Neural Control of Breathing

• What are the two main types of breathing control?

  • Voluntary control (Cortex → Corticospinal tract → Respiratory muscles)
  • Involuntary control (Brainstem respiratory centres → Automatic regulation)
• Where is the primary control centre for involuntary breathing located?

  In the medulla oblongata of the brainstem.
• What are the three main respiratory centres in the brainstem?

  • Medullary Respiratory Centres:

  1. Dorsal Respiratory Group (DRG) – Controls inspiration.
  2. Ventral Respiratory Group (VRG) – Controls expiration (forced breathing).

  • Pontine Respiratory Centers:3. Pontine Respiratory Group (PRG) – Modifies breathing rhythm.
• What is the function of the Dorsal Respiratory Group (DRG)?

  • Located in the medulla oblongata.
  • Generates inspiratory drive via the phrenic nerve (to diaphragm) and intercostal nerves (to external intercostals).
  • Receives sensory input from chemoreceptors and mechanoreceptors.
• What is the function of the Ventral Respiratory Group (VRG)?

  • Located in the medulla oblongata.
  • Controls forced expiration and some aspects of inspiration.
  • Active during exercise, speech, and coughing.
• What is the function of the Pontine Respiratory Group (PRG)?

  • Located in the pons.
  • Includes the Pneumotaxic Center (inhibits inspiration) and Apneustic Center (stimulates inspiration).
  • Regulates breathing rhythm and transitions between inspiration and expiration.
• What are the key nerves involved in controlling breathing?

  1. Phrenic nerve (C3-C5) → Controls the diaphragm.
  2. Intercostal nerves → Control external and internal intercostal muscles.
  3. Vagus nerve (CN X) → Transmits sensory feedback from the lungs to the brainstem.
  4. Glossopharyngeal nerve (CN IX) → Sends information from carotid bodies to the brainstem.
• What is the role of central chemoreceptors in breathing control?

  • Located in the medulla oblongata.
  • Detect changes in pH and CO₂ levels in cerebrospinal fluid (CSF).
  • High CO₂ → Low pH → Increases breathing rate to remove CO₂.
• What is the role of peripheral chemoreceptors in breathing control?

  • Located in carotid bodies (near carotid arteries) and aortic bodies (in aortic arch).
  • Detect low O₂ (hypoxia), high CO₂, and low pH.
  • Stimulate respiratory centres via the glossopharyngeal (CN IX) and vagus (CN X) nerves.
• How does the Hering-Breuer reflex regulate breathing?

  • Mechanoreceptors in the lungs (stretch receptors) detect excessive lung inflation.
  • Signal sent via the vagus nerve (CN X) to the medulla.
  • Inhibits inspiration to prevent overinflation of lungs.
• How does the body respond to increased CO₂ levels?

  • High CO₂ detected by central chemoreceptors in the medulla.
  • Stimulates DRG → Increases breathing rate and depth (hyperventilation).
  • Removes excess CO₂, restoring normal levels.
• How does the body respond to low O₂ levels (hypoxia)?

  • Detected by peripheral chemoreceptors (carotid & aortic bodies).
  • Sends signals to the medullary respiratory centres to increase breathing rate.
  • Ensures more oxygen intake.
• What is the role of proprioceptors in breathing?

  • Found in muscles and joints.
  • Detect movement and increase breathing rate during exercise.
  • Signals sent to respiratory centers to match O₂ demand.
• How does voluntary control of breathing work?

  • Motor cortex (cerebrum) can override the brainstem.
  • Allows activities like speaking, singing, holding breath.
  • Uses corticospinal pathways to activate respiratory muscles.
• How does emotional control affect breathing?

  • Limbic system & hypothalamus influence respiration (e.g., anxiety → hyperventilation).
  • Signals sent via brainstem connections to respiratory centres.
• What happens during hyperventilation?

  • Rapid breathing → Excess CO₂ loss → Blood pH rises (alkalosis).
  • Can lead to dizziness, tingling, and fainting.
• What happens during hypoventilation?

  • Slow breathing → CO₂ retention → Blood pH drops (acidosis).
  • Can cause confusion, fatigue, and respiratory failure.
•  How does Chronic Obstructive Pulmonary Disease (COPD) affect neural control of breathing?

  • Chronic CO₂ retention → Reduced central chemoreceptor sensitivity
  • Hypoxic drive dependence: Peripheral chemoreceptors become primary stimulus for breathing
  • Airflow limitation increases respiratory effort → Involves greater brainstem control
  • Muscle fatigue in diaphragm due to increased work of breathing
• How can stroke disrupt neural control of breathing?

  • Stroke in the medulla can damage respiratory centers (Pre-Bötzinger complex, VRG, DRG) → Respiratory arrest
  • Stroke in the pons disrupts rhythm generation → Apneustic or irregular breathing patterns
  • Impaired corticospinal & corticobulbar tracts affect voluntary breathing (e.g., in speech, coughing)
• What are the effects of Amyotrophic Lateral Sclerosis (ALS) on breathing control?

  • Progressive motor neuron degeneration affects:
  • Phrenic nerve → Weakened diaphragm
  • Intercostal nerves → Weak chest wall muscles
  • Leads to respiratory failure as disease progresses
  • Impaired cough reflex, increasing risk of infections
• How does Parkinson’s Disease impact respiratory control?

  • Bradykinesia & rigidity affect respiratory muscle coordination
  • Reduced upper airway control → Higher risk of aspiration & obstructive breathing patterns
  • Blunted chemoreceptor response → Decreased sensitivity to CO₂ changes
• What is Ondine’s Curse (Congenital Central Hypoventilation Syndrome - CCHS)?

  • Rare disorder due to PHOX2B gene mutation
  • Impairs automatic breathing control → Patients stop breathing during sleep
  • Central chemoreceptors fail to detect CO₂ levels properly
• How does Multiple Sclerosis (MS) affect respiratory function?

  • Demyelination of brainstem pathways disrupts automatic breathing
  • Weakness of respiratory muscles due to nerve damage
  • Increased risk of aspiration pneumonia due to impaired swallowing reflex
• What is the impact of Spinal Cord Injury (SCI) on breathing?

  • Injury at C3-C5 affects the phrenic nerve, leading to diaphragm paralysis
  • Damage to T1-T12 affects intercostal muscle function
  • High cervical injury (C1-C2) results in complete loss of voluntary and automatic breathing
• How does Opioid Overdose cause respiratory depression?

  • Opioids (e.g., morphine, fentanyl) inhibit medullary respiratory centers
  • Reduced responsiveness of central chemoreceptors to CO₂
  • Leads to hypoventilation, hypoxia, and potentially respiratory arrest
• How does Guillain-Barré Syndrome (GBS) affect breathing?

  • Autoimmune attack on peripheral nerves, including the phrenic nerve
  • Leads to progressive muscle weakness & respiratory failure
  • Requires ventilatory support in severe cases