Question: What makes us go to sleep?

Ruth Elderfield answered on 18 Jun 2015:

We have a 24-hour repeating signal in our body (it is called a circadian rhythm) that might be controlled by the build up of a chemical called adenosine. The more adenosine, the more sleepy we get.
We also have body clock that reacts to the amount of light it is exposed to, as it gets dark another chemical to builds up, Melatonin, signalling your body that it is time to sleep. In the morning, when the sun comes up, yet another chemical appears, cortisol, this signals the brain that it is time to wake up.