Neural Mechanisms and Generation of Breathing Rhythm
The medulla oblongata contains the ventral respiratory group, or
inspiratory center, with neurons that act as the pacesetting respiratory
group (inspiratory and expiratory, influence each other), and the
dorsal respiratory group, which functions mostly as an integrative
center for inputs from peripheral stretch and chemoreceptors.
VRG = inspiratory center; inspiratory neurons fire and stimulate the
diaphragm and external intercostal muscles to expand the thoracic
cavity. Expiratory neurons in the VRG fire and inhibit output from the
inspiratory neurons, inspiration stops and expiration occurs passively
- inspiratory muscles relax and recoil of elastin fibers decrease lung
volume (increasing intrapulmonary pressure and forcing air out of the
lungs).
DRG = integration of peripheral sensory input (stretch and
chemoreceptors), modifies rhythm generated by the VRG by sending
the information along to the VRG.