Respiratory Physiology: Control of Breathing

Question 1

Pre-Botzinger Complex

Answer 1

Believed to be the site which generates the timing (frequency) of the respiratory rhythm.

Question 2

In the 1920’s, it was observed that lesions of
the PRG also changed respiratory timing.

Answer 2

• When the PRG is lesioned, we lose the ability to turn inspiration off without additional sensory information from the vagus nerves.
• The PRG is therefore considered part of the network that controls the length of inspiration under normal circumstances

Question 3

Dorsal Respiratory Group (DRG)

Answer 3

• 95% premotor to phrenic
• receives lots of sensory info.

Question 4

Ventral Respiratory Group (VRG)

Answer 4

• rostral (red): premotor to phrenic, other inspiratory m.
• Caudal (blue): premotor to upper airway, other muscles of expiration.

Question 5

Describe the four major respiratory centers in the brainstem, comparing and contrasting their locations and hypothesized roles in respiratory control.

Answer 5

• Pre-Botzinger
• Medullary
• Generates ‘core’ rhythm

• Pontine Respiratory Group
• Pons
• Modifies inspiratory timing (activity turns off inspiration)

• Dorsal Respiratory group
• Medullary
• Depth of breathing (tidal volume)
• Ventral Respiratory group
• Medullary
• Inspiration and Expiration
• Depth

Question 6

Pontine damage

Answer 6

Apneusis (Maintained inspiratory discharge)

Question 7

Central Chemoreceptors

Answer 7

Located on ventral surface of medulla sensitive (indirectly) to CO2 in blood.

CO2 + H2O -> H2CO3 (using carbonic anhydrase) -> H+ and HCO3-

Question 8

Peripheral Chemoreceptors

Answer 8

Located in Aortic Arch and Carotid Body

Oxygen sensitivity

Increased f.r. of
afferents from carotid
body/aortic arch

Increased f; Vt

Question 9

Slowly Adapting Pulmonary Stretch Receptors

Answer 9

• Located in airways
• Sensitive to: Stretch of airways (directly proportional to lung volume)
• Fibers travel to brain in Vagus nerve.
• Effect: inhibition of inspiration (inspiratory termination) and prolongation of expiration.

Question 10

The Slowly-adapting Pulmonary Stretch Receptors are important for controlling respiration in:

Answer 10

• Infants
• Adults during exercise

They are probably not crucial in
controlling tidal volume in adults at rest.

Question 11

The mechanoreceptors

Answer 11

1. Slowly Adapting Pulmonary Stretch Receptors
2. Rapidly Adapting Pulmonary Stretch Receptors
3. J Receptors

Question 12

Rapidly Adapting Pulmonary Stretch Receptors

Answer 12

• Located in airways
• Sensitive to: Irritation, foreign bodies in airway; Stretch
• Fibers travel to brain in Vagus nerve.
• Effect: COUGH

Question 13

J Receptors

Answer 13

• Located near blood vessels of alveoli
• Sensitive to: Pulmonary Edema
• Fibers travel to brain in Vagus nerve.
• Effect: cough, tachypnea

Question 14

Cortical Influences on Breathing

Answer 14

In these cases, the cortex appears to be bypassing the medullary centers completely and sending input directly to the muscles of respiration.