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
Dominant influence of vagal afferent feedback
PSR feedback to switch Inspiration to Expiration
Major peripheral neural feedback system
vagal and muscle afferents
Respiratory muscle afferent modulation method of action and 3 types
afferents in respiratory muscles discharge according to respiratory muscle contraction to alter I and E durations. Have direct connections to I and E neurons and spinal neurons. 3 types: 1) muscle spindles 2) tendon organs 3) joint receptors
What do muscle spindles report on?
muscle length
what do tendon organs report on?
muscle tension
what do joint receptors report on?
rib joint motion
Where are O2 chemoreceptors located?
Carotid bodies in carotid sinus and aortic bodies in ascending aorta. Monitor arterial PO2
How are chemoreceptors for oxygen stimulated?
decrease in PO2. O2 content and BP have no effect
How to functionally denervate O2 receptors?
inhale 100% O2
T or F: there are no central sensors for monitoring O2
T
hypoxic response
Response to decreased PO2. More dependent on PCO2 than PO2, because ventilatory response is very weak until PO2 falls below 60mmHg. If PCO2 is increased slightly however, results in large increase in ventilation by increasing respiratory frequency (?)
increased dead space –> ventilatory drive ?
increases
decreased alveolar PO2 –> arterial PO2?
decreases
Location of CO2 chemoreceptors
Peripheral (same as O2 in the carotid sinus and aorta), and central inside the blood brain barrier
What do CO2 chemoreceptors ACTUALLY recognize?
concentration of H+
T or F: peripheral CO2 receptors are the same as peripheral O2 receptors
T. Receptors have dual sensitivity
Main method of CO2 feedback
central feedback
ventilatory response to CO2
increased CO2 = increased ventilation in mostly linear relationship. steepness of slope = lvl of sensitivity. (ex-anesthesia decreases sensitivity and decreases slope)
Effect of CO2 diffusing across BBB?
Rapid influence on medullary chemoreceptors. Delayed effect on medullary chemoreceptors once it dissociates into H+. Medullary chemoreceptors act on oscillator to alter ventilation to restore normal CO2 levels
Types of higher brain center modulation of medullary oscillator
sensorimotor cortex, cerebellum, limbic system
sensorimotor cortex influence on resp
effects timing, resp. sensation
cerebellum influence on resp.
changes the rate and depth of respiration
limbic system effect on resp.
changes both rate and depth of respiration
Increases in carotid baroreceptor –> respiration?
inhibits resp.
Pain –> resp.?
stimulates resp.
Hyperthermia –> resp.
causes hyperpnea
hypothermia –> VE?
increases
exercise –> ventilation?
increases
activation of skeletal muscle proprioceptors –> ventilation?
increases
How does breathing pattern change if caudal pons is “stacked back on”?
changes from phasic to apneustic pattern (long inspiration, short expirations) because of addition of apneustic center
What happens to breathing pattern if rostral pons is “stacked back on”?
Changes from apneustic breathing to close to regular breathing due to addition of pneumotaxic center
Most important nerve for peripheral sensory feedback
vagus nerve
Hering-Breuer Reflex
hyperinflation of lung induces apnea
