Control of Breathing

Question 1

pulmonary mechanoreceptors

Answer 1

slowly adapting pulonary stretch receptors (PSR or SAR)

irritant or rapidly adapting pulmonary stretch receptors (RAR)

C-fibers

Question 2

chemoreceptors

Answer 2

peripheral chemoreceptors - carotid bodies and aortic bodies

central chemoreceptors - potentially at several locations in the CNS

Question 3

slowly adapting pulmonary stretch receptors

Answer 3

located in airway smooth muscle

large, myelinated fibers

activated by lung inflation or bronchoconstriction

Question 4

consequences of PSR activation

Answer 4

Breuer-Hering reflex

abdominal expiratory muscle activation

bronchodilation

Question 5

Breuer-Hering reflex

Answer 5

facilitates expiration

terminates inspiration if V_T elevated

prolongs expiration (slows breathing)

happens when lung inflation is 3x the Vt

Question 6

irritant or rapidly adapting pulmonary stretch receptors

Answer 6

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

Question 7

protective reflexes resulting from RAR activation

Answer 7

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

Question 8

C-fibers

Answer 8

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

Question 9

What activates C-fibers?

Answer 9

left heart failure

interstitial lung disease

pneumonia

pulmonary embolism

Question 10

A-delta fibers

Answer 10

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

Question 11

peripheral chemoreceptors

Answer 11

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

Question 12

central chemoreceptors

Answer 12

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

Question 13

other inputs on breathing

Answer 13

muscle spindles in respiratory muscles

tendon organs and joint receptors

arterial baroreceptors - inhibit ventilation

metabolic factors - exercise, hormone levels

cortical factors - sleep, stress, etc.

Question 14

ventilatory responses to PCO₂ and PO₂

Answer 14

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

Question 15

effect of chronic changes in PaCO₂

Answer 15

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

Question 16

central pattern generator (CPG)

Answer 16

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

Question 17

ponto-medullary respiratory neurons

Answer 17

dorsal respiratory group (DRG)

ventral respiratory column (VRC)

pontine respiratory group (PRG)

Question 18

Dorsal Respiratory Group (DRG)

Answer 18

found within nucleus of the solitary tract (NTS)

processing of respiratory afferent input from cranial nerves IX and X

Question 19

ventral respiratory column (VRC)

Answer 19

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)

Question 20

pontine respiratory group (PRG)

Answer 20

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

Question 21

Retrotrapezoid nucleus (RTN)

Answer 21

central chemoreceptor

Question 22

PreBotzinger complex (preBotC)

Answer 22

inspiratory rhythm generation

Question 23

parafacial respiratory group (pFRG)

Answer 23

hypothesized to be important for expiratory rhythm generation

Question 24

rostral ventral respiratory group (rVRG)

Answer 24

inspiratory premotor neurons

Question 25

caudal ventral respiratory group (cVRG)

Answer 25

expiratory premotor neurons

Question 26

Cheyne-stokes breathing

Answer 26

decrease in sensitivity of central chemoreceptors

decreased cardiac output - leads to increased delay between change in P_ACO₂ and detection of change by chemoreceptors

patient experiences periods of sleep apnea as a result

Question 27

Congenital Central Hypoventilation Syndrome (CCHS)

Answer 27

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

Question 28

Rett Syndrome (RTT)

Answer 28

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)