17- Control of Breathing

Question 1

3 major parts of the respiratory control system

Answer 1

1. Controller: neurons in brainstem that send signals to the respiratory muscles
   - there are multiple sites in the brainstem that have some role in the control for breathing. either in rhythm generation, pattern generation, or chemoreception
2. Effector: components of the system that carry out gas exchange processes (muscles/lungs)
3. Sensor elements: provide feedback and excitatory input (levels of PO2 and PCO2 that are registered by chemoreceptors)

Question 2

Respiratory Controllers

Answer 2

1. rhythm generator
   - timing
   - neurons in brainstem (intrinsic oscillator with info from neuromodulators, temp, exercise, etc.) provides trigger or signal that initiates the respiratory cycle
   - activates pattern generating neurons which provide proper sequential activation of respiratory pump and airway motoneurons
2. pattern formation
   - shaping
   - starts muscle contractions (pump motorneurons in spinal cord and resistance motor neurons in crania)
3. pre-motor neurons
   - integration
4. motoneurons
   - motor output (activating respiratory muscles)

Question 3

Central pattern generator and motoneurons

Answer 3

Prototypical pattern generator

• activates motoneurons in consistent sequence
• motoneurons discharge in a consistent pattern

Question 4

phrenic nerve

Answer 4

activates the diaphragm

Question 5

thoracic nerve

Answer 5

activates external intercostal muscles

Question 6

nerves/muscles during inspiration and expiration

Answer 6

INSPIRATION

• Phrenic nerve activates diaphragm
• thoracic nerve activates external intercostal muscles

EXPIRATION
-thoracic nerve activation of internal intercostal muscles occurs

Question 7

what occurs when the diaphragm gets activated?

Answer 7

esophageal pressure decreases which results in inspiratory airflow to increase inspiratory volume

Question 8

what happens to frequency and tidal volume of breathing when you lesion above the brainstem (separate brainstem from rest of brain)

Answer 8

neither change

• respiratory rhythm and pattern were not affected
• suggesting that more rostral sites are not critical for breathing

Question 9

what happens to frequency and tidal volume of breathing when you lesion in the pons

Answer 9

slowed breathing and increased tidal volume (something to shut off inspiration was messed up)
-neurons within medulla and pons regulate breathing

Question 10

what happens to frequency and tidal volume of breathing when you lesion between the pons and medulla

Answer 10

breathing becomes irregular

-neurons within medulla and pons regulate breathing

Question 11

what happens to frequency and tidal volume of breathing when you lesion between the medulla and the spinal cord

Answer 11

• breathing completely stopped

- minimum substrate for breathing was rostral to the spinal cord

Question 12

Vagus Nerve and breathing control

Answer 12

important determinant of respiratory rhythm and pattern

Question 13

Pre-Botzinger Complex

Answer 13

-critical site for respiratory
rhythm generation.

-respiratory frequency ceased after the caudal border of this area was lesioned.

Question 14

explain the plasticity of rhythm generating mechanisms

Answer 14

Weekly neurotoxin preBötC injections

• Progressive increasing doses
• Incrementally totally destroyed the pre-BötC.
• Within a day after each injection, breathing was normal.

Respiratory control system is highly “plastic” because if given time for “remodeling”, breathing is normalFigure 7 without the preBötC.

Question 15

How does rhythm generator work?

Answer 15

Neurons active in different phases of respiratory cycle

-individual brainstem respiratory neurons active in one of three phases (inspiration, late inspiration, expiration)

Question 16

network model of rhythm generation

Answer 16

network of neurons
-interconnected for reciprocal inhibition

-maybe be exclusively in preBotC or may include more rostral neurons

Question 17

network model of pattern generation

Answer 17

• no definitive site or mechanism
• mediated by network of interacting neurons
• rhythm and pattern might be generated by same network

Question 18

Postulated scheme for coordination of respiratory and non-respiratory behaviors

Answer 18

• same parts used for both respiratory and non-respiratory functions so we need some way to control which is acting when
• there are multiple different triggers (respiratory, cough, swallow, sneeze, vomit, speech) that go into the pattern generator and whichever of the signals is the strongest is what the respiratory muscles do (perform behavior with highest priority)

Question 19

breathing vs vomiting

Answer 19

breathing
-Inspiratory and expiratory muscles and brainstem neurons are activated in different phases of a breath

vomiting
-muscles and neurons are both activated simultaneously during two different phases

Question 20

pulmonary functional residual volume is

Answer 20

the lung volume reflecting the balance b/w the tendency of the lungs to completely collapse and the chest wall to expand to 60% of vital capacity