Where is a cycle of inspiration and expiration automatically generated?
In the CNS central pattern generator (CPG)
What drives the CPG?
Chemoreceptors (both central and peripheral) sensing PO2, PCO2 and pH
What does the CPG regulate specifically?
Respiratory muscles, most importantly the diaphragm
What is eupnea?
Quiet, normal, easy breathing
What does negative feedback on the CPG come from?
An increase in alveolar ventilation
How is the CPG affected b higher center respiratory motor activity?
They send inputs to the CPG during intense exercise
Where is the central pattern generator located?
Ventrolateral medulla oblongata
What does the pons do in respiration?
It only modulates respiratory output but is not necessary for respiratory output itself
What is the dorsal respiratory group (DRG)?
Has sensory input and contains primarily inspiratory neurons
Where are the DRG found?
Nucleus of solitary tract in the medulla
What is the ventral respiratory group (VRG)?
Primarily motor and contains both inspiratory and expiratory neurons
What is the CPG composed of?
DRG and VRG
What center can terminate inspiration?
Pontine apneustic center
What modulates the apneustic center and fine tunes respiration?
Pneumotaxic center
What do peripheral chemoreceptors respond to?
Primarily sensitive to decreasing PO2 less so to increase in PCO2 and decreased pH
What are central chemoreceptors sensitive to?
Increase in arterial PCO2 (H+)
What generates the respiratory rhythm?
Pacemaker neurons or synaptic interactions within the CPG
What is the chemosensor in the carotids and aortic bodies?
Glomus cell
What does acidosis cause in the carotid chemosensors?
Makes it more sensitive to arterial PCO2
What occurs when PaCO2 goes from 40 to 45 mmHg?
Ventilation will double
How does the central chemoreceptor respond to CO2 and H+?
CO2 can cross BBB but H+ cannot therefore the brain responds to local acidosis
What stimulates ventilation more hypoxia or respiratory acidosis?
Respiratory acidosis
What do juxtacapillary (J receptors) do?
Sense mechanical or chemical irritants and elicit rapid and shallow breathing, bronchoconstriction and mucous secretion as a defense mechanism
What do the slowly-adapting pulmonary stretch mechanoreceptors (PSR) do?
Detect lung volume and inhibit the medullary output to phrenic motor neurons producing Hering-Breuer Reflex
What does the Hering-Breuer reflex do?
Stops over-inflation of the lungs
