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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

ā€œJā€ Receptors- pulmonary C-fibres

Irritant receptors of lungs

Proprioceptors

Thermoreceptors

Pain receptors

Cough reflex

Sneezing reflex

Deglutition relfex

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25
What higher centres can override respiratory centres?
Limbic system Hypothalamus
26
Describe the Hering-Breur Reflex
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
27
How does "J" Receptors- pulmonary C-fibres affect respiratory centres?
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
How do irritant receptors of lungs override the respiratory centres?
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
How do proprioceptors change breathing?
Aim is for reflexes form muscles and joints to stabilize ventilation in the face of changing mechanical conditions
30
Where are proprioceptors found in regards to the respiratory system?
In joints to measure velocity of ribs Tendons to detect strength of muscle contraction Muscle spindles to monitor length of fibres
31
What are the function of thermoreceptors?
Cutaneous Supply signals to cerebral cortex, stimulates respiratory centre, hyperventilation
32
What is the function of pain receptors?
Supply signals to cerebral cortex, stimulating respiratory centres and inducing hyperventilation
33
How does the cough reflex change ventilation?
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
How does the sneezing reflex change ventilation?
Irritation of nasal mucous membranes causes a deep inspiration followed by forceful expiration with opened glottis
35
How does the deglutition reflex change breathing?
Respiration arrested during swallowing of food
36
Describe how you can voluntarily control your breathing
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
What do chemoreceptors respond to?
Changes in chemical constituents of blood or CSF
38
What chemical changes can chemoreceptors respond to?
Hypoxia Hypercapnia Increased hydrogen concentration
39
What are the two types of chemoreceptors?
Central chemoreceptors Peripheral chemoreceptors
40
What is hypercapnia?
Elevated carbon dioxide in blood
41
Where are the central chemoreceptors located?
Medulla oblongata close to DRG
42
What is the action of central chemoreceptors?
Sensitive to increase in hydrogen concentration in CSF Sensitive to increase in PaCO2 in blood
43
How does central chemoreceptors detect hydrogen ions in the CSF when hydrogen can't pass across the BBB barrier?
C02 crosses into CSF and forms carbonic acid This is unstable and dissociates into hydrogen and bicarbonate Hydrogen then stimulates central chemoreceptors
44
Where are peripheral chemoreceptors?
Close in location but distinct from baroreceptors
45
What are peripheral chemoreceptors?
Specialised receptor cells that are stimulated primary by a decrease in PO2 and an increase in hydrogen ions
46
What do peripheral chemoreceptors synapse on?
With afferent nerves which run to the brainstem Sensory portion of cranial nerve 10 from aortic bodies Cranial nerve 9 from carotid bodies
47
Which peripheral chemoreceptor is more important in respiration?
Carotid
48
What are peripheral chemoreceptors sensitive to?
PaO2 PaCO2 pH Blood flow Temperature 10x less sensitive than central receptors
49
Where are peripheral chemoreceptors?
Carotid sinus and aortic arch
50
What are peripheral chemoreceptors also known as?
Glomus Cells
51
Describe the pathway in chemoreceptors?
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
What nerve innervates the carotid bodies?
Vagus nerve
53
What nerve innervates the carotid bodies?
Glossopharyngeal nerve
54
What gas measurement is the most important in respiration?
PCO2
55
What is normal PCO2?
40mmHg or 5.3 kPa
56
What happens if there is an increase in PCO2?
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
How can decreased CO2 during hyperventilation signal a decrease in breathing rate?
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
How much must oxygen pressure levels drop in the blood for peripheral chemoreceptors to stimulate ventilation?
From 100mmHg to 60mmHg or 8kPA
59
Why can't you put COPD patients on 100% oxygen masks?
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
How does pH affect ventilation?
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
How does damage to the CNS affect breathing?
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
How does poliomyelitis affect breathing?
25% of patients require mechanical ventilation during acute phase Reinnervation of fibres can recover respiratory strength
63
How does diptheria affect breathing?
Demyelinating neuropathy that can lead to respiratory failure
64
How does botulism affect breathing?
Innervation of respiratory muscles seems particularly vulnerable, ventilation may be required for extended period
65
How does DMD affect breathing?
From age 10 vital capacities declines Nocturnal hypoxaemia develops first Common cause of death is respiratory failure secondary to pulmonary infection
66
How does the CSF differ as a buffer to plasma (blood)
Plasma is a better buffer meaning rises in CO2 will have a greater impact on pH in the CSF
67
what is central chemoreceptors not sensitive to?
PaO2

MD3001 Week 8 (7 decks)

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