Neural Control of Breathing

Question 1

What part of the brain contains the primary respiratory control centers?

Answer 1

The brainstem (specifically, the medulla and pons).

Question 2

What does the Dorsal Respiratory Group (DRG) do?

Answer 2

Controls inspiration by sending rhythmic signals to the diaphragm and external intercostals via the phrenic nerve.

Question 3

Where is the DRG located?

Answer 3

In the nucleus tractus solitarius (NTS) of the medulla.

Question 4

What does the Ventral Respiratory Group (VRG) control?

Answer 4

Primarily expiration and forced breathing; active during exertion.

Question 5

Where is the VRG located?

Answer 5

Anterior and lateral to the DRG in the medulla.

Question 6

What does the Pre-Bötzinger Complex do?

Answer 6

Acts as a central pattern generator for the basic rhythm of breathing.

Question 7

What is the function of the Botzinger Complex?

Answer 7

Provides expiratory inhibition of inspiration, shaping the respiratory rhythm.

Question 8

What role does the Pontine Respiratory Group (PRG) play?

Answer 8

Modulates the rhythm of breathing and transitions between inspiration and expiration (formerly called the pneumotaxic center).

Question 9

What do central chemoreceptors respond to?

Answer 9

Changes in pH of the cerebrospinal fluid (CSF), driven by CO₂ diffusion across the blood-brain barrier.

Question 10

Where are central chemoreceptors located?

Answer 10

In the ventral surface of the medulla, near the VRG.

Question 11

What do peripheral chemoreceptors detect?

Answer 11

Decreased PaO₂, increased PaCO₂, and decreased pH (especially in metabolic acidosis).

Question 12

Where are peripheral chemoreceptors found?

Answer 12

Carotid bodies (CN IX) and aortic bodies (CN X).

Question 13

Why do central chemoreceptors dominate in long-term regulation of ventilation?

Answer 13

Because they respond directly to CSF pH, which is tightly linked to CO₂ levels.

Question 14

How do opiates (e.g., fentanyl) affect respiratory centers?

Answer 14

Suppress activity in the medulla, reducing responsiveness to CO₂.

Question 15

What is the respiratory risk of benzodiazepines?

Answer 15

They enhance GABA activity but rarely cause fatal respiratory depression unless combined with other depressants.

Question 16

What is the effect of barbiturates on breathing?

Answer 16

Profound suppression of respiratory drive by direct inhibition of medullary centers.

Question 17

Why are volatile anesthetics dangerous in respiratory control?

Answer 17

They impair chemoreceptor responsiveness and can reduce spontaneous ventilation.

Question 18

What effect do neuromuscular blockers (paralytics) have on breathing?

Answer 18

Completely paralyze respiratory muscles, requiring mechanical ventilation.

Question 19

How does a brainstem stroke or injury affect breathing?

Answer 19

May cause apnea or irregular breathing due to direct damage to control centers.

Question 20

What effect does high spinal cord injury (above C3-C5) have on respiration?

Answer 20

Can eliminate phrenic nerve output, resulting in loss of diaphragmatic function.

Question 21

How can kyphoscoliosis impair neural control of breathing?

Answer 21

Alters chest wall mechanics and may restrict lung expansion, reducing afferent feedback and ventilatory response.

Question 22

What is the danger of severe acidosis in the CSF?

Answer 22

Excess protons can inhibit neuronal function and shut down respiratory drive.

Question 23

Where does most neural control of breathing occur?

Answer 23

In the brainstem, specifically the medulla, pons, and adjacent areas of the reticular formation.

Question 24

What are the three major respiratory centers in the brainstem?

Answer 24

The Dorsal Respiratory Group (DRG), Ventral Respiratory Group (VRG), and Pontine Respiratory Group (PRG).

Question 25

Where is the DRG located?

Answer 25

In the nucleus tractus solitarius (NTS) of the medulla within the reticular formation.

Question 26

What is the primary function of the DRG?

