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

What is the significance of ventilation?

Answer 2

Ventilation is regulated to meet the varying O₂ demand and CO₂ production

ventilation is usually proportional to PaCO₂

Question 3

What is the effect of increased ventilation?

Answer 3

greater ventilation due to more breathing quicker and deeper = more alveolar air -> atm air so blood takes O₂ from air into tissues and removes CO₂

Question 4

How often does the body demand O₂?

Answer 4

O₂ demands are always constant - the body adjusts homeostasis of blood gases to meet metabolic demands

Question 5

How is breathing initiated?

Answer 5

Breathing is initiated by neural activation of respiratory muscles, which provide the movement required for ventilation

Question 6

What stimulates the respiratory muscles?

Answer 6

As respiratory muscles consist of skeletal muscle, they require neural input to contract
Innervation from motor neurons synapsing from descending spinal tracts provide the contractile signal
C3 - C9 via medulla –> phrenic nerve
T1 - T12 to the intercostals

Question 7

Which muscles are involved in quiet breathing?

Answer 7

Inspiration: Diaphragm

Expiration; Elastic recoil

Question 8

Which muscles are involved in Forced ventilation?

Answer 8

Respiratory
Inspiration: External intercostals
Expiration: Elastic recoil, Internal intercostals

Accessory
Inspiration: Pectorals, scalene, stemomastoid
Expiration: Abdominals

Question 9

How does the diaphragm enable quiet breathing to occur?

Answer 9

Contraction and relaxation of diaphragm creates a force for quiet breathing causing heart contractions and relaxtaions

Question 10

What is the role of elastic recoil?

Answer 10

Elastic recoil pushes air out

Question 11

How does forced ventilation occur?

Answer 11

A greater speed/force of breathing requires external intercostals for forced inspiration and internal intercostals for forced expiration
This is due to a positive P(intrapleural)

Question 12

What are accessory muscles?

Answer 12

Their primary role isn’t ventilation, but aid forced breathing movements e.g.
abdominal muscles
Intercostal muscles

Question 13

How is the breathing mechanism generated?

Answer 13

The basic breathing pattern is generated by neuronal systems within the brain stem

Question 14

What is the role of the central pattern generator (CPG)?

Answer 14

The central pattern generator can determine how often and how hard to breathe

Question 15

How does the CPG regulate breathing?

Answer 15

Signals from various inputs provide feedback which are integrated to regulate breathing

Question 16

What innervations make up the CPG?

Answer 16

Higher brain centres (cerebral cortex - voluntary control over breathing)

• Other receptors (e.g. pain) and emotional stimuli act
  through hypothalamus
• Respiratory centres; medulla and pons
• Peripheral chemoreceptors; ↓O₂, ↑CO₂, ↓H⁺
• stretch receptors in lungs
• Central chemoreceptors; ↑CO₂, ↑H⁺
• Irritant receptors
• Receptors in muscles and joints

Question 17

What is the role of central chemoreceptors?

Answer 17

Respond (indirectly) to changes in arterial PaCO₂

Question 18

Where are central chemoreceptors found?

Answer 18

In the medulla

Question 19

How do chemoreceptors indirectly respond to blood pH changes?

Answer 19

Central chemoreceptors respond to changes in [H⁺] within the cerebrospinal fluid
H⁺ doesn’t cross blood brain barrier so receptors don’t directly respond to changes in blood pH (except via CO₂)

Question 20

What is the function of peripheral chemoreceptors?

Answer 20

Respond to changes in arterial O₂, CO₂ and pH

Question 21

How are peripheral chemoreceptors activated?

Answer 21

Stimulated by a decrease in PaO₂, increased PaCO₂ and acidemia

Question 22

Where are peripheral chemoreceptors located in the body?

Answer 22

aortic and carotid bodies

Question 23

How do peripheral chemoreceptors respond to changes in arterial CO₂ and O₂?

Answer 23

Signal to respiratory centres in the medulla, via sensory nerve fibres to increase ventilation (negative feedback)

Question 24

How do chemoreceptors produce an appropriate level of breathing?

Answer 24

These chemoreceptors work to figure out the metabolic demands of the body so they can send signals to the brain which integrates the signals to produce an appropriate level of breathing

Question 25

What is hypoxaemia?

Answer 25

low O₂ - stimulates increased ventilation

Question 26

What is central sleep apnoea?

Answer 26

Temporary cessation of breathing caused by a dysfunction of breathing initiation processes

Question 27

What are the potential negative health effects of sleep apnoea?

Answer 27

• tiredness
• CVS complication
• Metabolic dysfunction

Question 28

What are the potential causes of sleep apnoea?

Answer 28

Stroke
- damages respiratory centres in the brain

Drugs (opioids)
- Suppressing neuronal activity

Central hypoventilation syndrome

• injury / trauma to brain stem
• congenital Ondine’s curse

Altitude
- Cheyene stokes respiration

Question 29

What is cheyenes-stokes respiration?

Answer 29

Oscillating apnoea and hyperapnoea

• different systems start to over compensate for each
  other
• Hyperventilation followed by hypoventilation to try
  manage changes in partial pressure