Neural Control of Respiration

Overview of Respiration Control

• Respiration is controlled both voluntarily and involuntarily.
• Neural control has a complex structure requiring multiple centers for regulation.

Involuntary Neural Regulation of Respiration

• Neural Centers Involved:
  • Located in the Medulla and Pons.
  • Medulla:
    • Dorsal Respiratory Group (DRG)
    • Ventral Respiratory Group (VRG)
  • Pons:
    • Pneumotaxic Center
    • Apneustic Center

Initiation of Respiration

• Pacemaker for Respiration:
  • Pre-Bötzinger Complex (in medulla)
  • Sets the rhythm for respiration by firing rhythmically.
  • Excites inspiratory neurons in the DRG, activating alpha motor neurons in spinal cord.

Inspiration and Expiration Process

• Inspiration Initiation:
  • Rhythm from pre-Bötzinger Complex activates DRG's inspiratory neurons.
  • Contraction of inspiratory muscles leads to inspiration.
• Stopping Inspiration:
  • Automatic cessation of firing in the pre-Bötzinger Complex stops activation of inspiratory neurons.

Increased Depth and Rate of Respiration

• Requires additional neural control beyond DRG:
  • Ventral Respiratory Group (VRG):
    • Contains inspiratory (I) and expiratory (E) neurons.
    • Activated during increased respiratory needs.
  • Mutual Inhibition:
    • I neurons inhibit E neurons and vice versa for coordinated control.

Role of Pons Centers

• Pneumotaxic Center:
  • Inhibits DRG leading to expiration.
  • Acts as a switch for transitioning from inspiration to expiration.
• Apneustic Center:
  • Excites DRG, aiding smooth transitions between phases of respiration.

Regulation of Respiration Rate and Depth

• Negative Feedback Mechanism:
  • Stretch receptors in the tracheobronchial tree respond to lung inflation.
  • Stretch receptors send signals via vagus nerve to pneumotaxic center, promoting expiration.
  • Related to Hering-Breuer reflex (lung inflation threshold at 1 liter).

Voluntary Control of Respiration

• Controlled via the Cerebral Cortex:
  • Involves corticospinal tract to alpha motor neurons for inspiratory and expiratory muscles.

Protective Reflexes

• Cough Reflex and Sneeze Reflex:
  • Triggered by irritant receptors in the larynx, trachea, and bronchi.
  • Result in bronchoconstriction and hyper apnea.
• J Reflex:
  • Involves J receptors in the interstitium responding to stretch.
  • Results from increased pulmonary hydrostatic pressure (e.g. high altitude, exercise).
  • Leads to apnea, bradycardia, hypotension, inhibiting stretch reflex.

Effects of Brainstem Lesions on Respiration

1. Lesion Above Pons:
   • Loss of voluntary control; involuntary control remains normal.
   • If vagus is intact: normal respiration.
   • If vagus is cut: decreased rate, increased depth.
2. Lesion Between Pneumotaxic and Apneustic Centers:
   • Increased depth of respiration (apneusis); decreased rate.
   • If vagus is cut: further increase in depth, decreased rate.
3. Lesion Between Pons and Medulla:
   • Some respiratory pattern present but lack fine-tuning.
   • If vagus is cut: some pattern still but increased depth.
4. Lesion Below Medulla:
   • Complete cessation of respiration (apnea).

Conclusion

• Importance of various neural centers in adjusting respiration to body needs.
• Helps in involuntary and voluntary control of respiration.