So what's behind this mysterious epidemic of yawning? First, let's look at what this bodily motion 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're born: According to Robert Provine, a developmental neuroscientist at the University of Maryland, Baltimore County, research has shown that 11-week-old fetuses yawn. And while yawning is commonly associated with relaxation and drowsiness, your heart rate can rise as much as 30 percent during a yawn, and yawning is a sign of arousal, including sexual arousal [sources: Alexander, The Stress of Life].
Many parts of the body are in action when you yawn. First, your mouth opens, and your jaw drops, allowing as much air as possible to be taken in. When you inhale, the air taken in is filling your lungs. Your abdominal muscles flex, and your diaphragm is pushed down. The air you breathe in expands the lungs to capacity and then some of the air is blown back out.
Now that we know what a yawn is, let's look at what causes us to do it. On the next page, we'll discuss four popular theories that explain why we open wide and breathe deep.Read More
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