Week 21: (C.2) Neuroanatomy & Neurophysiology of breathing

Question 1

What is a respiratory rhythm generator? (RRG)

Answer 1

A network of interneurons that produce a predictable and repetitive motor pattern.
In the case of breathing, inspiratory neurons must be activated before expiratory Neurons

Question 2

What must be activated first inspiratory of expiratory neurones?

Answer 2

RRG must generate inspiratory neurones first

Question 3

Does the RRG need conscious input?

Answer 3

No, it is always active even in the absence of conscious input.

Question 4

What is the name of circuit generating regular and repeated sequences of neural activity?

Answer 4

endogenous
cyclical oscillation
(body’s natural clock)

Question 5

What does the RRG innervate?

Answer 5

respiratory muscles in an orderly sequence

Question 6

What does the RRG respond to inputs from?

Answer 6

parts of the brain
(eg limbic system – emotions)
as well as sensory afferents (eg pulmonary stretch receptors, peripheral
chemoreceptors)

Question 7

What are the 3 phases of breathing cycle?

Answer 7

inspiration
post-inspiration
late expiration

Question 8

What are the 6 types of neural discharge from the RRG?

Answer 8

Pre-I
early-I
I
late-I
early-E
E

Question 9

What happens in phase pre-I?

Answer 9

neurons inhibit expiratory neural circuit

Expiratory muscles relax

Question 10

What happens in phase Early-I?

Answer 10

neurons inhibit output from entire RRG

Refractory period. No breathing movements

Question 11

What happens in I phase?

Answer 11

> Neurons ramp fire. As frequency increases so more I neurons contribute. Activate motorneuron circuit to inspiratory muscles & inhibit E and Pre-I neural circuits
Inspiratory muscles contract as intensity of I firing increases. Exp muscles relaxed

Question 12

What happens in Late-I phase?

Answer 12

> I neurons feed back to suppress I neuronal firing when at peak intensity. May involve stretch receptor input (eg from Vagus)

> Inspiratory muscles relax and lung begins to deflate due to elastic recoil

Question 13

What happens in early-E phase?

Answer 13

> neurons repress all I & E neuronal firing. Creates refractory period at peak inhalation

> Inspiratory muscles relax and lung begins to deflate by elastic recoil

Question 14

What happens in E phase?

Answer 14

> neurons ramp fire. Activate motorneuron circuit to expiratory muscles. Major point of conscious input into breathing (eg during exercise).

> Expiratory muscles contract as E firing intensity increases. Insp muscles relaxed.

Question 15

What can change breathing patterns?

Answer 15

DRG

in the medullary respiratory centre

Question 16

What innervates the DRG?

Answer 16

1) Central Chemoreceptors:
Medulla Surface

2) Peripheral Chemoreceptors:
> Carotid Body (blood)
> Aortic Bodies (blood)
> Neuroepithelial Bodies (airway)

Question 17

What are the peripheral chemoreceptors?

Answer 17

> Carotid Body (blood)
Aortic Bodies (blood)
Neuroepithelial Bodies (airway)

Question 18

What does the input on the DRG modulate?

Answer 18

RRG rhythm

Question 19

What does the DRG innervate?

Answer 19

VRG–> Pre-Bötzinger Complex

Question 20

What is the Pre-Bötzinger Complex?

Answer 20

is a bilateral and symmetrical neural network located in the brainstem which is essential for the generation and modulation of respiratory rhythm.

Question 21

What are phrenic nerves?

Answer 21

contain motor, sensory, and sympathetic nerve fibres. These nerves provide the only motor supply to the diaphragm as well as sensation to the central tendon. In the thorax, each phrenic nerve supplies the mediastinal pleura

Question 22

What does the firing of phrenic nerves cause?

Answer 22

diaphragm contraction and inhalation

Question 23

What does an increased tital vol do to AP and breathing?

Answer 23

Increased action potentials per burst gives

stronger diaphragm contraction & deeper breathing

Question 24

What is the effect of increased total ventilation volume?

Answer 24

increased tital vol 
increased frequency (bursts per minute)

Question 25

What is the tital vol? (in terms of AP)

Answer 25

AP per min

Question 26

How does Vt and frequency effect total ventilation volume?

Answer 26

Increased burst per minute gives Increased breathing frequency (↑f).

When combined with increased action potentials per burst (↑VT) then VE increases.