All mammals produce tears round the clock to make sure their eyes don?t dry out and in response to irritation, but ?psychic? tears?the type produced as part of an emotional response that lead to crying?are exclusive to humans. They even have a different chemical makeup, which includes leucine-enkephalin, an endorphin and natural pain killer. Hence, that feeling of having had ?a good cry.?
Crying begins in the limbic system, which is the part of our brains that manages emotion through the autonomic nervous system and controls involuntary responses. That system is divided into two parts: sympathetic, which produces aggressive responses; and parasympathetic, which helps us process our emotions and ultimately rest. ?Crying will often begin as part of a sympathetic response??I can?t have that cookie? or ?I want more screen time??but the full-on waterworks only arrive as part of a parasympathetic response,? says Deborah MacNamara, a developmental science expert and clinical counsellor. ?So by the time a child is sad-sobbing, their brain has shifted from pursuit to sadness, and it has already processed the futility of the outcome they were hoping for.? Then the brain moves toward acceptance and adaptation, she explains. 
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