Control of Breathing

Question 1

Respiratory Centers

Answer 1

1.Dorsal Respiratory Group
2. Ventral Respiratory Group
3. Pontine Respiratory Group (Pneumotaxic and Apneustic center)

Question 2

Function of Respiratory center

Answer 2

-generate rhythmic breathing via inputs from the higher brain and central or peripheral receptors (pH, CO2, O2)
-signals sent via nerves to respiratory muscles
-some voluntary control

Question 3

Dorsal respiratory group function

Answer 3

-mainly initiates respiration

Question 4

Ventral respiratory group function

Answer 4

-involved in forceful expiration and inspiration

Question 5

Pontine respiratory group

Answer 5

-Two parts: pneumontaxic and apneustic centers
-controls rate and depth of breathing

Question 6

Respiratory pattern generated by Dorsal respiratory group

Answer 6

1.emits rhythmic bursts of action potential
2.sends impulses to phrenic and intercostal nerves to initiate contraction of diaphragm and external intercostal muscles

Question 7

What regulates dorsal respiratory group activity?

Answer 7

-a collection of neurons in the nucleus tractus solitarius (NTS)

Question 8

Nucleus tractus solitarius

Answer 8

-sensory terminal for:
1.vagus nerve (X)- signals aortic body
2.glossopharyngeal nerve (IX)- signals from carotid body
**peripheral inputs through these nerves will alter the dorsal respiratory group

Question 9

Apneustic center

Answer 9

-“on switch”
-sends excitatory nerve impulses to respiratory group neurons that activate and prolong inspiration
-receives inhibitory signals from the pneumotaxic center to terminate inspiration (works together to set rhythm)

Question 10

Apenusis

Answer 10

-prolonged inspiration
-observed in brain that is sectioned above this area

Question 11

Pneumotaxic center

Answer 11

-“off switch”
-send inhibitory signal to apneustic centre to terminate inspiration
-receives signals from other brain centers (voluntary control, pain, emotion)
-affects respiration rate: if it’s a strong inhibitory signal then increased respiration rate, if weak then decreased respiration rate

Question 12

Neuronal activity during inspiration

Answer 12

-neuronal activity increases drastically
oprogressive contraction of diaphragm and external intercostal muscles
oexpansion of thoracic cavity volume, decrease in alveolar pressure = inspiration

-neuronal activity abruptly ceases (inhibitory signal provided by pneumotaxic centre)
opassive relaxation of diaphragm and external intercostal muscles
oreduction of thoracic cavity volume (aided by elastic recoil), increases alveolar pressure = expiration

Question 13

Strong inhibitory signal from Pneumotaxic

Answer 13

-results in short inspiration and short expiration
-duration is short; fast rate

Question 14

Weak inhibitory signal from pneumotaxic

Answer 14

-results in long inspiration and long expiration
-duration is long; slow rate

Question 15

Ventral respiratory group activation

Answer 15

-remains mostly inactive during normal quiet respiration
-engaged when pulmonary ventilation becomes greater than normal (eg. Exercise) and extra stimulation is required

Question 16

Three cell groups of ventral respiratory group

Answer 16

1.Nucleus retrofacilais
2. nucleus retroambiguus
3. nucleus para-ambiguous

Question 17

Nucleus retrofacilais

Answer 17

-innervate internal intercostal and abdominal muscle allowing for forced exhalation

Question 18

Nucleus retroambiguus

Answer 18

-innervate diaphragm and external intercostal muscles allowing for inspiration

Question 19

Nucleus para-ambiguous

Answer 19

-innervate laryngeal and pharyngeal muscles allowing for breathing and opening of upper airway

Question 20

Rate of ventilation regulation

Answer 20

-nervous system controls the rate of ventilation based on demand (changing activity levels)
GOAL: MAINTAIN STABLE O2 AND CO2 PRESSURES UNDER EXERCISE AND RESPIRATORY STRESS

Question 21

Receptors that signal nervous system to control respiratory muscles

Answer 21

1.central/peripheral chemoreceptors
2.Stretch receptors
3.irritant receptors
4.J receptors
5. Joint/muscle receptors

Question 22

Stretch receptors location

Answer 22

located in smooth muscles on the walls of bronchi and bronchioles

Question 23

Stretch receptors

Answer 23

-detect stretch in airway and send the signal via vagus nerve to inhibit the apneustic centre to discontinue inspiration (similar to signals from pneumotaxic centre)
-GOAL: PROTECT AGAINST OVER-INFLATION OF LUNGS

