Neural Control of Breathing

Question 1

How is breathing initiated?

Answer 1

Neural activation of respiratory muscles - this provides the movement required for ventilation.

Question 2

What causes respiratory muscles to contract?

Answer 2

Require neural inputs/ stimulations to contract - because they are skeletal muscle

Question 3

Which muscles are utilised in quiet inspiration ?

Answer 3

Diaphragm

Question 4

Which muscles are utilised in forced inspiration?

Answer 4

• Contraction of diaphragm and internal intercostal muscles

Question 5

What is involved in quiet expiration?

Answer 5

• Elastic recoil
• Relaxation of the diaphragm

Question 6

What is involved in forced expiration?

Answer 6

Elastic recoil and contraction of internal intercostal/abdominal muscles
- Relaxation of diaphragm

Question 7

How does the central pattern generator (CPG) determine how often and hard to breathe?

Answer 7

The CPG integrates data from various neuronal inputs to regulate ventilation.

Question 8

Give examples of signals that integrate to regulate breathing.

Answer 8

• pH of arterial blood
• amount of CO2 and O2 in arterial blood
• current lung volume

Question 9

List the two main chemoreceptors

Answer 9

CENTRAL CHEMORECEPTORS
PERIPHERAL CHEMORECEPTORS

Question 10

Where are central chemoreceptors located?

Answer 10

Ventrolateral surface of the medulla oblongata

Question 11

What do central chemoreceptors detect?

Answer 11

pH changes of the spinal fluid

Question 12

What can desensitise central chemoreceptors?

Answer 12

Chronic hypoxia and increased carbon dioxide

Question 13

Where are peripheral chemoreceptors located?

Answer 13

• Aortic body
• Carotid body

Question 14

What do peripheral chemoreceptors detect?

Answer 14

AORTIC BODY - detect changes in blood O2 and CO2
CAROTID BODY - detect changes in blood O2 and CO2, and pH

Question 15

Do peripheral chemoreceptors desensitise?

Answer 15

No

Question 16

What is hypoxic drive?

Answer 16

• Form of respiratory drive
• Oxygen chemoreceptors used instead of carbon dioxide receptors to regulate the respiratory cycle
• Increased ventilation is response to decreased levels of O2 within arterial blood

Question 17

A swimmer dives into shallow waters. What happens? PART 1

Answer 17

HYPERVENTILATION:
- Overbreathing, either consciously or as a results of overexertion, artificially lowers carbon dioxide levels (hypocapnia).

Question 18

A swimmer dives into shallow waters. What happens? PART 2

Answer 18

OXYGEN DROPS:
- As the breath hold begins, oxygen is metabolised and carbon dioxide levels increase.
- As the breath hold continues, the body becomes starved of oxygen.

Question 19

A swimmer dives into shallow waters. What happens? PART 3

Answer 19

UNCONSCIOUSNESS:
- Under normal circumstances, increased carbon dioxide would trigger a breath
- CO2 levels were low upon submersion (due to hyperventilation)
- Not enough CO2 to initiate a breath, and the swimmer loses consciousness.

Question 20

A swimmer dives into shallow waters. What happens? PART 4

Answer 20

• Once consciousness lost, the body reacts and forces a breath.
• Lungs to fill with water
• Death if no immediate rescue

Question 21

Describe what sleep apnoea is.

Answer 21

Temporary cessation of breathing during sleep.

Question 22

What are the health effects of sleep apnoea?

Answer 22

• tiredness (poor sleep quality)
• cardiovascular complications (due to stress and increased sympathetic nervous system tone)
• obesity and diabetes (due to inflammation and metabolic disfunction)

Question 23

How can sleep apnoea be investigated?

Answer 23

Polysomnography

Question 24

What is obstructive sleep apnoea?

Answer 24

Blockage of the upper respiratory tract during sleep

Question 25

What physiological process causes obstructive sleep apnoea?

Answer 25

Relaxation of the genioglossus muscle

Question 26

What are the risk factors for obstructive sleep apnoea?

Answer 26

- obesity - alcohol/ sedatives - smoking

Question 27

What is central sleep apnoea?

