AP BIOLOGY

Detailed explanation-1: -Remarkably, at an average of 86 billion neurons and 85 billion nonneuronal cells (25), the human brain has just as many neurons as would be expected of a generic primate brain of its size and the same overall 1:1 nonneuronal/neuronal ratio as other primates (26).

Detailed explanation-2: -All this sums up to the fact that the human brain has the largest number of cortical neurons (about 15 billion), despite the fact that the human brain and cortex are much smaller in size than those of cetaceans and elephants (with 10–12 billion or even fewer cortical neurons).

Detailed explanation-3: -The human brain has often been viewed as outstanding among mammalian brains: the most cognitively able, the largest-than-expected from body size, endowed with an overdeveloped cerebral cortex that represents over 80% of brain mass, and purportedly containing 100 billion neurons and 10× more glial cells.

Detailed explanation-4: -The human brain contains about 86 billion nerve cells (neurons)-called “gray matter, ” according to a 2012 study published in the Proceedings of the National Academy of Sciences.