why do we yawn?

Answer 1

Yawning is an involuntary action that causes us to open our mouths wide and breathe in deeply. There are many parts of the body that are in action when you yawn. First, your mouth opens and jaw drops, allowing as much air to be taken in as possible. When you inhale, the air taken in is filling your lungs. Your abdominal muscles flex and your diaphragm is pushed down. The air you breath in expands the lungs to capacity and then some of the air is blown back out.

Normally, when you breathe in, you inhale oxygen and your body uses it up. The body makes a waste product called as carbon dioxide that is exhaled from the lungs when you breathe out.

When you are sleepy, bored or tired, you breathe more slowly. Your body requires oxygen and needs to throw out the carbon dioxide. So, your brain makes you take an extra breath, which is deep and long called a yawn, so that you can take in more of oxygen and give out carbon dioxide fully.

Hope I helped.
=)

Answer 2

The truth is that we don’t completely understand why people, or animals for that matter, yawn. It’s widely assumed that yawning occurs because we are tired or bored or because we see someone else doing it, but there isn’t any hard evidence to support these beliefs.

The most plausible explanation, and the one that is taught in medical school, is that we yawn because oxygen levels in our lungs are low. Studies have shown that during normal, at-rest breathing, we don’t use anywhere near our lung capacity; for the most part, we just use the air sacs at the bottom of the lungs. If the air sacs, called alveoli, don’t get fresh air, they partially collapse and the lungs stiffen a bit. As a result, it’s believed, our brain prompts the body to either sigh or take a yawn to get more air into the lungs.

Answer 3

I agree with all the others Re: increasing oxygen into the bloodstream.
The supposed reason why yawning is "contagious" is thought to be beacuse when one person yawns, the brains of the other people around him/her associate this with a percieved lack of oxygen, so their brains instigate the same reaction to get the oxygen rush!

I'm an engineer, but I read that somewhere...

Answer 4

It's a lack of oxygen in your system, and yawning is a way your body reacts to it, to get more oxygen in. It's something we do subconsciously when we're bored, is breathe more shallow. So that's why we yawn then, too.

Answer 5

it is a subconscious, reflex action when we are tired, to get more oxygen into the system. The reason yawning is so catching is because we often don't realise we are tired until we see someone else yawning

Answer 6

Lack of oxygen/because someone else has yawned and it's contageous/tired

Answer 7

anyone else yawning reading this
to get oxygen

Answer 8

we yawn because our body tries to get more oxygen by opening the mouth .it also indicates tiredness

Answer 9

when you yawn you breath in more oxygen which in return gives you energy.

Answer 10

we yawn to get more oxygen in to our lungs