Why we sleep?

Glial cells, also called glial cells or neuroglia, are cells that, together with the neurons, form the nervous system. They function and nutritional support for neurons, ensure the insulation of nerve tissue and protection from foreign bodies in the event of injury. For over a century, it was believed that they had no role in the transmission of electrical signals; Recent studies have discredited this theory, although their mechanism of operation is not yet well understood.
Reproduction of glial cells occurs very frequently in mitosis, in contrast to neurons for which the phenomenon occurs rarely.
The glial cells were discovered in 1891 by Santiago Ramón y Cajal. The number of glial cells in the brain exceeds five times that of the neurons. The fact was discovered in the early twentieth century and from this was born the myth that we only use 10% of our brain to think. The active role of glial cells in the synapses and thus the speed of learning has been established only in 2004.
Some glia act mainly as a support to neurons, other regulate the internal environment of the brain and in particular the fluids that surround the neurons and their synapses, thus providing the nourishment of nerve cells. Some types of glial cells produce molecules that can affect the growth of axons. Other functions have been discovered recently, such as the ability of astrocytes to communicate.
However, recent studies seem to have shown that, during sleep, these cells are appointed to drain toxic substances derived from the metabolism of the brain that accumulate in its interstices. Because the lymphatic system is usually responsible for this function in the rest of the body does not reach the brain, this is the only way we have a cleansing effect on the brain by pollutants catabolic. Being a very complex function (to perform this task are pumped fluid between neurons) which apparently inhibits the faculties of wakefulness (ie consciousness, since the body continues to function while we sleep and even to move, as it happens in the extreme case of sleepwalkers) this operation is carried out during sleep, or sleep is the best way in which the body makes such a mechanism as necessary as delicate, involving not only humans, but many living beings. That's why we need sleep and why sleep deprivation causes hallucinations, such as toxic substances that accumulate may bear even permanent damage and even death. I dream at this point are not more likely that the result of cognition and consciousness altered drainage during this action.