blood reaches critical levels
  e.g. drowning victims eventually reinstate breathing with the result of water in the lungs

Question 14

Describe the control mechanisms of the hypothalamus (in breathing)

Answer 14

• Strong emotions, pain, and changes in temperature can alter the respiration rate and rhythm
• Apnoea (suspension of breathing) can be induced by anger, pain, or decreasing temperature
• Tachypnoea (rapid breathing) can be induced by excitation or an increase in temperature

Question 15

List the different types of respiratory receptors

Answer 15

• Stretch receptors
• Juxtapulmonary receptors
• Irritant receptors

Question 16

Describe the function of stretch receptors:

Answer 16

• Located in smooth muscles of trachea and bronchi
• Prevent over-expansion of lungs
• Sensitive to lung expansion
  > Lung expansion ->
  > Respiratory centre ->
  > Inspiration is shorter and shallower
  > Prevent over-inflation of the lungs

Question 17

Describe the function of juxtapulmonary (J or C fibres) receptors

Answer 17

• They lie alveolar wall between epithelium and endothelium - close to pulmonary capillaries
• They are stimulated by congestion, oedema, histamine
• Activation results in apnea or rapid shallow breathing, bronchoconstriction and mucus secretion

Question 18

Describe the function of irritant receptors

Answer 18

• Located between epithelial cells
• Sensitive to irritant gases, smoke, and dust
• Activation results in rapid, slow breathing, cough, bronchoconstriction, mucus secretion, augmented breaths (gasps)

Question 19

Describe the factors influencing the rate and depth of breathing

Answer 19

• Pulmonary irritant reflex is stimulated by accumulated mucus inhaled smoke dist, lint, or noxious fumes
• Irritant receptors send signals to the respiratory centres via afferent fibres of the vagus nerve
• Stimulation of receptors in the brain = airway constriction (asthma)
• Stimulation of receptors in the trachea and bronchi = coughing
• Stimulation of receptors in the nasal cavity = sneezing