Traditional lap pools are about 10 feet wide, though widths between 8 and 10 feet are common. (In competition pools, swim lanes are 2.5 meters wide, or about 8.2 feet.) You don't want to go too narrow with a lap pool.
The number of neurons in the brain varies dramatically from species to species. One estimate (published in 1988) puts the human brain at about 100 billion (10 11) neurons and 100 trillion (10 14) synapses.
While humans have about 100 billion nerve cells in their bodies, other mammals, such as blue whales, boast at least twice that number. The University of Tennessee points out that the elephant's brain is about three times as big as that of a human and contains about three times as many nerves.