Why/when do we yawn?

-Karthik Gurumurthy

Research has shown that we yawn when we are fatigued, as well as when we are getting up and when our state of alertness is changing.

It is symbolized by a single deep inhalation (with the mouth open) and stretching of the muscles of the jaw and trunk. It happens in many animals and involves interactions between the unconscious brain and the body.

Initially  low oxygen in lungs was attributed to this. Now it is deduced that low oxygen levels in the paraventricular nucleus (PVN) of the hypothalamus of the brain causes yawning.  PVN contains a number of chemical messengers that can induce yawns such as dopamine, glycine, oxytocin and adenocorticotropic hormone which is usually referred to as ACTH . Production of nitric oxide by certain neurons stimulates and activates brain stem cells which results in yawning. 

As I am typing this I am yawning…I guess my state of alertness is changing