Respiratory 3

Question 1

The Basics of Neural Control of Breathing
- Healthy people do not need to make a conscious effort to breath It is initiated and controlled by the —- nervous system
Breathing is a —- activity

Answer 1

autonomic

rhythmic

Question 2

What happens in inspiration and expiration?

Answer 2

Inspiration:
Respiratory muscles contract

Expiration:
Respiratory muscles relax and lungs empty primarily though elastic recoil

Question 3

What are the 3 respiratory muscles?
What type of muscle are they?
What input do they require?

Answer 3

Diaphragm, intercostals, abdominals.

Skeletal.

Require neural input for stimulation.

Question 4

What nerve innovates the diaphragm?
Where does this nerve originated from?
What innervates the intercostal muscles?

Answer 4

Phrenic nerve.

From the brain stem between cervical vertebrae C2 and C5.

Segmental spinal nerves.

Question 5

Where is the basic rhythmicity of breathing generated?

Answer 5

Medulla oblongata

Question 6

How do these brain centres initiate and regulate breathing?

• explain the DRG

Answer 6

There is a dorsal respiratory group on either side of the medulla.
This contains the inspiratory neurones.
These demonstrate rhythmic activity and stimulate inspiratory muscles.
Dorsal respiratory group also receives afferent inputs from lung receptors via the vagus nerve.

Question 7

Explain the VRG

where does it also receive inputs from?

Answer 7

Ventral Respiratory Group:
- Either side of the medulla
- VRG contains neurons with a degree of spontaneous rhythmic electrical pacemaker activity
- VRG contains neurons that stimulate respiratory muscles to initiate:
Inspiration = inspiratory neurons
Expiration = expiratory neurons

VRG also receives inputs from DRG and central chemoreceptors.

Question 8

The medulla has neurons for what?

Answer 8

Recognise changes in gas concentrations in the blood.

Question 9

Explain how the ventral and dorsal respiratory group work together
- in normal quiet breathing

Answer 9

They form the central respiratory rhythm generator.

Inspiratory and expiratory neurons tend to inhibits each other, inspiratory neurons are more active. Net result is more stimulation of inspiratory neurons as these are more active - more stimulation of inspiratory muscles in quiet breathing.

Question 10

During normal quiet breathing, what stimulates inspiratory neurons causing contraction of inspiratory muscles?

Answer 10

Respiratory rhythmic generator

Question 11

How does expiration mainly occur?

Answer 11

By passive elastic recoil, so neurone activity is minimal.

Question 12

What happens to expiratory muscles during exercise?

Give the key point about this

Answer 12

Expiratory neurons are actively stimulated, thus stimulating expiratory muscles (abdominals).

Mutual inhibition of inspiratory and expiratory neurons results in alternate stimulation of inspiratory and expiratory muscles.

Question 13

Where does the pons receives input from and what are the two centres of the pons region?

Answer 13

Receives input from cerebrum and hypothalamus and feed them into the medullary respiratory centre.

• pneumotaxic centre (smooth transitions between inspiration and expiration by regulating apneustic and DoralRespiratoryGroup
• apneustic centre (stimulates the DRG to promote inspiration, thus increasing breath duration

Question 14

Where is pons found and what does it add to the medulla?

Answer 14

Found about the medulla.

Offers a fine-tuning of the basic rhythmicity generates in the medulla.

Question 15

What are the two systems that lead to a change in temperature and emotional state?

What takes over in hyperventilation?

Answer 15

Hypothalamus and limbic system.

Limbic system

Question 16

Why does someone need voluntary control?

Explain this

Answer 16

Damage to the brain stem - means they can still breathe.

The voluntary system can over-ride the respiratory centre.
Motor neurons in the cerebral cortex concoct directly to motor nerves supplying the respiratory muscles, in the spinal column, bypassing the medulla.
Important in speech, which eating, diving.

Question 17

Explain how stretch receptors work in the lungs

Answer 17

Inspiration stretches airways which activates stretch receptors in bronchial smooth muscle. The vagus nerve sends impulses to dorsal respiratory group are inhibited. This inhibits further inspiration giving expiration to occur
(negative feedback).

Question 18

What is the name of the reflex which can sense where the lungs stop being inflated?

Answer 18

Hering-Breur Inflation reflex

This is important in exercise to give the body time to breath out again when you are taking deep breaths.

