Neuron expiratory

Respiratory rhythmicity is an emergent property of the RCPG resulting from mutual inhibition of inspiratory and expiratory related neurons. A minimal model due to Duffin [1991] postulated the early-burst inspiratory (I) neurons and Botzinger complex expiratory (E) neurons to be the mutually inhibiting pair. Adaptation of the I neurons (e.g., by calcium-activated potassium conductance) results in sustained relaxation oscillation in the network under constant chemical excitation. Both neuron groups are assumed to have monosynaptic inhibitory projections to bulbospinal inspiratory (Ir) output neurons (Figure 11.3). The model equations are ... 

FIGURE 11.3 A minimal neural network model of RCPG. I and E denote respectively the early-burst inspiratory neurons and Botzinger complex expiratory neurons P is a fictive adaptation neuron S is an excitation neuron or pacemaker cell. Not shown is the bulbospinal output neuron (1 ). Numbers denote connection strengths. (From Masakazu and coworkers [1998]. With permission.)... 

The primary center, located in the medulla, is made up of a complex of interconnected neurons that are part of the reticular system. Although the neurons are not condensed to form typical nuclei, it is possible to distinguish, on the basis of stimulation by microelectrodes, neurons that generate impulses responsible for inspiration from neurons generating impulses that lead to expiration. Therefore, we speak of an inspiration and an expiration center. Researchers believe that these centers are widely interconnected, and that inspiratory neurons are intermingled with expiratory neurons. 

In certain cold-blooded species, the brain stem continues to discharge impulses to the respiratory muscles after all afferent paths have been disconnected. This spontaneous activity of the respiratory neurons is controlled by the combined activation of the inspiratory and expiratory centers. 

The primary control resides in the inspiratory center, and the expiratory center acts in a secondary fashion by intermittently interrupting the respiratory discharge. The excited inspiratory center is believed to send impulses to the pneumotaxic center, which stimulates neurons in the expiratory center to discharge impulses that inhibit the inspiratory center. 

Lahrmann H, Wild M, Zdrahal F, et al. Expiratory muscle weakness and assisted cough in ALS. Amyotroph Lateral Scler Other Motor Neuron Disord 2003 4(1) 49-51. 

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