Lecture 8 - Neural & Chemical Control of Breathing

Question 1

Where is the respiratory pattern generator (RPG) found & what is its role?
What 3 things does the RPG receive information from?

Answer 1

• RPG is found within the medulla of the hindbrain and produces the rhythmic motor patterns of the respiratory muscles to control RR

1) CN lX - gives chemical information regarding O2, CO2 + pH
2) CN X - gives chemical information regarding O2, CO2 + pH AND lung stretch
3) Central chemoreceptors - gives information regarding CO2 in CSF

Question 2

How does the RPG control the muscles of inspiration & expiration?

Answer 2

• Inspiratory & Expiratory neurones in medulla connect to RPG, and connect to muscles of inspiration . RPG stimulate these neurones at a given frequency (12-20bpm)
• Inhibitory system where inhibitory group inhibits expiratory group of neurones and vice versa to make sure we’re only inspiring or expiring

Question 3

What connections are present to give us voluntary control of breathing?
In what condition do these connections become primary controllers?

Answer 3

• Voluntary connections from the cerebral cortex allow us to override RPG and give us voluntary control of breathing.
• Ondine’s curse - RPG is destroyed so can only breathe voluntarily, which means they need ventilators when sleeping.

Question 4

What do peripheral and central chemoreceptors sense?

What does the information they send to brain respiratory centres adjust?

Answer 4

Peripheral = PO2, PCO2 & pH (primarily PO2)
Central = PCO2 + pH

They send information to brain respiratory centres resulting in adjustment in depth and frequency of ventilation

Question 5

Where are peripheral chemoreceptors found?

What is their major function?

Answer 5

1) In the carotid bodies at the bifurcation of the common carotid arteries (branch of CN lX)
2) In the aortic arch (branch of CN X)

• Both bodies primarily sensitive to changes in PO2, so sense hypoxaemia and signal to medulla to increase ventilation. These are rapid responders, first to respond.

Question 6

How does the response to peripheral chemoreceptor firing of increasing ventilation decrease pH during acidosis?

Answer 6

• Low PO2/High PCO2/Low pH sensed, increased minute ventilation
• Reaction is shifted to the left, reducing H+ levels, increasing pH
• Conversely, if PCO2 is decreased, reaction shifts to right (in respiratory alkalosis) so pH will decrease

Question 7

Where are central chemoreceptors located?

What is their role?

Answer 7

• Located just beneath the ventral surface of the medulla, close to brainstem respiratory centres and on the brain side of the BBB.
• Sense increases in arterial PCO2, and (much more slowly) decreases in arterial pH
• If PCO2 increases, then ventilation increases rapidly thanks to firing of central chemoreceptors.

Question 8

How do central chemoreceptors sense changes in PCO2 and pH?

Answer 8

• BBB separates central chemoreceptors from arterial blood
• BBB has low permeability to HCO- & H+ ions, but high permeability to small molecules such as CO2
• CO2 diffuses in CSF between blood and central chemoreceptors, across BBB
• CNS has limited HCO3- buffering capacity so acidosis develops quickly
• Small decreases in pH raise firing rate of central chemoreceptors increasing minute ventilation

Question 9

Give a summary of chemical control of ventilation

Answer 9

• Peripheral + central chemoreceptors send signals to RPG to adjust minute ventilation.
• Acutely peripheral chemoreceptors quick to respond, and only ones to respond to hypoxaemia (low arterial PO2)
• Both chemoreceptors respond to high PCO2 (hypercapnia) and low pH (acidosis)
• Hypoxaemia, Hypercapnia & Acidosis all cause an increase in minute ventilation, raising PO2, lowering PCO2, normalising pH and correcting imbalances

Question 10

Answer Questions on slide 18-26

Answer 10

No dramas b.

Question 11

Answer Questions on slide 18-26

Answer 11

No dramas b.