Suzana Herculano-Houzel (1972-) The Human Advantage (2016)
A New Understanding of How Our Brain Became Remarkable
9 So How Much Does It Cost?
...On the other hand, the human brain does seem special in the amount of energy that it requires. As mentioned in chapter 1, even though it represents only around 2 percent of body mass, the human brain alone costs some 500 kilocalories per day to operate, a disproportional 25 percent of the daily energy required for the entire human body to work. In comparison, the brains of other vertebrate species cost at most 10 percent of the daily energy budget of the body. The remarkably higher relative energy cost of the human brain certainly makes it seem special. The source of all this energy is usually glucose from the blood, which crosses the blood-brain barrier, may or may not be broken down first into lactate by glial cells, and is shuttled to neurons as required according to their activity. This explains why blood flow to the brain is tightly regulated: to keep the human brain running on blood glucose requires a remarkably constant average of 750 milliliters of blood flowing through the brain per minute, and even a 1 percent drop in flow may cause fainting and loss of consciousness.
It's no surprise to find that the brain is relatively expensive, given that it is the second most energy-costly organ in the body, ranking in total organ metabolic cost below the liver only.
9 So How Much Does It Cost?
...On the other hand, the human brain does seem special in the amount of energy that it requires. As mentioned in chapter 1, even though it represents only around 2 percent of body mass, the human brain alone costs some 500 kilocalories per day to operate, a disproportional 25 percent of the daily energy required for the entire human body to work. In comparison, the brains of other vertebrate species cost at most 10 percent of the daily energy budget of the body. The remarkably higher relative energy cost of the human brain certainly makes it seem special. The source of all this energy is usually glucose from the blood, which crosses the blood-brain barrier, may or may not be broken down first into lactate by glial cells, and is shuttled to neurons as required according to their activity. This explains why blood flow to the brain is tightly regulated: to keep the human brain running on blood glucose requires a remarkably constant average of 750 milliliters of blood flowing through the brain per minute, and even a 1 percent drop in flow may cause fainting and loss of consciousness.
It's no surprise to find that the brain is relatively expensive, given that it is the second most energy-costly organ in the body, ranking in total organ metabolic cost below the liver only.