Neural Control of Breathing Flashcards
How is breathing initiated?
Neural activation of respiratory muscles - this provides the movement required for ventilation.
What causes respiratory muscles to contract?
Require neural inputs/ stimulations to contract - because they are skeletal muscle
Which muscles are utilised in quiet inspiration ?
Diaphragm
Which muscles are utilised in forced inspiration?
- Contraction of diaphragm and internal intercostal muscles
What is involved in quiet expiration?
- Elastic recoil
- Relaxation of the diaphragm
What is involved in forced expiration?
Elastic recoil and contraction of internal intercostal/abdominal muscles
- Relaxation of diaphragm
How does the central pattern generator (CPG) determine how often and hard to breathe?
The CPG integrates data from various neuronal inputs to regulate ventilation.
Give examples of signals that integrate to regulate breathing.
- pH of arterial blood
- amount of CO2 and O2 in arterial blood
- current lung volume
List the two main chemoreceptors
CENTRAL CHEMORECEPTORS
PERIPHERAL CHEMORECEPTORS
Where are central chemoreceptors located?
Ventrolateral surface of the medulla oblongata
What do central chemoreceptors detect?
pH changes of the spinal fluid
What can desensitise central chemoreceptors?
Chronic hypoxia and increased carbon dioxide
Where are peripheral chemoreceptors located?
- Aortic body
- Carotid body
What do peripheral chemoreceptors detect?
AORTIC BODY - detect changes in blood O2 and CO2
CAROTID BODY - detect changes in blood O2 and CO2, and pH
Do peripheral chemoreceptors desensitise?
No
What is hypoxic drive?
- 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
A swimmer dives into shallow waters. What happens? PART 1
HYPERVENTILATION:
- Overbreathing, either consciously or as a results of overexertion, artificially lowers carbon dioxide levels (hypocapnia).
A swimmer dives into shallow waters. What happens? PART 2
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.
A swimmer dives into shallow waters. What happens? PART 3
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.
A swimmer dives into shallow waters. What happens? PART 4
- Once consciousness lost, the body reacts and forces a breath.
- Lungs to fill with water
- Death if no immediate rescue
Describe what sleep apnoea is.
Temporary cessation of breathing during sleep.
What are the health effects of sleep apnoea?
- tiredness (poor sleep quality)
- cardiovascular complications (due to stress and increased sympathetic nervous system tone)
- obesity and diabetes (due to inflammation and metabolic disfunction)
How can sleep apnoea be investigated?
Polysomnography
What is obstructive sleep apnoea?
Blockage of the upper respiratory tract during sleep
What physiological process causes obstructive sleep apnoea?
Relaxation of the genioglossus muscle
What are the risk factors for obstructive sleep apnoea?
- obesity
- alcohol/ sedatives
- smoking
What is central sleep apnoea?
Dysfunction in the process that initiates breathing
What are the causes of central sleep apnoea? PART 1
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
What are the causes of central sleep apnoea? PART 2
NEONATES: still continuing development of the respiratory centres in the brain
ALTITUDE: eg. Cheyne-Stoke respiration
Describe Cheyne-Stokes respiration
Oscillating apnoea and hyperpnoea
- Irregular pattern of breathing caused by chemoreceptor dysfunction and heart failure
What is the steps behind Cheyne Stokes respiration? PART 1
- 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.
What is the steps behind Cheyne Stokes respiration? PART 2
- Body decreases its respiratory drive, and the body will compensate with hypoventilation.
- Causes hypercapnia and hypoxaemia, and the cycle continues.
Where are contractile signals initiated and where does the pathway follow?
- 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.
What are peripheral chemoreceptors activated by?
- Low O2, high CO2, and low pH
- Will signal to medullar centres to increase ventilation.
What do stretch receptors do and where are they located?
Stretch receptors within the lungs that prevent damage due to over-inflation
What do irritant receptors do and where are they located?
Irritant receptors within the airways that initiate cough.
What is the level of ventilation proportional to?
Level of PaCO2
What feedback response provides the predominant stimulus for respiration in healthy individuals?
Hypercapnic drive
- Increased ventilation in response to increased levels of CO2 within arterial blood
When does hypoxic drive become the dominant stimulus for respiration?
Low PaO2 levels, or in chronically hypercapnic individuals
Describe muscle dystrophy
- Atrophy of respiratory muscles
- Failure to generate sufficient muscular contractile force to generate the movements required to breathe.
Describe motor neuron disease
- Degradation of the motor neurons required to conduct signals from the brainstem to respiratory muscles.
Describe spinal cord injury
- Damage to the pathway required to conduct signals from the brainstem to respiratory muscles.
How are the right balances in blood gases maintained?
By maintaining pressure gradients between alveoli and blood
Why does the O2 demand increase in exercise?
Increased ATP production, and increased consumption of O2
What is the formula linking ventilation, tidal volume and respiratory rate?
Ventilation = Tidal volume x respiratory rate
Why do central respiratory chemoreceptors not respond to changes in [H+]?
H+ doesnt cross the blood brain barrier
What happens when you fall asleep (relating to ventilation)?
- decreased metabolic rate (as less respiratory demands)
- decreased heart rate, blood pressure and cardiac output
- decreased tidal volume, breathing frequency and minute volume
Why is the rate of ventilation being modulated constantly?
Adjusted to meet the body’s changing O2 demand and for adequate expulsion of CO2
In what circumstances does O2 demand and/or CO2 production increase?
- With increased physical activity
- During infection
How can activation of respiratory muscles be impaired?
- 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.
How do central respiratory chemoreceptors indirectly monitor arterial CO2 levels?
- 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.
How does a change in [CO2] affect central respiratory chemoreceptors?
- 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