Question 24

Hering-Breuer inflation reflex

Answer 24

-prevent over-inflation of the lungs
-in humans it only activated when tidal volume is greater than 3x normal

Question 25

Irritant receptors location

Answer 25

-located in epithelial cells of nasal pharynx to bronchi

Question 26

Irritant receptors

Answer 26

-detect dust, allergens, noxious gas etc.
-stimulate increase in airway resistance via mucous secretion, bronchoconstriction, coughing/sneezing. Includes activation of parasympathetic nervous system and an increased respiration rate
-GOAL: TO CLEAR IRRITANT MATERIALS FROM RESPIRATORY TRACT

Question 27

When are irritant receptors hypersensitive?

Answer 27

-in asthmatic patients

Question 28

Juxta-alveolar “J” receptors location

Answer 28

-located in alveolar wall in close proximity to the capillaries
-also associated to C-fibres associated with pain detection

Question 29

J receptors

Answer 29

-detect physical enlargement/degree of distention in pulmonary capillaries or interstitial fluid
-also associated to C-fibres associated with pain detection
-FUNCTIONAL ROLE IS UNCLEAR.
-increases pulmonary hydrostatic pressure and interstitial volume- affects thickness in gas diffusion
*Does stimulate rapid and shallow breathing (dyspnea-shortness of breath) in patients with pulmonary hypertension and left-sided heart failure

Question 30

Central chemoreceptors location

Answer 30

-specialized neuronal cells in the medulla

Question 31

Central chemoreceptors

Answer 31

-detect changes in chemical composition of blood or other fluid around it (CSF)
-primary stimulus is elevated H+, secondary is elevated CO2
*does not detect O2 levels
-Results in increase in ventilation rate and depth (helps maintain pH level through shift right or left)

Question 32

Central chemoreceptors steps

Answer 32

1. H+ and HCO3- do not freely cross the BBB, only CO2 can diffuse into the brain tissue
2. Central chemoreceptors will be activated by CO2 in the brain tissue

3.CO2 diffuses into the CSF, is converted into H+, which can then enter brain tissue and can also activate chemoreceptors in the brain tissue

4. Brain metabolism will also produce CO2
5. Excess CO2 in brain (from metabolism) will be removed in the arterial blood
   -pressure difference of CO2 in arterial blood must be lower than that of the brain tissue so that it can more from high to low concentration. If diffusion is impaired than central chemoreceptors will be activated
6. Activated chemoreceptors will increase ventilation rate and depth to prevent CO2/H+ accumulation and lowering of brain pH

Question 33

Peripheral chemoreceptors location

Answer 33

-located outside the brain

Question 34

Peripheral chemoreceptors

Answer 34

-respond to high CO2, high H+, or low O2 and will increase ventilation rate and depth
-stimulation occurs 5x faster than central chemoreceptors; important for response to acute changes such as exercise

Question 35

Aortic bodies

Answer 35

-peripheral chemoreceptors along the arch of aorta
-provide feedback via afferent fibers connected to the vagus nerve which triggers dorsal respiratory group

Question 36

Carotid bodies

Answer 36

-peripheral chemoreceptors located bilaterally in bifurcation of carotid arteries
-provide feedback via afferent fibers connected to glossopharyngeal nerves which triggers dorsal respiratory group

Question 37

Additive effects of O2 and CO2 pressure

Answer 37

-Little change of ventilation occurs until O2 falls below 50-60 mm Hg
-If CO2 pressure increases at the same time that O2 decreases, the change in ventilation will occur earlier (with only a smaller drop in O2). Therefore an increased sensitivity to low O2 when CO2 is high
-At normal O2 pressure, ventilation increases steadily with increase in CO2 pressure. If O2 pressure decreases at same time, rate of ventilation sharply increases with increased CO2 pressure. Therefore increased sensitivity to high CO2 when O2 is low

Question 38

What drives ventilation increase with strenuous exercise?

Answer 38

-once aerobic threshold is exceeded:
1.increase in lactate production (anaerobic glycolysis)
2.lactic acidosis results in decrease in blood pH
3. peripheral and central chemoreceptors detect H+ increases which causes ventilation to sharpely increase
4. increase in rate of CO2 expiration
5. decrease in CO2 arterial pressure
6. Arterial O2 pressure also increases. The intake is greater than metabolic capacity

Question 39

What is the primary driver of increased ventilation in exercise?

Answer 39

H+/low pH from lactic acid
**not the arterial gas pressures