Sleep arising from conventions of the different reactions in the brain and the sleep key is turn on and off. As a result of the various reactions in the brain.
Sleep caused by the pattern of the different reactions in the brain. More important sleep is to be opened and closed. As a result of the reaction in the brain.
Sleep arises from the pattern of different reactions in the brain. And most importantly, sleep is open and close. As a result of the various reactions in the brain.