Pulmonary Physiology: Control of Respiration

Question 1

Transection of the spinal cord above the origin of the _________ nerves at C1 stops breathing.

Answer 1

phrenic nerves

Question 2

Where are the centers for autonomic control of breathing located? Where are the centers for voluntary control located?

Answer 2

Autonomic centers are in the medulla.

Voluntary control originates in the cerebral cortex.

Question 3

What is eupnea?

Answer 3

Normal breathing

Question 4

What is hyperpnea?

Answer 4

Increased rate AND depth

Question 5

What is Cheyne-Stokes respiration?

Answer 5

Abnormal breathing characterized by tidal volume fluctuation and periodic apnea. Indicative of a severe CNS disorder.

Question 6

What is Kussmaul breathing?

Answer 6

Regular rapid rate with large tidal volume due to metabolic acidosis.

Question 7

What is ataxic breathing?

Answer 7

Highly irregular inspirations usually separated by long periods of apnea. Seen with lesions in the medulla.

Question 8

What is apneusis?

Answer 8

Prolonged inspirations separated by brief expirations.

Question 9

What are the two groups of nerves called located in the medulla that are responsible for autonomic control of breathing?

Answer 9

Dorsal respiratory group (DRG) and ventral respiratory group (VRG)

Question 10

Afferent signals come into the DRG in the medulla via the ______ and ________ nerves.

Answer 10

vagus and glossopharyngeal nerves

Question 11

Have experiments shown that the pons can be severed from the medulla while still preserving basic breathing patterns?

Answer 11

Yeah

Question 12

Describe how action potentials from the DRG affect breathing.

Answer 12

The DRG generates a RAMP SIGNAL (APs that progressively increase in frequency over ~3 seconds), which initiates inspiration. The ramp signal stimulates phrenic nerve activity, which sends APs to the diaphragm for contraction and inspiration. The APs suddenly stop for ~3 seconds, allowing for exhalation.

Question 13

What two major connections does the DRG make with other nerves?

Answer 13

1. Phrenic nerve –> diaphragm

2. Spinal nerves –> EXTERNAL intercostals and scalenes (that contract for inspiration)

Question 14

What connections does the VRG make with other nerves?

Answer 14

VRG makes connections with phrenic nerve and spinal nerves also but this is poorly understood.

It also sends out motor neurons to upper respiratory muscles (larynx, pharynx, mouth, nostrils, etc.) that activate during heavy breathing.

Question 15

From which respiratory group (DRG or VRG) does expiratory output come from?

Answer 15

VRG exclusively. It stimulates INTERNAL intercostals and abdominal muscles for expiration.

Question 16

What is the Botzinger complex?

Answer 16

A section in the upper part of the VRG that may act as a respiratory rhythm generator, containing pacemaker cells that are thought to excite the DRG to make ramp signals.

Question 17

What is the apneustic center and what does it do?

Answer 17

It is located in the lower pons and may exhibit an excitatory effect on the DRG and VRG and prolong ramp potentials.

Question 18

What is the pneumotaxic center and what does it do?

Answer 18

It is located in the upper pons and it switches off inspiration when activated.

Question 19

What are the two main peripheral structures/things that respond to PaO2, PaCO2, and arterial pH?

Answer 19

The aortic and carotid bodies.

Question 20

How do the aortic and carotid bodies work?

Answer 20

Located in the aortic arch and carotid bifurcation, they contain Type 1 Glomus cells (specialized nerve cells that send APs in response to low PaO2, low pH, or high PaCO2) that travel to the DRG via cranial nerves IX (glossopharyngeal) and X (vagus) to increase ventilation.

Question 21

Which of the two peripheral chemoreceptors (aortic bodies or carotid bodies) are more sensitive to hypoxia?

Answer 21

The carotid bodies are more sensitive to hypoxia

Question 22

Why is the DRG response to increase ventilation much more sensitive to increased PaCO2 than to low PaO2?

Answer 22

The body is more resistant to low PaO2 levels because Hb has a reserve O2 storage that doesn’t run out until PaO2 levels get quite low.

Question 23

Is there a stronger increase in ventilation by the DRG if PaCO2 is high concomitantly with low PaO2 levels?

Answer 23

Yeah

Question 24

How do central (CNS) chemoreceptors work when H+ ions don’t cross the blood-brain barrier?

Answer 24

CO2 can cross the BB barrier, which then combines with H2O to make H2CO3 –> H+ + HCO3-. The increase in H+ in the CSF (lower pH) triggers the receptors, which provide input to the DRG.

Question 25

What is the Hering-Breuer Reflex?

Answer 25

Mechanoreceptors within the tracheobronchial tree fire when lung volume increases –> vagus nerve to the pneumotaxic center –> TERMINATION of inspiration. Protective against overinflation of the lungs.

Question 26

What can happen is the Hering-Breuer reflex doesn’t work?

Answer 26

Apneustic breathing (deep and prolonged inspiration)

Question 27

Are there rapidly-adapting stretch receptors in the upper airways, lung parenchymal tissues and in extrapulmonary airways that respond to distension of the tissue and irritation?

Answer 27

Yeah

Question 28

Where are receptors for the sneeze reflex located?

Answer 28

In the nasal mucosa and pharynx

Question 29

Where are receptors for coughing located?

Answer 29

Larynx, trachea, and bronchi

Question 30

What is the main difference between how a sneeze works vs how a cough works?

Answer 30

With a cough, pressure is built up against a closed glottis, which opens to rapidly expel pressurized air. With a sneeze, the glottis doesn’t close.

Question 31

Where are irritant receptors located and what do they do?

Answer 31

They are scattered throughout airway epithelium and respond to chemicals like SO2, NH3, NO2, particles, smoke, cold air. They also respond to histamine and leukotrienes. Stimulation –> respiratory centers to constrict airways and promote rapid, shallow breathing to limit penetration of noxious agents.

Question 32

What are J receptors?

Answer 32

Small, unmyelinated receptors within alveoli and lower conducting airways that respond to interstitial edema and engorgement of pulmonary capillaries. When stimulated, they mediate closure of the larynx and apnea followed by rapid, shallow breathing.

Question 33

How do J receptors respond to pulmonary embolism?

Answer 33

If that happens they trigger tachypnea.

Question 34

What are the chest wall mechanoreceptors and what do they do?

Answer 34

They include muscle spindles in ribs and inspiratory muscles and when they detect impediments to breathing in the chest wall they stimulate increased respiratory activity. Some project to the cortex of the brain to provide conscious sensation of respiratory movements.

Question 35

Input from the ________ can override autonomic control of breathing.

Answer 35

cortex

Question 36

Does the CNS balance ventilation with non-respiratory activities like walking, eating, talking, vomiting, etc.?

Answer 36

Yeah

Question 37

Can voluntary control of breathing be overridden by autonomic control? Name an example.

Answer 37

Yeah - example is voluntary breath holding will be overcome by ventilatory drive from chemoreceptors.