Scientists are still unraveling all the reasons why we need sleep. The article "Sleep 'boosts brain cell numbers'" discusses how sleep helps with the vital process of building myelin, a material that surrounds parts of nerve cells and is vital to their proper functioning.More specifically, you may remember from your biology or psychology classes that nerves communicate to one another through electrical impulses and neurotransmitters. The receiving end of a nerve cell is usually the axon and this can range from a millimeter to as long as a meter long. Myelin electrically insulate the axon, significantly accelerating the speed of the signal.The article below talks about how the cells that make myelin double their production rate in mice as they slept. For more information about this as well as other neurological benefits of sleep, you can read the article from BBC news here: http://www.bbc.co.uk/news/health-23932577.