Source of respiratory drive
Introduction
Ventilation occurs under the control of the autonomic nervous system from parts of the brain stem, the medulla oblongata and the pons
This area of the brain forms the respiration regulatory center
The sections are:
the apneustic center
the dorsal and ventral respiratory groups
Central chemoreceptors
Located on the ventrolateral medullary surface
Sensitive to the pH of their environment
These act to detect the changes in pH of nearby cerebral spinal fluid (CSF) that are indicative of altered oxygen or carbon dioxide concentrations available to brain tissues
A change in plasma pH alone will not stimulate central chemoreceptors as H+ are not be able to diffuse across the blood-brain barrier into the CSF
Only CO2 levels affect this as it can diffuse across, reacting with H2O to form carbonic acid and thus decrease pH
Central chemoreception remains, in this way, distinct from peripheral chemoreceptors.
Peripheral chemoreceptors
Act principally to detect variation of the oxygen concentration in the arterial blood, whilst also monitoring arterial carbon dioxide and pH
Located in the aortic body and carotid body, on the arch of the aorta and on the common carotid artery, respectively
The carotid bodies are most sensitive to changes in partial pressure of arterial oxygen and pH
The aortic bodies are most sensitive to the content of arterial oxygen
A continual signal is sent, via cranial nerves IX and X, from the peripheral chemoreceptors to the brainstem
With a decrease in arterial oxygen tension and content or drop in plasma pH, the signal intensifies, and results in an increase in ventilation rate.