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 pneumotaxic center

    • 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.