Summary:
There are 3 types of tears: basal tears, reflex tears, and emotional tears. Basal tears keep eyes from drying out. Reflex tears act in response to irritants. Irritants such as onions can cause a chain reaction to occur so the brain releases hormones and the tear glands release tears. Emotional tears are only exclusive to humans, and there are a few hypotheses about why humans produce emotional tears. First, emotional tears could act as a signal of distress to other people. This would be helpful from an evolutionary viewpoint, because then other people would feel sympathy for the person crying and help the person, increasing that person's rate of survival. An experiment was performed, and it was shown that people rated other people to look more sad with tears than without. Also, emotional tears contain more proteins, especially stress hormones. However, reflex tears contain more water. Therefore, one hypothesis is that the function of tears is releasing stress, but research for this hypothesis is not conclusive.
Relevance:
We have learned about the nervous system in class, and the autonomic nervous system controls crying and produces tears.
Source:
Author: asapSCIENCE
Publication Date: April 18, 2013
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