Week 2 Control of Ventilation ✅

Question 1

Where do the automatic impulses for breathing come from?

Answer 1

Brainstem - pons and medulla

Question 2

What structure can override automatic impulses for breathing for voluntary control?

Answer 2

The cerebral cortex

Question 3

What injury to the spinal cord stops breathing?

Answer 3

If spinal cord transected above origin of phrenic nerves

Question 4

What 2 neuro mechanisms regulate breathing?

Answer 4

Voluntary control
Automatic control

Question 5

How does the voluntary control of breathing work?

Answer 5

Sends impulses to respiratory motor neurones via corticospinal tracts

Question 6

How does the automatic process of breathing work?

Answer 6

Outflow from pons and medulla to respiratory motor neurones is located in lateral and ventral portions of spinal cord

Question 7

What is the respiratory centre made up of?

Answer 7

Several groups of neurons located bilaterally in medulla oblongata and pons of brainstem

Question 8

What are the 3 main collections of neurones in the respiratory centre? Where are they based and what do they do?

Answer 8

Dorsal respiratory group - located in dorsal portion of medulla - responsible for inspiration

Ventral respiratory group - located in ventral lateral portion of medulla - responsible for expiration

Pontine respiratory group - located in pons - pneumotaxic centre and apneustic centre

Question 9

What does the pneumotaxic centre do?

Answer 9

Assists with switching off inspiration and involved in respiratory rate and volume

Question 10

What does the apneustic centre do?

Answer 10

Excitatory effect on inspiration

Question 11

What is the ramp signal?

Answer 11

Nervous signal to diaphragm is weak but then ramps up steadily over 2 seconds then ceases abruptly for 3 seconds which turns off excitation of diaphragm and allows elastic recoil etc

Question 12

What is the benefit of ramp signal?

Answer 12

Steady increase of volume into lungs rather than inspiratory gasps

Question 13

The sooner the ramp ceases, the shorter the…?

Answer 13

Duration of inspiration AND duration of expiration

Question 14

Which centre switches off ramp signal and therefore controls the duration of the filling phase in the lung cycle?

Answer 14

Pneumotaxic

Question 15

What happens when the pneumotaxic signal is strong?

Answer 15

Inspiration can be little as 0.5s and fill lungs only slightly

Question 16

What happens when the pneumotaxic signal is weak?

Answer 16

Inspiration can continue for 5s+ and allowing filling of lungs with excessive air

Question 17

Which centre controls rate of breathing?

Answer 17

Pneumotaxic

Question 18

Normal quiet breathing comes from which group?

Answer 18

Dorsal respiratory group

Question 19

Does the ventral respiratory group help control inspiration or expiration?

Answer 19

Both!

Question 20

What does the ventral respiratory group during heavy expiration?

Answer 20

Stimulate abdominal accessory muscles

Question 21

When does ventral respiratory group act?

Answer 21

When high levels of pulmonary ventilation required e.g. during heavy exercise

Question 22

Where are central chemoreceptors located?

Answer 22

Near ventral surface of medulla, in vicinity of exit of 9th and 10th nerves

Question 23

What are the central chemoreceptors surrounded by?

Answer 23

Brain ECF

Question 24

What do central chemoreceptors respond to?

Answer 24

Changes in H+ concentration in ECF

Question 25

What does an increase in H+ in ECF do?

Answer 25

Stimulates increase in ventilation

Question 26

What does a decrease of H+ in ECF do?

Answer 26

Inhibits ventilation

Question 27

What controls composition of ECF around central chemoreceptors?

Answer 27

CSF, local blood flow and local metabolism

Question 28

What separates CSF from blood?

Answer 28

Blood brain barrier

Question 29

Is the blood brain barrier impermeable or permeable to H+ and HCO3- ions?

Answer 29

Impermeable

Question 30

Is the blood brain barrier impermeable or permeable to CO2?

Answer 30

Permeable - can diffuse across easily

Question 31

What happens when blood PCO2 rises?

Answer 31

Diffuses into CSF from cerebral blood vessels, liberates H+ which stimulates the chemoreceptors

Question 32

How does CO2 levels regulate ventilation?

Answer 32

Affect of pH of CSF

Question 33

Increased arterial PCO2 - does this cause cerebral vasodilation or vasoconstriction? Why?

Answer 33

Vasodilation - enhances diffusion of CO2 into CSF and ECF

Question 34

What is the normal pH of CSF?

Answer 34

7.3-7.4

Question 35

Where are peripheral chemoreceptors located?

Answer 35

In carotids at bifurcation of the common carotid arteries In aortic bodies above and below the aortic arch

Question 36

Are central chemoreceptors also sensitive to PO2 of blood?

Answer 36

No

Question 37

What are peripheral chemoreceptors good for?

Answer 37

Detecting oxygen changes in the blood and can respond to changes of CO2 and H+ concentration to a lesser extent

Question 38

What arterial changes can peripheral chemoreceptors respond to?

Answer 38

PO2 PCO2 H+

Question 39

Do peripheral chemoreceptors respond to PO2 or oxygen concentration?

Answer 39

PO2

Question 40

Is the response to peripheral chemoreceptors rapid or gradual?

Answer 40

Rapid

Question 41

What is the potential effect of hypoxaemia with absence of peripheral chemoreceptors? What condition with complete absence of hypoxic ventilatory drive can you see this effect?

Answer 41

Depress ventilation through direct effect on respiratory centres? Bilateral carotid body resection

Question 42

What can be an effect of chronic hypoxia?

Answer 42

Hypertrophy of carotid bodies

Question 43

Which is more important - central or peripheral chemoreceptors?

Answer 43

Central, however peripheral is more rapid

Question 44

What do CAROTID peripheral chemoreceptors respond to?

Answer 44

Fall in arterial pH - regardless of respiratory or metabolic

Question 45

What is the mechanism of central control modified by peripheral chemoreceptors?

Answer 45

1. Increased PCO2/decreased PO2 2. Chemoreceptors (carotid body) 3. Respiratory control centre 4. Respiratory muscles 5. Increased frequency and depth of breathing

Question 46

What is the Hering-Breuer inflation reflex?

Answer 46

Pulmonary stretch receptors discharge in response to distension in lung - stimulation of these slows respiratory frequency (self-regulatory negative feedback) I.e. inflation of lungs inhibits further inspiratory muscle activity and deflation of lungs initiates inspiratory activity

Question 47

What are irritant receptors and where do they lie?

Answer 47

They respond to irritants and lie between epithelial cells

Question 48

How do irritant receptors work?

Answer 48

Stimulated - impulses travel up vagus nerve via large myelinated fibres Causes bronchoconstriction and hypernea

Question 49

Give 3 examples of when hypernea might occur

Answer 49

Coughing, sneezing, exercise

Question 50

What conditions might irritant receptors cause bronchoconstriction?

Answer 50

Asthma and emphysema

Question 51

What are J receptors? What are the features?

Answer 51

(Juxtacapillary) Endings of non-myelinated C fibres In the alveolar walls close to capillaries Respond quickly to chemicals injected into pulmonary circulation Impulses pass up vagus nerve slow conducting non myelinated fibres and result in rapid shallow breathing Involved in difficulty of breathing with left heart failure and interstitial lung disease Stimulated by pulmonary capillaries engorged with blood or pulmonary oedema