Respiration Lecture 13: Control of Breathing Flashcards
afferent and efferent feedback control
afferent monitors and acts on the efferent to regulate efferent output (positive and negative feedback loops)
3 factors that stimulate the drive for breathing
1) central neural activity
2) peripheral sensory neural feedback
3) chemical status of blood & CSF
Where is basic respiratory neural oscillator?
medulla (near the obex). Medullary centers are both essential and sufficient for automatic rhythmic respiration, but other inputs are needed for more NORMAL breathing
Inspiratory neurons
active during inflation phase of ventilatory cycle
Expiratory neurons
discharge in phase with the deflation phase. Switches off with inspiratory neurons
Dorsal respiratory groups (DRG)
Primarily inspiratory; provide rhythmic drive; project to the VRG
Ventral respiratory groups (VRG)
mostly EXPIRATORY; provide rhythmic drive; connect to Pons and DRG
Source of inspiratory drive AND inhibition
Central Inspiratory Afferents (CIA)
Source of expiratory drive AND inhibition?
Central Expiratory Afferents (CEA)
Two regions of the pons in the brainstem that exert a major influence on medullary oscillator
Apneustic and pneumotaxic center
Apneustic center
Loacted in caudal pons; allows for abnormally long inspiration. (inhibits switch of I to E)
Pneumotaxic center
Located in rostral pons; facilitates inspiratory off-switching (but only when apneustic center had caused a long inspiration) (promotes switch of I to E)
3 components needed for near normal breathing
Medullary oscillator, apneustic center, pneumotaxic center
3 types of peripheral vagal mechanical afferent modulators of medullary oscillator
1) Slowly adapting pulmonary stretch receptors (PSR)
2) Rapidly adapting receptors (RAR)
3) Vagal lung C-fibers
What do peripheral vagal mechanical afferents do?
enter CNS via vagus to modulate medullary oscillator. Most effective of the peripheral sensory neural feedback system
Pulmonary Stretch receptors
Mechanoreceptors in smooth muscle of airways (generally insensitive to chemicals). Discharge with increased inflation. Mediate Hering-Breuer reflex, inhibit inspiration. Regulate transition between inspiration and expiration
Rapidly adapting receptors (RAR)
Mechanoreceptors in airway epithelium and smooth muscle that discharge in response to both inflation and deflation. Also sensitive to chemical irritants. Involved in cough, most likely stimulate inspiration. Report on rate of volume change between inspiration and expiration
Vagal lung C-fibers
Unmyelinated slow conducting nerve fibers in airway epithelium and interstitial spaces. Chemosensitive. Will produce response to interstitial space thickening (i.e. edema). Report on the status of the epithelium in the airway
2 types of C-fibers
Pulmonary and Bronchial
Pulmonary C-fibers cause:
cardiac slowing, decreased BP, apnea
Bronchial C-fibers cause:
cardiac slowing, INCREASED BP, hyperapnea, cough