Question 19

Explain irritant receptors in the lungs

Answer 19

Irritant chemicals&smoke and dust activated the irritant receptors between epithelial cells. Vagus nerve sends impulses to medullae which either causes…

• coughing (help remove irritants)
• bronchoconstriction (prevent irritants from getting into alveoli)
• stimulates surfactant release&deep augmented breaths (prevents slow collapse of lungs)

Question 20

What neurones are activated in the dorsal and ventral respiratory groups?

Answer 20

Dorsal - inspiratory neurones

Ventral - inspiratory and expiratory neurones

Question 21

What is alveolar PCO2 determined by?

Answer 21

Balance between ventilation and carbon dioxide production.

Question 22

Explain hyper-ventiliation

• what is it in proportion to?
• what two things can it lead to?

Answer 22

• In proportion to metabolism
• Can lead to hypocapnia (lowers arterial PCO2 below normal levels) and respiratory alkalosis (less bicarbonate produced)

Question 23

What does low PCO2 cause and what are the effects of this?

Answer 23

Causes cerebral vasoconstriction and this causes cerebral hypoxia and dizziness.

Question 24

What can hypo-ventilation lead to?

Answer 24

• hypercapnia (raise in arterial PCO2)
• respiratory acidosis
• hypoxia

Question 25

explain chemical control of breathing

Answer 25

Metabolism by tissues results in carbon dioxide production and oxygen consumption and H+ production.
The most important of these is PCO2.

Question 26

How do PCO2 changes affect respiration?

Answer 26

Increase in PCO2, linear increase in ventilation.
Small increases in PCO2 has a large affect on ventilation rate. Ventilation never goes to zero even at very low PC02 (so death does not occur!)
Depression at very high PCO2 because this means that breathing uses more oxygen in the skeletal muscle than it is taking in (counter-productive).

Question 27

Acidosis
Hard physical exercise, producing —- acid in muscle, thus lowering pH. This is normal and transien.t
Patho-physiological situations such as HCO3- loss in —- disease or in gut due to diarrhoea or diabetes.
These are examples of —- acidosis

Metabolic alkalosis
Occurs if there is an increase of pH, e.g. H+ loss from the stomach during —-, or during diuretic use, which causes loss of water but retention of HCO3- in —- space
How do these changes affect the PCO2 – ventilation relationship?
Low pH (acidosis) increases ventilation
High pH (alkalosis) decreases ventilation

Answer 27

lactic

renal

metabolic

vomiting

extracellular

Question 28

On a alveolar PCO2 and ventilation graph, what does acidosis and alkalosis do to to the graph?

Answer 28

Acidosis pushes it left (higher ventilation at lower pCO2).

Alkalosis pushes it right.

Question 29

What is the name for the how PCO2 and PO2 values work?

What fold increase in ventilation do these cause?

• individually mild hypercapnia or hypoxia
• combined mild hypercapnia and hypoxia

Answer 29

Synergy

2 fold increase
6 fold increase

Question 30

What are the two chemoreceptors called?
Where are they found?
What do they detect?

Answer 30

1) Central chemoreceptor found in the medulla. Detect [H+] and PCO2.
2) Peripheral chemoreceptor found in carotid and aortic bodies. Detect PO2, PCO2 and [H+].

Question 31

Where are central chemoreceptors located and how do they indirectly detect changes in blood PCO2?

Answer 31

Located on the ventrolateral surface of medulla, near the entry of the vagus and glossopharyngeal nerves.

They sense pH of cerebrospinal fluid rather than of blood.
Blood-brain barrier prevents permeation of H+ and HCO3- into brain tissue.
CO2 is free to cross the blood-brain barrier.
Conversion back to H+ and HCO3- means that H+ IN css is directly proportional to PCO2 in blood.

Question 32

Where are peripheral chemoreceptors found?

Details

Answer 32

• Aortic and carotid bodies

Aortic bodies present on upper part of the aortic arch and innervated by the vagus.
Carotid body present at the top of the bifurcation of the common carotid artery, innervated by the carotid sinus nerve.

Question 33

What does the carotid body contain and what does this do?

Answer 33

Glomus cells - respond to decrease in PO2, increase in PO2 and [H+]. Main O2 sensing cells in respiration. .

Upon activation they release dopamine at nerve endings.

Show synergistic response of releasing dopamine to combined stimuli (PO2 and PC02).

Very fast response to acute changes in blood gas pressure such as oscillations in partial pressures during inspiration and expiration.