Lecture 5C

Question 1

Breathing is an involuntary process? What parts of the brainstem controls it

Answer 1

Yes. The medulla and pons ultimately control breathing

Question 2

What three groups of neurons or brainstem centers regulate breathing

Answer 2

Medullary Respiratory Center
Apneustic Center
Pneumotaxic Center

Question 3

What two groups are found within the Medullary Respiratory Center?

Answer 3

Dorsal Respiratory group (DRG)

Ventral Respiratory group (VRG)

Question 4

What is the DRG responsible for?

Answer 4

Primarily responsible for inspiration and generates the basic rhythm for breathing

Question 5

What two cranial nerves give input to the DRG and what kind of information does each give?

Answer 5

CN X –> peripheral chemoreceptors and mechanoreceptors

CN IX–> Peripheral chemoreceptors

Question 6

Output from the DRG travels how and where?

Answer 6

Via the phrenic nerve to the diaphragm and external intercostals

Question 7

What is VRG responsible for?

Answer 7

Primarily responsible for expiration

Question 8

When is the VRG active?

Answer 8

When expiration becomes an active process, Like during exercise. It is not active during normal, quiet breathing when expiration is passive

Question 9

What muscles contract when DRG is active?

Answer 9

Diaphragm and External intercostals actively contract. Normal INSPIRATION

Question 10

Where is the Apneustic Center located in the brainstem?

Answer 10

In the lower pons

Question 11

What is the role of Apneustic Center?

Answer 11

Stimulates inspiration, producing deep and prolonged inspiratory gasps (apneusis), followed by occasional brief exhalations

Question 12

Explain the mode by which the Apneustic center functions

Answer 12

Stimulations of these neurons apparently excites the inspiratory center in the medulla, prolonging the period of action potentials in the phrenic nerve, and thereby prolonging the contraction of the diaphragm

Question 13

Where is the Pneumotaxic center located?

Answer 13

In the upper pons

Question 14

What is the role of Pneumotaxic center?

Answer 14

• Inhibits inspiration and limits the burst of action potentials in the phrenic nerve
• Does this by limiting the size of the Tidal volume

Question 15

Does the Cerebral cortex have a role in Breath?

Answer 15

Yes it can temporarily override the brainstem centers. For example, a person can voluntarily hyperventilate.

Question 16

What happens to the pressures in hyperventilation?

Answer 16

Decrease in PaCO2, which causes arterial pH to increase. Hyperventilation is self-limiting because the decrease in PaCO2 will produce unconsciousness and person will revert to a normal breathing pattern

Question 17

Can a person hypoventilate?

Answer 17

Yes but it is difficult. This causes a decrease in PaO2 and an increase in PaCO2 both of which are strong drives for ventilation.

Question 18

Where are the central chemoreceptors found?

Answer 18

Bilaterally in the ventrolateral medulla

Question 19

Where are the peripheral chemoreceptors found?

Answer 19

In the aortic arch and carotid arteries

Question 20

Which chemical influencing respiration is the most potent and most closely controlled

Answer 20

CO2

Question 21

What is the normal arterial Pco2

Answer 21

40 mmHg with a +- 3 mmHg

Question 22

A decrease in pH of the CSF produces what?

Answer 22

Increase in breathing rate (hyperventilation)

Question 23

Does H+ cross the BBB?

Answer 23

Not as well as CO2 does

Question 24

Why does Co2 diffuse from arterial blood into the CSF?

Answer 24

it is lipid-soluble and readily crosses the BBB

Question 25

How does CO2 act on central chemoreceptors?

Answer 25

CO2 combines with H20 in CSF to produce H+ and HCO3-. The resulting H+ acts directly on the central chemoreceptors

Question 26

What is the enzyme that converts CO2 to HCO3-?

Answer 26

Carbonic Anhydrase

Question 27

Increases in Pco2 and H+ stimulate what?

Answer 27

breathing while decreases in Pco2 and H+ inhibit breathing

Question 28

Peripheral chemoreceptors are sensitive to what?

Answer 28

Arterial O2

Question 29

How much of an effect does declining Po2 have on ventilation?

Answer 29

A slight effect and mostly limited to enhancing the sensitivity of peripheral receptors to increased Pco2

Question 30

What must happen for O2 levels to become a major stimulus for increased ventilation?

Answer 30

Arterial Po2 must drop substantially to at least 60 mm Hg

Question 31

Increases in arterial Pco2 stimulate peripheral chemoreceptors to do what?

Answer 31

Increase breathing rate

Question 32

Which is more important, the response of peripheral chemoreceptors to Co2 or response of central chemoreceptors to Co2?

Answer 32

Response of the central chemoreceptors to Co2 (or H+)