Control of ventilation

Question 1

Ventilatory control requires the stimulation of…

Answer 1

Skeletal muscles of inspiration

Question 2

What stimulates the skeletal muscles of inspiration?

Answer 2

Phrenic nerve (to diaphrgam)

Intercostal nerves (to external intercostal muscles)

Question 3

The neural activity of rhythmic breathing is triggered by what neurones?

Answer 3

Medullary inspiratory neurones

Question 4

Breathing is triggered by the medullary inspiratory neurones with…

Answer 4

Voluntary override

Question 5

Ventilatory control resides within ill-defined centres located in the…

Answer 5

Pons and medulla (respiratory centes)

Question 6

Is ventilatory control normally conscious or subconscious?

Answer 6

Normally subconscious but can be subject to voluntary modulation

Question 7

If the spinal cord was severed above the origin of the phrenic nerve, what would happen to breathing?

Answer 7

Breathing would cease

Question 8

Where is the origin of the phrenic nerve?

Answer 8

C3-5

Question 9

What are the functions of respiratory systems?

Answer 9

To set an automatic rhythm of breathing

To adjust this rhythm in response to stimuli

Question 10

How do respiratory systems set an automatic rhythm of breathing?

Answer 10

Through co-ordinating the firing of smooth and repetitive bursts of action potentials in the dorsal respiratory group (DRG) which supply the inspiratory muscles via the phrenic and intercostal nerves

Question 11

What modulates the rhythm of respiratory centres?

Answer 11

Emotion

Voluntary override

Mechano-sensory input from the thorax (e.g. stretch reflex)

Chemical composition of the blood (PCO2, PO2 and pH, detected by chemoreceptors)

Question 12

The rhythm of respiratory centres is modulated by emotional input by what system?

Answer 12

The limbic system in the brain

Question 13

Voluntary over-ride of the rhythm of respiratory centres requires input from…

Answer 13

The higher centres in the brain

Question 14

Out of the 4 things that modulate the rhythm of respiratory centres, which is most significant?

Answer 14

The chemo-receptor input

Question 15

What does the ventral respiratory group (VRG) of neurons supply?

Answer 15

Tongue
Pharynx
Larynx
Expiratory muscles

Question 16

Where are central chemoreceptors located?

Answer 16

Medulla

Question 17

Central chemoreceptors detect changes in the concentration of what ions in the CSF around the brain?

Answer 17

H+ ions

Question 18

Why do the central chemoreceptors detect changes in the concentration of H+?

Answer 18

As it directly reflects the PCO2 which is the primary ventilation drive

Question 19

Where are the peripheral chemoreceptors found?

Answer 19

Carotid and aortic bodies

Question 20

What do the peripheral chemoreceptors respond to?

Answer 20

Mainly to plasma H+ conc and PO2

Less so to PCO2

Question 21

What do central chemoreceptors cause following a rise in [H+]?

Answer 21

Reflex stimulation of ventilation

Question 22

What is the term that refers to raised PCO2

Answer 22

Hypercapnea

Question 23

What effect will a decrease in arterial PCO2 have on ventilation?

Answer 23

Ventilation is reflexly inhibited therefore ventilation rate is slowed

Question 24

What do central chemoreceptors NOT respond to?

Answer 24

Direct changes in plasma H+ conc.

Question 25

What changes do peripheral chemoreceptors detect?

Answer 25

Changes in arterial PO2 and [H+]

Question 26

Peripheral chemoreceptors cause reflex stimulation of ventilation when...

Answer 26

There is a a significant fall in arterial PO2 or a rise in [H+]

Question 27

Do peripheral chemoreceptors respond to arterial PO2 or oxygen content?

Answer 27

Arterial PO2

Question 28

What usually accompanies a rise in arterial PCO2?

Answer 28

Increased H+ conc.

Question 29

Changes in plasma pH will alter ventilation through what pathways?

Answer 29

Peripheral chemoreceptor pathways

Question 30

If plasma pH falls, ventilation will be...

Answer 30

Stimulated

Question 31

What effect does alkalosis have on ventilation?

Answer 31

Inhibits it

Question 32

A large degree of voluntary control over breathing is allowed by...

Answer 32

Descending neural pathways from cerebral cortex to respiratory motor neurons

Question 33

Can we override involuntary stimuli like arterial PCO2 or H+ conc?

Answer 33

No, we can't

Question 34

What effect does hyperventilation have on ventilation?

Answer 34

Ventilation is reflexly inhibited by an increase in arterial PO2 or a decrease in arterial PCO2

Question 35

What common drugs depress respiratory centre and can result in death following an overdose?

Answer 35

Barbiturates | Opioids

Question 36

What effect does gaseous anesthetic agents have?

Answer 36

Increase RR, but decrease Tidal Volume so decrease Alveolar Ventilation

Question 37

What effect does nitrous oxide have on peripheral chemoreceptor response to falling PaO2? Is this safe or dangerous?

Answer 37

It blunts the response Safe in most patients, problematic in chronic lung disease cases where individual often on “hypoxic drive”

Question 38

Respiration is inhibited during swallowing to avoid what?

Answer 38

Aspiration of food or fluids into the airways

Question 39

Swallowing is followed by an expiration because?

Answer 39

So that any particles are dislodged outwards from the region of the glottis.