Respiration: control of breathing

Question 1

Function of breathing

Answer 1

maintains blood gas homeostasis (CO2, O2, pH)

Question 2

What is the partial pressure of CO2 at rest?

Answer 2

pCO2 = 40+-2 mmHg

Question 3

What is the partial pressure of O2 at rest?

Answer 3

pO2 = 100+-2 mmHg

Question 4

What is the gas exchange rate at rest?

Answer 4

250ml O2/min, 200 ml CO2/min

Question 5

What is the gas exchange rate when walking?

Answer 5

800ml O2/min, 750ml CO2/min

Question 6

What is the gas exchange rate during severe exercise?

Answer 6

5000ml O2/min, 6000ml CO2/min

Question 7

What factors affect breathing?

Answer 7

reflexes (e.g. coughing), phonation, emotion, sleep, exercise, volitional control, mechanoreception, chemoreception

Question 8

Which structures does the brain receive breathing input from?

Answer 8

chemoreceptors and mechanoreceptors

Question 9

What are chemoreceptors?

Answer 9

sensory receptors that detect chemical changes in the surrounding environment

Question 10

What changes do respiratory system chemoreceptors detect?

Answer 10

pO2, pCO2, pH in blood

Question 11

Function of mechanoreceptors

Answer 11

provide feedback on mechanical status of lungs, chest wall and airways to brain

Question 12

Where does the brain send impulses to for breathing regulation?

Answer 12

respiratory muscles (e.g. diaphragm, intercostals), upper airway muscles (e.g. laryngeal, pharyngeal, tongue). Can produce reflexes to keep airways patent

Question 13

Where are the nuclei (neuronal cell groups) that regulate breathing located?

Answer 13

Brainstem

Question 14

What is the term for a decrease in O2?

Answer 14

hypoxia

Question 15

What is the term for an increase in CO2?

Answer 15

hypercapnia

Question 16

What are the 2 types of chemoreceptors?

Answer 16

peripheral and central chemoreceptors

Question 17

Where are peripheral chemoreceptors located?

Answer 17

arch of aorta and carotid sinuses (bifurcation of carotid artery)

Question 18

Where do peripheral chemoreceptors send information to?

Answer 18

nucleus in brainstem called NTS (nucleus tractus solitarius)

Question 19

Which nerve do chemoreceptors in the aortic arch send impulses along to the NTS?

Answer 19

vagus nerve

Question 20

Which nerve do chemoreceptors in the carotid sinuses send impulses along to the NTS?

Answer 20

glossopharyngeal nerve (CN IX)

Question 21

What stimulus is detected by peripheral chemoreceptors?

Answer 21

decreased pO2 (hypoxia)

Question 22

What is the response to decreased pO2 (hypoxia)?

Answer 22

• reduction in arterial pO2
• stimulates peripheral chemoreceptors
• sends impulses from carotid/aortic bodies to NTS in brainstem via CN IX/X
• information processed by respiratory neurons
• ventilation increases to restore pO2

Question 23

Where is the ventilatory response to hypoxia triggered?

Answer 23

carotid and aortic bodies

Question 24

Down to which pO2 does progressive reduction in oxygen have a little effect on ventilation?

Answer 24

until about 60 mmHg

Question 25

What happens if pO2 decreases below 60 mmHg?

Answer 25

there is progressive hyperventilation

Question 26

Why does pO2 not play a major role in momentary breathing control?

Answer 26

pO2 has a little effect on ventilation until pO2 decreases to 60mmHg

Question 27

What stimulus activates central chemoreceptors?

Answer 27

increased pCO2 (hypercapnia) or decreased pH

Question 28

Where are central chemoreceptors located?

Answer 28

(clusters of neurons in) brainstem

Question 29

What is the response to increased arterial pCO2?

Answer 29

- stimulates central chemoreceptors (brainstem neurones) - send signals to respiratory neurons in brainstem that generate breathing rhythm - send signals to respiratory muscles - ventilation increases to restore pCO2

Question 30

Which stimulus has a major impact on momentary control of breathing?

Answer 30

hypercapnia (pCO2)

Question 31

What is the effect of small changes in pCO2?

Answer 31

large effect on ventilation (unlike O2)

Question 32

Where does the hypercapnic response originate?

Answer 32

central chemoreceptors in brainstem

Question 33

What are mechanoreceptors?

Answer 33

sensory receptors that detect changes in pressure, movement and touch

Question 34

What do mechanoreceptors in the respiratory system detect?

Answer 34

movement of lung and chest wall

Question 35

Function of mechanoreceptors

Answer 35

adapting / adjusting breathing and integrating with other movements e.g. posture, locomotion

Question 36

What receptor / pathway is activated during inhalation?

Answer 36

- inflation of lungs activates mechanoreceptors - signal sent via vagus nerve to Nucleus Tractus Solitarius (NTS) in brainstem - ventilation adjusted accordingly

Question 37

Which nerve transmits signals from mechanoreceptors to NTS?

Answer 37

Vagus nerve

Question 38

Examples of locations of different mechanoreceptors

Answer 38

airway smooth muscle, airway epithelium

Question 39

What stimulus and resulting reflex from mechanoreceptors in airway smooth muscle?

Answer 39

inflation/distension of airways activates mechanoreceptors in airway smooth muscle resulting in termination of inspiration

Question 40

What is the stimulus and reflex for mechanoreceptors in airway epithelium?

Answer 40

rapid lung inflation/deflation/oedema stimulates airway epithelium mechanoreceptors which results in a sigh / shortened expiration.

Question 41

Which structures does the NTS receive information from?

Answer 41

mechanoreceptors and peripheral chemoreceptors

Question 42

Which structures process information from the NTS?

Answer 42

respiratory pattern and rhythm generating neurones (send rhythmic signals to respiratory muscles)

Question 43

What are the different types of respiratory pattern generating neurones in the brainstem?

Answer 43

inspiratory neurons (active during inspiration) and expiratory neurons (active during expiration)

Question 44

What are respiratory rhythm generating neurones?

Answer 44

bilateral cluster of neurones with rhythm generating properties.

Question 45

What happens if you isolate respiratory rhythm generating neurones?

Answer 45

they continue to produce a respiratory-like rhythmic output

Question 46

Which nerve innervates the diaphragm?

Answer 46

Phrenic nerve

Question 47

Where does the phrenic nerve exit the spinal cord?

Answer 47

C3, 4, 5

Question 48

Where do the intercostal nerves exit the spinal cord?

Answer 48

thoracic region

Question 49

Describe the pathway taken by outputs from the brainstem to the respiratory muscles?

Answer 49

rhythmic neural signals travel from the brainstem to the spinal cord and exit at C3-5 via the phrenic nerve to innervate the diaphragm, and exit at thoracic region to innervate the intercostal muscles

Question 50

Which brainstem groups are involved in generating respiratory rhythm?

Answer 50

Pontine, ventral and dorsal respiratory groups

Question 51

Which respiratory group contains respiratory pattern generating and rhythm generating neurones?

Answer 51

Ventral respiratory group

Question 52

Which respiratory group contains the Nucleus Tractus Solitarius (NTS)?

Answer 52

dorsal respiratory group

Question 53

Where are the dorsal and ventral respiratory groups located?

Answer 53

in the medulla oblongata of the brainstem

Question 54

Where is the pontine respiratory group located?

Answer 54

in the pons of the brainstem

Question 55

How does the brainstem control breathing?

Answer 55

neural inputs (chemoreceptors and mechanoreceptors), higher centre modulation (volitional and emotional) and medullary rhythm generating neurones and NTS which all contribute to neural outputs.