CNS centers

3 centres that may influence respiration

1. Respiratory centre
   * Most important
2. Cortex
   * Can override respiratory centre to limited extent
3. Others 
   * Limbic system and hypothalamus can alter patterns of respiration

Respiratory centre include:

1. Medullary respiratory centre
   * Excitatory
   * Affects both inspiration and expiration
2. Apneustic centre
   * Excitatory
   * Affects inspiration only
3. Pneumotaxic centre
   * Inhibitory
   * Affects inspiration only

NB:

• Output via phrenic nerve

1. Medullary respiratory centre

Location

In reticular formation of medulla, beneath floor of 4th ventricle

Has 2 parts:

1. Dorsal respiratory group
   * Excitatory
   * Inspiratory
2. Ventral respiratory group
   * Excitatory
   * Expiratory

Dorsal respiratory group

• Mainly associated with inspiratory
• "May" have intrinsic periodic firing
  --> responsible for basic rhythm
• Inhibited by pneumotaxic centre
• Stimulated by apneustic centre
• Also modulated by vagal (CN10) and glossopharyngeal (CN9)

Ventral respiratory group

• Mainly for expiration
• Not active during quiet breathing
• During exercise, causes active expiration

2. Apneustic centre

Located in lower pons

Causes excitatory effect on dorsal respiratory group
--> Longer inspiration
--> Thus slower rate

3. Pneumotaxic centree

Located in upper pons

Inhibits dorsal respiratory group
--> shorten inspiration
--> thus faster (not slower) rate

Summary

• Controlled respiratory rate
• Located in medulla and pons (in the brain stem)
• Output via phrenic nerve