The human brain, its nervous projections, layers, and cortical blood vessels
Though we’re probably subconsciously aware of our brains on a day-to-day basis, most of us generally don’t pay much direct attention to them. Of course, lots can go wrong in the mind, resulting in mental illness, physical illness, and in the worst cases, death.
But aside from everything that can go wrong in the brain, did you know that the mind, despite being only 2% of the average body mass, uses almost 25% of the oxygen we consume, and over 70% of the glucose we ingest? It’s a tiny organ, but it manages almost everything outside of the parasympathetic nervous system, and it requires a relatively high energy input (especially compared to other organs in the body) just to function on a daily basis.
The cells in the brain require, on average, twice as much pure energy as other cells, just to function, and when you’re focusing hard on a big paper, or trying to brainstorm and be creative, your mind is in overdrive! Even if you haven’t moved in two hours, if you’re focusing hard on an essay and coming up with lots of great ideas, your lunch isn’t going to last long, with what your brain is demanding.
Since it’s not a muscle, and you’re not necessarily doing anything physical when you think, it can be hard to believe that the brain needs so much energy.
However, the cerebellum, and especially the frontal and prefrontal cortices (where our personality and “creative minds” exist, for the most part) demand more energy than our stomachs, livers, spleens, and kidneys combined! Depending on how your brain is wired, that fact can make it extremely exhausting to deal with other people, as you’re engaging your prefrontal cortex to a high degree. Thinking hard and being creative can sap your energy, too - that’s why I always had an apple or banana to eat midway through my morning courses!
Tabulae Anatomicae. Bartholomeo Eustachi, 1570 (Published 1783).
The Anatomy of the Brain, Explained in a Series of Engravings. Charles Bell, 1803.