The modern human brain weighs 3 pounds (1.36 kilograms)
However, 5,000 years ago humans had brains that were even larger! Maybe it evolved and got slimmer to be more efficient or maybe our skulls are getting smaller because our diets include more easily chewable foods and so large, strong jaws are no longer required.
Whatever the reason; thankfully, the brain size doesn't directly correlate with intellect! The weight of Albert Einstein’s brain was 1,230 grams and that is less than an average weight of the human brain!
The human brain boasts of 100 billion neurons (nerve cells) and 100,000 miles of blood vessels! The number of neurons is maximum at six years of age though everyone has almost the same number at birth.
Brain develops from ectoderm (outermost covering of a developing embryo) this makes skin, hair and lens its siblings!!
The brain surface is wrinkled into folds (gyri and sulci) and these increase the surface area and thus, more processing power gets packed into the limited confines of the skull. The Cerebro Spinal fluid (CSF) surrounds and bathes the brain while coverings called the Dura, Pia and Arachnoid Mater ensheath it.
The brain is actually a fatty organ because it is rich in lipids! The living brain is so soft you could cut it with a knife. Some compare the consistency to toothpaste but I guess the ‘tofu-like’ comparison is the nearest!
The brain is a recluse! There exists a BBB (blood-brain barrier) which bars any and every molecule from having a free entry into the brain tissues! The capillaries that feed the brain are lined with tightly bound cells, which keep out large molecules. This is at once protective and inconvenient because for any drug to reach the brain, it must have the capacity to cross the BBB!
Brain hogs energy! 20% of oxygen and 25% glucose in the circulating blood go to the brain!
It is so sensitive that it cannot survive for more than 4-6 minutes without oxygen/blood supply. Most times death of a brain cell is permanent.
For all its sensations, the brain is pain insensitive! However the coverings (Dura, Pia, arachnoid) have pain sensors and are capable of pain!