Neural Control of Respiration

Overview

This lecture explains the neural control of respiration, including the role of medullary and pontine centers, protective reflexes, and the effects of brainstem lesions.

Neural Centers Controlling Respiration

• Respiration is controlled both involuntarily and voluntarily.
• Involuntary control involves centers in the medulla and pons.
• Medulla contains dorsal respiratory group (DRG) and ventral respiratory group (VRG).
• Pons contains pneumotaxic center and apneustic center.

Initiation and Regulation of Respiration

• Pre-Bötzinger complex (in medulla) acts as the respiratory pacemaker, setting rhythm.
• Pre-Bötzinger complex excites DRG inspiratory neurons, which activate alpha motor neurons of inspiratory muscles.
• Inspiration is initiated by muscle contraction; ends when these neurons stop firing.
• During quiet breathing, expiration is passive via inspiratory muscle relaxation.

Modulation of Respiration Depth and Rate

• VRG contains both inspiratory (I) and expiratory (E) neurons; active during forced breathing.
• Mutual inhibition between I and E neurons in VRG coordinates inspiration and expiration.
• Pneumotaxic center inhibits DRG to switch to expiration and increases respiratory rate.
• Apneustic center excites DRG to prolong inspiration; balance with pneumotaxic center ensures smooth transitions.
• Stretch receptors in lungs activate the vagus nerve, leading to pneumotaxic center stimulation (Hering-Breuer reflex), preventing overinflation.

Voluntary Control and Protective Reflexes

• Voluntary control originates from the cerebral cortex via corticospinal tracts to respiratory muscles.
• Cough and sneeze reflexes are triggered by irritant receptors, mediated via the vagus nerve.
• J reflex, from J receptors in the lung interstitium, is triggered by increased pulmonary pressure and leads to apnea, bradycardia, and hypotension.

Effects of Brainstem Lesions

• Lesion above pons: voluntary control lost; involuntary control remains.
• Lesion between pneumotaxic and apneustic centers: leads to apneusis (deep, slow respiration); cutting vagus worsens it.
• Lesion between pons and medulla: irregular respiratory pattern, loss of fine control.
• Lesion below medulla: complete respiratory arrest (apnea).

Key Terms & Definitions

• Pre-Bötzinger complex — respiratory pacemaker in the medulla that sets the rhythm.
• Dorsal respiratory group (DRG) — medullary neurons controlling inspiration.
• Ventral respiratory group (VRG) — medullary neurons for forced inspiration and expiration.
• Pneumotaxic center — pons center that inhibits DRG to switch to expiration.
• Apneustic center — pons center that excites DRG to prolong inspiration.
• Alpha motor neurons — neurons innervating respiratory muscles.
• Hering-Breuer reflex — lung inflation reflex limiting inspiration via stretch receptors.
• J receptors — sensory receptors in lung interstitium responding to increased pressure.
• Apneusis — abnormal breathing: prolonged deep inspiration.

Action Items / Next Steps

• Review brainstem diagrams showing respiratory centers and pathways.
• Practice drawing the flowchart of neural control of respiration.
• Prepare for questions on respiratory reflexes and effects of specific brainstem lesions.