Consciousness Rediscovered. Advances in Neuroscience
The brain has roughly a trillion brain cells, five for every one of the 200 billion stars in our galaxy, or 150 for every person on our planet. Cambridge, Massachusetts, the home of MIT and Harvard, has 100,000 people living in an area of 18.5 square kilometers. If the brain cells of a human were spread out over this area, there would be five cells per square centimeter. If all residents of Cambridge counted them, it would take them a year to finish, assuming an eight-hour workday, no breaks, and an average counting speed of one per second. What’s more, the brain has between 1000 trillion and 10,000 trillion intercellular connections. If the residents counted these, it would take them between 1000 and 10,000 years. There are also hundreds of different kinds of messenger molecules traveling over those connections. Moreover, neurons can substantially change their physical organization in seconds by rearranging their connections. Also, neurons constitute only a minority of all brain cells. They are outnumbered by so-called glial cells, which are important for understanding anything from degenerative diseases to mental life. The human brain is the most complex entity we know in our universe. Given its complexity, how can we understand it?
-  A rough estimate of the sum of the neurons and glia. © Springer International Publishing AG 2017 A. Hedman, Consciousness from a Broad Perspective, Studies in Neuroscience,Consciousness and Spirituality 6, DOI 10.1007/978-3-319-52975-2_5