Neural Control of Breathing

Neural Control of Breathing

• Breathing is controlled by neural mechanisms, including medullary centers, pontine centers, and higher centers.
• Spontaneous breathing originates from rhythmic discharges of motor neurons innervating respiratory muscles. These signals are entirely dependent on nerve impulses from the brain.
• Chemical control regulates the brain's rhythmic discharges via alterations in arterial oxygen (PO2), carbon dioxide (PCO2), and hydrogen ion (H+) concentration.

Medullary Centers

• Located bilaterally in the medulla oblongata, and bilaterally connected.
• Dorsal Respiratory Group (DRG): generates the basic rhythm of respiration; pacemaker cells in the pre-Bötzinger complex (pre-BÖTC) are involved.
  • Stimulation of DRG leads to contraction of diaphragm and external intercostals (inspiration).
  • Inhibition of DRG results in relaxation of diaphragm and external intercostals (expiration).
• Ventral Respiratory Group (VRG):
  • Located in the ventral part of the medulla.
  • Inactive during normal quiet breathing but active during deep expiration.
  • Stimulation leads to contraction of abdominal and internal intercostals, resulting in expiration.

Pontine Centers

• Located in the lower part of the pons.
• Apneustic center:
  • Prolongs inspiration by stimulating DRG inspiratory neurons, preventing them from shutting down.
• Pneumotaxic center:
  • Located in the upper pons.
  • Plays a role in the switch between inspiration and expiration.
  • Inhibits DRG inspiratory neurons (shortening inspiration), increasing the respiratory rate (30-40 breaths per minute).
  • Damage to the pneumotaxic center results in prolonged slower breathing with deeper volume.

Hering-Breuer Reflex

• Afferent impulses from the vagus nerve trigger the same effect as the pneumotaxic center.
• Overstimulation of lungs (stretching) through stretch receptors in bronchi and bronchioles leads to inhibition of the inspiratory center.
• This decreases the duration of inspiration and increases the respiratory rate.

Other Influences on Respiration

• Higher centers: The cerebral cortex, limbic system, and hypothalamus can influence breathing rate and depth.
  • Emotions and pain activate the sympathetic center in the hypothalamus, impacting breathing rate and volume.
  • Temperature regulation in the hypothalamus is involved in controlling breathing in extreme temperatures (e.g., heat).
• Pulmonary stretch receptors, lung irritant receptors, Juxta medullary capillary receptors are other respiratory mechanisms that help control breathing according to lung conditions and needs.
• Air passages are controlled and protected based on reflexes like coughing, sneezing, and swallowing to prevent any irritation from reaching the lungs.
• Muscle and joints: Proprioceptors from muscles, joints, and ligaments influence breathing during exercise by stimulating the respiratory center.
• Viscera: Swallowing and vomiting cause inhibition of breathing and closure of the glottis to prevent aspiration.
• Circulatory system: blood pressure and venous return are crucial for proper respiration. Changes in blood pressure impact breathing patterns, and venous return influences the respiratory system to maintain ventilation.

Review Questions

• Which structure inhibits inspiration to regulate breathing rate and volume?
  • Pneumotaxic center