Control of Breathing Flashcards
pulmonary mechanoreceptors
slowly adapting pulonary stretch receptors (PSR or SAR)
irritant or rapidly adapting pulmonary stretch receptors (RAR)
C-fibers
chemoreceptors
peripheral chemoreceptors - carotid bodies and aortic bodies
central chemoreceptors - potentially at several locations in the CNS
slowly adapting pulmonary stretch receptors
located in airway smooth muscle
large, myelinated fibers
activated by lung inflation or bronchoconstriction
consequences of PSR activation
Breuer-Hering reflex
abdominal expiratory muscle activation
bronchodilation
Breuer-Hering reflex
facilitates expiration
terminates inspiration if VT elevated
prolongs expiration (slows breathing)
happens when lung inflation is 3x the Vt
irritant or rapidly adapting pulmonary stretch receptors
stimulated by inhaled irritants and rapid large inflation
located between airway epithelial cells
have somewhat smaller myelinated fibers than PSR
activation causes airway protective reflexes
protective reflexes resulting from RAR activation
increased respiratory rate
bronchoconstriction - may contribute to bronchoconstriction triggered by histamine in asthma
facilitate cough/zneeze - may be dedicated cough receptors
elicit increased mucus production and a rapid, shallow breathing pattern that increases turbulant flow
C-fibers
located in close proximity to the alveoli and stimulated by edema
also located within airway epithelium and stimulated by inhaled irritants
elicit rapid, shallow breathing pattern
may contribute to the sensation of dyspnea
What activates C-fibers?
left heart failure
interstitial lung disease
pneumonia
pulmonary embolism
A-delta fibers
recently identified neurons in guinea pigs that can elicit cough
termed cough receptors, give rise to myelinated axons with lower conduction velocities of about 5 m/sec
peripheral chemoreceptors
carotid and aortic bodies
stimulated by decreased PaO2, increased PaCO2, and decrase pHa
PaO2 rather than arterial O2 content provides stimulus
peripheral chemoreceptors not directly stimulated in anemia
central chemoreceptors
on/near ventrolateral surface of medulla and other CNS sites
a subset localized to the retrotrapezoid nucleus, which is the rostral end of the ventral respiratory column in the medulla
other sites in the brain stem
responsive to increases in PaCO2 or decreases in pHa
NOT responsive to changes in PaO2
most responsive to PaCO2 because of the blood-brain barrier
other inputs on breathing
muscle spindles in respiratory muscles
tendon organs and joint receptors
arterial baroreceptors - inhibit ventilation
metabolic factors - exercise, hormone levels
cortical factors - sleep, stress, etc.
ventilatory responses to PCO2 and PO2
ventilation can double with a 2mmHg increase in PaCo2
hypoxia augments the ventilatory response to hypercapnia
hypercapnia or acidosis augments the ventilatory response to hypoxia
effect of chronic changes in PaCO2
compensatory increase in arterial bicarbonate that leads to an increase in kidney retention of bicarbonate over a period of days
brain bicarbonate will also increase even though it does not readily cross the blood-brain-barrier
increased bicarbonate “resets” the medullary chemoreceptors
CO2 sensitivity is reduced as a result
central pattern generator (CPG)
a neuronal circuit within the CNS that can produce a patterned motor behavior such as breathing, locomotion, vocalization, or chewing without requiring phasic sensory feedback
phasic sensory input may modify the motor output but is not essential for generating the basic motor pattern
ponto-medullary respiratory neurons
dorsal respiratory group (DRG)
ventral respiratory column (VRC)
pontine respiratory group (PRG)
Dorsal Respiratory Group (DRG)
found within nucleus of the solitary tract (NTS)
processing of respiratory afferent input from cranial nerves IX and X
ventral respiratory column (VRC)
forms a continuous column in the ventrolateral medulla extending from around the facial nucleus to the medullary spinal junction
includes the retrotrapezoid nucleus (RTN) and the PreBotzinger complex (preBotC)
pontine respiratory group (PRG)
located int he rostral dorsolateral pons with the parabrachial and Kulliker-Fuse nuclei
responsible for the coordination of the respiratory control system with other systems such as the cardiovascular control and pain
also responsible for coordinating with higher brain functions such as emotions
major relay between brainstem and forebrain to control breathing
Retrotrapezoid nucleus (RTN)
central chemoreceptor
PreBotzinger complex (preBotC)
inspiratory rhythm generation
parafacial respiratory group (pFRG)
hypothesized to be important for expiratory rhythm generation
rostral ventral respiratory group (rVRG)
inspiratory premotor neurons
caudal ventral respiratory group (cVRG)
expiratory premotor neurons
Cheyne-stokes breathing
decrease in sensitivity of central chemoreceptors
decreased cardiac output - leads to increased delay between change in PACO2 and detection of change by chemoreceptors
patient experiences periods of sleep apnea as a result
Congenital Central Hypoventilation Syndrome (CCHS)
potentially life-threatening genetic disorder that involves hypoventilation, especially during sleep due to an impaired ventilatory response to PCO2 and PO2
also asosciated with functional impairments of the autonomic nervous system and tumors of neural crest derivatives
defining mutation is a polyalanine expansion in Phox2b
appears to result in a loss of retrotrapezoid neurons
Rett Syndrome (RTT)
dvelopmental disorder of the central nervous system resulting from mutationsin the X-linked gene methyl-CpG-binding protine 2
usually seen in girls
results in severe neurological symptoms that include speech and movement disorders as well as irregular breathing (Cheyne-Stokes)
