insert for course notes for PHYSIOL 220: Human Physiology: the neural machine 2003




Lecture 21



Control of Breathing



Denis de Castro




abbreviations: arterial partial pressure of oxygen, Pa02; of carbon dioxide, PaCO2; basal metabolic rate, BMR.

  •   the system for control of breathing in humans and other vertebrates demonstrates a central control (from the brain) of a peripheral physiological function, in this case, the action of the lungs. The pathway by which the signal is carried out is revealed by certain injuries, which will be discussed. A separate local system within the lungs regulates bronchial and arterial vessel calibre.

  •    the anatomy of the respiratory system contains (among others) these elements: upper airways (including larynx and cords), bronchi, bronchioles, alveoli, pulmonary blood vessels, bronchial blood vessels, the diaphragm and other respiratory muscles, and the chest wall (including ribs and intercostal muscles). These elements are not considered further here, but an understanding of the respiratory system is important in allowing an understanding of its control.

  •    the respiratory control system is located anatomically within these structures: centrally‹the medulla oblongata within the brainstem; efferents‹("output" pathways) the cervical spinal cord (including phrenic motor nucleus) and phrenic nerves; afferents‹("inputs") brain chemoreceptors, the vagus and glossopharyngeal nerves, stretch receptors within the lungs, and the carotid body.

  •    the body requires that the respiratory system performs in such a way as to keep blood gas concentrations stable (alveolar ventilation sufficient to keep Pa02 above about 80 mmHg and PaCO2 below around 40 mmHg) and pH within a narrow range around 7.4. It must respond rapidly to the requirements to clear the airways by cough, cease movement for breath-holding, and regulate expiration for speech. Finally, energy use should be small (<5% of BMR).

  •    in summary, the respiratory control system
    is composed of neurons
    mainly inside the brainstem
    which project to the respiratory muscles
    and provide a rhythmic input...
    to the cyclic gas pump of the lungs
      which satisfies metabolic requirements
      and allows behavioural interrupts
      while minimising energy expenditure
    ...by collecting feedback signals

  •    possible topics for examination questions;
    anatomical pathways in respiratory control
    function of the brainstem respiratory control centre‹its input and output signals
    organisation of the brainstem respiratory "centre"
    the demands of the body on respiratory function


    references. Respiratory physiology‹in one page: www.pul.unimaas.nl/respir.htm. Gary Owens' slides on the control of breathing: http://hsc.virginia.edu/med-ed/phys/pdf/2003/section8.pdf. A sample of the research literature: www.rybak-et-al.net/burst.html.