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Question: Why and how do people laugh and cry?
At the turn of the fifth century B.C.E., the ancient Greeks, as part of their annual Dionysian festivals, created the first tragic and comedic theatrical productions for the enjoyment of the Athenian citizenry. In these plays, the Greek actors portrayed two of the deepest themes of human life experience – or human drama – by donning the now-famous laughing and crying masks which have been emblematic of the theater ever since. But what are human laughter and tears? What can science tell us about them?
How do we laugh? Laughter is similar to coughing, hiccupping and the act of speaking, since all the sounds produced by these events are related to the manner in which air flows through the larynx. But they have differing functions, of course: a cough is an involuntary act that may, for example, dislodge an obstruction in our airway; a hiccup, also an involuntary act, may serve to allow pockets of trapped air within the stomach to escape; and the voluntary act of speech involves the manipulation of air flow through our vocal chords to create variations in the pitch of the released sound, thereby allowing us to communicate through language. Our speech, of course, depends on the sounds we produce – but the meaning of what we communicate requires more than animal noises and sounds!
The outward phenomenon of tearing, on the other hand, results when stimulation of the central nervous system sends neural signals through the cranial nerve to one of our tear glands that, once stimulated, results in the emission of salty water into our eyes. Some tears – called basal tears – seem to simply function to keep our eyes moist. Other tears are generated to wash away dust or other small irritants that get into our eyes – the eye's "cough," as it were. And some tears – psychological or emotional tears – are associated with our inward emotion of sadness.
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