Control of Respiration

Question 1

Where is the major respiration rhythm generation located?

Answer 1

Medulla Oblongata

Question 2

What network of neurones generates the breathing rhythm?

Answer 2

Pre-Bötzinger Complex

Question 3

What type of activity do the neurones in the Pre-Bötzinger complex display?

Answer 3

Pacemaker activity

Question 4

Where is the Pre-Bötzinger complex located?

Answer 4

Near the upper end of the medullary respiratory centre

Question 5

How does the Pre-Bötzinger complex generate inspiration?

Answer 5

It excites the dorsal respiratory group neurones, whose firing leads to contraction of inspiratory muscles –> inspiration

Question 6

What happens when the firing of the dorsal respiratory group neurones stops?

Answer 6

Passive expiration

Question 7

How is hyperventilation/active inspiration initiated?

Answer 7

Increased firing of dorsal neurones excites ventral respiratory group neurones which stimulate the accessory muscles of breathing –> Forceful expiration

Question 8

Which centre in the pons modifies rhythm?

Answer 8

Pneumotaxic centre

Question 9

What does the pneumotaxic centre lead to?

Answer 9

Termination of inspiration

Question 10

When is the pneumotaxic centre stimulated?

Answer 10

When the dorsal respiratory group neurones fire

Question 11

What could be the consequence of the pneumotaxic centre NOT inhibiting inspiration?

Answer 11

Apneusis - breathing would consist of prolonged inspiratory gasps with brief expiration

Question 12

What do impulses from the apneustic centre lead to?

Answer 12

Excitation of the inspiratory area of the medulla; prolonging inspiration

Question 13

From where do higher brain centres send stimuli to control respiration?

Answer 13

Cerebral cortex
Limbic system
Hypothalamus

Question 14

What is the Hering-Breuer Reflex?

Answer 14

Pulmonary stretch receptors are activated during inspiration if tidal volume is much greater than 1L. Afferent discharge inhibits inspiration to prevent over-inflation of lungs during hard exercise

Question 15

Where are joint receptors located?

Answer 15

In the veins

Question 16

What do impulses from moving limbs sent to joint receptors lead to?

Answer 16

Increase breathing

Question 17

What stimulates juxta-pulmonary receptors (J-receptors)?

Answer 17

Pulmonary capillary oedema or pulmonary embolism

Question 18

What does stimulation of J-receptors leads to?

Answer 18

Rapid shallow breathing

Question 19

What results when baroreceptors sense a decrease in BP?

Answer 19

Increased ventilatory rate

Question 20

Which factors may increase ventilation during exercise?

Answer 20

Reflexes from body movement
Adrenaline release
Impulses from cerebral cortex
Increase in body temperature
Later on: Accumulation of carbon dioxide and hydrogen ions

Question 21

Explain the Cough Reflex

Answer 21

Irritation/tightening of the airways leads to afferent discharge stimulating the sequence:
a short breath intake
closure of the larynx
contraction of abdominal muscles (increasing intra-alveolar pressure)
Opening of the larynx
Expulsion of air at high speed

Question 22

What is the physiological benefit of the cough reflex?

Answer 22

Helps clear airways of dust, dirt or excessive secretions

Question 23

Where is the cough reflex centred?

Answer 23

In the medulla oblongata

Question 24

Chemical control of respiration involves negative feedback control of mainly _______ blood cast tension which is measured by chemoreceptors.

Answer 24

Carbon dioxide

Question 25

What do peripheral chemoreceptors sense?

Answer 25

Tension of oxygen and carbon dioxide and hydrogen ions in the blood

Question 26

Where are central chemoreceptors situated?

Answer 26

Near the surface of the medulla of the brainstem

Question 27

What do central chemoreceptors respond to?

Answer 27

Hydrogen ions of the CSF

Question 28

Out of the following, which diffuses readily across the BBB?

• Hydrogen ions
• Bicarbonate
• Carbon dioxide

Answer 28

Carbon dioxide

Question 29

How is bicarbonate formed

Answer 29

CO2 + H2O H2CO3 H+ + HCO3-

Question 30

What accumulates very quickly during hypercapnia and hyperventilation?

Answer 30

Carbon dioxide

Question 31

What does an accumulation of CO2 stimulate via central chemoreceptors?

Answer 31

Initiation of mechanisms to increase breathing - increase volume of air inspired per minute

Question 32

What is the hypoxic drive of Respiration?

Answer 32

When partial pressure of oxygen in arterial blood is low, ventilation increases

Question 33

Over which receptors does the hypoxic drive of respiration take place?

Answer 33

Peripheral chemoreceptors

Question 34

Below which level doe PO2 have to fall for peripheral chemoreceptors to be activated?

Answer 34

<8 kPa

Question 35

When does hypoxic drive become important?

Answer 35

CO2 retention / Type II Respiratory Failure

Question 36

What causes hypoxia at high altitudes?

Answer 36

Decreased partial pressure of inspired oxygen (PiO2)

Question 37

What is the acute response to hypoxia at high altitudes?

Answer 37

Hyperventilation and increased cardiac output

Question 38

What condition is caused by high altitude hypoxia?

Answer 38

Acute Mountain Sickness

Question 39

What are the symptoms of acute mountain sickness?

Answer 39

Headache
Fatigue
Nausea
Tachycardia
Dizziness
Sleep disturbance
Exhaustion
Dyspnoea
Unconsciousness

Question 40

What are chronic adaptation to high altitudes?

Answer 40

Increase in RBC production (polycythaemia)
Increase in 2,3 BPG produced within RBCs
Increase in number of mitochondria
Acid conservation by kidneys

Question 41

The hydrogen ion drive effect is via which receptors?

Answer 41

peripheral chemoreceptors

Question 42

How do peripheral chemoreceptors adjust for acidosis caused by addition of non-carbonic acid hydrogen ions to the blood?

Answer 42

Hyperventilation and increased CO2 elimination reducing the H+ load in the body