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MD3001 Week 8 > Ventilation- Neural Control of Breathing > Flashcards

Ventilation- Neural Control of Breathing Flashcards

1
Q

Describe the neuronal firing during breathing?

A

The activity of inspiratory neurons increases steadily, apparently through a positive feedback mechanism

At the end of inspiration, the activity shuts off abruptly and expiration takes place through recoil of elastic lung tissue

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2
Q

Where is respiratory rhythm generated?

A

Medulla

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3
Q

What happens if the brainstem is cut above the level of the pons?

A

Basic rhythm continues

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4
Q

What happens id all the afferent nerves to the brainstem are cut?

A

Basic rhythm continues

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5
Q

What happens if you section the spinal cord below C3-C5?

A

Intercostal muscles are paralysed

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6
Q

What is respiration regulated by?

A

Nervous or neural

Chemical

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7
Q

Where does breathing originate?

A

Brainstem

Medulla

Pons

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8
Q

Where are respiratory centres located?

A

Medulla oblongata

Pons

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9
Q

What is the function of respiratory centres?

A

Collect sensory information about the levels of oxygen and carbon dioxide in blood

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10
Q

What Is the overall arching function of respiratory centres collectively?

A

Matching the changes in physical properties of the lungs with the correct breathing pattern

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11
Q

What are the two medullary centres?

A

Inspiratory

Expiratory

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12
Q

Where is the inspiratory centre and what is its function?

A

Located in upper part of medulla oblongata

Function is concerned with inspiration- exclusively inspiratory neurons

Control external intercostal muscles and diaphragm

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13
Q

Where is the expiratory centre?

A

Situated in medulla oblongata, anterior and lateral to the inspiratory centre

Also called ventral respiratory group

Controls internal intercostal muscles

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14
Q

What is the function of the expiratory centre?

A

Centre is inactive during quiet breathing and when inspiratory centre is active, but during forced breathing or when inspiratory centre is inhibited it becomes active

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15
Q

What are the two pontine centres?

A

Pneumotaxic centre

Apnuestic

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16
Q

Where is the pneumotaxic centre?

A

Situated in upper pons

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17
Q

What is the function of pneumotaxic centre?

A

Controls medullary respiratory centres, especially the inspiratory centre through the apneustic centre

It influences duration of inspiration

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18
Q

What is the function of the apnuestic centre?

A

Increases depth of inspiration by acting on inspiratory centre

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19
Q

Where is the apnuestic centre?

A

Lower pons

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20
Q

What do afferent pathways deliver?

A

Impulses via vagus and glossopharyngeal nerves

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21
Q

What do efferent pathways deliver?

A

Signals that drive inspiration and expiration

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22
Q

Where do afferent pathways get their signals from?

A

Thoracic region and lungs

Also chemoreceptors

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23
Q

Describe the flow of signals in the efferent pathway

A

Nerves from respiratory centre leave brain in anterior part of lateral column in spinal cord

Terminate in motor neurons in cervical and thoracic segments of spinal cord

Supply phrenic nerve that controls diaphragm

Supply fibres for intercostal muscles

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24
Q

What ten things can affect respiratory centres?

A

Impulses from higher centres

Stretch receptors of lung slowly adapting pulmonary receptors- Hering-Breur Reflex

“J” Receptors- pulmonary C-fibres

Irritant receptors of lungs

Proprioceptors

Thermoreceptors

Pain receptors

Cough reflex

Sneezing reflex

Deglutition relfex

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25
Q

What higher centres can override respiratory centres?

A

Limbic system

Hypothalamus

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26
Q

Describe the Hering-Breur Reflex

A

Smooth muscle of upper airways has slowly adap1ng stretch receptors. When lung is inflated these neurones send impulses to DRG via the vagus nerve. This input is inhibitory, limi1ng inspira1on, prevents overinfla1on of lungs

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27
Q

How does “J” Receptors- pulmonary C-fibres affect respiratory centres?

A

These are juxtacapiilary receptors present in the all of alveoli

Once stimulated by conditions such as pulmonary oedema, congestion pneumonia and histamine, then induce apnea

Temporary suspension of breathing- followed by rapid shallow breathing

28
Q

How do irritant receptors of lungs override the respiratory centres?

A

Powerfully simulated by inhalation of irritants

Found on walls of bronchi and bronchioles

Induces rapid shallow breathing from shortening of expiration

Then long deep augmented breaths, which are taken every 5-20 mins to reverse slow collapse of lungs

29
Q

How do proprioceptors change breathing?

A

Aim is for reflexes form muscles and joints to stabilize ventilation in the face of changing mechanical conditions

30
Q

Where are proprioceptors found in regards to the respiratory system?

A

In joints to measure velocity of ribs

Tendons to detect strength of muscle contraction

Muscle spindles to monitor length of fibres

31
Q

What are the function of thermoreceptors?

A

Cutaneous

Supply signals to cerebral cortex, stimulates respiratory centre, hyperventilation

32
Q

What is the function of pain receptors?

A

Supply signals to cerebral cortex, stimulating respiratory centres and inducing hyperventilation

33
Q

How does the cough reflex change ventilation?

A

Irritation of parts beyond the nose stimulates vagus nerve and cough is induced

Deep inspiration followed by forceful expiration with closed glottis

Glottis opens and explosive outflow of air at high velocity

34
Q

How does the sneezing reflex change ventilation?

