Control of Ventilation

Question 1

How are the skeletal muscles of inspiration stimulated

Answer 1

diaphragm = phrenic nerves

intercostal muscles = intercostal nerves

Question 2

Where is ventilation controlled in the brain

Answer 2

in ill-defined centres in the pons (superior) and medulla (inferior)

Question 3

What is the function of respiratory centres in the brain

Answer 3

• automatic rhythm of breathing set by smooth repetitive bursts of action potentials in the DRG which travel to inspiratory muscles

Question 4

What is the function of the DRG

Answer 4

• dorsal respiratory group

- output to inspiratory muscles

Question 5

What is the function of the VRG

Answer 5

• ventral respiratory group
• output to expiratory muscles during high respiratory load
• output to some inspiratory muscles to maintain their tone in order to maintain airway patency
• for smooth/controlled expiration

Question 6

How can respiratory centres have their rhythm modulated

Answer 6

• emotion via limbic system
• voluntary override via higher centres
• mechanosensory input from the thorax (stretch reflex)
• chemical composition of the blood via chemoreceptors

Question 7

What is the function of the stretch reflex that comes about from mechanosnesory input

Answer 7

acts as a safety mechanism to prevent over-inflation of the lung

Question 8

Which factor has the most significant effect on the respiratory rhythm

Answer 8

chemical composition of the blood that is detected and acted upon by chemoreceptors

Question 9

What do central chemoreceptors respond to

Answer 9

CSF H+ (directly reflects PCO2)

Question 10

What do peripheral chemoreceptors respond to

Answer 10

Plasma H+ and PO2

Question 11

Where are central chemoreceptors located

Answer 11

in the medulla

Question 12

How do central chemoreceptors work

Answer 12

• increased PCO2 causes CO2 to cross the blood brain barrier into the CSF
• bicarbonate and H+ are formed
• receptors respond to increased H+ levels
• ventilation increases

Question 13

Where are peripheral chemoreceptors located

Answer 13

in the carotid and aortic bodies

Question 14

How do peripheral chemoreceptors work

Answer 14

• detect changes in arterial PO2 and H+

- causes increased ventilation following fall in blood PO2 or an increase in blood H+

Question 15

What does an increase in arterial H+ usually accompany

Answer 15

a rise in arterial PCO2 (acidosis)

Question 16

How do changes in plasma pH alter ventilation

Answer 16

• via the peripheral chemoreceptor pathways
• plasma pH falls (increased H+), ventilation stimulated
• plasma pH increases (H+ falls), ventilation inhibited

Question 17

How can voluntary control over breathing be exhibited

Answer 17

via descending neural pathways from the cerebral cortex to respiratory motor neurons

Question 18

What stimuli cannot be overridden

Answer 18

involuntary stimuli;

• arterial PCO2
• arterial H+