MadSci Network: Neuroscience

Re: wich part of the brain do we use to yawn?

Date: Mon Nov 8 22:23:24 1999
Posted By: Rhonda E. Lowe, Undergraduate, Biology & graduate science education
Area of science: Neuroscience
ID: 941681051.Ns

Hi Elizabeth--

Gosh, you certainly have asked some good questions!  So, here are my 
answers to your questions:

(1)  The part of the brain that makes us yawn is in the reticular 
formation and it is part of the brain stem, which is the lower part of our 
brain that is not consciously controlled.  This area is made up of small 
gray matter with threads of white matter woven in.   This part also 
extends down into the spinal cord, and it has both sensory and motor 
nerves.  Sensory nerves allow us to feel and touch and smell whereas the 
motor nerves allow us to move, dance, ride a bike and other similar 
things.  This formation receives input from higher levels of the brain 
that control our skeletal muscles, and it alerts the large cerebral 
cortex, where we "think," to any incoming signals.  So, this system, the 
reticular activating system (RAS), controls things like waking up, going 
to sleep, and yawning too.

(2)  As for how we yawn, basically yawning is a semi-involuntary act or 
reflex that occurs.  Yawning is a deep inspiration (breath in) in which 
the mouth opens very widely and which makes the mandible, your lower jaw 
bone, depress downwards more than normal.  In addition, scientists have 
found out that there are several different chemicals in the brain that are 
involved in yawning.  Some of these chemicals include dopaminergic, 
acetylcholinergic, and others too.  One thing I want to point out to you 
is that the mechanisms and functional role of yawning are not completely 
known.  As you yawn, you take a deep long breath in and this expands the 
lungs and air is brought in to fill the lungs to cpacity, and then you 
exhale some of the air back out.  So, there are many parts of the brain 
that are operating when we yawn because there are parts of the brain that 
make the lungs expand to fill with air from yawning.  In addition, the 
abdominal muscles and diaphragm, which is depressed downwards allowing for 
your lungs to expand, are involved so the parts of the brain like the 
motor cortex in the cerebrum and areas in the cerebellum that conrol those 
structures also help in the yawning process.  Also, the higher parts of 
the brain "tell" your mouth muscles to move and stretch so that the 
mandible can be depressed which then lets your mouth open wide. Suffice it 
to say, there are actually several areas of the brain that are involved in 
the complete yawning process.  Most yawning occurs about an hour before 
sleep and an hour after wakening.

(3)  Actually, as for why we yawn, research indicates that scientists and 
doctors do know some reasons why  both people and animals yawn, and that 
they will learn more reasons why as study of the brain goes on in time.  
Some people think we yawn because we are bored, fatigued and tired, lose 
interest in our surroundings, because we see another person doing it, and 
finally because it may be that your body is lacking enough oxygen.  This 
lack of proper oxygen, hypoxia, can make you yawn so that you get in the 
correct amount of oxygen. Several studies have been done that showed 
normal, at-rest breathing does not near our current lung capacity.  These 
studies show that the air sacs, or alveoli, at the bottom of the lungs, 
don't always get sufficient air (oxygen) supply.  Thus the sacs partially 
collapse, and then, our brains send messages to the RAS telling it to get 
air into our bodies!!  Then the yawn reflex happens.  In addition, 
scientists have found that people tend to yawn when they are feeling 
sleepy too.  A study was done in which heart rate, skin temperature, and 
muscle tension were measured before, during, and after yawns.  They found 
that yawning did increase the people's level of arousal for a little 
while.  As for yawning, one other interesting thing to know is that even 
fetuses in the womb can yawn.

(4)  To answer your question regarding if animals yawn, I found some 
interesting things in my search for this.  There is actually a scientist 
who studies yawning and he uses rats.  He has found out that rats do yawn 
most frequently during the early hours of the afternoon.  He believes it 
is connected to the circadian rhythms, which help us to know when to go to 
sleep and when to awaken.  There seems to be a body of evidence that 
supports the fact that yawning occurs in not only humans, but also in 
animals.  If the person or animal yawns, the body takes in that air and 
the surfactant, the sticky like fluid within the alveoli, is 
redistributed.  This surfactant decreases surface tension in the air sacs 
to prevent the sacs from collapsing so that you couldn't breath in.  
Animals definitely yawn especially the ones that have surfactant-like 
fluid in their lungs.  In addition, there have even been cases in 
Veterinary literature that shows that yawning may be a symptom of an 
animal's illness.  For instance, an owner had a 6 year old mixed breed 
that was brought into the Vet, and the animal would yawn which was 
followed by tremors and chattering.  This seemed to happen most often at 
night.  I'm not sure if the answer was found for why the animal yawned and 
then it had tremors, but this shows you that even animals yawn.  On 
another note, excessive yawning may be a symptom of disease in both aimals 
and humans such as this mixed breed.  For people, it seems lie illnesses 
like epilepsy, brain tumors, and multiple sclerosis are associated with 
yawning.  Monkeys, dogs, lions, and other vertebrates seem to all yawn.  
As a matter of fact, I have a male red and white 5 1/2 year old Basenji 
dog, Ruddy, and I can tell you that he yawns because I have seen him do it 
like at nightime, and other times too.

(5)  As for psychological reasons about why we yawn, some of those were 
given to you in question 2, and it may be that when we are bored we do 
yawn. So, since boredom results from a behavior type of aspect, then it 
seems that yawning may be due to psychological things. Whether or not it 
is contagious, scientists have not clearly decided if that is true. They 
still are not sure why people yawn when they see others yawn.  

Well, Elizabeth, I hope this information helps you.  Good luck on your 
research and your science fair project on yawning.  

Current Queue | Current Queue for Neuroscience | Neuroscience archives

Try the links in the MadSci Library for more information on Neuroscience.

MadSci Home | Information | Search | Random Knowledge Generator | MadSci Archives | Mad Library | MAD Labs | MAD FAQs | Ask a ? | Join Us! | Help Support MadSci

MadSci Network,
© 1995-1999. All rights reserved.