A

Irritation of nasal mucous membranes causes a deep inspiration followed by forceful expiration with opened glottis

35
Q

How does the deglutition reflex change breathing?

A

Respiration arrested during swallowing of food

36
Q

Describe how you can voluntarily control your breathing

A

The cortex and by pass the medulla and affect lower motor neurones directly

During this voluntary control there are signals coming from the cerebral cortex to medulla, influencing basic pattern generation by the DRG

37
Q

What do chemoreceptors respond to?

A

Changes in chemical constituents of blood or CSF

38
Q

What chemical changes can chemoreceptors respond to?

A

Hypoxia

Hypercapnia

Increased hydrogen concentration

39
Q

What are the two types of chemoreceptors?

A

Central chemoreceptors

Peripheral chemoreceptors

40
Q

What is hypercapnia?

A

Elevated carbon dioxide in blood

41
Q

Where are the central chemoreceptors located?

A

Medulla oblongata close to DRG

42
Q

What is the action of central chemoreceptors?

A

Sensitive to increase in hydrogen concentration in CSF

Sensitive to increase in PaCO2 in blood

43
Q

How does central chemoreceptors detect hydrogen ions in the CSF when hydrogen can’t pass across the BBB barrier?

A

C02 crosses into CSF and forms carbonic acid

This is unstable and dissociates into hydrogen and bicarbonate

Hydrogen then stimulates central chemoreceptors

44
Q

Where are peripheral chemoreceptors?

A

Close in location but distinct from baroreceptors

45
Q

What are peripheral chemoreceptors?

A

Specialised receptor cells that are stimulated primary by a decrease in PO2 and an increase in hydrogen ions

46
Q

What do peripheral chemoreceptors synapse on?

A

With afferent nerves which run to the brainstem

Sensory portion of cranial nerve 10 from aortic bodies

Cranial nerve 9 from carotid bodies

47
Q

Which peripheral chemoreceptor is more important in respiration?

A

Carotid

48
Q

What are peripheral chemoreceptors sensitive to?

A

PaO2

PaCO2

pH

Blood flow

Temperature

10x less sensitive than central receptors

49
Q

Where are peripheral chemoreceptors?

A

Carotid sinus and aortic arch

50
Q

What are peripheral chemoreceptors also known as?

A

Glomus Cells

51
Q

Describe the pathway in chemoreceptors?

A

When partial oxygen is high the potassium channel is open

When partial oxygen falls the potassium channel closes and causes depolarization

The calcium channels open and stimulates a response in sensory afferents

52
Q

What nerve innervates the carotid bodies?

A

Vagus nerve

53
Q

What nerve innervates the carotid bodies?

A

Glossopharyngeal nerve

54
Q

What gas measurement is the most important in respiration?

A

PCO2

55
Q

What is normal PCO2?

A

40mmHg or 5.3 kPa

56
Q

What happens if there is an increase in PCO2?

A

CO2 crosses the BBB so as it rises the pH of the CSF decreases

That has excitory input to DRG in medulla and resulting in increased ventilation

As PCO2 returns to normal, pH returns to normal and stimulus for respiration is reduced

57
Q

How can decreased CO2 during hyperventilation signal a decrease in breathing rate?

A

At normal PCO2 there is a resting discharge action potential from chemoreceptors

If PCO2 falls the firing rate also falls so there is a corresponding decrease in excitatory input to DRG, with the result of respiration being inhibited

58
Q

How much must oxygen pressure levels drop in the blood for peripheral chemoreceptors to stimulate ventilation?

A

From 100mmHg to 60mmHg or 8kPA

59
Q

Why can’t you put COPD patients on 100% oxygen masks?

A

Over a long time the central and peripheral chemoreceptors become insensitive to PCO2

As a result the patient relies on a decline in PO2 to stimulate breathing- hypoxic drive

If you put a patient on 100% oxygen the breathing will stop as the peripheral chemoreceptors will fall and depress ventilatory drive

60
Q

How does pH affect ventilation?

A

If the PO2 and PCO2 are normal peripheral chemoreceptors will detect a lower pH

This increases the breathing rate to drive CO2 out of the body

61
Q

How does damage to the CNS affect breathing?

A

Cause partial or total loss of respiratory function

Vasoconstriction, hypertension, mucus secretion and oedema and result from uncontrolled activity

Strokes can also interfere with the dorsal medullary centres and cause fatal apnoea

62
Q

How does poliomyelitis affect breathing?

A

25% of patients require mechanical ventilation during acute phase

Reinnervation of fibres can recover respiratory strength

63
Q

How does diptheria affect breathing?

A

Demyelinating neuropathy that can lead to respiratory failure

64
Q

How does botulism affect breathing?

A

Innervation of respiratory muscles seems particularly vulnerable, ventilation may be required for extended period

65
Q

How does DMD affect breathing?

A

From age 10 vital capacities declines

Nocturnal hypoxaemia develops first

Common cause of death is respiratory failure secondary to pulmonary infection

66
Q

How does the CSF differ as a buffer to plasma (blood)

A

Plasma is a better buffer meaning rises in CO2 will have a greater impact on pH in the CSF

67
Q

what is central chemoreceptors not sensitive to?

A

PaO2

MD3001 Week 8 (7 decks)

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