Human Yawn

       

                          Yawn is a reflex consisting of the simultaneous inhalation of air and the stretching of the eardrums, followed by an exhalation of breath. Yawning  most often occurs in adults immediately before and after sleep, during tedious activities and as a result of its contagious quality. It is commonly associated with tiredness, stress, sleepiness, or even boredom and hunger, though studies show it may be linked to the cooling of the brain. In humans, yawning is often triggered by others yawning (e.g., seeing a person yawning, talking to someone on the phone who is yawning) and is a typical example of positive feedback. This "contagious" yawning has also been observed in chimpanzees, dogs, and can occur across species. Approximately 20 physiological reasons for yawning have been proposed by scholars, but there is little agreement about its main functions. 

                                                                                                                                                        There are a number of theories that attempt to explain why animals and people yawn.  It is likely that there are a number of triggers for the behavior. However, there are comparatively few theories that attempt to explain the primary evolutionary reason for the yawn.

                                                               Study states that yawning occurs when one's blood contains increased amounts of carbon dioxide and therefore becomes in need of the influx of oxygen (or expulsion of carbon dioxide) that a yawn can provide. Yawning may in fact reduce oxygen intake compared to normal respiration.  However, neither providing more oxygen nor reducing carbon dioxide in air decreased yawning.

                                             Another speculated reason for yawning is the desire to stretch one's muscles. The tongue and throat are some of the most used muscles in the body, used for speech, breathing and swallowing. The need to stretch these muscles and refresh them arises just like in other muscles of the body, to circulate lymph. Yawns are often accompanied by the urge to stretch. Still another proposal points out that animals subject to predation or other dangers must be ready to physically exert themselves at any given moment. At least one study suggests that yawning, especially psychological "contagious" yawning, may have developed as a way of keeping a group of animals alert. If an animal is drowsy or bored, it may not be as alert as it should be to spring into action. Therefore, the "contagious" yawn could be an instinctual reaction to a signal from one member of the group reminding the others to stay alert.

                                                      Nervousness has also been suggested as a possible reason. Nervousness often indicates the perception of an impending need for action. Anecdotal evidence suggests that yawning helps increase the state of alertness of a person. Paratroopers have been noted to yawn in the moments before they exit the aircraft.

                                                                             Another notion states that yawning is the body's way of controlling brain temperature. In 2007, researchers including a professor of psychology from the University of Albany proposed that yawning may be a means to keep the brain cool. Mammalian brains operate best within a narrow temperature range. In two experiments, they demonstrated that both subjects with cold packs attached to their foreheads and subjects asked to breathe strictly nasally exhibited reduced contagious yawning when watching videos of people yawning. A similar hypothesis is that yawning is used for regulation of body temperature. Similarly Guttmann and Dopart (2011) found that when a subject wearing earplugs yawned, a breeze is heard caused by the flux of the air moving between the subject's ear and the environment. Guttmann and Dopart determined that a yawn causes one of three possible situations to occur: the brain cools down due to an influx or out flux of oxygen, the pressure in the brain is reduced by an out flux of oxygen, or the pressure of the brain is increased by an influx of air caused by increased cranial space.

                                                Another hypothesis is that yawns are caused by the some chemicals (neurotransmitters) in the brain that affect emotions, mood, appetite, and other phenomena. These chemicals include serotonin, dopamine, glutamic acid, and nitric oxide. As more (or less) of these compounds are activated in the brain, the frequency of yawning increases. Conversely, a greater presence in the brain of opioid neurotransmitters such as endorphins reduces the frequency of yawning. Individuals in opioid withdrawal exhibit a greatly increased frequency of yawning. Patients taking the selective serotonin reuptake inhibitors (SSRIs) Paxil (paroxetine HCl) or Celexa (citalopram) have been observed yawning more often. Excessive yawning is more common during the first three months of taking the SSRIs. Anecdotal reports by users of psilocybin mushrooms often describe a marked stimulation of yawning while intoxicated, often associated with excess lacrimation (eyes producing tears) and nasal mucosal stimulation, especially while "peaking" (undergoing the most intense portion of the psilocybin experience).

                                                                      While opioids have been demonstrated to reduce this yawning and lacrimation provoked by psilocybin, it is not clear that the same pathways that induce yawning as a symptom of opioid abstinence in habituated users are the mode of action in yawning in mushroom users. While even opioid-dependent users of psilocybin on stable opioid therapy often report yawning and excess lacrimation while undergoing this entheogenic mushroom experience, there are no reports on mushrooms in the literature regarding habituated users experiencing other typical opioid withdrawal symptoms such as cramping, physical pain, anxiety, gooseflesh, etc.