Respiration Lecture 13: Control of Breathing Flashcards Preview

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Flashcards in Respiration Lecture 13: Control of Breathing Deck (54):
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3 factors that stimulate the drive for breathing

1) central neural activity
2) peripheral sensory neural feedback
3) chemical status of blood & CSF

1

afferent and efferent feedback control

afferent monitors and acts on the efferent to regulate efferent output (positive and negative feedback loops)

2

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

3

Inspiratory neurons

active during inflation phase of ventilatory cycle

4

Expiratory neurons

discharge in phase with the deflation phase. Switches off with inspiratory neurons

5

Dorsal respiratory groups (DRG)

Primarily inspiratory; provide rhythmic drive; project to the VRG

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Ventral respiratory groups (VRG)

mostly EXPIRATORY; provide rhythmic drive; connect to Pons and DRG

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Source of inspiratory drive AND inhibition

Central Inspiratory Afferents (CIA)

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Source of expiratory drive AND inhibition?

Central Expiratory Afferents (CEA)

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Two regions of the pons in the brainstem that exert a major influence on medullary oscillator

Apneustic and pneumotaxic center

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Apneustic center

Loacted in caudal pons; allows for abnormally long inspiration. (inhibits switch of I to E)

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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)

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3 components needed for near normal breathing

Medullary oscillator, apneustic center, pneumotaxic center

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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

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What do peripheral vagal mechanical afferents do?

enter CNS via vagus to modulate medullary oscillator. Most effective of the peripheral sensory neural feedback system

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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

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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

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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

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2 types of C-fibers

Pulmonary and Bronchial

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Pulmonary C-fibers cause:

cardiac slowing, decreased BP, apnea

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Bronchial C-fibers cause:

cardiac slowing, INCREASED BP, hyperapnea, cough

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Dominant influence of vagal afferent feedback

PSR feedback to switch Inspiration to Expiration

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Major peripheral neural feedback system

vagal and muscle afferents

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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

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What do muscle spindles report on?

muscle length

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what do tendon organs report on?

muscle tension

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what do joint receptors report on?

rib joint motion

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Where are O2 chemoreceptors located?

Carotid bodies in carotid sinus and aortic bodies in ascending aorta. Monitor arterial PO2

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How are chemoreceptors for oxygen stimulated?

decrease in PO2. O2 content and BP have no effect

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How to functionally denervate O2 receptors?

inhale 100% O2

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T or F: there are no central sensors for monitoring O2

T

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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 (?)

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increased dead space --> ventilatory drive ?

increases

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decreased alveolar PO2 --> arterial PO2?

decreases

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Location of CO2 chemoreceptors

Peripheral (same as O2 in the carotid sinus and aorta), and central inside the blood brain barrier

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What do CO2 chemoreceptors ACTUALLY recognize?

concentration of H+

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T or F: peripheral CO2 receptors are the same as peripheral O2 receptors

T. Receptors have dual sensitivity

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Main method of CO2 feedback

central feedback

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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)

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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

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Types of higher brain center modulation of medullary oscillator

sensorimotor cortex, cerebellum, limbic system

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sensorimotor cortex influence on resp

effects timing, resp. sensation

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cerebellum influence on resp.

changes the rate and depth of respiration

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limbic system effect on resp.

changes both rate and depth of respiration

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Increases in carotid baroreceptor --> respiration?

inhibits resp.

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Pain --> resp.?

stimulates resp.

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Hyperthermia --> resp.

causes hyperpnea

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hypothermia --> VE?

increases

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exercise --> ventilation?

increases

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activation of skeletal muscle proprioceptors --> ventilation?

increases

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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

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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

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Most important nerve for peripheral sensory feedback

vagus nerve

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Hering-Breuer Reflex

hyperinflation of lung induces apnea

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