Scientific research has led to the discovery of opiate like chemicals in the body that associate with receptors in the brain and spinal cord, including serotonin, a hormone manufactured by your brain. Release of serotonin causes the other nerves to fire and continue the message along ?cable?.
Serotonin is a chemical that helps maintain a happy feeling, and seems to help keep our moods under control by helping with sleep, calming anxiety and relieving depression. The brain also makes Dopamine, which makes people more talkative and excitable.

I've also heard talk of endorphins which give you that same feeling you get after winning a race. It really is a crazy concept that our feelings can be the combination of various chemicals telling our brain what is good, what is bad, etc. Who know....maybe there's more to it.