NEUROGENESIS OF RESPIRATION

A. Introduction

1. Neurogenesis define: function of CNS structures responsible for establishing the basic respiratory rhythm

2. Terms:

• apnea:  no ventilation
• hyperpnea:  high frequency of ventilation (breaths/minute)
• hypoventilation:  insufficient ventilation for metabolic needs; indicated by P_A-CO2 > 42 mmHg
• hyperventilation:  excess ventilation in relation to metabolic needs; indicated by P_A-CO2 < 38 mmHg
• dyspnea:  subjective sensation of difficulty in breathing; generally indicates the physiological demand for ventilation exceeds the person’s ability to respond

Note:  Normal P_A-CO2 is 40 ± 2 mmHg (some books say 40 ± 3 mmHg)
Question:  Why use P_A-CO2 to define hypo/hyperventilation instead of P_A-O2?
Question:  Why not use blood partial pressures rather than alveolar partial pressures to define hypo/hyperventilation?

3. Two neurogenic systems (both CNS)

a. involuntary (automatic): involve medulla, pons, limbic system (emotional responses), hypothalamus (temperature regulation), and other subcortical structures

b. voluntary: initiated by cerebral cortex

(see figure =>)

Note 1:  systems independent
Note 2:  both systems require intact innervation of respiratory muscles (descending pathways and alpha motoneurons)
Note 3: the muscles of respiratory ventilation are controlled by the somatic motor system, not the autonomic system (the autonomic system controls airway smooth muscle contraction and secretion)