Answer 26

Controls inspiration, regulates respiratory rate, and processes input from chemoreceptors and baroreceptors.

Question 27

What is the VRG responsible for?

Answer 27

Controls expiration, upper airway tone, and generates the respiratory rhythm through the pre-Bötzinger and Bötzinger complexes.

Question 28

What is the function of the Pontine Respiratory Group (PRG)?

Answer 28

Limits inspiratory time and processes input from stretch and irritant receptors in the lungs and trachea.

Question 29

What happens if the PRG is lesioned?

Answer 29

Results in apneustic breathing: prolonged inspiration and brief expiration.

Question 30

What is reciprocal inhibition in the context of breathing?

Answer 30

When the inspiratory center is active, it inhibits the expiratory center and vice versa to avoid simultaneous activation.

Question 31

How do stretch receptors in the lungs affect breathing?

Answer 31

Send signals via the vagus nerve to limit inspiration (Hering-Breuer reflex).

Question 32

What type of feedback loop is used in neural breathing control?

Answer 32

A negative feedback loop, adjusting ventilation to maintain pH, PaCO₂, and PaO₂.

Question 33

Where are peripheral chemoreceptors located?

Answer 33

In the carotid bodies and aortic bodies.

Question 34

What do peripheral chemoreceptors respond to?

Answer 34

Decreased PaO₂, increased PaCO₂, and low pH.

Question 35

Through which nerves is peripheral chemoreceptor input transmitted?

Answer 35

Glossopharyngeal (CN IX) from the carotid body and Vagus (CN X) from the aortic body.

Question 36

Where are central chemoreceptors located?

Answer 36

In the ventral medulla, near the VRG.

Question 37

What do central chemoreceptors primarily detect?

Answer 37

Protons (H⁺) in cerebrospinal fluid (CSF), indirectly reflecting CO₂ levels.

Question 38

Why do central chemoreceptors respond more slowly to nonvolatile acids like lactic acid?

Answer 38

Because these acids (and their protons) cross the blood-brain barrier very slowly.

Question 39

What triggers an increase in tidal volume before respiratory rate during exertion?

Answer 39

Stronger activation of Aα motor neurons by inspiratory centers in the brainstem.

Question 40

Which neurons innervate respiratory muscles?

Answer 40

Aα motor neurons — fast, large, myelinated neurons that allow immediate muscle response.

Question 41

Why is motor block a sign of effective local anesthesia?

Answer 41

Motor fibers are larger and harder to block, so blocking them likely means sensory fibers are also affected.

Question 42

What part of the brain allows voluntary breathing override?

Answer 42

Motor cortex and frontal lobe, which send input to brainstem respiratory centers.

Question 43

What causes a loud cough, and why is it significant?

Answer 43

Strong muscle recruitment and good lung function; can move up to 2L of air.

Question 44

What effect does pain have on ventilation?

Answer 44

Can cause tachypnea or brief apnea, depending on stimulus and location.

Question 45

What effect does exercise planning have on breathing?

Answer 45

Cerebral cortex preemptively increases ventilation, even before blood gas changes occur.

Question 46

What happens during hypercapnia (high CO₂)?

Answer 46

Immediate increase in ventilation and cerebral vasodilation to enhance CO₂ clearance.

Question 47

What happens to arterial pressure during hypercapnia or acidosis?

Answer 47

It increases due to increased cardiac output and sympathetic tone.

Question 48

What is the normal CSF pH?

Answer 48

Approximately 7.31–7.32, lower than arterial pH due to higher CO₂.

Question 49

Why is the CSF pCO₂ higher than in blood?

Answer 49

Because the brain produces CO₂ and it must diffuse through CSF before entering circulation.

Question 50

What makes bicarb less effective in CSF buffering?

Answer 50

Low protein content in CSF compared to plasma.

Question 51

What cells regulate CSF composition?

Answer 51

Glial cells, particularly astrocytes, help maintain pH and bicarb balance.