Neural Control of Respiration

Overview

• Respiration can be controlled voluntarily and involuntarily.
• Neural control is complex and involves various centers in the medulla and pons.

Involuntary Neural Regulation

Neural Centers

• Medulla:
  • Dorsal Respiratory Group (DRG)
  • Ventral Respiratory Group (VRG)
• Pons:
  • Pneumotaxic Center
  • Apneustic Center

Initiation of Respiration

• Pacemaker:
  • Pre-Bötzinger complex in medulla sets the rhythm for respiration.
  • Neurons fire rhythmically to initiate respiratory impulses.

Mechanism of Inspiration

• Pre-Bötzinger complex excites DRG neurons (inspiratory neurons).
• DRG neurons activate alpha motor neurons in spinal cord, causing contraction of inspiratory muscles leading to inspiration.

Regulation of Expiration

• Inspiration Stops:
  • Automatic stoppage of firing in pre-Bötzinger complex leads to cessation of DRG activation.
• Depth and Rate Changes:
  • Increased depth during activities (talking, exercise, anxiety) requires additional control from VRG.

Ventral Respiratory Group (VRG)

• Contains Inspiratory (I) and Expiratory (E) neurons.
• I neurons activate during increased respiration needs, also activating expiratory muscles.

Mutual Inhibition

• I neurons inhibit E neurons in VRG, preventing simultaneous activation during respiration.
• Connections from pons (pneumotaxic center) aid the transition from inspiration to expiration.
• Pneumotaxic Center:
  • Inhibits DRG, facilitating expiration.
• Apneustic Center:
  • Excites DRG, ensuring smooth transitions in the respiratory cycle.

Negative Feedback Mechanism

• Stretch receptors in the tracheobronchial tree respond to lung inflation.
• Activation via vagus nerve inhibits I neurons, promoting expiration (Hering-Breuer reflex).

Voluntary Control

• Controlled by the cerebral cortex via the corticospinal tract.
• Influences alpha motor neurons for inspiratory and expiratory muscles.

Protective Reflexes

• Cough Reflex:
  • Triggered by irritant receptors in the airways.
• Sneezing:
  • Similar mechanism to cough, expelling irritants.
• J Reflex:
  • Involves J receptors in pulmonary interstitium; activated by stretch due to pulmonary hydrostatic pressure.

Effect of Brain Stem Lesions

1. Above Pons:
   • Loss of voluntary control, involuntary control remains intact.
2. Between Pneumotaxic and Apneustic Centers:
   • Increased depth of respiration (apneusis), decreased rate.
3. Between Pons and Medulla:
   • Basic respiratory pattern without fine-tuning.
4. Below Medulla:
   • Complete stoppage of respiration (apnea).

Conclusion

• Complex neural control allows for adaptability in respiration based on body needs, both involuntarily and voluntarily.