Why do we yawn when we feel sleepy?
339257
Yeah, the previous answers are right - lack of oxygen to the brain.\n\nBut the big question is why are yawns contagious? Even experts don't know that.
288559
A yawn is a reflex of deep inhalation and exhalation associated with being tired, with a need to sleep, or from boredom. \n\nThe yawn reflex is often described as contagious: if one person yawns, this will cause another person to "sympathetically" yawn. The reasons for this are unclear; however, recent research suggests that yawning might be a herd instinct.\n\nHerd instinct\n------------\nThe so-called herding instinct is a social tendency in humans to identify with and model many behaviors and beliefs after a larger group of individuals with whom they identify.\n\n\nOther theories suggest that the yawn serves to synchronize mood behavior among gregarious animals, similar to the howling of the wolf pack during a full moon. It signals tiredness to other members of the group in order to synchronize sleeping patterns and periods of activity. It can serve as a warning in displaying large, canine teeth, thus proclaiming, "don't attack while I am sleeping...
300748
WHen you see another person yawning, the message goes across your brain that may be you too needs more oxygen and in attempt to get more air in, you open your mouth wide open, your lungs expand and you yawn. That's why it's called reflex yawning
345712
It is herd behavior, it signals when the herd needs to move on to something else. When one person yawns, it is passed along to 'pass the message.'
37416
I asked the same question KIND OF go to the website below and it gives you the answers to the most common myths. Yawning is included in one of them.
1049703
Good question!\nMany people believe that we yawns are the cause of to get rid of extra carbon dioxide and to take in more oxygen. Not entirely true (see ref 1 and 3). Sometimes we yawn as we shift phases from being awaken, to feeling sleepy, and anytime during our awakened state. And sometimes they simply are contagious(2).\n\n"Giving people additional oxygen didn't decrease yawning and decreasing the amount of carbon dioxide in a subject's environment also didn't prevent yawning. "(3)
410453
we yawn b/c our body is craving more oxygen.. this is fact
335882
It is a "associative" reaction. You see someone yawn and it triggers the same reaction because in our experience yawning represents being tired. We therefore associate yawning by others or ourself with being tired.\n\nI get a similar associative reaction when my daughters and I say the Lord's Prayer every night at bedtime. Halfway thru the prayer they will both yawn like clockwork. They both associate the prayer with being sleepy. Puts them right to sleep every time!
378590
People yawn when the level of carbon dioxide in their blood is a little too high, this is bad and eventually can cause unconsciousness.  To stop this you yawn, yawning means you take in a big gulp of oxygen and expel carbon dioxide.  They are thought to be contagious because if I see you yawning my brain thinks.. uh oh there is too much carbon dioxide in this room that person is already feeling the effects, to protect myself I will yawn too!\n\nBy the way you also yawn if you're tired because you're breathing naturally slows which makes carbon dioxide build up more easily.  You will yawn when you are tired to expel this excess carbon dioxide!
664075
Researchers aren't really sure. They seem to have pinpointed the initiation to a particular part of the brain, and speculate that it's a synchronized social reflex that may serve an evolutionary goal of greater tribal cohesiveness and mutual protection. See the referenced web page. I've noticed that it's not just other people yawning, but even reading the word 'yawn' that does it for me, even if I'm well oxygenated and wide awake!
861000
When we yawn our brains are telling us that it needs more oxygen.The stretching is to kind of "wake up "your muscles.Hope this answers your queston.
33139
we yawn to equalise the pressure difference between our ears and the outside. when u yawn you equalise the pressure in your ears but there is a disbalance created in the atmosphere and hence others around you also start yawning....!!!!
635799
1. because your body needs oxygen\n2. becaus you are bored and it is a way for your body to tell you to do something else\n3. becaus other people yawn. it is a social behavior that makes a group "stay together" \n\nhow? not sure, but I think your brain open your mouth and make your lungs draw in lots of air without letting you know first.
510901
Dr. Barry Make, a pulmonologist at National Jewish Medical and Research Center in Denver, says the answer is not because we are tired or bored — although that’s the common perception. Read on for his explanation.\n\nThe most plausible explanation, and the one that is taught in medical school, is that we yawn because oxygen levels in our lungs are low.\n\nTHE 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.\n\nThe 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.\n\nBut certain aspects of yawning remain even more mysterious. Fetuses, for instances, have been observed yawning in the womb, yet it’s known that they don’t take oxygen in through their lungs. And yawning seems to be a symptom of multiple sclerosis and other medical conditions, for reasons unclear.\n\nAnother puzzling phenomenon is that some male animals, men included, yawn in association with penile erection (although it’s presumptuous to assume they’re bored with their sex lives).\n\nNext time you're in a meeting, try this little experiment: Take a big yawn, cover your mouth out of courtesy, and watch and see how many people yawn. There's a good chance that you'll set off a chain reaction of yawns. Before you finish reading this question of the day, it's likely that you will yawn at least once. Don't misunderstand, we aren't intending to bore you, but just reading about yawning will make you yawn, just as seeing or hearing someone else yawn makes us yawn. \n\nInteresting Yawning Facts\n•The average yawn lasts about six seconds. \n•Your heart rate can rise as much as 30 percent during a yawn. \n•55 percent of people will yawn within five minutes of seeing someone else yawn. \n•Blind people yawn more after hearing an audio tape of people yawning. \n•Reading about yawning will make you yawn. \n•Olympic athletes often yawn before competition. \n\nWhat's behind this mysterious epidemic of yawning? First, let's look at what a yawn is. Yawning is an involuntary action that causes us to open our mouths wide and breathe in deeply. We know it's involuntary because we do it even before we are born. Research shows that 11-week-old fetuses yawn. \n\nThere 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. \n\nWhile the dictionary tells us that yawning is caused by being fatigued, drowsy or bored, scientists are discovering that there is more to yawning than what most people think. Not much is known about why we yawn or if it serves any useful function and very little research has been done on the subject. However, there are several theories about why we yawn. \n\nHere are the three most common theories: \n•The Physiological Theory -- Our bodies induce yawning to drawn in more oxygen or remove a build-up of carbon dioxide. This theory helps explain why we yawn in groups. Larger groups produce more carbon dioxide, which means our bodies would act to draw in more oxygen and get rid of the excess carbon dioxide. Howeve
198710
When you yawn, you are attempting to take in as much air as possible, more oxygen gives more energy.  People in the immediate area are in competition for this air too and yawn as a response to retrieve air themselves
75237
I'm a registered sleep technologist.  There is no known cause to yawning. It is still a mystery. There are many, many theories, but none proven, thus far.
433222
because they make one tired so then they person that isn't tires suddenly becomes tires and yawns. but yawns shouldn't make one another person yawn because the person is just releasing co2 from their bodies.