Answer 27

Dysfunction in the process that initiates breathing

Question 28

What are the causes of central sleep apnoea? PART 1

Answer 28

STROKE: damage to the respiratory centres in the brain DRUGS (EG. OPIODS): suppression of neuronal activity CENTRAL HYPOVENTILATION SYNDROME: may come about through injury/ trauma to the brain stem, or may be congenital - results in respiratory arrest during sleep

Question 29

What are the causes of central sleep apnoea? PART 2

Answer 29

NEONATES: still continuing development of the respiratory centres in the brain ALTITUDE: eg. Cheyne-Stoke respiration

Question 30

Describe Cheyne-Stokes respiration

Answer 30

Oscillating apnoea and hyperpnoea - Irregular pattern of breathing caused by chemoreceptor dysfunction and heart failure

Question 31

What is the steps behind Cheyne Stokes respiration? PART 1

Answer 31

- Pathological stimulus (such as increased altitude, CR disfunction, heart failure, etc.) that results in hypercapnia and hypoxaemia. - To compensate, body starts hyperventilating. - Causes hypocapnia, and thus alkalosis.

Question 32

What is the steps behind Cheyne Stokes respiration? PART 2

Answer 32

- Body decreases its respiratory drive, and the body will compensate with hypoventilation. - Causes hypercapnia and hypoxaemia, and the cycle continues.

Question 33

Where are contractile signals initiated and where does the pathway follow?

Answer 33

- Initiated in the brain and descend via spinal tracts. - Signals then pass from descending upper motor neuron tracts within the spinal cord to lower motor neurons that innervate (respiratory) skeletal muscles causing them to contract.

Question 34

What are peripheral chemoreceptors activated by?

Answer 34

- Low O2, high CO2, and low pH - Will signal to medullar centres to increase ventilation.

Question 35

What do stretch receptors do and where are they located?

Answer 35

Stretch receptors within the lungs that prevent damage due to over-inflation

Question 36

What do irritant receptors do and where are they located?

Answer 36

Irritant receptors within the airways that initiate cough.

Question 37

What is the level of ventilation proportional to?

Answer 37

Level of PaCO2

Question 38

What feedback response provides the predominant stimulus for respiration in healthy individuals?

Answer 38

Hypercapnic drive - Increased ventilation in response to increased levels of CO2 within arterial blood

Question 39

When does hypoxic drive become the dominant stimulus for respiration?

Answer 39

Low PaO2 levels, or in chronically hypercapnic individuals

Question 40

Describe muscle dystrophy

Answer 40

- Atrophy of respiratory muscles - Failure to generate sufficient muscular contractile force to generate the movements required to breathe.

Question 41

Describe motor neuron disease

Answer 41

- Degradation of the motor neurons required to conduct signals from the brainstem to respiratory muscles.

Question 42

Describe spinal cord injury

Answer 42

- Damage to the pathway required to conduct signals from the brainstem to respiratory muscles.

Question 43

How are the right balances in blood gases maintained?

Answer 43

By maintaining pressure gradients between alveoli and blood

Question 44

Why does the O2 demand increase in exercise?

Answer 44

Increased ATP production, and increased consumption of O2

Question 45

What is the formula linking ventilation, tidal volume and respiratory rate?

Answer 45

Ventilation = Tidal volume x respiratory rate

Question 46

Why do central respiratory chemoreceptors not respond to changes in [H+]?

Answer 46

H+ doesnt cross the blood brain barrier

Question 47

What happens when you fall asleep (relating to ventilation)?

Answer 47

- decreased metabolic rate (as less respiratory demands) - decreased heart rate, blood pressure and cardiac output - decreased tidal volume, breathing frequency and minute volume

Question 48

Why is the rate of ventilation being modulated constantly?

Answer 48

Adjusted to meet the body’s changing O2 demand and for adequate expulsion of CO2

Question 49

In what circumstances does O2 demand and/or CO2 production increase?

Answer 49

- With increased physical activity - During infection

Question 50

How can activation of respiratory muscles be impaired?

Answer 50

- Damage to the pathway of electrical stimuli from the brain to the respiratory muscle can impair activation of respiratory muscles. - Damage to the medulla, spinal cord, motor neurones etc.

Question 51

How do central respiratory chemoreceptors indirectly monitor arterial CO2 levels?

Answer 51

- CO2 diffuses and passes through the blood brain barrier into the cerebrospinal fluid - In the fluid CO2 reacts with H20 to form H2CO3 (carbonic acid) which ionises into H+ - So the chemoreceptor detects changes in [H+] which corresponds to changes in CO2.

Question 52

How does a change in [CO2] affect central respiratory chemoreceptors?

Answer 52

- Increase in [CO2] will form more carbonic acid which will dissociate into more [H+] - pH will decrease causing activation of chemoreceptors to increase - Increased activation of chemoreceptors will cause more stimuli to be sent to the brain stem - Ventilation will increase a greater amount - More CO2 is expelled from the body