RESPIRATION PHYSIOLOGY: RESPIRATION REGULATION -- Neurogenesis: Other Neural Contributions

NEUROGENESIS OF RESPIRATION (continued)

C. Lung Stretch Receptors (feedback for lung volume size)

1. afferent endings (mechanoreceptors) in airway smooth muscle; stimulus is lung volume increase

2. associated with a variety of reflexes, the best studied of which is:

3. Hering-Breuer Reflex

a. initiated by increasing lung volume
b. afferent pathway is via the vagus nerve
c. action: inhibit further inspiration
d. role: aid in establishing uniform pattern of respiration, particularly in deep inspiration

D. Pneumotaxic Center

1. Located in the pons

2. Appears to inhibit "I" neurons of the respiratory center

Note: section (cutting) of the brain between the medulla and the pons and section of the vagus nerve results in apneustic breathing: sustained inhalation with occasional expiratory gasps

3. Function of pneumotaxic center: aid in establishing the normal respiratory rhythm

E. Reticular Activating System (RAS)

1. Located in the reticular system of the brain stem; activity associated the "awake" or "conscious" state

2. When active, simulates respiratory ventilation

3. When RAS activity is reduced, as during sleep, ventilation is reduced and P_A-CO2 increases by a few mmHg

a. Sleep Apnea: in some individuals, ventilation ceases temporarily (10+ seconds) during sleep

b. types of sleep apnea

1) central apnea: reduced CNS respiratory drive
2) obstructive apnea: increased upper airway resistance (laryngospasm and/or bronchospasm) (snoring)

c. in infants, can lead to SIDS (Sudden Infant Death Syndrome) (in general, infants should sleep on their backs!)

4. RAS may be an important drive in individuals with decreased spontaneous Respiratory Center activity (drug overdose, Ondine's Curse, CCHS -- Congenital Central Hypoventilation Syndrome)

F. Other Neural Structures

1. Hypothalamus: change in respiration associated with temperature regulation (not important in humans)

2. Limbic System: respiratory changes in emotion

3. Cerebral cortex: voluntary control (limited), learning

4. Irritant receptors: airway receptors responding to inhaled irritating substances; cause hyperpnea and bronchoconstriction

5. J receptors (juxtacapillary): located near pulmonary capillaries; may contribute to dyspnea in pulmonary edema, etc.

6. Respiratory muscle spindle receptors and joint receptors; may contribute to respiratory drive in exercise