Hmm,,,, I cry almost everyday, when I cut an onion or when I sneeze really hard.(You know allergies!)  But, I guess you are not asking about such a sort of crying, so here goes.... Crying is a common response  when we are dealing with a highly emotional situation. Emotions help us to deal witht a situation. We cry when we are happy, sad, angry or  sometimes when we are just plain bored.(A yawn also releases tears)

Experts distinguish between three main types of tears; basal, reflex and psychic tears. Basal tears are released all the time, to stop your eyes drying out. Reflex tears help you to wash out sudden irritants, like the particles of a freshly chopped onion. Then there are psychic tears, the tears released in response to an emotion – sadness, distress, grief, but also relief, pleasure and laughter.

At a biological level, tears are released because the limbic system – the part of the brain that deals with emotions – is connected to the autonomic nervous system, which controls bodily functions but isn’t always within our control. However, the nervous system does have some control over the lacrimal, tear-producing system, through the deployment of neurotransmitters, which order the tear ducts into action.

The neurons in your hippocampus play a role in our emotions!

Do animals also experience emotions? Yes, they do! Here is the link to why they do.

http://www.abc.net.au/radionational/programs/archived/bodysphere/features/4837824