S2: Neural Control of Breathing

Question 1

What is breathing?

Answer 1

Breathing is a rhythmic process that maintains O2 and CO2 pressure gradients between alveoli and blood.

Question 2

List some factors that increase O2 demand and CO2 production

Answer 2

• Excersize (increase activity increases ATP production and increases VO2 - volume of O2 consumed)
• Injury
• Infection
• Metabolic Dysfunction

Question 3

What does alveolar ventilation depend on?

Answer 3

Alveolar ventilation depends on the volume of fresh air inhaled each breath and the rate of breathing

VA = (VT - VD) x f

Question 4

Explain neural control of breathing

Answer 4

Breathing is produced by neural activation of respiratory muscles.
- Respiratory muscles provide the movement required for ventilation. As respiratory muscles consist of skeletal muscle, they require neural input/stimulation to contract.

• Innervation from motor neurones synapsing from descending spinal tracts provide contractile signal

Question 5

Muscles utilised in inspiration

Answer 5

Quiet breathing: Diaphragm

Respiratory: External intercostals

Accessory: Pectorals, Sternomastoid, Scalene

Question 6

Muscles utilised in expiration

Answer 6

Quiet breathing:
Elastic Recoil

Respiratory:
Elastic recoil
Internal Intercostals

Accessory:
Abdominals

Question 7

What is the respiratory pattern generator/central pattern generator?

Answer 7

The basic breathing pattern is generated by neuronal systems within the brainstem.

The brain receives inputs from various sources and integrates this to determine our breathing by generating output to the lungs.

Dorsal respiratory group (inspiratory neurones - initiates inspiration unconsciously)
Ventral (all inspiration and expiration)

Question 8

What do central chemoreceptors respond to?

Answer 8

Central chemoreceptors respond indirectly to changes in arterial PCO2

Question 9

Where are central respiratory chemoreceptors (CRC) found?

Answer 9

Central respiratory chemoreceptors (CRC) present in the medulla

Question 10

How do central chemoreceptors indirectly measure changes in arterial pCO2?

Answer 10

Although CRC respond to changes in [H+] within the cerebrospinal fluid as H+ doesn’t cross the blood brain barrier.
CRC do not directly respond to changes in blood pH except via CO2.

H+ stimulates central chemoreceptors which takes information to the respiratory control centres that increase or decrease ventilation.

Question 11

What is the main stimulus of breathing?

Answer 11

Chemoreceptors

Question 12

What do peripheral chemoreceptors respond to?

Answer 12

Peripheral chemoreceptors respond to changes in arterial O2, CO2 and PH.

They are activated by decreased PaO2, increased PaCO2 and acidaemia.

Question 13

What do peripheral chemoreceptors do?

Answer 13

They respond to changes in arterial O2, CO2 and pH.

They then signal to respiratory centres in the medulla (via sensory nerves) to increase ventilation (negative feedback)

Question 14

What is hypercapnic drive?

Answer 14

This is where the body uses carbon dioxide chemoreceptors to regulate the respiratory cycle

Ventilation is generally proportional to PaCO2 so the higher the levels of CO2, the more ventilation occurs.

Question 15

What is hypoxic drive?

Answer 15

The hypoxicdriveis a form of respiratorydrivein which the body uses oxygen chemoreceptors instead of carbon dioxide receptors to regulate the respiratory cycle

Hypoxic drive only kicks in during hypoxaemia (low PaO2) stimulates increased ventilation

Question 16

Describe the stages of shallow water blackout

Answer 16

HYPERVENTILATION
Overbreathing (consciously or due to overexertion) artificially lowes CO2 levels

OXYGEN DROPS
In the water breath is held. Oxygen is metabolised and CO2 levels increase. Body gradually becomes starved of oxygen.

UNCONSCIOUSNESS
Under normal circumstances, increased CO2 would trigger a breath but because CO2 levels were low upon submertion, CO2 levels are not high enough to trigger a breath and swimmer loses consciousness.

DROWNING
Once the swimmer loses consciousness, the body reacts and forces a breath. This causes the lungs to fill with water which can cause drowning if individual is not rescued.

Question 17

What can be used to investigate sleep apnoea?

Answer 17

Polysomnography

Question 18

What is sleep apnoea?

Answer 18

Temporary cessation of breathing during sleep

Question 19

Effect of sleep apnoea on health

Answer 19

• Tiredness (poor sleep quality)
• Cardiovascular complications (stress and increased SNS tone)
• Obesity/Diabetes (inflammation and metabolic dysfunction)

Question 20

What is obstructive sleep apnoea?

Name some risk factors

Answer 20

Obstructive sleep apnoea: Blockade of upper respiratory tract during sleep e.g. by tongue

Risk factors:

• Obesity
• Alcohol/Sedatives
• Smokers

Question 21

What is central sleep apnoea?

Name some causes

Answer 21

Central sleep apnoea is dysfunction in the process that initiates breathing

Causes:

• Stroke which damages respiratory centres in the brain
• Drugs e.g. opiods that suppress neuronal activity
• Central hypoventilation syndrome - injury/trauma to brainstem, or congenital (‘ondines curse’)
• Neonates - Continuing development of respiratory centres
• Altitude e.g. cheyne stokes respiration

Question 22

What is cheyne-stokes respiration?

Answer 22

Oscillating apnoea and hyperpnoea (increased depth and rate of breathing)