Emotional Lacrimation (Crying)
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There are three types of lacrimation (shedding of tears, or "crying"): basal, reflexive, and psychic. These types of tears can be differentiated by the stimuli that elicit them and their chemical composition. While humans across the world produce psychic tears in response to both positive and negative emotions, and while similar emotions have been identified in other animal species, no reports exist of other animals showing psychic lacrimation.
Basal tears protect and lubricate the eyes, and are produced constantly. Reflexive tears are produced in response to an acute irritant such as dust or dirt. Psychic tears, on the other hand, are produced during strong emotional responses (both positive and negative), and contain more of certain hormones (prolactin, adrenocorticotropic hormone, and leucine enkephalin).
The lacrimal system is rather complex. The lacrimal gland, the major source for tear production, is situated just above the eye. The lacrimal nucleus, the major source for innervating the lacrimal gland, is a subnucleus of the superior salivary nucleus in the tegmentum of the pons (part of the brain stem). The lacrimal nucleus receives projections from the autonomic nervous system as well as from various brain structures, including the frontal lobe, globus pallidus, thalamus, and hypothalamus. The projections from the frontal lobe are thought to be important in human psychic lacrimation.
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