Biological complexity: breathing controls (Introduction)

by David Turell , Wednesday, November 09, 2016, 17:38 (2936 days ago) @ David Turell

It is found there are three neural networks to control each phase of breathing:

http://www.the-scientist.com/?articles.view/articleNo/47266/title/Neural-Network-Found-...

"There are three stages to mammalian breathing: inspiration, passive expiration (postinspiration), and active expiration—a conditional phase used during labored breathing. Inspiration and active expiration have been linked to rhythm-generating excitatory neural circuits in the medulla: the pre-Bötzinger complex and the lateral parafacial region, respectively. A recent study has revealed a third excitatory network—the postinspiratory complex (PiCo)—that drives postinspiration, suggesting that the coordination of breathing may rely on alternating inhibitory interactions between three networks.

"A lot can happen after we take a breath—from swallowing a sip of coffee to singing in the shower—and the nervous system has to coordinate all these behaviors without sending fluids into the lungs or disrupting airflow. But studying the neural control of breathing has been a challenge, not least because researchers haven’t found all the circuitry involved.

"Two breathing phases, inspiration and active expiration (the forced expulsion of air during labored breathing), have each been linked to rhythm-generating excitatory networks in the medulla, the lowest portion of the brainstem. But scientists have been stumped as to the source of excitation generating the third: the passive release of air from the lungs after breathing in, or postinspiration. From this incomplete picture, most models of breathing have assumed that just two rhythm-generating circuits—inspiratory and expiratory—set the timing of all three breathing phases, with coordination coming about as each active phase inhibits the other two.

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" Using this preparation, the team has finally discovered the excitatory network that generates postinspiration, which the group has named the postinspiratory complex (PiCo).

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"Through pharmacological and optogenetic experiments, the researchers demonstrated that the PiCo is necessary and sufficient to generate postinspiration in vitro and in adult transgenic mice. What’s more, like the networks driving inspiration and active expiration, the PiCo appears to generate its own rhythm. “That was astonishing to us,” Ramirez says. The team is now exploring a model of breathing coordinated by the interactions of three, not two, rhythm-generating excitatory networks."

Comment: Another precise example of feedback loops for tight control of biologic processes. This cannot be developed stepwise, but must come all at once all parts working.