Lecture 15: Control of Ventilation

Question 1

what are the 4 components of neural control of ventilation?

Answer 1

• generation of rhythmic pattern of alt. insp and exp
• regulation of rate and depth of vent
• voluntary - speech, breath holding
• involuntary - coughing, sneezing

Question 2

where is the respiratory centre located?

Answer 2

within the brainstem

Question 3

what is the brainstem?

Answer 3

the rostral continuation of the spinal cord

Question 4

the respiratory centre is composed of 5 aggregations of neuronal cell bodies, what are they and where are they?

Answer 4

within the:
Medulla oblongata - dorsal respiratory group (DRG), ventral respiratory group (VRG), pre-Botzinger complex

Pons - apneustic centre and the pneumotaxic centre

Question 5

what do the efferent fibres from the DRG stimulate?

Answer 5

inspiratory spinal motor neurons innervating the diaphragm

Question 6

rhythmic firing of the DRG is in response to what?

Answer 6

rhythmic action potentials originating in the pre-Botzinger complex

Question 7

what does firing of the DRG neurone result in?

Answer 7

inspiration –> cessation of firing = expiration

Question 8

axons from the VRG project to and stimulate what?

Answer 8

project to the spinal motor neurone of both expiratory and accessory inspiratory muscles

Question 9

when is the VRG activated and how?

Answer 9

activated by the DRG when demands for ventilation increase

Question 10

what two centres does the DRG receive input from?

Answer 10

the pneumotaxic and apneustic centres

Question 11

what does the pneumotaxic centre do?

Answer 11

acts to terminate inspiration

Question 12

what does the apneustic centre prevent?

Answer 12

switching off inspiratory neurons

Question 13

stretch receptors in the smooth muscle of the airway prevent initiate what reflex? why?

Answer 13

the hering-breuer reflex

–> inhibition of firing of inspiratory neurons to prevent over-inflammation of lungs

Question 14

mechanoreceptors in the airway initiate what reflex?

Why?

Answer 14

the coughing/sneezing

–> to remove unwanted material

Question 15

what are the two locations of chemoreceptors

Answer 15

1. peripheral - located in
   - -> carotid bodies - located at origin of internal carotid artery
   - -> aortic bodies - located in aortic arch
2. central chemoreceptors - located in ventral part of medulla oblongata

Question 16

how is rate and depth of ventilation regulated?

Answer 16

carried out by the medullary centre - DRG and VRG in response to body’s need for gas exchange

Question 17

what is another name for the regulation of rate and depth of ventilation by lowered arterial PO2?

Answer 17

hypoxic drive

Question 18

how is arterial PO2 monitored?

Answer 18

by peripheral chemoreceptors

Question 19

what kind of change in PO2 is needed to initiate the hypoxic drive? what is the response?

Answer 19

only sensitive to DRAMATIC change in arterial PO2

e. g <60mmHg = point where Hb saturation 90%
- -> detected by aortic and carotid chemoreceptors –> this stimulates medullary inspiratory neurone –> increases ventilation

Question 20

why is the hypoxic drive a necessary life saving mechanism?

Answer 20

because low PO2 depresses all neural function except for chemoreceptors

Question 21

what is another name for the regulation of rate and depth of ventilation by increased arterial PCO2?

Answer 21

hypercapnic drive

Question 22

is arterial PO2 or PCO2 more important in regulating ventilation under normal conditions

Answer 22

PCO2

Question 23

does stimulation of peripheral chemoreceptors produce a strong or weak response to increased PCO2?

Answer 23

weak response

Question 24

does stimulation of central chemoreceptors produce a strong or weak response to increased PCO2?

Answer 24

strong response

–> most important regulation of ventilation in response to changing PCO2

Question 25

in varying levels of PCO2 what do the central chemoreceptors actually measure and what is the response?

Answer 25

CO2 diffuse’s very rapidly across the blood brain barrier
CO2 levels in the medullary ECF = accurate level of CO2 in the peripheral fluid
the central chemoreceptors actually measure [H]+ derived from CO2 that crosses membrane

increase PCO2 –> Increase [H]+ Brain ECF
–> medullary chemoreceptor detect –> stem of medullary inspiratory neurone –> increase in ventilation

Question 26

although you can measure hypoxic or hypercaprinic drive, what is another arterial regulatory measure rate and depth of ventilation?

Answer 26

arterial H+ concentration

Question 27

what chemoreceptors are responsible for detecting arterial H+ concentration?

Answer 27

PERIPHERAL
increase In blood = acidosis = increase ventilation
decrease in blood = alkalosis = decrease ventilation

Question 28

why is it that peripheral chemoreceptors are responsible for detecting arterial H+ receptors?

Answer 28

H+ cannot cross the blood brain barrier (where the central chemoreceptors are located)

Question 29

what are some “conscious” higher controls of ventilation

Answer 29

• stopping breathing during swallowing
• vocalisation
• defection –> push down abdominal muscles
• parturition
• breath holding
• changes in gait in some species
  higher control is overriden by chemotactic centres with extreme change in arterial PCO2