Breathing (wk 10)

Question 1

Describe the respiratory control functions and the main 3 systems it needs to regulate:

Answer 1

-Respiratory control functions -> The respiratory control system is remarkably complex and incompletely understood. The respiratory control system must be able to regulate
1. Blood-gas tensions and acid-base balance (alveolar ventilation)
2. Speech and breath-holding
3. Airway defence (cough, swallow)

Question 2

What are the 3 basic elements of the respiratory control systems?

Answer 2

-Sensors
-Central controller
-Effectors

Question 3

What is the primary regulated variable?

Answer 3

In the case of breathing, the primary regulated variable is arterial CO2 pressure (PaCO2). The CO2 mass balance equation explains how the respiratory control system operated with regards to PaCO2 homeostasis

Question 4

What is PaCO2 regulation?
-Feedforward and feedback control

Answer 4

-> Feedback is PaCO2 regulation by closed-loop negative chemo feedback. Feedforward is PaCO2 regulation by commands that translate goals, targets and information about potential disturbances, independent of chemoreception. However, the respiratory control system is not a fixed system

Question 5

What is PaCO2 regulation?
-Adaptive control

Answer 5

-Unlike the moment-to-moment regulation offered by feedforward and feedback control, adaptive control is PaCO2 regulation by long-lasting modifications to the control system e.g. neuroplasticity. Occurs at multiple levels of respiratory control.

Question 6

What is respiratory neuroplasticity?

Answer 6

-> ‘A persistent change in the neural control system based on experience’. This change in neural control behaviour is essential to ensure PaCO2 homeostasis in the face of recurrent or enduring pertubations e.g. injury/disease.

Question 7

Draw and describe the 3-compartmental model of the respiratory control system:

Answer 7

-Respiratory rhythm generators are in red
-Respiratory pattern generators are in grey
-Cranial nerves are in green
-Ventral respiratory group (VRG) -> The VRG is split into rostral (r VRG) and caudal (c VRG) aspects. r VRG = inspiratory (diaphragm and external intercostals). c VRG = expiratory (abdominal and internal intercostals)
-Dorsal respiratory group (DRG) -> The DRG is a small collection of inspiratory (predominantly diaphragm) premotor neurons located in the caudal NTS. The NTS integrated sensorimotor information, receiving input from CN IX, X and XII.
-Pontine respiratory group (PRG) -> The PRG contains the Kolliker-Fuse (KF) nucleus and parabrachial (PB) nucleus. These neurons inhibit inspiration and prolong expiration. Responsible for the Hering-Bruer lung inflation index.

Question 8

Describe the innervation of spinal respiratory motorneurons

Question 9

Draw the inspiratory and expiratory pump muscles:

Question 10

What is voluntary versus automatic?

Answer 10

-> Breathing is often mistaken as ‘autonomic’ – breathing is more akin to somatic processes and is largely an automatic behaviour. Phrenic motor neurons receive input from the primary motor cortex and from the brainstem. Direct input from the cortex allow for voluntary control of breathing. Direct inputs from the brainstem allow for automatic control of breathing. A relay from the cortex to brainstem exists via corticobulbar tracts and allows the cortex to override automatic breathing e.g. speech

Question 11

What is cortical/ voluntary control?

Answer 11

-> Breathing is under both automatic and voluntary control – the cortex can override automatic processes. Examples of voluntary behaviours include: speech/swallow, singing, sniffing, coughing, spirometry tests, breath-holding. Deep-sea divers lower PaCO2 via hyperventilation prior to breath-holding. Hyperventilation halves PaCO2, resulting in alkalosis. Urge to breathe during a breath-hold occurs around 50 mmHg PaCo2.

Question 12

Describe central chemoreceptors:

Answer 12

-> Located primarily in the ventral surface of the medulla, known as the retrotrapezoid nucleus. H+ does not cross the blood-brain-barrier (BBB) – Co2 diffuses through into the cerebral spinal fluid (CSF). CO2 binds with H2O to form carbonic acid. Carbonic acid disassociates into bicarbonate and H+. Changes in CSF Co2/ pH activate central chemoreceptors.

Question 13

Describe peripheral chemoreceptors:

Question 14

What is central and peripheral chemoreceptor interdependence?

Answer 14

-> The central and peripheral chemoreceptors do not work independently. Isolating the carotid body from the systemic and cerebral circulation.

Question 15

What is CB stimulation and CB inhibition?

Answer 15

1. CB stimulation (hypoxia and hypercapnia) = increased controller gain
2. CB inhibition (hyperoxia and hypocapnia) = decreased controller gain