Why do you Yawn?

Why do we yawn? What are the Connections with Praanaayaama? How does breathing space gets adjusted, after longer periods of Praanaayaama??

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Astrocytes, the brain cells named after their characteristic star-shape, play a key role in the regulation of breathing.

Scientists at the University College London and the University of Bristol demonstrated that astrocytes are able to sense the levels of carbondioxide in the blood, reports Science Express. They then activate brain neuronal (nerve cell) respiratory networks to increase our breathing in accord with prevailing metabolism and activity.

Astrocytes are a subtype of a group of brain cells known as glia ('glue' in Greek), according to a Cambridge statement.

Now, astrocytes have been found to have a unique ability to "taste" the composition of arterial blood entering the brain by sensing increases in arterial levels of carbon dioxide.

They then release a chemical messenger called ATP, which stimulates brain respiratory centres to increase our breathing in order for extra carbon dioxide to be removed from the blood and exhaled.

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This also has an indirect connection