Figure 5.

Schematic illustration of the sequential phase of the pontine mediated inspiratory off-switch (IOS). The figure is adapted from Mörschel and Dutschmann 2009. Excitatory neurons and excitatory drive are highlighted in green; inhibitory neurons and interactions, red; and inactive cell populations and connections, gray. The model is based on the concept that ascending drive from the medullary respiratory neurons is required for the pontine mediated IOS. Panels on right show three time points in the cycle. (A) During the inspiratory phase, a pontine early-I population receives excitatory synaptic input (efference copy 1) from inspiratory driver neurons (I-driver) located in the pre-Bötzinger complex. The pontine early-I populations are inhibitory interneurons of the pons. The pontine early I neurons inhibit the pontine inspiratory/expiratory phase spanning neuron (I/E) and pontine postinspiratory premotoneurons (post-I) to prevent initiation of phase transition during early and mid-inspiration. With ongoing inspiration the pontine I/E neurons receive increasing excitatory drive (efference copy 2) from medullary augmenting-inspiratory premotor neurons that override the inhibition of early-I causing firing onset around late inspiration. (B) The pontine I/E neurons are excitatory pontobulbar neurons that activate the medullary late-I neurons to initiate the inspiratory/expiratory phase transition. (C) Finally, the inhibitory late-I neurons of the medulla terminate the activity of the medullary early-I neurons and release the medullary post-I population (inhibitory interneurons) from synaptic inhibition. These inhibitory post-I neurons inhibit the inspiratory populations (medullary and pontine). Consequently, the pontine and medullary postinspiratory premotor population innervating thyroarytenoid motoneurons starts firing.