neuronal control of breathing

Question 1

What is breathing?

Answer 1

Rhythmic process that maintains oxygen and carbon dioxide pressure gradients between alveoli and blood

Question 2

How is breathing initiated? What causes respiratory muscles to contract?

Answer 2

1. Breathing is initiated by the neural activation of respiratory muscles, which provides the movement required for ventilation.
2. As respiratory muscles consist of skeletal muscle, they require neural inputs/ stimulations to contract.
3. Innervation from motor neurons synapsing from descending spinal tracts provide the contractile signal.

Question 3

Give some examples of diseases that negatively effect breathing

Answer 3

Spinal cord injury: nerves cannot stimulate the skeletal muscle

Motor neuron disease: degradation of motor neurons

Muscular dystrophy: weakening/breakdown of skeletal muscle

Question 4

Which muscles are utilised in quiet inspiration?

Answer 4

Diaphragm

Question 5

Which muscles are utilised in forced inspiration?

Answer 5

elastic recoil

Question 6

Which muscles are utilised in increased/forced inspiration?

Answer 6

Accessory muscles:
→ Pectorals
→ Sternomastoid
-Scalene

Question 7

What muscles are utilised in increased/forced expiration?

Answer 7

• Elastic recoil
• Internal intercostal muscles
• Accessory abdominal muscle

Question 8

What is the basic breathing pattern generated by? Name the 3 respiratory groups involved in this

Answer 8

Neuronal systems within the brainstem

1. PRG: pontine respiratory group
2. DRG: dorsal respiratory group 3. VRG: ventral respiratory group

Question 9

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

Answer 9

Signals from various inputs provide feedback, which integrate to regulate breathing.
These signals include:
- the pH of CSF-cerebral spinal fluid(PaCO2)
- the amount of CO2 and O2 and H+ in arterial blood
- current lung volume
- how stretched the lungs are
-stimulation from higher emotion centres or ANS

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

Question 10

Name the two main chemoreceptors involved in respiratory feedback

Answer 10

1. Central chemoreceptors: respond indirectly to changes in arterial PCO2
2. Peripheral chemoreceptors: respond to changes in arterial O2, CO2, pH

Question 11

Where are the central chemoreceptors located?

Answer 11

Ventrolateral surface of the medulla oblongata

Question 12

Where are the peripheral chemoreceptors located?

Answer 12

Aortic bodies

Question 13

Why are central respiratory chemoreceptors described as indirectly acting?

Answer 13

Although CRC respond to changes in [H+] within cerebrospinal fluid (as H+ does not cross the blood brain barrier), CRC do NOT directly respond to changes in blood pH (except via CO2)

Question 14

What are peripheral chemoreceptors activated by?

Answer 14

Low PaO2

High PaCO2

Acidaemia

Question 15

Describe the mechanism (brief) by which peripheral chemoreceptors work

Answer 15

Signal to respiratory centers in medulla, via sensory nerves, to increase ventilation (this is a type of negative feedback)

Question 16

Peripheral chemoreceptors signal to respiratory centers in medulla, via sensory nerves, to increase ventilation. By which mechanism does this work?

Answer 16

Negative feedback

Question 17

What is meant by hypercapnic drive?

Answer 17

It is where ventilation is proportional to PaCO2.

As PaCO2 increases, ventilation increases

Question 18

What is meant by hypoxic drive?

Answer 18

Hypoxia stimulates increased ventilation
The hypoxic drive is a form of respiratory drive in which the body uses oxygen chemoreceptors instead of carbon dioxide receptors to regulate the respiratory cycle.
Hypoxic drive only kicks I at very low PaO2

Question 19

What is meant by central sleep apnoea?

Answer 19

Temporary cessation of breathing during sleep caused by dysfunction of the processes that initiate breathing

Question 20

What are the 3 potential negative effects of central sleep apnoea?

Answer 20

1. Tiredness
   
   2. Cardiovascular complications
2. Metabolic dysfunction

Question 21

What are the 4 causes of central sleep apnoea?

Answer 21

1. Stroke
   Damage to respiratory centers in the brain
   
   2. Drugs
      For example, opioids: suppression of neuronal activity
   3. Central hypoventilation syndrome
      Injury/trauma to brainstem or congenital
   4. Altitude
      For example, Cheyne-Stokes respiration
      These all effect the brainstem

Question 22

Describe Cheyne-Stokes respiration

Answer 22

Cheyne-Stokes respiration is oscillating apnoea and hyperpnoea.
First, there is a pathological stimulus (such as increased altitude, CR disfunction, heart failure, etc.) that results in hypercapnia and hypoxaemia. To compensate, the body starts hyperventilating. This causes hypocapnia, and thus alkalosis. This causes the body to decrease its respiratory drive, and the body will compensate with hypoventilation. This causes hypercapnia and hypoxaemia, and the cycle continues.
Cheyne–Stokes respirationis an abnormal pattern ofbreathing characterized by progressively deeper, and sometimes faster,breathingfollowed by a gradual decrease that results in a temporary stop inbreathingcalled an apnoea.

Question 23

What is the difference between central and obstructive sleep apnoea?

Answer 23

Central= dysfunctional initiation of breathing 
Obstructive= blockage of upper respiratory tract