Figure 3. Central pattern generators encode the respiratory rhythm.

(A) Connections between the pre-Bötzinger complex that organizes inspiration, the Kölliker-Fuse nucleus that relates to the inspiration/expiration switch, the lateral parafacial nucleus that triggers active expiration, and the Bötzinger complex related to expiration. (B) Neuronal activity in the central pattern generators varies during the respiratory cycle. The schematized traces represent action potential firing of selected neuronal cell types in relation to activity of the phrenic nerve that drives the main inspiratory pump muscle, the diaphragm. From top to bottom: augmenting inspiratory neurons (I-AUG) from the pre-Bötzinger complex and the Kölliker-Fuse nucleus, a decreasing expiratory neuron (E-DEC) from the Kölliker-Fuse nucleus, and an augmenting expiratory neuron (E-AUG) from the Bötzinger complex. These representations are based on in vitro studies of Marchenko et al., 2016 (pre-Bötzinger complex), Ezure and Tanaka, 2006 (Kölliker-Fuse nucleus), and Flor et al., 2020 (Bötzinger complex). (C) During eupnea, thus in the absence of active expiration, neither the expiratory pump muscles of the abdomen, nor the neurons of the lateral parafacial nucleus are active. (D) During hyperpnea, thus when active expiration takes place, abdominal expiratory pump muscles are active when the lateral parafacial nucleus neurons produce action potentials. Schematized based on in vivo recordings of anesthetized rats by Pagliardini et al., 2011. Insp.=inspiration, Exp.=expiration.