Why do we yawn?
When we are tired our lungs and the rest of the respiratory system slows down.because there is too little air in the lungs.so our body set of a spasm in the muscles of our mouth throat and chest.this forces us to take a deep breath of air to take in more air
When the amount of oxygen in our brain decreases then we yawn to take some oxygen
As far as I know, it is because when we r very tired our body needs extra oxygen nd that is not sufficient by respiration through nose..so it takes more oxygen by opening the mouth.
We yawn when our body gets tired and lacks oxygen. Yawning helps to inhale the required amount of oxygen our body requires at the moment
There is no exact theory or answer why do we yawn.Some says we yawn when we are tired or stress.Some reseachers also says some parts or our body is stretch or our brain is cooling but whatever the real reason is only God knows..
We yawn because of deficiency of oxygen than needed by the body. So, to fulfil the the need we yawn.