|MadSci Network: Neuroscience|
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.
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