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.
The enteric nervous system in humans consists of some 500 million neurons (including the various types of Dogiel cells), one two-hundredth of the number of neurons in the brain, five times as many as the one hundred million neurons in the human spinal cord, and about 2/3 as many as in the whole nervous system of a cat.